Refereed Publications
Year Author Word



2009

Biasutti, M. and A. H. Sobel, 2009: Delayed Sahel rainfall and global seasonal cycle in a warmer climate. Geophysical Research Letters, 36( L23707, doi:10.1029/2009GL041303). ABS
Biasutti, M., A. H. Sobel and S. J. Camargo, 2009: The Role of the Sahara Low in Summertime Sahel Rainfall Variability and Change in the CMIP3 Models. Journal of Climate, 22(21): 5755-5771. ABS
Camargo, S. J. and A. G. Barnston, 2009: Experimental Dynamical Seasonal Forecasts of Tropical Cyclone Activity at IRI. Weather and Forecasting, 24(2): 472-491. ABS
Camargo, S. J., M. C. Wheeler and A. H. Sobel, 2009: Diagnosis of the MJO modulation of tropical cyclogenesis using an empirical index. Journal of the Atmospheric Sciences, 66(2009): 3061-3074, doi: 10.1175/2009JAS3101.1. ABS
Camargo, S.J., 2009: Tropical Cyclones, Western North Pacific Basin. In: T.C. Peterson and M.O. Baringer (Editors), State of the Climate in 2008. Bull. Amer. Meteor. Soc., pp. S85-S88.
Cane, M.A., 2009: Das Klima in den Strömungen der Geschichte. In Die Ursprüng der modernen Welt. Eds. J. Robinson and Klaus Weigandt, In German; [Climate in the Currents of History, In Emergence of the Modern World: comparative History and Science].
Cook, B. I., R. L. Miller and R. Seager, 2009: Amplification of the North American "Dust Bowl" drought through human-induced land degradation. Proceedings of the National Academy of Sciences of the United States of America, 106(13): 4997-5001. PDF ABS
German, C. R., A. M. Thurnherr, J. Knoery, J. L. Charlou, P. Jean-Baptiste and H. N. Edmonds, 2009: Export fluxes from submarine venting to the ocean: A synthesis of results from the Rainbow hydrothermal field, 36 degrees N MAR. Geochimica Et Cosmochimica Acta, 73(13): A428-A428.
Gordon, A. L., A. H. Orsi, R. Muench, B. A. Huber, E. Zambianchi and M. Visbeck, 2009: Western Ross Sea continental slope gravity currents. Deep-Sea Research Part Ii-Topical Studies in Oceanography, 56(13-14): 796-817. ABS
Gordon, A. L., L. Padman and A. Bergamasco, 2009: Southern Ocean shelf slope exchange Preface. Deep-Sea Research Part Ii-Topical Studies in Oceanography, 56(13-14): 775-777.
Guan, X. R., H. W. Ou and D. K. Chen, 2009: Tidal effect on the dense water discharge, Part 2: A numerical study. Deep-Sea Research Part Ii-Topical Studies in Oceanography, 56(13-14): 884-894. ABS
Han, W. Q., A. M. Moore, J. Levin, B. Zhang, H. G. Arango, E. Curchitser, E. Di Lorenzo, A. L. Gordon and J. L. Lin, 2009: Seasonal surface ocean circulation and dynamics in the Philippine Archipelago region during 2004-2008. Dynamics of Atmospheres and Oceans, 47(1-3): 114-137. ABS
Horner-Devine, Alexander R., David A. Jay, Philip M. Orton and Emily Y. Spahn, 2009: A conceptual model of the strongly tidal Columbia River plume. Journal of Marine Systems, 78(3): 460-475. PDF
Huang, H. P., A. W. Robertson, Y. Kushnir and S. L. Peng, 2009: Hindcasts of Tropical Atlantic SST Gradient and South American Precipitation: The Influences of the ENSO Forcing and the Atlantic Preconditioning. Journal of Climate, 22(9): 2405-2421. ABS
Ihara, C. and Y. Kushnir, 2009: Change of mean midlatitude westerlies in 21st century climate simulations. Geophysical Research Letters, 36: -. ABS
Ihara, C., Y. Kushnir, M. A. Cane and V. H. de la Pena, 2009: Climate Change over the Equatorial Indo-Pacific in Global Warming. Journal of Climate, 22(10): 2678-2693. PDF ABS
Jay, David A., Jiayi Pan, Philip M. Orton and Alexander R. Horner-Devine, 2009: Asymmetry of Columbia River tidal plume fronts. Journal of Marine Systems, 78(3): 442-459. PDF
Karnauskas, K. B. and A. J. Busalacchi, 2009: Mechanisms for the interannual variability of SST in the east Pacific warm pool. J. Climate., 22(6): 1375-1392.
Karnauskas, K. B., R. Seager, A. Kaplan, Y. Kushnir and M. A. Cane, 2009: Observed Strengthening of the Zonal Sea Surface Temperature Gradient across the Equatorial Pacific Ocean. Journal of Climate, 22(16): 4316-4321. PDF ABS
Kim, D., K. Sperber, W. Stern, D. Waliser, I. S. Kang, E. Maloney, W. Wang, K. Weickmann, J. Benedict, M. Khairoutdinov, M. I. Lee, R. Neale, M. Suarez, K. Thayer-Calder and G. Zhang, 2009: Application of MJO Simulation Diagnostics to Climate Models. Journal of Climate, 22(23): 6413-6436. PDF ABS
Kossin, J. P. and S. J. Camargo, 2009: Hurricane track variability and secular potential intensity trends. Climatic Change, 97: 329-337.
Kug, J. S., K. P. Sooraj, D. Kim, I. S. Kang, F. F. Jin, Y. N. Takayabu and M. Kimoto, 2009: Simulation of state-dependent high-frequency atmospheric variability associated with ENSO. Climate Dynamics, 32(5): 635-648. PDF ABS
Legg, S., B. Briegleb, Y. Chang, E. P. Chassignet, G. Danabasoglu, T. Ezer, A. L. Gordon, S. Griffies, R. Hallberg, L. Jackson, W. Large, T. M. Ozgokmen, H. Peters, J. Price, U. Riemenschneider, W. L. Wu, X. B. Xu and J. Y. Yang, 2009: Improving Oceanic Overflow Representation in Climate Models the Gravity Current Entrainment Climate Process Team. Bulletin of the American Meteorological Society, 90(5): 657-+. ABS
Liepert, B. G. and M. Previdi, 2009: Do Models and Observations Disagree on the Rainfall Response to Global Warming? Journal of Climate, 22(11): 3156-3166. ABS
Liu, P., Y. Kajikawa, B. Wang, A. Kitoh, T. Yasunari, T. Li, H. Annamalai, X. H. Fu, K. Kikuchi, R. Mizuta, K. Rajendran, D. E. Waliser and D. Kim, 2009: Tropical Intraseasonal Variability in the MRI-20km60L AGCM. Journal of Climate, 22(8): 2006-2022. PDF ABS
Lyon, B. and S. J. Camargo, 2009: The seasonally-varying influence of ENSO on rainfall and tropical cyclone activity in the Philippines. Climate Dynamics, 32: 125-141, doi: 10.1007/s00382-008-0380-z.
Montes-Hugo, M., S.C. Doney, H.W. Ducklow, W. Fraser, D.G. Martinson, S.E. Stammerjohn and O. Schofield, 2009: Recent Changes in Phytoplankton Communities Associated with Rapid Regional Climate Change along the Western Antarctic Peninsula. Science, 323: 1470-1473, doi: 10.1126/science.1164533.
Nakamura, J., U. Lall, Y. Kushnir and S. J. Camargo, 2009: Classifying North Atlantic Tropical Cyclone Tracks by Mass Moments. Journal of Climate, 22(20): 5481-5494. PDF ABS
Nan, S. L., J. P. Li, X. J. Yuan and P. Zhao, 2009: Boreal spring Southern Hemisphere Annular Mode, Indian Ocean sea surface temperature, and East Asian summer monsoon. Journal of Geophysical Research-Atmospheres, 114: -. PDF ABS
Orton, Philip M. and Martin Visbeck, 2009: Variability of internally generated turbulence in an estuary, from 100 days of continuous observations. Continental Shelf Research, 29(1): 61-77. PDF
Ou, H. W., X. R. Guan and D. K. Chen, 2009: Tidal effect on the dense water discharge, Part 1: Analytical model. Deep-Sea Research Part Ii-Topical Studies in Oceanography, 56(13-14): 874-883. ABS
Patoux, J., X. J. Yuan and C. H. Li, 2009: Satellite-based midlatitude cyclone statistics over the Southern Ocean: 1. Scatterometer-derived pressure fields and storm tracking. Journal of Geophysical Research-Atmospheres, 114: -. PDF ABS
Previdi, M., K. Fennel, J. Wilkin and D. Haidvogel, 2009: Interannual variability in atmospheric CO2 uptake on the northeast US continental shelf. Journal of Geophysical Research-Biogeosciences, 114: -. ABS
Schubert, S., D. Gutzler, H. L. Wang, A. Dai, T. Delworth, C. Deser, K. Findell, R. Fu, W. Higgins, M. Hoerling, B. Kirtman, R. Koster, A. Kumar, D. Legler, D. Lettenmaier, B. Lyon, V. Magana, K. Mo, S. Nigam, P. Pegion, A. Phillips, R. Pulwarty, D. Rind, A. Ruiz-Barradas, J. Schemm, R. Seager, R. Stewart, M. Suarez, J. Syktus, M. F. Ting, C. Z. Wang, S. Weaver and N. Zeng, 2009: A US CLIVAR Project to Assess and Compare the Responses of Global Climate Models to Drought-Related SST Forcing Patterns: Overview and Results. Journal of Climate, 22(19): 5251-5272. PDF ABS
Seager, R., A. Tzanova and J. Nakamura, 2009: Drought in the Southeastern United States: Causes, Variability over the Last Millennium, and the Potential for Future Hydroclimate Change. Journal of Climate, 22(19): 5021-5045. PDF ABS
Seager, R., M. Ting, M. Davis, M. Cane, N. Naik(Henderson), J. Nakamura, C. Li, E. Cook and D. W. Stahle, 2009: Mexican drought: an observational modeling and tree ring study of variability and climate change. Atmosfera, 22(1): 1-31. PDF ABS
Shaw, W. J., T. P. Stanton, M. G. McPhee, J. H. Morison and D. G. Martinson, 2009: Role of the upper ocean in the energy budget of Arctic sea ice during SHEBA. Journal of Geophysical Research-Oceans, 114. ABS
Smerdon, J. E., H. Beltrami, C. Creelman and M. B. Stevens, 2009: Characterizing land surface processes: A quantitative analysis using air-ground thermal orbits. Journal of Geophysical Research-Atmospheres, 114: doi:10.1029/2009JD011768. PDF ABS
Son, S. W., M. F. Ting and L. M. Polvani, 2009: The Effect of Topography on Storm-Track Intensity in a Relatively Simple General Circulation Model. Journal of the Atmospheric Sciences, 66(2): 393-411. ABS
Sooraj, K. P., D. Kim, J. S. Kug, S. W. Yeh, F. F. Jin and I. S. Kang, 2009: Effects of the low-frequency zonal wind variation on the high frequency atmospheric variability over the tropics. Climate Dynamics, 33(4): 495-507. PDF ABS
Stahle, D. W. , E. R. Cook, J. Villanueva Diaz, F. K. Fye, D. J. Burnette, R. D. Griffin, R. Acuna Soto, R. Seager and Jr. R. R. Heim, 2009: Early 21st-Century Drought in Mexico. EOS, Vol. 90(11): 89-100. PDF
Tillinger, D. and A. L. Gordon, 2009: Fifty Years of the Indonesian Throughflow. Journal of Climate, 22(23): 6342-6355. ABS
Ting, M. F., Y. Kushnir, R. Seager and C. H. Li, 2009: Forced and Internal Twentieth-Century SST Trends in the North Atlantic. Journal of Climate, 22(6): 1469-1481. PDF ABS
Visbeck, M. and A. M. Thurnherr, 2009: High-resolution velocity and hydrographic observations of the Drygalski Trough gravity plume. Deep-Sea Research Part Ii-Topical Studies in Oceanography, 56(13-14): 835-842. ABS
Waliser, D., K. Sperber, H. Hendon, D. Kim, M. Wheeler, K. Weickmann, C. Zhang, L. Donner, J. Gottschalck, W. Higgins, I. S. Kang, D. Legler, M. Moncrieff, F. Vitart, B. Wang, W. Wang, S. Woolnough, E. Maloney, S. Schubert, W. Stern and Clivar Madden-Julian Oscillation, 2009: MJO Simulation Diagnostics. Journal of Climate, 22(11): 3006-3030. PDF ABS
Wells, A. J., C. Cenedese, J. T. Farrar and C. J. Zappa, 2009: Variations in Ocean Surface Temperature due to Near-Surface Flow: Straining the Cool Skin Layer. Journal of Physical Oceanography, 39(11): 2685-2710. ABS
Yuan, X. J., J. Patoux and C. H. Li, 2009: Satellite-based midlatitude cyclone statistics over the Southern Ocean: 2. Tracks and surface fluxes. Journal of Geophysical Research-Atmospheres, 114: -. PDF ABS
Zappa, C. J., D. T. Ho, W. R. McGillis, M. L. Banner, J. W. H. Dacey, L. F. Bliven, B. Ma and J. Nystuen, 2009: Rain-induced turbulence and air-sea gas transfer. Journal of Geophysical Research-Oceans, 114: -. ABS



Abstracts

Biasutti, M. and A. H. Sobel, 2009: Delayed Sahel rainfall and global seasonal cycle in a warmer climate. Geophysical Research Letters, 36( L23707, doi:10.1029/2009GL041303).

Twenty-first century projections of global rainfall and sea surface temperature in the current generation of climate models indicate a delay in the seasonal cycle in response to increasing greenhouse gases, with important implications for the regional monsoons. In particular, the rainy season of the semi-arid African Sahel is projected to start later and become shorter. The robust agreement across models on the seasonal distribution of Sahel rainfall changes stands in contrast with large uncertainty for summertime rainfall totals there. Citation: Biasutti, M., and A. H. Sobel (2009), Delayed Sahel rainfall and global seasonal cycle in a warmer climate, Geophys. Res. Lett., 36, L23707, doi: 10.1029/2009GL041303.


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Biasutti, M., A. H. Sobel and S. J. Camargo, 2009: The Role of the Sahara Low in Summertime Sahel Rainfall Variability and Change in the CMIP3 Models. Journal of Climate, 22(21): 5755-5771.

Projections for twenty-first-century changes in summertime Sahel precipitation differ greatly across models in the third Coupled Model Intercomparison Project (CMIP3) dataset and cannot be explained solely in terms of discrepancies in the projected anomalies in global SST.


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Camargo, S. J. and A. G. Barnston, 2009: Experimental Dynamical Seasonal Forecasts of Tropical Cyclone Activity at IRI. Weather and Forecasting, 24(2): 472-491.

The International Research Institute for Climate and Society (IRI) has been issuing experimental seasonal tropical cyclone activity forecasts for several ocean basins since early 2003. In this paper the method used to obtain these forecasts is described and the forecast performance is evaluated. The forecasts are based on tropical cyclone-like features detected and tracked in a low-resolution climate model, namely ECHAM4.5. The simulation skill of the model using historical observed sea surface temperatures (SSTs) over several decades, as well as with SST anomalies persisted from the previous month's observations, is discussed. These simulation skills are compared with skills of purely statistically based hindcasts using as predictors recently observed SSTs. For the recent 6-yr period during which real-time forecasts have been made, the skill of the raw model output is compared with that of the subjectively modified probabilistic forecasts actually issued. Despite variations from one basin to another, the levels of hindcast skill for the dynamical and statistical forecast approaches are found, overall, to be approximately equivalent at fairly modest but statistically significant levels. The dynamical forecasts require statistical postprossessing (calibration) to be competitive with, and in some circumstances superior to, the statistical models. Skill levels decrease only slowly with increasing lead time up to 2-3 months. During the recent period of real-time forecasts, the issued forecasts have had higher probabilistic skill than the raw model output, due to the forecasters' subjective elimination of the "overconfidence'' bias in the model's forecasts. Prospects for the future improvement of dynamical tropical cyclone prediction are considered.


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Camargo, S. J., M. C. Wheeler and A. H. Sobel, 2009: Diagnosis of the MJO modulation of tropical cyclogenesis using an empirical index. Journal of the Atmospheric Sciences, 66(2009): 3061-3074, doi: 10.1175/2009JAS3101.1.

The modulation of tropical cyclone activity by the Madden-Julian Oscillation (MJO) is explored using an empirical genesis potential (GP) index. Composite anomalies of the genesis index associated with the different MJO phases are consistent with the composite anomalies in TC genesis frequency which occur in the same phases, indicating that the index captures the changes in the environment which are at least in part responsible for the genesis frequency changes. Of the four environmental variables which enter the genesis potential index, the mid-level relative humidity makes the largest contribution to the MJO composite GP anomalies. The second largest contribution comes from the low-level absolute vorticity, and only very minor contributions come from the vertical wind shear and potential intensity.When basin-integrated MJO composite anomalies of the GP index are regressed against basin-integrated composite anomalies of TC genesis frequency, the results differ quantitatively from those obtained from the analogous calculation performed on the annual climatologies in the two quantities. The GP index captures the MJO modulation of TC genesis to a lesser degree than the climatological annual cycle of genesis (to which it was originally tuned). This may be due to weaknesses of the reanalysis or indicative of the importance of precursor disturbances, not well captured in the GP index computed from weekly data, to the intraseasonal TC genesis frequency fluctuations.


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Cook, B. I., R. L. Miller and R. Seager, 2009: Amplification of the North American "Dust Bowl" drought through human-induced land degradation. Proceedings of the National Academy of Sciences of the United States of America, 106(13): 4997-5001.

The "Dust Bowl" drought of the 1930s was highly unusual for North America, deviating from the typical pattern forced by "La Nina" with the maximum drying in the central and northern Plains, warm temperature anomalies across almost the entire continent, and widespread dust storms. General circulation models (GCMs), forced by sea surface temperatures (SSTs) from the 1930s, produce a drought, but one that is centered in southwestern North America and without the warming centered in the middle of the continent. Here, we show that the inclusion of forcing from human land degradation during the period, in addition to the anomalous SSTs, is necessary to reproduce the anomalous features of the Dust Bowl drought. The degradation over the Great Plains is represented in the GCM as a reduction in vegetation cover and the addition of a soil dust aerosol source, both consequences of crop failure. As a result of land surface feedbacks, the simulation of the drought is much improved when the new dust aerosol and vegetation boundary conditions are included. Vegetation reductions explain the high temperature anomaly over the northern U.S., and the dust aerosols intensify the drought and move it northward of the purely ocean-forced drought pattern. When both factors are included in the model simulations, the precipitation and temperature anomalies are of similar magnitude and in a similar location compared with the observations. Human-induced land degradation is likely to have not only contributed to the dust storms of the 1930s but also amplified the drought, and these together turned a modest SST-forced drought into one of the worst environmental disasters the U.S. has experienced.


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Gordon, A. L., A. H. Orsi, R. Muench, B. A. Huber, E. Zambianchi and M. Visbeck, 2009: Western Ross Sea continental slope gravity currents. Deep-Sea Research Part Ii-Topical Studies in Oceanography, 56(13-14): 796-817.

Antarctic Bottom Water of the world ocean is derived from dense Shelf Water that is carried downslope by gravity currents at specific sites along the Antarctic margins. Data gathered by the AnSlope and CLIMA programs reveal the presence of energetic gravity currents that are formed over the western continental slope of the Ross Sea when High Salinity Shelf Water exits the shelf through Drygalski Trough. Joides Trough, immediately to the east, offers an additional escape route for less saline Shelf Water, while the Glomar Challenger Trough still farther east is a major pathway for export of the once supercooled low-salinity Ice Shelf Water that forms under the Ross Ice Shelf. The Drygalski Trough gravity currents increase in thickness from similar to 100 to similar to 400 m on proceeding downslope from similar to 600 m (the shelf break) to 1200 m (upper slope) sea floor depth, while turning sharply to the west in response to the Coriolis force during their descent. The mean current pathway trends similar to 35 degrees downslope from isobaths. Benthic-layer current and thickness are correlated with the bottom water salinity, which exerts the primary control over the benthic-layer density. A 1-year time series of bottom-water current and hydrographic properties obtained on the slope near the 1000 m isobath indicates episodic pulses of Shelf Water export through Drygalski Trough. These cold (< -1 degrees C), salty (>34.75) pulses correlate with strong downslope bottom flow. Extreme examples occurred during austral summer/fall 2003, comprising concentrated High Salinity Shelf Water (-1.9 degrees C; 34.79) and approaching 1.5 m s(-1) at descent angles as large as similar to 60 degrees relative to the isobaths. Such events were most common during November-May, consistent with a northward shift in position of the dense Shelf Water during austral summer. The coldest, saltiest bottom water was measured from mid-April to mid-May 2003. The summer/fall export of High Salinity Shelf Water observed in 2004 was less than that seen in 2003. This difference, if real, may reflect the influence of the large iceberg C-19 over Drygalski Trough until its departure in mid-May 2003, when there was a marked decrease in the coldest, saltiest gravity current adjacent to Drygalski Trough. Northward transport of cold, saline, recently ventilated Antarctic Bottom Water observed in March 2004 off Cape Adare was similar to 1.7 Sv, including similar to 0.4 Sv of High Salinity Shelf Water. (C) 2008 Published by Elsevier Ltd.


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Guan, X. R., H. W. Ou and D. K. Chen, 2009: Tidal effect on the dense water discharge, Part 2: A numerical study. Deep-Sea Research Part Ii-Topical Studies in Oceanography, 56(13-14): 884-894.

In Part 1 of this two-part paper, an analytical model is presented to examine the tidal effect on the dense water discharge. it is hypothesized that the tide-induced shear dispersion would augment the benthic-layer thickness to significantly enhance the spread of dense water on the shelf and its descent down the continental slope. Here in Part 2, we carry out a numerical process study to assess the analytical model and to aid the interpretation of the observed phenomenon in the western Ross Sea.


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Han, W. Q., A. M. Moore, J. Levin, B. Zhang, H. G. Arango, E. Curchitser, E. Di Lorenzo, A. L. Gordon and J. L. Lin, 2009: Seasonal surface ocean circulation and dynamics in the Philippine Archipelago region during 2004-2008. Dynamics of Atmospheres and Oceans, 47(1-3): 114-137.

The dynamics of the seasonal surface circulation in the Philippine Archipelago (117 degrees E-128 degrees E, 0 degrees N-14 degrees N) are investigated using a high-resolution configuration of the Regional Ocean Modeling System (ROMS) for the period of January 2004-March 2008. Three experiments were performed to estimate the relative importance of local, remote and tidal forcing. On the annual mean, the circulation in the Sulu Sea shows inflow from the South China Sea at the Mindoro and Balabac Straits, outflow into the Sulawesi Sea at the Sibutu Passage, and cyclonic circulation in the southern basin. A strong jet with a maximum speed exceeding 100 cm, s(-1) forms in the northeast Sulu Sea where currents from the Mindoro and Tablas Straits converge. Within the Archipelago, strong westward currents in the Bohol Sea carry the surface water of the western Pacific (WP) from the Surigao Strait into the Sulu Sea via the Dipolog Strait. In the Sibuyan Sea, currents flow westward, which carry the surface water from the WP near the San Bernardino Strait into the Sulu Sea via the Tablas Strait.


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Huang, H. P., A. W. Robertson, Y. Kushnir and S. L. Peng, 2009: Hindcasts of Tropical Atlantic SST Gradient and South American Precipitation: The Influences of the ENSO Forcing and the Atlantic Preconditioning. Journal of Climate, 22(9): 2405-2421.

Hindcast experiments for the tropical Atlantic sea surface temperature (SST) gradient G1, defined as tropical North Atlantic SST anomaly minus tropical South Atlantic SST anomaly, are performed using an atmospheric general circulation model coupled to a mixed layer ocean over the Atlantic to quantify the contributions of the El Nino-Southern Oscillation (ENSO) forcing and the preconditioning in the Atlantic to G1 in boreal spring. The results confirm previous observational analyses that, in the years with a persistent ENSO SST anomaly from boreal winter to spring, the ENSO forcing plays a primary role in determining the tendency of G1 from winter to spring and the sign of G1 in late spring. In the hindcasts, the initial perturbations in Atlantic SST in boreal winter are found to generally persist beyond a season, leaving a secondary but nonnegligible contribution to the predicted Atlantic SST gradient in spring. For 1993/94, a neutral year with a large preexisting G1 in winter, the hindcast using the information of Atlantic preconditioning alone is found to reproduce the observed G1 in spring. The seasonal predictability in precipitation over South America is examined in the hindcast experiments. For the recent events that can be validated with high-quality observations, the hindcasts produced dryness in boreal spring 1983, wetness in spring 1996, and wetness in spring 1994 over northern Brazil that are qualitatively consistent with observations. An inclusion of the Atlantic preconditioning is found to help the prediction of South American rainfall in boreal spring. For the ENSO years, discrepancies remain between the hindcast and observed precipitation anomalies over northern and equatorial South America, an error that is partially attributed to the biased atmospheric response to ENSO forcing in the model. The hindcast of the 1993/94 neutral year does not suffer this error. It constitutes an intriguing example of useful seasonal forecast of G1 and South American rainfall anomalies without ENSO.


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Ihara, C. and Y. Kushnir, 2009: Change of mean midlatitude westerlies in 21st century climate simulations. Geophysical Research Letters, 36: -.

Changes in midlatitude westerlies over the Pacific jet region between the 20th century and 21st century in general circulation models participating in the recent IPCC-Forth Assessment are delineated. Outputs derived from individual models reveal that in almost all models analyzed the seasonal mean midlatitude jet streams in the northern hemispheric Pacific and west Atlantic during boreal winter and in the southern hemispheric Pacific during boreal summer are significantly intensified in warmer 21st century climate compared to the state in the 20th century at the upper part of the core, at 200-100 mb. Citation: Ihara, C., and Y. Kushnir (2009), Change of mean midlatitude westerlies in 21st century climate simulations, Geophys. Res. Lett., 36, L13701, doi: 10.1029/2009GL037674.


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Ihara, C., Y. Kushnir, M. A. Cane and V. H. de la Pena, 2009: Climate Change over the Equatorial Indo-Pacific in Global Warming. Journal of Climate, 22(10): 2678-2693.

The response of the equatorial Indian Ocean climate to global warming is investigated using model outputs submitted to the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. In all of the analyzed climate models, the SSTs in the western equatorial Indian Ocean warm more than the SSTs in the eastern equatorial Indian Ocean under global warming; the mean SST gradient across the equatorial Indian Ocean is anomalously positive to the west in a warmer twenty-first-century climate compared to the twentieth-century climate, and it is dynamically consistent with the anomalous westward zonal wind stress and anomalous positive zonal sea level pressure (SLP) gradient to the east at the equator. This change in the zonal SST gradient in the equatorial Indian Ocean is detected even in the lowest-emission scenario, and the size of the change is not necessarily larger in the higher-emission scenario.


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Karnauskas, K. B., R. Seager, A. Kaplan, Y. Kushnir and M. A. Cane, 2009: Observed Strengthening of the Zonal Sea Surface Temperature Gradient across the Equatorial Pacific Ocean. Journal of Climate, 22(16): 4316-4321.

Decadal variations of very small amplitude [similar to 0.3 degrees C in sea surface temperature (SST)] in the tropical Pacific Ocean, the genesis region of the interannual El Nino-Southern Oscillation (ENSO) phenomenon, have been shown to have powerful impacts on global climate. Future projections from different climate models do not agree on how this critical feature will change under the influence of anthropogenic forcing. A number of attempts have been made to resolve this issue by examining observed trends from the 1880s to the present, a period of rising atmospheric concentrations of greenhouse gases. A recent attempt concluded that the three major datasets disagreed on the trend in the equatorial gradient of SST. Using a corrected version of one of these datasets, and extending the analysis to the seasonal cycle, it is shown here that all agree that the equatorial Pacific zonal SST gradient has strengthened from 1880 to 2005 during the boreal fall when this gradient is normally strongest. This result appears to favor a theory for future changes based on ocean dynamics over one based on atmospheric energy considerations. Both theories incorporate the expectation, based on ENSO theory, that the zonal sea level pressure (SLP) gradient in the tropical Pacific is coupled to SST and should therefore strengthen along with the SST gradient. While the SLP gradient has not strengthened, it is found that it appears to have weakened only during boreal spring, consistent with the SST seasonal trends. Most of the coupled models included in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report underestimate the strengthening SST gradient in boreal fall, and show almost no change in the SLP gradient in any season. The observational analyses herein suggest that both theories are at work but with relative strengths that vary seasonally, and that the two theories need not be inconsistent with each other.


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Kim, D., K. Sperber, W. Stern, D. Waliser, I. S. Kang, E. Maloney, W. Wang, K. Weickmann, J. Benedict, M. Khairoutdinov, M. I. Lee, R. Neale, M. Suarez, K. Thayer-Calder and G. Zhang, 2009: Application of MJO Simulation Diagnostics to Climate Models. Journal of Climate, 22(23): 6413-6436.

The ability of eight climate models to simulate the Madden-Julian oscillation (MJO) is examined using diagnostics developed by the U. S. Climate Variability and Predictability (CLIVAR) MJO Working Group. Although the MJO signal has been extracted throughout the annual cycle, this study focuses on the boreal winter (November-April) behavior. Initially, maps of the mean state and variance and equatorial space-time spectra of 850-hPa zonal wind and precipitation are compared with observations. Models best represent the intraseasonal space-time spectral peak in the zonal wind compared to that of precipitation. Using the phase-space representation of the multivariate principal components (PCs), the life cycle properties of the simulated MJOs are extracted, including the ability to represent how the MJO evolves from a given subphase and the associated decay time scales. On average, the MJO decay (e-folding) time scale for all models is shorter (similar to 20-29 days) than observations (similar to 31 days). All models are able to produce a leading pair of multivariate principal components that represents eastward propagation of intraseasonal wind and precipitation anomalies, although the fraction of the variance is smaller than observed for all models. In some cases, the dominant time scale of these PCs is outside of the 30-80-day band.


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Kug, J. S., K. P. Sooraj, D. Kim, I. S. Kang, F. F. Jin, Y. N. Takayabu and M. Kimoto, 2009: Simulation of state-dependent high-frequency atmospheric variability associated with ENSO. Climate Dynamics, 32(5): 635-648.

High-frequency atmospheric variability depends on the phase of El Nino/Southern Oscillation (ENSO). Recently, there is increasing evidence that state-dependent high-frequency atmospheric variability significantly modulates ENSO characteristics. Hence, in this study, we examine the model simulations of high-frequency atmospheric variability and, further, its dependency on the El Nino phase, using atmospheric and coupled GCMs (AGCM and CGCM). We use two versions of physical packages here-with and without convective momentum transport (CMT)-in both models. We found that the CMT simulation gives rise to a large climatological zonal wind difference over the Pacific. Also, both the climate models show a significantly improved performance in simulating the state-dependent noise when the CMT parameterization is implemented. We demonstrate that the better simulation of the state-dependent noise results from a better representation of anomalous, as well as climatological, zonal wind. Our further comparisons between the simulations, demonstrates that low-frequency wind is a crucial factor in determining the state-dependency of high-frequency wind variability. Therefore, it is suggested that the so-called state-dependent noise is directly induced by the low-frequency wind anomaly, which is caused by SST associated with ENSO.


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Legg, S., B. Briegleb, Y. Chang, E. P. Chassignet, G. Danabasoglu, T. Ezer, A. L. Gordon, S. Griffies, R. Hallberg, L. Jackson, W. Large, T. M. Ozgokmen, H. Peters, J. Price, U. Riemenschneider, W. L. Wu, X. B. Xu and J. Y. Yang, 2009: Improving Oceanic Overflow Representation in Climate Models the Gravity Current Entrainment Climate Process Team. Bulletin of the American Meteorological Society, 90(5): 657-+.

Oceanic overflows are bottom-trapped density currents originating in semienclosed basins, such as the Nordic seas, or on continental shelves, such as the Antarctic shelf. Overflows are the source of most of the abyssal waters, and therefore play an important role in the large-scale ocean circulation, forming a component of the sinking branch of the thermohaline circulation. As they descend the continental slope, overflows mix vigorously with the surrounding oceanic waters, changing their density and transport significantly. These mixing processes occur on spatial scales well below the resolution of ocean climate models, with the result that deep waters and deep western boundary currents are simulated poorly. The Gravity Current Entrainment Climate Process Team was established by the U. S. Climate Variability and Prediction (CLIVAR) Program to accelerate the development and implementation of improved representations of overflows within large-scale climate models, bringing together climate model developers with those conducting observational, numerical, and laboratory process studies of overflows. Here, the organization of the Climate Process Team is described, and a few of the successes and lessons learned during this collaboration are highlighted, with some emphasis on the well-observed Mediterranean overflow. The Climate Process Team has developed several different overflow parameterizations, which are examined in a hierarchy of ocean models, from comparatively well-resolved regional models to the largest-scale global climate models.


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Liepert, B. G. and M. Previdi, 2009: Do Models and Observations Disagree on the Rainfall Response to Global Warming? Journal of Climate, 22(11): 3156-3166.

Recently analyzed satellite-derived global precipitation datasets from 1987 to 2006 indicate an increase in global-mean precipitation of 1.1%-1.4% decade(-1). This trend corresponds to a hydrological sensitivity (HS) of 7% K-1 of global warming, which is close to the Clausius-Clapeyron (CC) rate expected from the increase in saturation water vapor pressure with temperature. Analysis of two available global ocean evaporation datasets confirms this observed intensification of the atmospheric water cycle. The observed hydrological sensitivity over the past 20-yr period is higher by a factor of 5 than the average HS of 1.4% K-1 simulated in state-of-the-art coupled atmosphere-ocean climate models for the twentieth and twenty-first centuries. However, the analysis shows that the interdecadal variability in HS in the models is high-in particular in the twentieth-century runs, which are forced by both increasing greenhouse gas (GHG) and tropospheric aerosol concentrations. About 12% of the 20-yr time intervals of eight twentieth-century climate simulations from the third phase of the Coupled Model Intercomparison Project (CMIP3) have an HS magnitude greater than the CC rate of 6.5% K-1. The analysis further indicates different HS characteristics for GHG and tropospheric aerosol forcing agents. Aerosol-forced HS is a factor of 2 greater, on average, and the interdecadal variability is significantly larger, with about 23% of the 20-yr sensitivities being above the CC rate. By thermodynamically constraining global precipitation changes, it is shown that such changes are linearly related to the difference in the radiative imbalance at the top of the atmosphere (TOA) and the surface (i.e., the atmospheric radiative energy imbalance). The strength of this relationship is controlled by the modified Bowen ratio (here, global sensible heat flux change divided by latent heat flux change). Hydrological sensitivity to aerosols is greater than the sensitivity to GHG because the former have a stronger effect on the shortwave transmissivity of the atmosphere, and thus produce a larger change in the atmospheric radiative energy imbalance. It is found that the observed global precipitation increase of 13 mm yr(-1) decade(-1) from 1987 to 2006 would require a trend of the atmospheric radiative imbalance (difference between the TOA and the surface) of 0.7 W m(-2) decade(-1). The recovery from the El Chichon and Mount Pinatubo volcanic aerosol injections in 1982 and 1991, the satellite-observed reductions in cloudiness during the phase of increasing ENSO events in the 1990s, and presumably the observed reduction of anthropogenic aerosol concentrations could have caused such a radiative imbalance trend over the past 20 years. Observational evidence, however, is currently inconclusive, and it will require more detailed investigations and longer satellite time series to answer this question.


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Liu, P., Y. Kajikawa, B. Wang, A. Kitoh, T. Yasunari, T. Li, H. Annamalai, X. H. Fu, K. Kikuchi, R. Mizuta, K. Rajendran, D. E. Waliser and D. Kim, 2009: Tropical Intraseasonal Variability in the MRI-20km60L AGCM. Journal of Climate, 22(8): 2006-2022.

This study documents the detailed characteristics of the tropical intraseasonal variability (TISV) in the MRI-20km60L AGCM that uses a variant of the Arakawa-Schubert cumulus parameterization. Mean states, power spectra, propagation features, leading EOF modes, horizontal and vertical structures, and seasonality associated with the TISV are analyzed. Results show that the model reproduces the mean states in winds realistically and in convection comparable to that of the observations. However, the simulated TISV is less realistic. It shows low amplitudes in convection and low-level winds in the 30-60-day band. Filtered anomalies have standing structures. Power spectra and lag correlation of the signals do not propagate dominantly either in the eastward direction during boreal winter or in the northward direction during boreal summer. A combined EOF (CEOF) analysis shows that winds and convection have a loose coupling that cannot sustain the simulated TISV as realistically as that observed. In the composited mature phase of the simulated MJO, the low-level convergence does not lead convection clearly so that the moisture anomalies do not tilt westward in the vertical, indicating that the low-level convergence does not favor the eastward propagation. The less realistic TISV suggests that the representation of cumulus convection needs to be improved in this model.


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Nakamura, J., U. Lall, Y. Kushnir and S. J. Camargo, 2009: Classifying North Atlantic Tropical Cyclone Tracks by Mass Moments. Journal of Climate, 22(20): 5481-5494.

A new method for classifying tropical cyclones or similar features is introduced. The cyclone track is considered as an open spatial curve, with the wind speed or power information along the curve considered to be a mass attribute. The first and second moments of the resulting object are computed and then used to classify the historical tracks using standard clustering algorithms. Mass moments allow the whole track shape, length, and location to be incorporated into the clustering methodology. Tropical cyclones in the North Atlantic basin are clustered with K-means by mass moments, producing an optimum of six clusters with differing genesis locations, track shapes, intensities, life spans, landfalls, seasonal patterns, and trends. Even variables that are not directly clustered show distinct separation between clusters. A trend analysis confirms recent conclusions of increasing tropical cyclones in the basin over the past two decades. However, the trends vary across clusters.


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Nan, S. L., J. P. Li, X. J. Yuan and P. Zhao, 2009: Boreal spring Southern Hemisphere Annular Mode, Indian Ocean sea surface temperature, and East Asian summer monsoon. Journal of Geophysical Research-Atmospheres, 114: -.

The relationships among the boreal spring Southern Hemisphere Annular Mode (SAM), the Indian Ocean (IO) sea surface temperature (SST), and East Asian summer monsoon (EASM) are examined statistically in this paper. The variability of boreal spring SAM is closely related to the IO SST. When the SAM is in its strong positive phase in boreal spring, with low-pressure anomalies over the south pole and high-pressure anomalies over middle latitudes, SST over the subtropics and middle latitudes of the South Indian Ocean (SIO) increases, which persists into the summer. Following the positive SST anomalies over the subtropics and midlatitudes of the SIO, SST in the equatorial Indian Ocean and Bay of Bengal increases in summer. Moreover, the variability of SST in the equatorial Indian Ocean and Bay of Bengal is closely related to EASM. When SST in the equatorial Indian Ocean and Bay of Bengal increases, EASM tends to be weak. Therefore the IO SST may play an important role bridging boreal spring SAM and EASM. The atmospheric circulations and surface heat exchanges contribute to the SST anomalies in the SIO. When the spring SAM is in its strong positive phases, the regional Ferrel Cell weakens, and the anomalous upward motions at 20 degrees S-30 degrees S cause an increase of low cloud cover and downward longwave radiation flux. The surface atmospheric circulations also transport more (less) warmer (cooler) air from middle latitudes north of 50 degrees S (high latitudes south of 60 degrees S) into 50 degrees S-60 degrees S and warm the air, which reduces the temperature difference between the ocean and atmosphere and consequently reduces sensible heat flux from the ocean to atmosphere. The increased downward longwave radiation and decreased sensible heat are responsible for the SST increase in the SIO. The atmospheric circulation and surface heat flux anomalies are of opposite signs following the strong negative phases of SAM.


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Ou, H. W., X. R. Guan and D. K. Chen, 2009: Tidal effect on the dense water discharge, Part 1: Analytical model. Deep-Sea Research Part Ii-Topical Studies in Oceanography, 56(13-14): 874-883.

It is hypothesized that tidally induced shear dispersion may significantly enhance the spread and descent of the dense water. Here, we present an analytical model to elucidate the basic physics, to be followed (in Part 2) by a numerical study using a primitive-equation model.


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Patoux, J., X. J. Yuan and C. H. Li, 2009: Satellite-based midlatitude cyclone statistics over the Southern Ocean: 1. Scatterometer-derived pressure fields and storm tracking. Journal of Geophysical Research-Atmospheres, 114: -.

A wavelet-based method is described for incorporating swaths of surface pressure derived from scatterometer measurements into surface pressure analyses obtained from the European Centre for Medium-range Weather Forecasts (ECMWF). The resulting modified pressure fields are used to identify low-pressure centers over the Southern Ocean and to build statistics of midlatitude cyclones during 7 years of the SeaWinds-on-QuikSCAT operational period (July 1999 to June 2006). The impact of the scatterometer-derived pressure swaths is assessed with a statistical analysis of cyclone characteristics (central pressure, radius, depth) performed in parallel on the ECMWF and on the modified pressure fields. More low-pressure centers (5-10% depending on the season) are identified with the modified pressure fields, in particular incipient lows captured earlier than ECMWF and more short-lived mesoscale cyclones (with a life span less than 4 days). The cyclones identified with the modified pressure fields are characterized by lower central pressure and tighter isobars on average. A parallel spectral analysis reveals similar to 1% additional energy at scales less than 2000 km in the modified pressure fields.


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Previdi, M., K. Fennel, J. Wilkin and D. Haidvogel, 2009: Interannual variability in atmospheric CO2 uptake on the northeast US continental shelf. Journal of Geophysical Research-Biogeosciences, 114: -.

Continental shelf systems are thought to play an important role in the exchange of carbon dioxide (CO2) between the atmosphere and ocean. Currently, our ability to quantify the air-sea flux of CO2 on continental shelves is limited due to large spatial and temporal variability coupled with historically sparse oceanographic measurements (e.g., of surface water pCO(2)). Here we use the Regional Ocean Modeling System (ROMS) to quantify the air-sea flux of CO2 and its interannual variability on the northeast U. S. continental shelf, which includes the Middle Atlantic Bight (MAB) and Gulf of Maine (GOM). Two years marked by opposite phases of the North Atlantic Oscillation (NAO) are considered in the study. A novel analysis method, second-order Taylor series decomposition, is used to identify the important processes responsible for producing NAO-related changes in the CO2 air-sea flux. On the northeast U. S. shelf, atmospheric CO2 uptake as simulated by ROMS decreases from 2.4 Mt C yr(-1) in 1985 ( low NAO) to 1.8 Mt C yr(-1) in 1990 (high NAO), with most of this decrease (0.5 Mt C yr(-1)) occurring in the MAB. In the MAB the difference in annual air-sea flux of CO2 is due mainly to changes in near-surface wind speed, while the flux difference in the GOM is controlled primarily by surface water pCO(2) ( CO2 partial pressure) changes resulting from changes in sea surface temperature and new production. The large magnitude of interannual variability in the air-sea flux of CO2 simulated here suggests the potential for even more significant flux changes in the future as climate change accelerates.


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Schubert, S., D. Gutzler, H. L. Wang, A. Dai, T. Delworth, C. Deser, K. Findell, R. Fu, W. Higgins, M. Hoerling, B. Kirtman, R. Koster, A. Kumar, D. Legler, D. Lettenmaier, B. Lyon, V. Magana, K. Mo, S. Nigam, P. Pegion, A. Phillips, R. Pulwarty, D. Rind, A. Ruiz-Barradas, J. Schemm, R. Seager, R. Stewart, M. Suarez, J. Syktus, M. F. Ting, C. Z. Wang, S. Weaver and N. Zeng, 2009: A US CLIVAR Project to Assess and Compare the Responses of Global Climate Models to Drought-Related SST Forcing Patterns: Overview and Results. Journal of Climate, 22(19): 5251-5272.

The U. S. Climate Variability and Predictability (CLIVAR) working group on drought recently initiated a series of global climate model simulations forced with idealized SST anomaly patterns, designed to address a number of uncertainties regarding the impact of SST forcing and the role of land-atmosphere feedbacks on regional drought. The runs were carried out with five different atmospheric general circulation models (AGCMs) and one coupled atmosphere-ocean model in which the model was continuously nudged to the imposed SST forcing. This paper provides an overview of the experiments and some initial results focusing on the responses to the leading patterns of annual mean SST variability consisting of a Pacific El Nino-Southern Oscillation (ENSO)-like pattern, a pattern that resembles the Atlantic multidecadal oscillation (AMO), and a global trend pattern.


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Seager, R., A. Tzanova and J. Nakamura, 2009: Drought in the Southeastern United States: Causes, Variability over the Last Millennium, and the Potential for Future Hydroclimate Change. Journal of Climate, 22(19): 5021-5045.

An assessment of the nature and causes of drought in the southeastern United States is conducted as well as an assessment of model projections of anthropogenically forced hydroclimate change in this region. The study uses observations of precipitation, model simulations forced by historical SSTs from 1856 to 2007, tree-ring records of moisture availability over the last millennium, and climate change projections conducted for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. From the perspective of the historical record, the recent drought that began in winter 2005/06 was a typical event in terms of amplitude and duration. Observations and model simulations are used to show that dry winter half-years in the Southeast are weakly associated with La Niñas in the tropical Pacific but that this link varies over time and was possibly of opposite sign from about 1922 to 1950. Summer-season precipitation variability in the Southeast appears governed by purely internal atmospheric variability. As such, model simulations forced by historical SSTs have very limited skill in reproducing the instrumental record of Southeast precipitation variability and actual predictive skill is also presumably low. Tree-ring records show that the twentieth century has been moist from the perspective of the last millennium and free of long and severe droughts that were abundant in previous centuries. The tree-ring records show a 21-yr-long uninterrupted drought in the mid-sixteenth century, a long period of dry conditions in the early to mid-nineteenth century, and that the Southeast was also affected by some of the medieval megadroughts centered in western North America. Climate model projections predict that in the near term, future precipitation in the Southeast will increase but that evaporation will also increase. The median of the projections predicts a modest reduction in the atmospheric supply of water vapor to the region; however, the multimodel ensemble exhibits considerable variation, with a quarter to a third of the models projecting an increase in precipitation minus evaporation. The recent drought, forced by reduced precipitation and with reduced evaporation, has no signature of model-projected anthropogenic climate change.


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Seager, R., M. Ting, M. Davis, M. Cane, N. Naik(Henderson), J. Nakamura, C. Li, E. Cook and D. W. Stahle, 2009: Mexican drought: an observational modeling and tree ring study of variability and climate change. Atmosfera, 22(1): 1-31.

Variability of Mexican hydroclimate, with special attention to persistent drought, is examined using observations, model simulations forced by historical sea surface temperature (SST), tree ring reconstructions of past climate and model simulations and projections of naturally and anthropogenically forced climate change. During the winter half year, hydroclimate across Mexico is influenced by the state of the tropical Pacific Ocean with the Atlantic playing little role. Mexican winters tend to be wetter during El Niño conditions. In the summer half year northern Mexico is also wetter when El Niño conditions prevail, but southern Mexico is drier. A warm tropical North Atlantic Ocean makes northern Mexico dry and southern Mexico wet. These relationships are reasonably well reproduced in ensembles of atmosphere model simulations forced by historical SST for the period from 1856 to 2002. Large ensembles of 100 day long integrations are used to examine the day to day evolution of the atmospheric circulation and precipitation in response to a sudden imposition of a El Niño SST anomaly in the summer half year. Kelvin waves propagate east and immediately cause increased column-integrated moisture divergence and reduced precipitation over the tropical Americas and Intra-America Seas. Within a few days a low level high pressure anomaly develops over the Gulf of Mexico. A forced nonlinear model is used to demonstrate that this low is forced by the reduced atmospheric heating over the tropical Atlantic-Intra-America Seas area. Tree ring reconstructions that extend back before the period of instrumental precipitation data coverage are used to verify long model simulations forced by historical SST. The early to mid 1950s drought in northern Mexico appears to have been the most severe since the mid nineteenth century and likely arose as a response to both a multiyear La Niña and a warm tropical North Atlantic. A drought in the 1890s was also severe and appears driven by a multiyear La Niña alone. The drought that began in the 1990s does not exceed these droughts in either duration or severity. Tree ring records extending back to the fourteenth century suggest that the late sixteenth century megadrought may have been the longest drought to have ever affected Mexico. While the last decade or so in north and central Mexico has been drier than preceding decades, the associated continental pattern of hydroclimate change does not fit that which models project to occur as a consequence of rising greenhouse gases and global warming. However, models robustly predict that Mexico will dry as a consequence of global warming and that this drying should already be underway. At least for now, in nature, this is likely obscured by strong natural atmosphere-ocean variability.


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Shaw, W. J., T. P. Stanton, M. G. McPhee, J. H. Morison and D. G. Martinson, 2009: Role of the upper ocean in the energy budget of Arctic sea ice during SHEBA. Journal of Geophysical Research-Oceans, 114.

As part of the 1997-1998 Surface Heat Budget of the Arctic Experiment (SHEBA), a nearly yearlong record of upper ocean observations was obtained below a drifting ice camp in the Beaufort Gyre. A combination of observational and numerical modeling techniques are used to estimate heat fluxes across the under-ice ocean boundary layer. Over the Canada Basin, the upper pycnocline contained moderate heat, but strong stratification effectively insulated it from mixed layer turbulence. Average resulting heat fluxes at the base of the mixed layer (F-pyc) and at the ocean-ice interface ( F-0) were small (0.3-1.2 and 0.2 W m(-2), respectively). Over the Chukchi Borderlands, the presence of relatively warm and salty Pacific origin water increased upper pycnocline heat content and reduced stratification, which permitted moderate F-pyc and F-0 (2.1-3.7 and 3.5 W m(-2), respectively). Solar insolation was the dominant heat source during the final, summertime portion of the drift. During the heating period, F-pyc was relatively small (0.4-1.5 W m(-2)) while F-0 was large (16.3 W m(-2)). The drift-averaged value of F-0 was 7.6 W m(-2). Energy budgets for the ice cover were constructed. The oceanic contribution to the budget during the portion of the drift over the Chukchi Borderlands, supported by entrainment of heat stored in the upper pycnocline, was responsible for a 15% reduction in ice growth. During the summer heating season, the F-0 estimates were larger than the latent energy changes associated with basal melting.


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Smerdon, J. E., H. Beltrami, C. Creelman and M. B. Stevens, 2009: Characterizing land surface processes: A quantitative analysis using air-ground thermal orbits. Journal of Geophysical Research-Atmospheres, 114: doi:10.1029/2009JD011768.

A quantitative analysis of thermal orbits is developed and applied to modeled air and ground temperatures. Thermal orbits are phase-space representations of air and ground temperature relationships that are generated by plotting daily or monthly ground temperatures against air temperatures. Thermal orbits are useful descriptive tools that provide straightforward illustrations of air and ground temperature relationships in the presence of land surface processes related to snow cover, soil freezing, and vegetation effects. The utility of thermal orbits has been limited, however, by the lack of quantitative analyses that describe changes in orbits across different environments or in time. This shortcoming is overcome in the present study by developing a linear regression analysis of thermal orbits that allows changes to be tracked in time and space and as a function of depth within the subsurface. The theory that underlies the thermal orbit regression analysis is developed herein, and the utility of the application is demonstrated using controlled model experiments.


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Son, S. W., M. F. Ting and L. M. Polvani, 2009: The Effect of Topography on Storm-Track Intensity in a Relatively Simple General Circulation Model. Journal of the Atmospheric Sciences, 66(2): 393-411.

The effect of topography on storm-track intensity is examined with a set of primitive equation model integrations. This effect is found to be crucially dependent on the latitudinal structure of the background flow impinging on the topography. If the background flow consists of a weak double jet, higher topography leads to an intensification of the storm track downstream of the topography, consistent with enhanced baroclinicity in that region. However, if the background flow consists of a strong single jet, topography weakens the storm track, despite the fact that the baroclinicity downstream of the topography is again enhanced.


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Sooraj, K. P., D. Kim, J. S. Kug, S. W. Yeh, F. F. Jin and I. S. Kang, 2009: Effects of the low-frequency zonal wind variation on the high frequency atmospheric variability over the tropics. Climate Dynamics, 33(4): 495-507.

Recently, there is increasing evidence on the interaction of atmospheric high-frequency (HF) variability with climatic low-frequency (LF) variability. In this study, we examine this relationship of HF variability with large scale circulation using idealized experiments with an aqua-planet Atmospheric GCM (with zonally uniform SST), run in different zonal momentum forcing scenarios. The effect of large scale circulation changes to the HF variability is demonstrated here. The HF atmospheric variability is enhanced over the westerly forced region, through easterly vertical shear. Our study also manifests that apart from the vertical wind shear, strong low-level convergence and horizontal zonal wind shear are also important for enhancing the HF variance. This is clearly seen in the eastern part of the forcing, where the HF activity shows relatively maximum increase, in spite of similar vertical shear over the forced regions. The possible implications for multi-scale interaction (e.g. MJO-ENSO interaction) are also discussed.


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Tillinger, D. and A. L. Gordon, 2009: Fifty Years of the Indonesian Throughflow. Journal of Climate, 22(23): 6342-6355.

Simple Ocean Data Assimilation (SODA) reanalysis data are used to produce a 50-yr record of flow through the Makassar Strait, the primary conduit for the Indonesian Throughflow (ITF). Two time series are constructed for comparison to the flow through the Makassar Strait as observed during 1997-98 and 2004-06: SODA along-channel speed within the Makassar Strait and Pacific to Indian Ocean interocean pressure difference calculated on isopycnal layers from SODA hydrology. These derived time series are compared to the total ITF as well as to the vertical distribution and frequency bands of ITF variability. The pressure difference method displays higher skill in replicating the observed Makassar ITF time series at periods longer than 9 months, particularly within the thermocline layer (50-200 m), the location of maximum flow. This is attributed to the connection between the thermocline layer and large-scale wind forcing, which affects the hydrology of the ITF inflow and outflow regions. In contrast, the surface layer (0-50 m) is more strongly correlated with local wind flow, and it is better predicted by SODA along-channel velocity. The pressure difference time series is extended over the 50-yr period of SODA and displays a strong correlation with ENSO as well as a correlation at the decadal scale with the island rule.


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Ting, M. F., Y. Kushnir, R. Seager and C. H. Li, 2009: Forced and Internal Twentieth-Century SST Trends in the North Atlantic. Journal of Climate, 22(6): 1469-1481.

In recent years, two alarming trends in North Atlantic climate have been noted: an increase in the intensity and frequency of Atlantic hurricanes and a rapid decrease in Greenland ice sheet volume. Both of these phenomena occurred while a significant warming took place in North Atlantic sea surface temperatures (SSTs), thus sparking a debate on whether the warming is a consequence of natural climate variations, anthropogenic forcing, or both; and if both, what their relative roles are. Here models and observations are used to detect and attribute long-term (multidecadal) twentieth-century North Atlantic (NA) SST changes to their anthropogenic and natural causes. A suite of Intergovernmental Panel on Climate Change (IPCC) twentieth-century (C20C) coupled model simulations with multiple ensemble members and a signal-to-noise maximizing empirical orthogonal function analysis are used to identify a model-based estimate of the forced, anthropogenic component in NA SST variability. Comparing the results to observations, it is argued that the long-term, observed, North Atlantic basin-averaged SSTs combine a forced global warming trend with a distinct, local multidecadal "oscillation" that is outside of the range of the model-simulated, forced component and most likely arose from internal variability. This internal variability produced a cold interval between 1900 and 1930, followed by 30 yr of relative warmth and another cold phase from 1960 to 1990, and a warming since then. This natural variation, referred to previously as the Atlantic Multidecadal Oscillation (AMO), thus played a significant role in the twentieth-century NA SST variability and should be considered in future, near-term climate projections as a mechanism that, depending on its behavior, can act either constructively or destructively with the region's response to anthropogenic influence, temporarily amplifying or mitigating regional climate change.


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Visbeck, M. and A. M. Thurnherr, 2009: High-resolution velocity and hydrographic observations of the Drygalski Trough gravity plume. Deep-Sea Research Part Ii-Topical Studies in Oceanography, 56(13-14): 835-842.

During the second cruise of the AnSlope project, the hydrography and velocity fields within a descending gravity plume in the northwestern Ross Sea Shelf area were sampled at high resolution. The observations give insights into small-scale fluctuations of the three-dimensional velocity field in and around the core of a strong gravity current, associated with peak velocities close to 2 m/s. There are two distinct layers of high acoustic backscatter (at 300 kHz) near the seabed associated with increased velocity variance and Richardson numbers near 0.25, suggesting that the high backscatter is caused by increased levels of turbulence resulting in increased acoustic Bragg scattering. (C) 2008 Elsevier Ltd. All rights reserved.


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Waliser, D., K. Sperber, H. Hendon, D. Kim, M. Wheeler, K. Weickmann, C. Zhang, L. Donner, J. Gottschalck, W. Higgins, I. S. Kang, D. Legler, M. Moncrieff, F. Vitart, B. Wang, W. Wang, S. Woolnough, E. Maloney, S. Schubert, W. Stern and Clivar Madden-Julian Oscillation, 2009: MJO Simulation Diagnostics. Journal of Climate, 22(11): 3006-3030.

The Madden-Julian oscillation (MJO) interacts with and influences a wide range of weather and climate phenomena (e. g., monsoons, ENSO, tropical storms, midlatitude weather), and represents an important, and as yet unexploited, source of predictability at the subseasonal time scale. Despite the important role of the MJO in climate and weather systems, current global circulation models (GCMs) exhibit considerable shortcomings in representing this phenomenon. These shortcomings have been documented in a number of multimodel comparison studies over the last decade. However, diagnosis of model performance has been challenging, and model progress has been difficult to track, because of the lack of a coherent and standardized set of MJO diagnostics. One of the chief objectives of the U. S. Climate Variability and Predictability (CLIVAR) MJO Working Group is the development of observation-based diagnostics for objectively evaluating global model simulations of the MJO in a consistent framework. Motivation for this activity is reviewed, and the intent and justification for a set of diagnostics is provided, along with specification for their calculation, and illustrations of their application. The diagnostics range from relatively simple analyses of variance and correlation to more sophisticated space-time spectral and empirical orthogonal function analyses. These diagnostic techniques are used to detect MJO signals, to construct composite life cycles, to identify associations of MJO activity with the mean state, and to describe interannual variability of the MJO.


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Wells, A. J., C. Cenedese, J. T. Farrar and C. J. Zappa, 2009: Variations in Ocean Surface Temperature due to Near-Surface Flow: Straining the Cool Skin Layer. Journal of Physical Oceanography, 39(11): 2685-2710.

The aqueous thermal boundary layer near to the ocean surface, or skin layer, has thickness O(1 mm) and plays an important role in controlling the exchange of heat between the atmosphere and the ocean. Theoretical arguments and experimental measurements are used to investigate the dynamics of the skin layer under the influence of an upwelling flow, which is imposed in addition to free convection below a cooled water surface. Previous theories of straining flow in the skin layer are considered and a simple extension of a surface straining model is posed to describe the combination of turbulence and an upwelling flow. An additional theory is also proposed, conceptually based on the buoyancy-driven instability of a laminar straining flow cooled from above. In all three theories considered two distinct regimes are observed for different values of the Peclet number, which characterizes the ratio of advection to diffusion within the skin layer. For large Peclet numbers, the upwelling flow dominates and increases the free surface temperature, or skin temperature, to follow the scaling expected for a laminar straining flow. For small Peclet numbers, it is shown that any flow that is steady or varies over long time scales produces only a small change in skin temperature by direct straining of the skin layer. Experimental measurements demonstrate that a strong upwelling flow increases the skin temperature and suggest that the mean change in skin temperature with Peclet number is consistent with the theoretical trends for large Peclet number flow. However, all of the models considered consistently underpredict the measured skin temperature, both with and without an upwelling flow, possibly a result of surfactant effects not included in the models.


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Yuan, X. J., J. Patoux and C. H. Li, 2009: Satellite-based midlatitude cyclone statistics over the Southern Ocean: 2. Tracks and surface fluxes. Journal of Geophysical Research-Atmospheres, 114: -.

Midlatitude cyclone tracks over the Southern Ocean are constructed for the 1999-2006 period using two surface data sets: European Centre for Medium-range Weather Forecasts (ECMWF) sea-level pressure analyses on one hand, and on the other hand modified analyses in which high-wavenumber pressure variability derived from scatterometer swaths has been injected with a wavelet-based method. A comparison of track statistics reveals the differences between the two data sets. The fluxes of momentum and sensible and latent heat associated with these midlatitude cyclones are calculated and sorted by life span. Three aspects of these cyclone flux statistics are investigated. (1) The momentum flux into the ocean is stronger inside cyclones than over the rest of the Southern Ocean, while the ocean loses more sensible and latent heat outside of the cyclones. (2) The momentum flux into the ocean and the loss of sensible and latent heat by the ocean are larger when calculated from the scatterometer-modified analyses than when calculated from the original ECMWF analyses. (3) Mesoscale cyclones (short-lived cyclones) contribute a significant amount of the fluxes between the atmosphere and the Southern Ocean, although over slightly different geographic areas from longer-lived cyclones.


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Zappa, C. J., D. T. Ho, W. R. McGillis, M. L. Banner, J. W. H. Dacey, L. F. Bliven, B. Ma and J. Nystuen, 2009: Rain-induced turbulence and air-sea gas transfer. Journal of Geophysical Research-Oceans, 114: -.

Results from a rain and gas exchange experiment (Bio2 RainX III) at the Biosphere 2 Center demonstrate that turbulence controls the enhancement of the air-sea gas transfer rate (or velocity) k during rainfall, even though profiles of the turbulent dissipation rate epsilon are strongly influenced by near-surface stratification. The gas transfer rate scales with epsilon(1/4) for a range of rain rates with broad drop size distributions. The hydrodynamic measurements elucidate the mechanisms responsible for the rain-enhanced k results using SF6 tracer evasion and active controlled flux technique. High-resolution k and turbulence results highlight the causal relationship between rainfall, turbulence, stratification, and air-sea gas exchange. Profiles of epsilon beneath the air-sea interface during rainfall, measured for the first time during a gas exchange experiment, yielded discrete values as high as 10(-2) W kg(-1). Stratification modifies and traps the turbulence near the surface, affecting the enhancement of the transfer velocity and also diminishing the vertical mixing of mass transported to the air-water interface. Although the kinetic energy flux is an integral measure of the turbulent input to the system during rain events, epsilon is the most robust response to all the modifications and transformations to the turbulent state that follows. The Craig-Banner turbulence model, modified for rain instead of breaking wave turbulence, successfully predicts the near-surface dissipation profile at the onset of the rain event before stratification plays a dominant role. This result is important for predictive modeling of k as it allows inferring the surface value of epsilon fundamental to gas transfer.


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The database was updated today.

Maintained by: Virginia DiBlasi, Lamont-Doherty Earth Observatory of Columbia University