Biasutti, M., D. S. Battisti and E. S. Sarachik, 2004: Mechanisms controlling the annual cycle of precipitation in the tropical Atlantic sector in an atmospheric GCM. Journal of Climate, 17(24): 4708-4723.
A set of AGCM experiments is used to study the annual cycle of precipitation in the region surrounding the tropical Atlantic Ocean. The experiments are designed to reveal the relative importance of insolation over land and the (uncoupled) SST on the annual cycle of precipitation over the tropical Atlantic Ocean, Africa, and the tropical Americas.
Black, D. E., R. C. Thunell, A. Kaplan, L. C. Peterson and E. J. Tappa, 2004: A 2000-year record of Caribbean and tropical North Atlantic hydrographic variability. Paleoceanography, 19(2): doi:10.1029/2003PA000982.
Here we present near-annually resolved oxygen isotope records from two species of planktic foraminifera from the Cariaco Basin that reflect sea surface temperature (SST) and Intertropical Convergence Zone (ITCZ) precipitation-related salinity variations over the Caribbean and tropical North Atlantic spanning the last 2000 years. A strong, broad spatial pattern of correlation exists between foraminiferal delta(18)O and SSTs over the period of instrumental overlap, but the correlations weaken as they are extended back in time and instrumental SST records become discontinuous. A long-term trend in the Globigerinoides ruber delta(18)O record can be explained by two different but equally plausible scenarios. First, the increase in delta(18)O may indicate that tropical summer-fall SSTs have cooled by as much as 2degreesC over the last 2000 years, possibly as a result of a long-term increase in upwelling intensity. Alternately, comparisons to other studies of ITCZ and regional evaporation/precipitation variability suggest that much of the delta(18)O record is influenced by decadal-tocentennial-scale variations in the mean annual position of the ITCZ and associated rainfall patterns. Similarities between the G. bulloides delta(18)O record and the 11-year sunspot cycle support prior studies that suggest solar variability plays a role in influencing the hydrologic balance of the circum-Caribbean.
Camargo, S. J. and A. H. Sobel, 2004: Formation of tropical storms in an atmospheric general circulation model. Tellus Series a-Dynamic Meteorology and Oceanography, 56(1): 56-67.
The formation of tropical storms in a low-resolution Atmospheric General Circulation model is studied over the western North Pacific region during the June-October season. The model simulates the mean annual cycle of storm number in this basin quite well. Time-dependent composites of the storms are formed and analyzed, with a focus on the temporal evolution of quantities averaged in space around the storm centers. Day zero of each composite corresponds to the time at which the disturbance passes criteria for detection. The composites depict the model storms as convectively coupled, synoptic-scale vortices whose degree of coupling to convection increases at some point, leading to intensification. Variables related to disturbance intensity have significant anomalies at day -7, indicating a finite amplitude disturbance prior to "genesis". Many of these variables show similar temporal evolution, with a local minimum two or three days before day zero, and a strong increase after that for several days, followed by an eventual decrease. The precipitation reaches its maximum on day 2, the net moist static energy forcing (surface fluxes minus net tropospheric radiative cooling, each of which has an anomaly of 20-30 W m(-2) in the sense of warming the atmosphere) a day later, and dynamical variables such as vorticity and temperature still later, with broad plateaus centered around day 4 or 5. The vorticity increases at the surface at the same time as at midlevels, unlike in observed storms. The mean composite environmental vertical wind shear has a maximum amplitude on day -2 and then decreases. This could indicate a causal role of shear in limiting development, but would also be consistent with a coincidental storm motion to regions of lower shear, with development controlled by other factors. A signal in the skewness of the lower-level relative humidity distribution over the ensemble suggests that a dry lower troposphere can prevent development of a model tropical disturbance.
Chen, D. K. and X. J. Yuan, 2004: A Markov model for seasonal forecast of Antarctic sea ice. Journal of Climate, 17(16): 3156-3168.
A linear Markov model has been developed to simulated and predict the short-term climate change in the Antarctic, with particular emphasis on sea ice variability. Seven atmospheric variables along with sea ice were chosen to define the state of the Antarctic climate, and the multivariate empirical orthogonal functions of these variables were used as the building blocks of the model. The predictive skill of the model was evaluated in a cross-validated fashion, and a series of sensitivity experiments was carried out. In both hindcast and forecast experiments, the model showed considerable skill in predicting the anomalous Antarctic sea ice concentration up to 1 yr in advance, especially in austral winter and in the Antarctic dipole regions. The success of the model is attributed to the domination of the Antarctic climate variability by a few distinctive modes in the coupled air-sea-ice system and to the model's ability to detect these modes. This model is presently being used for the experimental seasonal forecasting of Antarctic sea ice, and a current prediction example is presented.
Chen, D., M. A. Cane, A. Kaplan, S. E. Zebiak and D. J. Huang, 2004: Predictability of El Niño over the past 148 years. Nature, 428(6984): 733-736.
Forecasts of El Niño climate events are routinely provided and distributed, but the limits of El Niño predictability are still the subject of debate. Some recent studies suggest that the predictability is largely limited by the effects of high-frequency atmospheric 'noise'(1-7), whereas others emphasize limitations arising from the growth of initial errors in model simulations(8-10). Here we present retrospective forecasts of the interannual climate fluctuations in the tropical Pacific Ocean for the period 1857 to 2003, using a coupled ocean-atmosphere model. The model successfully predicts all prominent El Niño events within this period at lead times of up to two years. Our analysis suggests that the evolution of El Niño is controlled to a larger degree by self-sustaining internal dynamics than by stochastic forcing. Model-based prediction of El Niño therefore depends more on the initial conditions than on unpredictable atmospheric noise. We conclude that throughout the past century, El Niño has been more predictable than previously envisaged.
Chou, C. B. and H. P. Huang, 2004: A new procedure for estimating observation errors in AMSU data and its application to retrieval. Quarterly Journal of the Royal Meteorological Society, 130(596): 79-101.
An accurate estimate of observation errors is crucial to the retrieval of atmospheric profiles from satellite data using a variational method. In practice, observation errors, both systematic and random, are often estimated from the difference between satellite observations and simulated satellite observations obtained front a radiative-transfer operator with a 12 h forecast as its input. Observation errors estimated by this approach may be contaminated by errors in the 12 h forecast. This work describes a practical way to eliminate the 12 h forecast error and improve the estimate of the observation error in the Advanced Microwave Sounding Unit (AMSU) data. Following the philosophy of the National Meteorological Center (NMC) method (that derives the statistics of forecast error from the differences between pairs of forecasts at disparate ranges valid at the same time), in this study the pairs of forecasts at different ranges in the NMC method are first converted to brightness temperatures in the AMSU channels by a radiative-transfer operator. The 12 h forecast errors are then determined from the representations of these forecasts in radiance space spanned by the AMSU channels. Since most AMSU channels have beam position-dependent systematic observation errors, the procedure further takes into account this dependence by performing the statistics separately for sub-groups of data in each AMSU channel with different beam positions. In a case-study, after eliminating the 12 h forecast error obtained by this procedure from the total estimated observation error. the remaining random error of the satellite observation is shown to be smaller than the background error (provided by 12 It forecasts of a numerical weather-prediction model) in most of the AMSU temperature sounding channels. Using the error-corrected AMSU data in these channels, a retrieval experiment using a one-dimensional variational scheme shows an improvement of 0.2-0.4 K over the background error in the retrieved temperature profiles above 780 hPa.
Cook, B. I., M. E. Mann, P. D'Odorico and T. M. Smith, 2004: Statistical simulation of the influence of the NAO on European winter surface temperatures: Applications to phenological modeling. Journal of Geophysical Research-Atmospheres, 109(D16): doi:10.1029/2003JD004305.
We develop a modeling framework to investigate the influence of the North Atlantic Oscillation (NAO) on phenological variability in Europe through its influence on the distribution of wintertime synoptic-scale surface temperature variability. The approach employs an eigendecomposition of NCEP daily winter surface temperature estimates from the latter twentieth century to represent the spatial structure in the surface temperature field. The subset of statistically significant principal components are modeled as first-order autoregressive AR(1) processes, while the residual variance is modeled as spatially uncorrelated AR(1) noise. For those principal component time series that exhibit a statistically significant seasonal relationship with the NAO index, the parameters of the AR(1) model are conditioned on the phase ("high," "neutral," or "low'") of the NAO. This allows for realistic simulations of synoptic scale surface temperature variability over Europe as it is influenced by the NAO index. The model is applied to the simulation of trends in growing degree days (GDD) over Europe where simulated GDD variations are shown to agree well with growing degrees days from the data and evidence from available phenological records. Preliminary application of this model to a climate change scenario involving an increasing NAO 50 years into the future suggests the potential for a continued advancement of the start of the growing season.
Dery, S. J. and L. B. Tremblay, 2004: Modeling the effects of wind redistribution on the snow mass budget of polar sea ice. Journal of Physical Oceanography, 34(1): 258-271.
A two-dimensional numerical model of blowing snow specifically designed for sea ice environments is presented. This new model is used to quantify the snow mass lost because of blowing snow into leads, blowing snow sublimation, and the effects of snow redistribution in the presence of surface irregularities (e.g., pressure ridges and snowdrifts) and on the conductive heat flux through the ice. Results show that the percentage of blowing snow lost into open waters (i.e., the lead trap efficiency) ranges between 60% and 100%. The lead trap efficiency increases with fetch over open waters, decreases as the upwind fetch over sea ice expands, and diminishes as wind speeds and friction velocities are enhanced. Its dependence on air temperature and relative humidity, however, is relatively small. Results from the time evolution of a snowdrift show that considerable snow cover heterogeneity arises because of interactions between winds and the surface; however, the corresponding increase in the conductive heat flux through the ice remains small (an increase of approximately 0.13% for a typical snowdrift distribution over a 1-km fetch). Results show that the snow mass lost into leads (Q(l)) depends strongly on the number of leads (for a fixed total open water fraction), suggesting that the lead distribution also needs to be considered in a parameterization of Q(l) in terms of meteorological conditions and surface characteristics. The results of this study provide some basic information on the small-scale processes influencing blowing snow over sea ice; these can then be used to evaluate the precise role that blowing snow plays in the surface energy and mass balances of large-scale models.
Dong, C. M., H. W. Ou, D. Chen and M. Visbeck, 2004: Tidally induced cross-frontal mean circulation: Analytical study. Journal of Physical Oceanography, 34(1): 293-305.
An analytical model is developed to study the tidally induced mean circulation in the frontal zone. Four distinct forcing mechanisms are identified, which result in the generation of the counterclockwise Bernoulli cell, the clockwise Ekman cell, the clockwise frontal cell, and the Stokes drift (facing in the direction with the shallow water to the left). The decomposition of the cross-frontal circulation provides a dynamical framework for interpreting and understanding its complex structure. To illustrate the underlying physics, three model configurations are considered pertaining to a homogenous ocean and winter and summer fronts. For a homogeneous ocean, the circulation is dominated by three cells; for the winter front, the offshore Bernoulli cell is strengthened; and for the summer front, two counterrotating cells are found in the vertical direction, associated with the two branches of the front. The dependence of the cell structure on the Ekman, Burger, and other dimensionless numbers is examined.
Dong, C. M., R. Houghton, H. W. Ou, D. Chen and T. Ezer, 2004: Numerical study of the diapycnal flow through a tidal front with passive tracers. Journal of Geophysical Research-Oceans, 109(C5, Art. No. C05029).
A two-dimensional numerical model is used to study the diapycnal flow through a tidal front with passive tracers. In a basic numerical experiment a passive tracer is released into the bottom water at the offshore edge of a tidal front, and it subsequently moves on-bank with a velocity that decreases with time. This qualitatively agrees with a recent field experiment using a dye tracer on Georges Bank. Additional experiments are performed to investigate the sensitivity of the tracer dispersion to the tidal phase and the location of tracer release within the front. As the release point is moved on-bank across the front, the tracer velocity decreases until it weakly reverses on the on-bank edge of the front. This trend can be understood by considering the structure of the Lagrangian velocity field in the tidal front, the degree of vertical mixing of the tracer, and the concentration-weighted mean patch velocity. The tidal phase at the time of tracer release does not significantly affect the tracer dispersion.
Evans, M. N. and A. Kaplan, 2004: The Pacific sector Hadley and Walker Circulations in historical marine wind analyses. In: H.F.D.a.R.S. Bradley (Editor), The Hadley Circulation: Present, Past and Future. Kluwer Academic Publishers, Netherland, pp. 239-258.
We investigate the historical variation of the wintertime Pacific marine sector meridional atmospheric circulation, using simple diagnostics calculated from a statistical analysis of 140 years of surface wind data. Intensity of the wintertime expression of the Hadley circulation, as expressed by a wind divergence index, varies interannually and secularly. In agreement with previous studies, interannual variation is associated with variations in the Walker circulation; e.g., El Niño/Southern Oscillation (ENSO) activity. The secular variation, most likely affected by systematic measurement biases, is nevertheless consistent with results from simulation of the Indo-Pacific-sector Hadley circulation variability in the NCEP/NCAR reanalysis (see Chapter 3, “Change of the Tropical Hadley Cell since 1950,” Quan et al., this volume; and Chapter 5, “Interannual to Interdecadal Variations of the Hadley and Walker Circulations,” Minobe, this volume) and model simulations of the global atmospheric response to anthropogenic forcing (see Chapter 14, “The Response of the Hadley Circulation to Climate Changes, Past and Future,” Rind and Perlwitz, this volume; and Chapter 17, “Mechanisms of an Intensified Hadley Circulation in Response to Solar Forcing in the Twentieth Century,” Meehl et al., this volume). A proxy network tracking Hadley intensity as mirrored in sea surface temperature (SST), precipitation, surface winds, and/or ocean upwelling might be used to further study processes underlying long-term variability in the Hadley circulation over the past several hundred years.
Galperin, B., H. Nakano, H. P. Huang and S. Sukoriansky, 2004: The ubiquitous zonal jets in the atmospheres of giant planets and Earth's oceans. Geophysical Research Letters, 31(13): doi:10.1029/2004GL019691.
Recent eddy-permitting simulations of the North Pacific Ocean have revealed robust patterns of multiple zonal jets that visually resemble the zonal jets on giant planets. We argue that this resemblance is more than just visual because the energy spectrum of the oceanic jets obeys a power law that fits spectra of zonal flows on the outer planets. Remarkably, even the non-dimensional proportionality coefficient, C-Z, determined by data under that spectral law, appears to be constant for all cases and approximately equal to 0.5. These results indicate that the multiple jet sets in the ocean and in the atmospheres of giant planets are governed by the same dynamics characterized by an anisotropic inverse energy cascade, i.e., the flow of energy from isotropic small-scale eddies to anisotropic large-scales structures, as well as the unique anisotropic spectrum. Implications of these results for climate research and future designs of observational missions are discussed.
Garabato, A. C. N. , K. L. Polzin, B. A. King, K. J. Heywood and M. Visbeck, 2004: Widespread Intense Turbulent Mixing in the Southern Ocean. Science, 303: 210-213.
Between 1996 and 1998, a concerted effort was made to study the deep open ocean convection in the Labrador Sea. Both in situ observations and numerical models were employed with close collaboration between the researchers in the fields of physical oceanography, boundary layer meteorology, and climate. A multitude of different methods were used to observe the state of ocean and atmosphere and determine the exchange between them over the experiment's period. The Labrador Sea Deep Convection Experiment data collection aims to assemble the observational data sets in order to facilitate the exchange and collaboration between the various projects and new projects for an overall synthesis. A common file format and a browsable inventory have been used so as to simplify the access to the data.
Gordon, A. L., E. Zambianchi, A. Orsi, M. Visbeck, C. F. Giulivi, T. Whitworth and G. Spezie, 2004: Energetic plumes over the western Ross Sea continental slope. Geophysical Research Letters, 31(21, Art. No. L21302, November 4, 2004).
[ 1] Rapid descent of dense Drygalski Trough ( western Ross Sea, Antarctica) shelf water over the continental slope, within 100 to 250 m thick benthic plumes, is described. Speeds of up to 1.0 m/s are recorded flowing at an average angle of 35degrees to the isobaths, entraining ambient Lower Circumpolar Deep Water en route. This process is predominant in determining the concentration and placement of the shelf water injected into the deep sea as a precursor Antarctic Bottom Water. Nonetheless, a 4-hour duration pulse of undiluted shelf water was observed at depth ( 1407 m) directly north of the Drygalski Trough, moving at around 90 degrees to isobaths, and at a speed of 1.4 m/s. Thus the export of Ross Sea shelf water to the deep sea is accomplished within plumes descending at moderate angle to isobaths, punctuated by rapid downhill cascades.
Guilderson, T. P., D. P. Schrag and M. A. Cane, 2004: Surface water mixing in the Solomon Sea as documented by a high-resolution coral C-14 record. Journal of Climate, 17(5): 1147-1156.
A bimonthly coral-based record of the postbomb radiocarbon content of Solomon Sea surface waters is interpreted to reflect mixing of subtropical surface water and that advected in from the east by the equatorial branch of the South Equatorial Current (SEC). Annual mean Delta(14)C has a dynamic range of nearly 175%, with a total range of nearly 200%. Prebomb values average -56% and the annual mean postbomb maxima occurs in 1985 with a value of +117%. Interannual variability in the record reflects surface current variations in conjunction with surface wind changes associated with ENSO. During El Niño years the waters of the Solomon Sea reflect a stronger influence of waters advected in from the east by the SEC and less "pure" subtropical water. This is most likely accomplished by a southward shift of the equatorward branch of the SEC during El Niño. There is an overall decrease in the relative proportion of eastern tropical water that is interpreted as a decrease in the strength and intensity of the shallow circulation of the tropical Pacific during the latter portion of the twentieth century. If validated, this secular trend bears strongly upon the rate of extratropical-tropical recirculation and the redistribution of heat and salt within the tropical Pacific.
Hall, T. M., D. W. Waugh, T. W. N. Haine, P. E. Robbins and S. Khatiwala, 2004: Estimates of anthropogenic carbon in the Indian Ocean with allowance for mixing and time-varying air-sea CO2 disequilibrium. Global Biogeochemical Cycles, 18(1): doi:10.1029/2003GB002120.
 We apply to the Indian Ocean a novel technique to estimate the distribution, total mass, and net air-sea flux of anthropogenic carbon. Chlorofluorocarbon data are used to constrain distributions of transit times from the surface to the interior that are constructed to accommodate a range of mixing scenarios, from no mixing ( pure bulk advection) to strong mixing. The transit time distributions are then used to propagate to the interior the surface water history of anthropogenic carbon estimated in a way that includes temporal variation in CO2 air-sea disequilibrium. By allowing for mixing in transport and for variable air- sea disequilibrium, we remove two sources of positive bias common in other studies. We estimate that the anthropogenic carbon mass in the Indian Ocean was 14.3 - 20.5 Gt in 2000, and the net air- sea flux was 0.26 - 0.36 Gt/yr. The upper bound of this range, the no-mixing limit, generally coincides with previous studies, while the lower bound, the strong-mixing limit, is significantly below previous studies.
Harnik, N. and E. K. M. Chang, 2004: The effects of variations in jet width on the growth of baroclinic waves: Implications for midwinter Pacific storm track variability. Journal of the Atmospheric Sciences, 61(1): 23-40.
The effects of variations in jet width on the downstream growth of baroclinic waves are studied, using a simple quasigeostrophic model with a vertically varying basic state and variable channel width, as well as a simplified primitive equation model with a basic state that varies in latitude and height. This study is motivated by observations that in midwinter in the Pacific the storm track is weaker and the jet is narrower during years when the jet is strong.
Hazeleger, W., R. Seager, M. A. Cane and N. H. Naik(Henderson), 2004: How can tropical Pacific Ocean heat transport vary? Journal of Physical Oceanography, 34(1): 320-333.
Pacific Ocean oceanic heat transport is studied in an ocean model coupled to an atmospheric mixed-layer model. The shallow meridional overturning circulation cells in the Tropics and subtropics transport heat away from the equator. The heat transport by the horizontal gyre circulation in the Tropics is smaller and directed toward the equator. The response of the Pacific oceanic heat transport to El Nino-like winds, extratropical winds, and variations in the Indonesian Throughflow is studied. Large, opposing changes are found in the heat transport by the meridional overturning and the horizontal gyres in response to El Nino-like winds. Consequently, the change in total heat transport is relatively small. The overturning transport decreases and the gyres spin down when the winds decrease in the Tropics. This compensation breaks down when the Indonesian Throughflow is allowed to vary in the model. A reduced Indonesian Throughflow, as observed during El Nino-like conditions, causes a large reduction of poleward heat transport in the South Pacific and affects the ocean heat transport in the southern tropical Pacific. Extratropical atmospheric anomalies can affect tropical ocean heat transport as the tropical thermocline is ventilated from the extratropics. The authors find that changes in the heat loss in the midlatitudes affect tropical ocean heat transport by driving an enhanced buoyancy-driven overturning that reaches into the Tropics. The results are related to observed changes in the overturning circulation in the Pacific in the 1990s, sea surface temperarture changes, and changes in atmospheric circulation. The results imply that the ratio of heat transport in the ocean to that in the atmosphere can change.
Hintsa, E. J., J. W. H. Dacey, W. R. McGillis, J. B. Edson, C. J. Zappa and H. J. Zemmelink, 2004: Sea-to-air fluxes from measurements of the atmospheric gradient of dimethylsulfide and comparison with simultaneous relaxed eddy accumulation measurements. Journal of Geophysical Research-Oceans, 109(C01026): doi:10.1029/2002JC001617.
 We measured vertical profiles of dimethylsulfide (DMS) in the atmospheric marine boundary layer from R/P FLIP during the 2000 FAIRS cruise. Applying Monin-Obukhov similarity theory to the DMS gradients and simultaneous micrometeorological data, we calculated sea-to-air DMS fluxes for 34 profiles. From the fluxes and measured seawater DMS concentrations, we calculated the waterside gas transfer velocity, k(w). Gas transfer velocities from the gradient flux approach are within the range of previous commonly used parameterizations of k(w) as a function of wind speed but are a factor of 2 smaller than simultaneous determinations of transfer velocity using the relaxed eddy accumulation technique. This is the first field comparison of these different techniques for measuring DMS flux from the ocean; the accuracy of the techniques and possible reasons for the discrepancy are discussed.
Houghton, R. W., C. E. Tilburg, R. W. Garvine and A. Fong, 2004: Delaware River plume response to a strong upwelling-favorable wind event. Geophysical Research Letters, 31(7): doi:10.1029/2003GL018988.
The mixing and secondary circulation in the Delaware River plume during a strong (10 m/s) upwelling-favorable wind event in April 2003 have been observed using a dye tracer. The dye, injected into the halocline at the base of the plume, was surveyed for more than a day as it moved 28 km off shore. The secondary circulation within the plume was resolved as the dye patch dispersed. This flow pattern conformed with numerical model results of Fong and Geyer involving an upwelling flow 8.4x10(-5) m/s (similar to7.3 m/day) and a subsequent near surface, offshore flow (similar to0.09 m/s) across the plume. The salting rate of the plume implied a mean vertical diffusivity of similar to2x10(-4) m(2)/s where the gradient Richardson number was approximately 0.6.
Joseph, R., M. F. Ting and P. J. Kushner, 2004: The global stationary wave response to climate change in a coupled GCM. Journal of Climate, 17(3): 540-556.
The stationary wave response to global climate change in the Geophysical Fluid Dynamics Laboratory's R30 coupled ocean-atmosphere GCM is studied. An ensemble of climate change simulations that use a standard prescription for time-dependent increases of greenhouse gas and sulfate aerosol concentrations is compared to a multiple-century control simulation with these constituents fixed at preindustrial levels. The primary response to climate change is to zonalize the atmospheric circulation, that is, to reduce the amplitude of the stationary waves in all seasons. This zonalization is particularly strong in the boreal summer over the Tropics. In January, changes in the stationary waves resemble that of an El Nino, and all months exhibit an El Nino-like increase of precipitation in the central tropical Pacific.
Kaplan, A., M. A. Cane, D. Chen, D. L. Witter and R. E. Cheney, 2004: Small-scale variability and model error in tropical Pacific sea level. Journal of Geophysical Research-Oceans, 109(C02001, doi:10.1029/2002JC001743): 1-17.
 Monthly interannual anomalies of tropical Pacific sea level height from TOPEX/ Poseidon altimetry are compared with simulation and assimilation products from a variety of models, ranging from a simple linear long wave approximation to ocean general circulation models. Major spatial similarities in the error patterns are identified. These include zonally elongated maxima in the northwest and southwest tropical Pacific Ocean, a band of high values near 10 degreesN, slightly inclined toward the equator from the Central American coast, and low values on the equator and in the southeastern tropical Pacific. These features are also present in the pattern of small-scale variability (SSV) of sea level height. Spatial and temporal components of this SSV are analyzed for predominant variability types. Monte Carlo experiments identify the areas where high SSV is wind-driven, caused by a similar pattern of variability in the wind stress. Model products systematically underestimate signal variance in such areas. Variability in other areas is due to the instability of ocean currents. The major component of uncertainty in the gridded satellite altimeter analyses is due to sampling error, for which estimates are developed and verified.
Karspeck, A. R., R. Seager and M. A. Cane, 2004: Predictability of tropical Pacific decadal variability in an intermediate model. Journal of Climate, 17(14): 2842-2850.
The Zebiak - Cane (ZC) model for simulation of the El Nino-Southern Oscillation is shown to be capable of producing sequences of variability that exhibit shifts in the time-mean state of the eastern equatorial Pacific that resemble observations of tropical Pacific decadal variability. The model's performance in predicting these shifts is compared to two naive forecasting strategies. It is found that the ZC model consistently outperforms the two naive forecasts that serve as a null hypothesis in assessing the significance of results. Forecasts initialized during anomalously warm and anomalously cold decades are shown to have the highest predictability.
L'Heureux, M. L., M. E. Mann, B. I. Cook, B. E. Gleason and R. S. Vose, 2004: Atmospheric circulation influences on seasonal precipitation patterns in Alaska during the latter 20th century. Journal of Geophysical Research-Atmospheres, 109(D6): doi:10.1029/2003JD003845.
 A set of long, nearly complete daily precipitation series for Alaska spanning the latter half of the 20th century has been analyzed for seasonal relationships between variations in mean, heavy, and extreme precipitation and large-scale atmospheric circulation variations at interannual, decadal, and secular timescales. Relationships with four candidate predictors (the Pacific North American (PNA), Arctic Oscillation (AO), Pacific Decadal Oscillation (PDO), and Nino3 indices) are used for insights into possible large-scale climate forcing. Winter precipitation (mean and extreme) variability and trends along the south coast and interior of Alaska appear to be closely related to variations in the PNA pattern over this timeframe, while El Nino/Southern Oscillation (ENSO) influences, through the Nino3 index, appear to be significant along the south coast alone. Along the south coast the PNA and ENSO exert opposing influences on extreme (and mean) precipitation. Within interior Alaska the positive PNA pattern tends to suppress precipitation owing to orographic factors. Summer variations appear more closely related to the influence of the AO and PDO. The north slope region of Alaska appears to be too far removed from the influences of any of the examined predictors for any clear relationship to be evident.
Liu, J. P., X. J. Yuan, D. G. Martinson and D. Rind, 2004: Re-evaluating Antarctic sea-ice variability and its teleconnections in a GISS global climate model with improved sea ice and ocean processes. International Journal of Climatology, 24(7): 841-852.
This study re-evaluated simulated Antarctic sea-ice variability and its teleconnections in a NASA Goddard Institute for Space Studies (GISS) coupled global climate model (CGCM) with improved sea-ice and ocean processes. With the improvements to the parameterizations of sea-ice dynamics and thermodynamics and of sub-grid-scale ocean processes, the new version of the GISS/CGCM does indeed do a better job in the representations of the local/regional ice-ocean interactions with regard to (1) the seasonal distributions of the Antarctic sea-ice edges (SIE), and (2) the vertical temperature and salinity structure in the upper Southern Ocean and surface air temperature (SAT) climatology in the southern high latitudes compared with the control version. However, these encouraging local/regional improvements do not extend to the simulations of the polar and extrapolar climate teleconnections. There is no obvious change to the simulations of the dominant spatial covarying patterns of the SAT variability on either the regional (southern high latitudes) or global scales. The simulated teleconnections between Antarctic SIE and global SAT still show the weak El Nino-southern oscillation like correlation pattern in the eastern tropical Pacific, though the new version generates a stronger tropical Indian component. Some dominant observed teleconnection patterns in the western extreme of the tropical Pacific and over the tropical continents (in-phase relationship between tropical South America and Africa) are still not well represented or are missed in the Antarctic SIE and global SAT lead/lag correlation maps and the empirical orthogonal function analysis on those correlation maps. The possible causes of the weak teleconnections in the improved GISS/CGCM are briefly discussed. Copyright (C) 2004 Royal Meteorological Society.
Perovich, D. K., B. C. Elder, K. J. Claffey, S. Stammerjohn, R. Smith, S. F. Ackley, H. R. Krouse and A. J. Gow, 2004: Winter sea-ice properties in Marguerite Bay, Antarctica. Deep-Sea Research Part Ii-Topical Studies in Oceanography, 51(17-19): 2023-2039.
During the winter 2001 and 2002 cruises of the SO-GLOBEC experiment, we investigated the morphological properties, growth processes, and internal permeability of sea ice in the Marguerite Bay area of the Western Antarctic Peninsula. There was considerable interannual variability in ice thickness with, average values of 62 cm in 2001 and 102 cm in 2002, with medians of 43 and 68 cm, respectively. Snow depth averaged 16 cm in 2001 and 21 cm in 2002. At 40% of the thickness holes in 2001 and 17% in 2002, a combination of deep snow and thin ice resulted in negative freeboard and the potential for surface flooding. Ice production was strongly influenced by the snow cover. Deep snow resulted in negative freeboard, surface flooding, and the formation of snow ice, but also limited columnar ice growth on the bottom of the ice. A stratigraphic analysis of ice thin sections showed that more than half of the ice sampled was granular and that virtually all of the upper 20 cm of the ice cover was granular. Stable isotope (6180) analysis of samples from 2001 indicated that snow-ice formation at the surface contributed significantly to ice formation. Two-thirds of the cores had some snow-ice and 15% of the ice sampled in 2001 was snow-ice. For 95% of the ice sampled the combination of warm ice temperatures and large salinities resulted in brine volumes that were greater than the percolation threshold of 5%. Autonomous mass balance buoys indicated that the ice was above the percolation threshold throughout late winter and spring. The exceeding of the percolation threshold allows continuous flooding to occur throughout the late winter-spring period. The WAP sea-ice therefore represents a warm "end-member" of the sea-ice covers of Antarctica. An expected consequence of the lengthy flooding condition at the snow/ice interface is an earlier onset of an algal bloom in the flooded snow than elsewhere in Antarctic sea ice. (C) 2004 Elsevier Ltd. All rights reserved.
Pollack, H. N. and J. E. Smerdon, 2004: Borehole climate reconstructions: Spatial structure and hemispheric averages. Journal of Geophysical Research-Atmospheres, 109(D11): doi:10.1029/2003JD004163.
[ 1] Ground surface temperature ( GST) reconstructions determined from temperature profiles measured in terrestrial boreholes, when averaged over the Northern Hemisphere, estimate a surface warming of -1 K during the interval AD 1500 2000. Other traditional proxy-based estimates suggest less warming during the same interval. Mann et al. [ 2003a] have raised two issues with regard to borehole-based reconstructions. The first focuses on the need for spatial gridding and area-weighting of the ensemble of borehole-based GST reconstructions to yield an average hemispheric reconstruction. The second asserts that application of optimal detection techniques show that the GST only weakly displays the spatial structure of the surface air temperature ( SAT). We demonstrate the consistency of GST warming estimates by showing that over a wide range of grid element area and occupancy weighting schemes, the five-century GST change falls in the range of 0.89-1.05 K. We examine the subhemispheric spatial correlation of GST and SAT trends at various spatial scales. In the 5-degree grid employed for optimal detection, we find that the majority of grid element means are determined from three or fewer boreholes, a number that is insufficient to suppress site-specific noise via ensemble averaging. Significant spatial correlation between SAT and GST emerges in a 5-degree grid if low-occupancy grid elements are excluded, and also in a 30-degree grid in which grid element means are better determined through higher occupancy. Reconstructions assembled after excluding low-occupancy grid elements show a five-century GST change in the range of 1.02-1.06 K.
Rodgers, K. B., S. Charbit, M. Kageyama, G. Philippon, G. Ramstein, C. Ritz, J. H. Yin, G. Lohmann, S. J. Lorenz and M. Khodri, 2004: Sensitivity of Northern Hemispheric continental ice sheets to tropical SST during deglaciation. Geophysical Research Letters, 31(2): doi:10.1029/2003GL018375.
A thermomechanical ice sheet model ( ISM) is used to investigate the sensitivity of the Laurentide and Fennoscandian ice sheets to tropical sea surface temperature (SST) perturbations during deglaciation. The ISM is driven by surface temperature and precipitation fields from three different atmospheric general circulation models (AGCMs). For each AGCM, the responses in temperature and precipitation over the ice sheets nearly compensate, such that ice sheet mass balance is not strongly sensitive to tropical SST boundary conditions. It was also found that there is significant variation in the response of the ISM to the different AGCM output fields.
Smerdon, J. E., H. N. Pollack, V. Cermak, J. W. Enz, M. Kresl, J. Safanda and J. F. Wehmiller, 2004: Air-ground temperature coupling and subsurface propagation of annual temperature signals. Journal of Geophysical Research-Atmospheres, 109(D21): doi:10.1029/2004JD005056.
 Borehole-based reconstructions of ground surface temperature (GST) have been widely used as indicators of paleoclimate. These reconstructions assume that heat transport within the subsurface is conductive. Climatic interpretations of GST reconstructions also assume that GST is strongly coupled to surface air temperature ( SAT) on timescales of decades and longer. We examine these two assumptions using records of SAT and subsurface temperature time series from Fargo, North Dakota; Prague, Czech Republic; Cape Henlopen State Park, Delaware; and Cape Hatteras National Seashore, North Carolina. The characteristics of downward propagating annual temperature signals at each site clearly indicate that heat transport can be described as one-dimensional conduction in a homogeneous medium. Extrapolations of subsurface observations to the ground surface yield estimates of annual GST signals and allow comparisons to annual SAT signals. All annual GST signals are modestly attenuated and negligibly phase shifted relative to SAT. The four sites collectively demonstrate that differences between annual GST and SAT signals arise in both summer and winter seasons, in amounts dependent on the climatic setting of each site.
Song, Q. and A. L. Gordon, 2004: Significance of the vertical profile of the Indonesian Throughflow transport to the Indian Ocean. Geophysical Research Letters, 31(16, Art. No. L16307).
Using an ocean general circulation model, we find that the vertical profile of the Indonesian Throughflow (ITF) transport is important in regulating the stratification and surface heat fluxes of the Indian Ocean. With the same total ITF transport, a thermocline-intensified ITF, relative to a surface-intensified ITF, not only cools the surface layer of the Indian Ocean while warming the Indian Ocean below the thermocline, but also induces negative temperature anomalies at the sea surface throughout the Indian basin. As a consequence of this surface effect the net heat gain of the Indian Ocean is increased. The results suggest that it is necessary to properly represent the vertical profile of ITF transport within ocean and climate numerical models.
Song, Q., A. L. Gordon and M. Visbeck, 2004: Spreading of the Indonesian throughflow in the Indian Ocean. Journal of Physical Oceanography, 34(4): 772-792.
The Indonesian Throughflow (ITF) spreading pathways and time scales in the Indian Ocean are investigated using both observational data and two numerical tracer experiments, one being a three-dimensional Lagrangian trajectory experiment and the other a transit-time probability density function (PDF) tracer experiment, in an ocean general circulation model. The model climatology is in agreement with observations and other model results except that speeds of boundary currents are lower. Upon reaching the western boundary within the South Equatorial Current ( SEC), the trajectories of the ITF tracers within the thermocline exhibit bifurcation. The Lagrangian trajectory experiment shows that at the western boundary about 38% +/- 5% thermocline ITF water flows southward to join the Agulhas Current, consequently exiting the Indian Ocean, and the rest, about 62% +/- 5%, flows northward to the north of SEC. In boreal summer, ITF water penetrates into the Northern Hemisphere within the Somali Current. The primary spreading pathway of the thermocline ITF water north of SEC is upwelling to the surface layer with subsequent advection southward within the surface Ekman layer toward the southern Indian Ocean subtropics. There it is subducted and advected northward in the upper thermocline to rejoin the SEC. Both the observations and the trajectory experiment suggest that the upwelling occurs mainly along the coast of Somalia during boreal summer and in the open ocean within a cyclonic gyre in the Tropics south of the equator throughout the year. All the ITF water eventually exits the Indian Ocean along the western boundary within the Mozambique Channel and the east coast of Madagascar and, farther south, the Agulhas Current region. The advective spreading time scales, represented by the elapsed time corresponding to the maximum of transittime PDF, show that in the upper thermocline the ITF crosses the Indian Ocean, from the Makassar Strait to the east coast of the African continent, on a time scale of about 10 yr and reaches the Arabian Sea on a time scale of over 20 yr.
Thurnherr, A. M. and K. G. Speer, 2004: Representativeness of meridional hydrographic sections in the western South Atlantic. Journal of Marine Research, 62(1): 37-65.
Many studies of the oceanic circulation are based on data collected during quasi-synoptic hydrographic surveys. After spatial averaging, to filter out the effects of mesoscale variability, it is often explicitly or implicitly assumed that the synoptic hydrographic gradients are representative of a quasi-steady "mean" state. Climatological tracer fields and float data at the depth of the North Atlantic Deep Water in the western South Atlantic (Brazil Basin) support the notion of a quasi-steady mean circulation characterized by alternating bands of primarily zonal flow with meridional scales of several hundreds of km. Visually, the mean circulation appears to dominate three samples of the large-scale meridional-density-gradient field taken between 1983 and 1994. A quantitative comparison reveals, however, that the baroclinic temporal variability of the zonal velocities is of the same magnitude as the mean and is associated with similar spatial scales. The synoptic geostrophic flow field is, therefore, only marginally representative of the mean state. Thus, the data do not support one of the central assumptions of reference-velocity methods, such as linear box-inverse models and the P-spiral, because baroclinic temporal variability renders the equation systems underlying these methods inconsistent. A modal decomposition of the temporally varying baroclinic zonal velocity field in the Brazil Basin indicates that the first two dynamical modes dominate, accounting for approximate to90% of the rms velocities. The residual flow field that remains after removing the first two baroclinic modes from the three synoptic samples is dominated by the mean circulation. However, its magnitude is not sufficient to account for the float and tracer observations. Therefore, it is necessary to determine the projection of the mean zonal velocities onto the barotropic and the first two baroclinic modes in order to diagnose fully the mean zonal circulation in the western South Atlantic. There is evidence that the representativeness of synoptic hydrographic sections in other regions may be similarly marginal.
Yuan, X. J., 2004: ENSO-related impacts on Antarctic sea ice: a synthesis of phenomenon and mechanisms. Antarctic Science, 16(4): 415-425.
Many remote and local climate variabilities influence Antarctic sea ice at different time scales. The strongest sea ice teleconnection at the interannual time scale was found between El Niño-Southern Oscillation (ENSO) events and a high latitude climate mode named the Antarctic Dipole. The Antarctic Dipole is characterized by an out-of-phase relationship between sea ice and surface temperature anomalies in the South Pacific and South Atlantic, manifesting itself and persisting 3-4 seasons after being triggered by the ENSO forcing. This study examines the life cycles of ENSO warm and cold events in the tropics and associated evolution of the ADP in high latitudes of the Southern Hemisphere. In evaluating the mechanisms that form the ADP, the study suggests a synthesized scheme that links these high latitude processes with ENSO teleconnection in both the Pacific and Atlantic basins. The synthesized scheme suggests that the two main mechanisms responsible for the formation/maintenance of the Antarctic Dipole are the heat flux due to the mean meridional circulation of the regional Ferrel Cell and regional anomalous circulation generated by stationary eddies. The changes in the Hadley Cell, the jet stream in the subtropics, and the Rossby Wave train associated with ENSO link the tropical forcing to these high latitude processes. Moreover, these two mechanisms operate in phase and are comparable in magnitude. The positive feedback between the jet stream and stationary eddies in the atmosphere, the positive feedback within the air-sea-ice system, and the seasonality all reinforce the anomalies, resulting in persistent Antarctic Dipole anomalies.
Yuan, X. J., 2004: High-wind-speed evaluation in the Southern Ocean. Journal of Geophysical Research-Atmospheres, 109(D13, Art. No. D13101).
 Space-based scatterometer instruments provide crucial surface wind measurements with high resolution over global oceans. Midlatitude regions in the Southern Ocean are unique places to evaluate scatterometer winds at high-wind bands because these regions host the strongest wind fields at the ocean surface. The objective of this study is to evaluate high wind speeds observed by Quick Scatterometer (QuikSCAT) wind measurements and produced by simulation models and compare them with weather station data in the Southern Ocean. The occurrence and intensity of high-wind events in scatterometer measurements are compared with that of reanalysis winds, and the spatial and seasonal variability of high-wind characteristics is examined. The results show that the speeds of scatterometer winds are similar to model simulations in the monthly mean field but consistently stronger than both European Centre for Medium-Range Weather Forecasts and National Centers for Environmental Prediction/National Center for Atmospheric Research winds in high-wind bands. When scatterometer winds are compared with the weather station observations at Macquarie Island, the present study finds no systematic bias at high-wind bands across all months. However, both weather station and QuikSCAT winds are higher than the model simulations in high-wind bands most of the time. This suggests that model simulations may underestimate surface wind strength in high-wind bands. Such underestimation would lead to up to an 80% reduction in energy flux between the atmosphere and ocean. Even though high winds occur only sporadically and the reanalysis underestimation in high wind speed is not in itself of great magnitude, they have a significant impact on global climate.
Yuan, X. J., D. G. Martinson and Z. Q. Dong, 2004: Upper ocean thermohaline structure and its temporal variability in the southeast Indian Ocean. Deep-Sea Research Part I-Oceanographic Research Papers, 51(2): 333-347.
We examine the upper ocean thermohaline structure in the southeast Indian Ocean and its temporal variability based on XBT/XCTD observations from four cruises across the Southern Ocean from Fremantle, Australia to Prydz Bay, Antarctica. The transects were occupied in March 1998, November 1998, March 2000 and March 2002. Three major fronts-the subtropical front, subantarctic front and polar front-are clearly identified from our surveys and compared with earlier studies. Particularly, two polar fronts, separated by a few degrees of latitude, appear southeast the Kerguelen Plateau. The primary polar front is characterized by a strong horizontal thermal gradient extending deep in the water column, while the secondary polar front is identified by the 2degreesC isotherm at T-min depth and has a relatively shallow frontal expression. Dynamic height across the Antarctic Circumpolar Current (ACC) was calculated for the transects in 2000 and 2002. With a negligible yearly variation in the total transport across the ACC, the higher sample density in 2002 reveals more detailed structure of the ACC: two jets associated with the SAF and primary polar front are embedded within the broad ACC.
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