Beltrami, H., J. E. Smerdon, H. N. Pollack and S. P. Huang, 2002: Continental heat gain in the global climate system. Geophysical Research Letters, 29(8): doi:10.1029/2001GL014310.
 Recent estimates have shown the heat gained by the ocean, atmosphere, and cryosphere as 18.2 10(22) J, 6.6 . 10(21) J, and 8.1 . 10(21) J, respectively over the past half-century. However, the heat gain of the lithosphere via a heat flux across the solid surface of the continents (29% of the Earth's surface) has not been addressed. Here we calculate that component of Earth's changing energy budget, using ground-surface temperature reconstructions for the continents. In the last half-century there was an average flux of 39.1 mW m(-2) across the land surface into the subsurface, leading to 9.1 . 10(21) J absorbed by the ground. The heat inputs during the last half-century into all the major components of the climate system-atmosphere, ocean, cryosphere, lithosphere-reinforce the conclusion that the warming during the interval has been global.
Camargo, S. J. and S. E. Zebiak, 2002: Improving the detection and tracking of tropical cyclones in atmospheric general circulation models. Weather and Forecasting, 17(6): 1152-1162.
Dynamical seasonal forecasts of tropical storm frequency require robust and efficient algorithms for detection and tracking of tropical storms in atmospheric general circulation models (AGCMs). Tropical storms are generally detected when dynamic and thermodynamic variables meet specified criteria. Here, it is shown that objectively defined model- and basin-dependent detection criteria improve simulations of tropical storm climatology and interannual variability in low-resolution AGCMs. An improved tracking method provides more realistic tracking and accurate counting of storms.
Chiang, J. C. H., Y. Kushnir and A. Giannini, 2002: Deconstructing Atlantic Intertropical Convergence Zone variability: Influence of the local cross-equatorial sea surface temperature gradient and remote forcing from the eastern equatorial Pacific. Journal of Geophysical Research-Atmospheres, 107(D1-D2): doi:10.1029/2000JD000307.
We investigate causes of interannual variability in Atlantic Intertropical Convergence Zone (ITCZ) convection using a monthly mean global precipitation data set spanning 1979-1999. Starting from the hypothesis of two dominant influences on the ITCZ, namely, the cross-equatorial gradient in tropical Atlantic sea surface temperature (SST) and the anomalous Walker circulation due to the rearrangement of tropical Pacific convection associated with the El Niño-Southern Oscillation, we analyze anomaly composites over the 1979-1999 period that best isolate the effects of each mechanism. Our results suggest that to first order, a strong anomalous Walker circulation suppresses precipitation over the tropical Atlantic, whereas an anomalous warm north/cool south SST gradient shifts the meridional location of maximum ITCZ convection anomalously north. We examined the processes underlying each of the two mechanisms. For the anomalous Walker circulation we find consistency with the idea of suppression of convection through warming of the tropical troposphere brought about by anomalous convective heating in the eastern equatorial Pacific. For the SST gradient mechanism our results confirm previous studies that link convection to cross-equatorial winds forced by meridional SST gradients. We find that positive surface flux feedback brought about through the cross-equatorial winds is weak and confined to the deep tropics. On the basis of the results of this and other studies we propose an expanded physical picture that explains key features of Atlantic ITCZ variability, including its seasonal preference, its sensitivity to small anomalous SST gradients, and its role in the context of tropical Atlantic SST gradient variability.
Cook, E. R., J. G. Palmer, B. I. Cook, A. Hogg and R. D. D'Arrigo, 2002: A multi-millennial palaeoclimatic resource from Lagarostrobos colensoi tree-rings at Oroko Swamp, New Zealand. Global and Planetary Change, 33(3-4): 209-220.
We describe the first results of a new dendroclimatic study in New Zealand using Lagarostrobos colensoi (silver pine) growing at Oroko Swamp in the West Coast of the South Island. This research has produced the first millennium-length tree-ring chronology from New Zealand, covering the period AD 816-1998. Statistical analysis of the climate signal in the chronology indicates that it reflects Austral summer temperatures with a high degree of fidelity, except for the post-1957 period when a stand-wide disturbance apparently impacted the trees. Locally abundant sub-fossil wood on the swamp surface has been used to extend the present chronology back beyond the ages of the living trees. However, a large amount of material is still available, so the prospect of extending this chronology further back in time is good. A comparison of the pre-20th Century temperatures estimated using the chronology with instrumental data over the 1900-1999 period indicates a change in variability from that of the 20th century. In addition, it appears that summer temperatures estimated over the period of most reliable tree-ring data prior to the instrumental record (AD 1200-1865) were considerably more variable and persistent than those found in the "modern" record, This result has implications in detection and attribution studies of greenhouse gas forcing because it suggests that Austral summer temperatures in this sector of New Zealand have been anomalous during the 20th Century relative to earlier times. (C) 2002 Elsevier Science B.V. All rights reserved.
Cullen, H. M., A. Kaplan, P. A. Arkin and P. B. Demenocal, 2002: Impact of the North Atlantic Oscillation on Middle Eastern climate and streamflow. Climatic Change, 55(3): 315-338.
Interannual to decadal variations in Middle Eastern temperature, precipitation and streamflow reflect the far-field influence of the North Atlantic Oscillation (NAO), a dominant mode of Atlantic sector climate variability. Using a new sea surface temperature (SST) based index of the NAO and available streamflow data from five Middle Eastern rivers, we show that the first principal component of December through March streamflow variability reflects changes in the NAO. However, Middle East rivers have two primary flooding periods. The first is rainfall-driven runoff from December through March, regulated on interannual to decadal timescales by the NAO as reflected in local precipitation and temperature. The second period, from April through June, reflects spring snowmelt and contributes in excess of 50% of annual runoff. This period, known locally as the khamsin, displays no significant NAO connections and a less direct relationship with local climatic factors, suggesting that streamflow variability during this period reflects land-cover change, possibly related to agriculture and hydropower generation, and snowmelt.
Davey, M. K., M. Huddleston, K. R. Sperber, P. Braconnot, F. Bryan, D. Chen, R. A. Colman, C. Cooper, U. Cubasch, P. Delecluse, D. DeWitt, L. Fairhead, G. Flato, C. Gordon, T. Hogan, M. Ji, M. Kimoto, A. Kitoh, T. R. Knutson, M. Latif, H. Le Treut, T. Li, S. Manabe, C. R. Mechoso, G. A. Meehl, S. B. Power, E. Roeckner, L. Terray, A. Vintzileos, R. Voss, B. Wang, W. M. Washington, I. Yoshikawa, J. Y. Yu, S. Yukimoto and S. E. Zebiak, 2002: STOIC: a study of coupled model climatology and variability in tropical ocean regions. Climate Dynamics, 18(5): 403-420.
We describe the behaviour of 23 dynamical ocean-atmosphere models, in the context of comparison with observations in a common framework. Fields of tropical sea surface temperature (SST), surface wind stress and upper ocean vertically averaged temperature (VAT) are assessed with regard to annual mean, seasonal cycle, and interannual variability characteristics. Of the participating models, 21 are coupled GCMs. of which 13 use no form of flux adjustment in the tropics. The models vary widely in design, components and purpose: nevertheless several common features are apparent. In most models without flux adjustment, the annual mean equatorial SST in the central Pacific is too cool and the Atlantic zonal SST gradient has the wrong sign. Annual mean wind stress is often too weak in the central Pacific and in the Atlantic, but too strong in the west Pacific. Few models have an upper ocean VAT seasonal cycle like that observed in the equatorial Pacific. Interannual variability is commonly too weak in the models: in particular, wind stress variability is low in the equatorial Pacific. Most models have difficulty in reproducing the observed Pacific 'horseshoe' pattern of negative SST correlations with interannual Nino3 SST anomalies, or the observed Indian-Pacific lag correlations. The results for the fields examined indicate that several substantial model improvements are needed, particularly with regard to surface wind stress.
Dery, S. J. and M. K. Yau, 2002: Large-scale mass balance effects of blowing snow and surface sublimation. Journal of Geophysical Research-Atmospheres, 107(D23): doi:10.1029/2001JD001251.
 This study examines the effects of surface sublimation and blowing snow on the surface mass balance on a global and basin scale using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA15) data at a resolution of 2.5degrees that span the years 1979-1993. The combined processes of surface and blowing snow sublimation are estimated to remove 29 mm yr(-1) snow-water equivalent (swe) over Antarctica, disposing about 17 to 20% of its annual precipitation. In the Northern Hemisphere, these processes are generally less important in continental areas than over the frozen Arctic Ocean, where surface and blowing snow sublimation deplete upward of 100 mm yr(-1) swe. Areas with frequent blowing snow episodes, such as the coastal regions of Antarctica and the Arctic Ocean, are prone to a mass transport >100 Mg m(-1) yr(-1). Although important locally, values of the divergence of mass through wind redistribution are generally 2 orders of magnitude less than surface and blowing snow sublimation when evaluated over large areas. For the entire Mackenzie River Basin of Canada, surface sublimation remains the dominant sink of mass as it removes 29 mm yr(-1) swe, or about 7% of the watershed's annual precipitation. Although the first of its kind, this study provides only a first-order estimate of the contribution of surface sublimation and blowing snow to the surface mass balance because of limitations with the data set and some uncertainties in the blowing snow process.
Dery, S. J. and M. Stieglitz, 2002: A note on surface humidity measurements in the cold Canadian environment. Boundary-Layer Meteorology, 102(3): 491-497.
In the cold Canadian environment, humidity measurements can be very difficult to conduct. In this brief communication, humidity observations taken by two different sensors at six remote Canadian Arctic locations are compared. The observations collected by Vaisala HMP35CF sensors display a strong tendency toward the ice saturation point whereas dew cell instruments exhibit significantly lower values of relative humidity with respect to ice (RHi). Humidity data collected by HMP35CF hygrometers are therefore unreliable since they are subject to persistent icing that lead them to record values of RHi near 100%, irrespective of the air temperature. The high humidity bias emerges at meteorological stations mounted with the HMP35CF probes since these instruments are usually neither sheltered nor heated, and are not attended to at regular intervals. Thus, great care must be taken in utilizing humidity data recorded by HMP35CF sensors across the network of climate autostations in Canada.
Engel, V. C., M. Stieglitz, M. Williams and K. L. Griffin, 2002: Forest canopy hydraulic properties and catchment water balance: observations and modeling. Ecological Modelling, 154(3): 263-288.
We present observations and simulations examining plant-water relations in a forested catchment characterized by strong topographic control over surface hydrology and stand structure. The system is dominated by xeric and mesic ecotypes of Quercus rubra L. Soil depths are typically very thin and the severity of seasonal water stress in these trees is determined largely by position along the local topographic gradient. Water balance related ecotypic differences in Q. rubra were measured during the 2000 growing season at an upland and lowland site. Significant site differences in stomatal conductance, sap flux density, and leaf to sapwood area ratios were observed. However, mid-day leaf water potentials and the leaf area-specific canopy hydraulic conductance were not significantly different despite a 20% increase in soil moisture content, an average 10 m increase in tree height, and a higher leaf area index at the lowland site. These results suggest a close coordination of tree morphology, stand structure, and the hydraulic conductance of the combined soil-root-leaf pathway that governs leaf-level water vapor exchange rates similarly across the topographic gradient. To place these stand-level observations in the context of catchment-scale water balance we linked the SPA canopy model with a 1-D soil column model and TOPMODEL hydrologic formulations. The SPA model was used to represent the canopy because of its specific inclusion of hydraulic constraints on transpiration and leaf water potential. The combined model is spatially explicit in the distribution of ecotype morphology, and calculates transpiration rates for TOPMODEL-derived saturated and unsaturated area fractions within the watershed separately. Model predictions of stomatal conductance, upland latent energy flux, stream discharge, and soil moisture content compared favorably with observations. Sensitivity analyses of canopy model parameters indicate stream discharge in this system is most sensitive to changes in the maximum leaf area index, the minimum leaf water potential, and belowground resistance. Discharge was least sensitive to changes in stem hydraulic conductivity and capacitance. Model results and observations are discussed with respect to adaptations to water stress, hydraulic controls on canopy water use. and ecosystem water use. (C) 2002 Elsevier Science B.V. All rights reserved.
Evans, M. N., A. Kaplan and M. A. Cane, 2002: Pacific sea surface temperature field reconstruction from coral delta O-18 data using reduced space objective analysis. Paleoceanography, 17(1): 1007, doi:10.1029/2000PA000590.
A systematic methodology for the reconstruction of climate fields from sparse observational networks of proxy data, employing the technique of reduced space objective analysis, is applied to the reconstruction of gridded Pacific Ocean Basin sea surface temperature (SST) from coral stable isotope (delta(18)O) data for the period 1607-1990. In this approach we seek to reconstruct only the leading modes of large-scale variability which are both observed in the modern climate and resolved in the proxy data. We find that the coral data verifiably resolve two spatial patterns of SST variability. The first and dominant pattern is that of the El Niño-Southern Oscillation (ENSO). A second pattern reflects uniform changes over most of the Pacific Basin. Calibration and verification tests for 1856-1990 show that root-mean-square variance is small (less than or equal to0.5degreesC RMS) and reconstruction errors are large (less than or equal to0.6degreesC RMS), limiting interpretation to the tropical region. Periods of enhanced ENSO activity similar to those observed in the past two decades are evident in the reconstruction for the early nineteenth century. The changing frequency of ENSO warm phase events appears to coincide with warming of the Pacific mean state inferred from similar reconstruction efforts using tree ring indicators over the last two centuries.
Gordon, A. L., C. F. Giulivi, C. M. Lee, H. H. Furey, A. Bower and L. Talley, 2002: Japan/East Sea intrathermocline eddies. Journal of Physical Oceanography, 32(6): 1960-1974.
Intrathermocline eddies (ITE) with diameters of 100 km and of thickness greater than 100 m are observed within each of the three quasi-stationary meanders of the Tsushima Current of the Japan/East Sea. Within the ITE homogenous, anticyclonic flowing core, the temperature is near 10degreesC with a salinity of 34.12 psu. Because of compensatory baroclinicity of the upper and lower boundaries of the ITE core, the ITE has minor sea level expression. The ITE core displays positive oxygen and negative salinity anomalies in comparison to the surrounding thermocline water, indicative of formation from winter mixed layer water along the southern side of the Japan/East Sea subpolar front. The winter mixing layer is then overridden, or slips below, the regional upper thermocline stratification with its characteristic salinity maximum layer. The winter mixed layer off the coast of Korea closely matches the ITE core characteristics, and is considered as a potential source region. Other sources may be present along the southern boundary of the subpolar front, including a frequently observed warm eddy over the western side of Yamato Rise.
Gordon, A. L., C. F. Giulivi, T. Takahashi, S. Sutherland, J. Morrison and D. Olson, 2002: Bay of Bengal nutrient-rich benthic layer. Deep-Sea Research Part II-Topical Studies in Oceanography, 49(7-8): 1411-1421.
A nutrient- and carbon-rich, oxygen-poor benthic layer is observed in the lower 100 m of the central and western Bay of Bengal, at depths between 3400 to 4000 m. The observed ratios for the biogeochemical anomalies in the benthic layer water are similar to those observed for phytoplankton blooms in open oceans and hence suggest that the source of the high silica, phosphate, nitrate and carbon is likely to be due to decomposition of marine plankton deposited on the Ganges fan. While similar sediment types are expected to exist across a more extensive area of the Bay of Bengal, accumulation of nutrients only within a confined pool of bottom water is due to a greater degree of ventilation elsewhere. To the north of the nutrient-rich benthic pool, in shallower water, inflow of water from West Australian Basin minimizes anomalous benthic properties. To the south, in deeper water, ventilation by bottom water of the Central Indian Basin lifts the Bay of Bengal nutrient-rich benthic water off the sea floor. Thus the nutrient-rich benthic layer occupies zone between better ventilated regions. A counter-clockwise flow of bottom water is suggested for the Bay of Bengal, with nutrient-rich bottom water flowing westward south of Sri Lanka. (C) 2002 Elsevier Science Ltd. All rights reserved.
Greene, A. M., R. Seager and W. S. Broecker, 2002: Tropical snowline depression at the Last Glacial Maximum: Comparison with proxy records using a single-cell tropical climate model. Journal of Geophysical Research-Atmospheres, 107(D7-8): doi:10.1029/2001JD000670.
The substantial lowering of tropical snowlines at the Last Glacial Maximum (LGM), circa 21 kya, is examined using a modified version of the single-cell tropical climate model of Betts and Ridgway . These authors concluded that it was difficult to reconcile the large depression of snowlines at the LGM with the small reduction in mean tropical sea-surface temperature (SST) of the Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) reconstruction. Here, climatic implications of the snowline depression are compared, not with CLIMAP, but with temperature proxies (delta(18)O and Sr/Ca ratios in corals, noble gas concentrations in aquifers, alkenone and Mg/Ca ratios in deep-sea sediments and recent faunal reconstructions) whose LGM values have been interpreted as implying lower surface temperatures in the tropics. It proves difficult, in the framework of this model, to reconcile the coldest of the indicated paleotemperatures with the observed snowline depression, which by itself is found to be consistent with an SST reduction of similar to3 K. A cooling of this magnitude corresponds most closely to recent warm-pool LGM sea-surface temperature estimates based on Mg/Ca paleothermometry. Discordance among the various proxy reconstructions may result, at least in part, from regional variations in surface temperature change at the LGM.
Hall, A. and M. Visbeck, 2002: Synchronous variability in the southern hemisphere atmosphere, sea ice, and ocean resulting from the annular mode. Journal of Climate, 15(21): 3043-3057.
Zonally symmetric fluctuations of the midlatitude westerly winds characterize the primary mode of atmospheric variability in the Southern Hemisphere during all seasons. This is true not only in observations but also in an unforced 15 000-yr integration of a coarse-resolution (R15) coupled ocean-atmosphere model. Here it is documented how this mode of atmospheric variability, known as the Southern Annular Mode (SAM), generates ocean circulation and sea ice variations in the model integration on interannual to centennial timescales that are tightly in phase with the SAM. The positive phase of the SAM is associated with an intensification of the surface westerlies over the circumpolar ocean (around 60degreesS), and a weakening of the surface westerlies farther north. This induces Ekman drift to the north at all longitudes of the circumpolar ocean, and Ekman drift to the south at around 30degreesS. Through mass continuity, the Ekman drift generates anomalous upwelling along the margins of the Antarctic continent, and downwelling around 45degreesS. The anomalous flow diverging from the Antarctic continent also increases the vertical tilt of the isopycnals in the Southern Ocean, so that a more intense circumpolar current is also closely associated with positive SAM. In addition, the anomalous divergent flow advects sea ice farther north, resulting in an increase in sea ice coverage. Finally, positive SAM drives increases in poleward heat transport at about 30degreesS, while decreases occur in the circumpolar region. Ocean and sea ice anomalies of the opposite sign occur when the SAM is negative. The ocean and sea ice fluctuations associated with the SAM constitute a significant fraction of simulated ocean variability poleward of 30degreesS year-round. The robustness of the mechanisms relating the SAM to oceanic variability suggests that the SAM is likely an important source of large-scale variability in the real Southern Hemisphere ocean.
Harnik, N., 2002: The evolution of a stratospheric wave packet. Journal of the Atmospheric Sciences, 59(2): 202-217.
This work examines the extent to which a few basic concepts that apply to plane waves, for example, the refraction of waves up the gradient of the index of refraction, apply to stratospheric planetary waves. This is done by studying the relation between group velocity (C-g) and the wave activity velocity, which is defined as the Eliassen-Palm flux divided by the wave activity density (V-a = F/A). It is shown that although in the limit of plane waves V-a equals C-g, the two velocities are not equal for stratospheric waves, because of reflection, tunneling, and superposition. The use of conservation of wave activity to understand the spatial variations of wave structure is explored. This is done by defining a wave activity packet as part of the wave that moves with V-a. Integral lines of V-a are then used to keep track of the wave packet location and volume. In the idealized case of an almost-plane wave, conservation of wave activity leads to variations in the amplitude of the wave when it is refracted by the slowly varying basic state. This effect is related to changes in wave packet volume. The wave activity packet framework is used to examine the importance of the "volume effect'' for explaining the spatial variations of stratospheric waves.
Held, I. M., M. F. Ting and H. L. Wang, 2002: Northern winter stationary waves: Theory and modeling. Journal of Climate, 15(16): 2125-2144.
A review is provided of stationary wave theory. the theory for the deviations from zonal symmetry of the climate. To help focus the discussion the authors concentrate exclusively on northern winter. Several theoretical issues, including the external Rossby wave dispersion relation and vertical structure, critical latitude absorption, the nonlinear response to orography, and the interaction of forced wave trains with preexisting zonal asymmetries, are chosen for discussion while simultaneously presenting a decomposition of the wintertime stationary wave field using a nonlinear steady-state model.
Hellweger, F. L. and A. L. Gordon, 2002: Tracing Amazon River water into the Caribbean Sea. Journal of Marine Research, 60(4): 537-549.
Monthly Amazon River discharge is correlated to historical monthly sea surface salinity (SSS) in the western tropical Atlantic Ocean and the Caribbean Sea. At Barbados a very high inverse correlation (R-2 = 0.92) exists if the discharge is lagged by two months, which corresponds to the travel time from the Amazon mouth to Barbados. Due to its proximity to Barbados, a small amount of the correlation can also be attributed to the Orinoco River. Between Barbados and the central Caribbean Sea (75W) the peak correlation of Amazon River discharge and SSS occurs at progressively longer lag times, representing the longer travel time. The correlation is highest at Barbados and diminishes with distance downstream. Downstream of the central Caribbean Sea (75W) no correlation is evident, as the Amazon water becomes too diluted to be clearly defined by available data. The results of the analysis are used to calculate surface current speeds of 0.34 +/- 0.09 m/s from the Amazon mouth to Barbados and 0.10 +/- 0.02 m/s from Barbados to the central Caribbean Sea (75W). Downstream of Barbados a subsurface maximum in correlation develops. The correlation is eroded more strongly at shallower depths due to more intense surface processes (e.g., evaporation and precipitation).
Hohmann, R., P. Schlosser, S. S. Jacobs, A. Ludin and R. Weppernig, 2002: Excess helium and neon in the southeast Pacific: Tracers for glacial meltwater. Journal of Geophysical Research-Oceans, 107(C11): doi:10.1029/2000JC000378.
We analyze helium (He) and neon (Ne) isotope data sets from the southeast Pacific sector of the Southern Ocean collected in 1992 and 1994 and describe a new method to estimate glacial meltwater fluxes independent of previous approaches. The waters sampled during these cruises reveal large atmospheric He and Ne excess concentrations in the upper 500 m that are derived predominantly from the dissolution of air contained in glacial ice during melting underneath and at the front of floating ice shelves at elevated hydrostatic pressure. On the stations sampled, the meltwater fractions are largest near the northern and southern ice shelf fronts of George VI Ice Shelf (1.5-2.5%), consistent with prior inferences from delta(18)O. The inventories of He-4 and Ne with local glacial meltwater origin south of 70degreesS between 210degreesE and 295degreesE are (2.5 +/- 0.7) 10(11) cm(3) STP He-4 and (7.9 +/- 2.7) 10(11) cm(3) STP Ne, respectively. The associated meltwater volumes are 430 +/- 120 Gt for He-4 and 400 +/- 140 Gt for Ne. For an estimated seawater residence time of 2 years on the continental shelf, the amounts of glacial meltwater translate into bulk melting rates of 215 +/- 170 Gt yr(-1) for He-4 and 200 +/- 170 Gt yr(-1) for Ne. The values derived from He-4 are expected to be larger than those obtained from Ne because of the terrigenic He component, which accounts for 10-15% of the He excess in this region. Our regional melting rate of 200-215 Gt yr(-1) is comparable to a prior estimate but subject to uncertainties resulting from the station distribution, the air-sea gas exchange, and the estimate of the net transport through the study region.
Houghton, R. W. and M. H. Visbeck, 2002: Quasi-decadal salinity fluctuations in the Labrador Sea. Journal of Physical Oceanography, 32(2): 687-701.
The quasi-decadal salinity fluctuations in the upper 300 m of the Labrador Sea are investigated by partitioning all available salinity station data since 1948 by region and bottom depth. There are major freshwater anomalies in the early 1970s (the Great Salinity Anomaly), mid-1980s, and early 1990s. These vary in amplitude throughout the region, being least on the shelf and greatest over the slope region near the Labrador Current. The Labrador Sea cannot be considered a simple conduit for freshwater anomalies originating in the East Greenland Current. There is evidence that local processes modulate the anomaly. The freshwater anomalies in the Labrador Current are approximately twice as large as those in the East Greenland Current. The Baffin Island Current flowing southward through the western Davis Strait is the only local source of freshwater with sufficient volume to account for this increase. The propagation speed, 2-3 cm s(-1), of the anomaly along the Labrador Sea margin is much less than the advection speed indicating a highly damped system. The connection of the North Atlantic Oscillation (NAO) with these quasi-decadal salinity fluctuations is most obvious in the Labrador Sea interior, where increased surface buoyancy flux during positive NAO drives deep convective mixing and thus terminates the fresh surface anomalies. Less clear are the processes by which NAO-forced changes of lateral freshwater flux modulate the salinity along the margin. The authors propose a feedback mechanism where, during years of low wind speed, freshwater accumulates offshore of the slope front in the surface layer. The increased upper-layer buoyancy prohibits further mixing, and low salinities persist.
Houghton, R. W., 2002: Diapycnal flow through a tidal front: a dye tracer study on Georges Bank. Journal of Marine Systems, 37(1-3): 31-46.
A fluorescent dye tracer, fluorescein, injected into the bottom mixed layer (BML) at the off-bank edge of the tidal front on Georges Bank in late May and early June 1999 has provided the first quantitative measurement of an on-bank diapycnal Lagrangian flow through the front. From the warming of the dye patch, 1.9 x 10(-6) and 7.6 X 10(-6 degrees)C/s on the south flank and northeast peak, respectively, as it passed through the frontal temperature gradient, we infer a mean on-bank flow of 1.6 cm/s on the south flank and 3.1 cm/s on the northeast peak. The heat flux required for this warming is predominantly due to vertical mixing within the tidal front. From the dispersion of the dye patch, we estimate a vertical diffusivity of 1.6 and 3.1 X 10(-3) m(2)/s and a cross-front diffusivity of 18 and 30 m(2)/s on the south flank and northeast peak, respectively.
Karspeck, A. R. and M. A. Cane, 2002: Tropical Pacific 1976-77 climate shift in a linear, wind-driven model. Journal of Physical Oceanography, 32(8): 2350-2360.
A number of studies have attempted to explain the cause of decadal variability in the tropical Pacific and explore its possible link to decadal variability in the midlatitude Pacific. To investigate some of the current theories of Pacific decadal variability, a linear, wind-driven model, designed to simulate only baroclinic wave dynamics, was forced with wind stress anomalies in the Pacific Ocean basin from 1945 through 1992. An analysis technique designed to isolate the decadal/interdecadal scale variability from interannual ENSO variability was performed on the model's thermocline depth anomaly (TDA).
Khatiwala, S., P. Schlosser and M. Visbeck, 2002: Rates and mechanisms of water mass transformation in the Labrador Sea as inferred from tracer observations. Journal of Physical Oceanography, 32(2): 666-686.
Time series of hydrographic and transient tracer (H-3 and He-3) observations from the central Labrador Sea collected between 1991 and 1996 are presented to document the complex changes in the tracer fields as a result of variations in convective activity during the 1990s. Between 1991 and 1993, as atmospheric forcing intensified, convection penetrated to progressively increasing depths, reaching;2300 m in the winter of 1993. Over that period the potential temperature (theta)/salinity (S) properties of Labrador Sea Water stayed nearly constant as surface cooling and downward mixing of freshwater was balanced by excavating and upward mixing of the warmer and saltier Northeast Atlantic Deep Water. It is shown that the net change in heat content of the water column (150-2500 m) between 1991 and 1993 was negligible compared to the estimated mean heat loss over that period (110 W m(-2)), implying that the lateral convergence of heat into the central Labrador Sea nearly balances the atmospheric cooling on a surprisingly short timescale. Interestingly, the H-3-He-3 age of Labrador Sea Water increased during this period of intensifying convection. Starting in 1995, winters were milder and convection was restricted to the upper 800 m. Between 1994 and 1996, the evolution of H-3-He-3 age is similar to that of a stagnant water body. In contrast, the increase in theta and S over that period implies exchange of tracers with the boundaries via both an eddy-induced overturning circulation and along-isopycnal stirring by eddies [with an exchange coefficient of O(500 m(2) s(-1))].
Kukla, G. J., A. C. Clement, M. A. Cane, J. E. Gavin and S. E. Zebiak, 2002: Last interglacial and early glacial ENSO. Quaternary Research, 58(1): 27-31.
Although the link between insolation and climate is commonly thought to be in the high northern latitudes in summer, our results show that the start of the last glaciation in marine isotope stage (MIS) 5d was associated with a change of insolation during the transitional seasons in the low latitudes. A simplified coupled ocean-atmosphere model shows that changes in the seasonal cycle of insolation could have altered El Nino Southern Oscillation (ENSO) variability so that there were almost twice as many warm ENSO events in the early glacial than in the last interglacial. This indicates that ice buildup in the cooled high latitudes could have been accelerated by a warmed tropical Pacific. (C) 2002 University of Washington.
Kushnir, Y., R. Seager, J. Miller(Nakamura) and J. C. H. Chiang, 2002: A simple coupled model of tropical Atlantic decadal climate variability. Geophysical Research Letters, 29(23): 2133.
A linear, zonally averaged model of the interaction between the tropical Atlantic (TA) atmosphere and ocean is presented. A balance between evaporation and meridional heat advection in the mixed layer determines the sea surface temperature tendency. The atmosphere is a fixed-depth, sub-cloud layer in which the specific humidity anomaly is determined by a steady-state balance between evaporation, meridional advection, and a parameterized humidity exchange with the free atmosphere. When the model is integrated, forced with observed surface wind anomalies from 1965 to the present, its simulation of the observed sea surface temperature (SST) is realistic and comparable to a simulation with a full ocean GCM. A statistical representation of surface winds and their relationship to the SST gradient across the equator is used to formulate and test a coupled model of their regional variability. Forced on both sides of the equator, in the trade-wind regions, with "white-noise'' windspeed perturbations, the SST-wind relationship in the near-equatorial region feeds back positively on existing SST anomalies and gives rise to decadal variability.
Kushnir, Y., W. A. Robinson, I. Blade, N. M. Hall, S. Peng and R. Sutton, 2002: Atmospheric GCM response to extratropical SST anomalies: Synthesis and evaluation. Journal of Climate, 15(16): 2233-2256.
The advances in our understanding of extratropical atmosphere-ocean interaction over the past decade and a half are examined, focusing on the atmospheric response to sea surface temperature anomalies. The main goal of the paper is to assess what was learned from general circulation model (GCM) experiments over the recent two decades or so. Observational evidence regarding the nature of the interaction and dynamical theory of atmospheric anomalies forced by surface thermal anomalies is reviewed. Three types of GCM experiments used to address this problem are then examined: models with fixed climatological conditions and idealized, stationary SST anomalies; models with seasonally evolving climatology forced with realistic. time-varying SST anomalies; and models coupled to an interactive ocean. From representative recent studies, it is argued that the extratropical atmosphere does respond to changes in underlying SST although the response is small compared to internal (unforced) variability. Two types of interactions govern the response. One is an eddy-mediated process, in which a baroclinic response to thermal forcing induces and combines with changes in the position or strength of the storm tracks. This process can lead to an equivalent barotropic response that feeds back positively on the ocean mixed layer temperature. The other is a linear, thermodynamic interaction in which an equivalent-barotropic low-frequency atmospheric anomaly forces a change in SST and then experiences reduced surface thermal damping due to the SST adjustment. Both processes contribute to an increase in variance and persistence of low-frequency atmospheric anomalies and, in fact, may act together in the natural system.
Liu, J. P., D. G. Martinson, X. J. Yuan and D. Rind, 2002: Evaluating Antarctic sea ice variability and its teleconnections in global climate models. International Journal of Climatology, 22(8): 885-900.
This study evaluates simulated Antarctic sea ice edge (SIE) variability and its teleconnections in three global coupled climate models (GISS, NCAR and GFDL) against the observations. All models do a reasonable job in simulating the seasonal advance and retreat of the Antarctic sea ice fields. The simulated GISS and NCAR SIE distributions are in agreement with observations in summer and autumn, whereas the GFDL model does best in spring and winter. A common problem is the poor simulation of the observed SIE in the Weddell Sea. All models are not particularly good at simulating the observed regionally varying SIE trends. A comparison of dominant empirical orthogonal function modes of surface air temperature (SAT) variability in each model associated with observed modes show that the models generally capture features of the more prominent covarying spatial patterns such as an El Nino-southern oscillation (ENSO)-like pattern in the tropical Pacific.
Liu, J. P., X. J. Yuan, D. Rind and D. G. Martinson, 2002: Mechanism study of the ENSO and southern high latitude climate teleconnections. Geophysical Research Letters, 29(14): doi:10.1029/2002GL015143.
Evidence of El Nino-Southern Oscillation (ENSO) teleconnections in the southern high latitude climate has been identified, although the mechanisms that might lead to such far-reaching teleconnections remain unresolved. Here we propose one such mechanism-the regional mean meridional atmospheric circulation (the regional Ferrel Cell)-responsible for the covariability of the ENSO and Antarctic Dipole (ADP; a predominant interannually-varying signal in the southern high latitudes). It is found that the altered storm tracks associated with the ENSO variability influence the regional Ferrel Cell indirectly by changing the meridional eddy heat flux divergence and convergence, and shifting the latent heat release zone. The changes of the regional Ferrel Cell then influence the southern high latitude climate by modulating the mean meridional heat flux.
Matano, R. P., A. L. Gordon, R. D. Muench and E. D. Palma, 2002: A numerical study of the circulation in the northwestern Weddell Sea. Deep-Sea Research Part II-Topical Studies in Oceanography, 49(21): 4827-4841.
An eddy-permitting simulation is used to study the circulation of the northwestern Weddell Sea and its interaction with the Scotia Sea. The analysis focuses on the circulation pathways, associated stratification, and volume transports. Comparison between model results and observations show reasonable agreements with respect to the modeled thermohaline stratification and circulation such as export of Weddell Sea Deep Water through the Weddell-Scotia Confluence region. Using the model results, we estimated the relative contributions of the two main routes of escape of the Weddell Sea deep waters into the Scotia Sea and the South Sandwich Trench. The main route for inter-basin exchange is found to be through the Scotia Sea (via the South Orkney Passage and the Bransfield Strait). Our simulation does not show advective transport of deep or bottom waters through the South Sandwich Trench, and Lagrangian analysis of float trajectories indicates that the fluxes in this region are more likely related to eddy-driven mixing than to mean flow advection. The model shows, in addition, some sub-basin scale features that have not been reported in the observations. The Weddell western boundary current is seen as a diffuse, filamentous feature. A south-flowing jet was present over the outer shelf off the Antarctic Peninsula. Retroflection and return southward flow is seen for from the South Sandwich Trench, and there was a small inflow of Scotia Sea waters into the Powell Basin. (C) 2002 Elsevier Science Ltd. All rights reserved.
Molnar, P. and M. A. Cane, 2002: El Niño's tropical climate and teleconnections as a blueprint for pre-Ice Age climates. Paleoceanography, 17(2): 1021, doi:10.1029/2001PA000663.
At similar to 2.7 million years ago the warm equable climates of early and "middle'' Pliocene time (used here to mean from similar to5 to similar to2.7 Ma) were replaced by recurring ice ages. Most attempts to explain the change appeal either to changes in CO2 in the atmosphere or reduced heat transport by the Atlantic Ocean. The sources of the strongest teleconnections in the current climate, however, lie in the tropics, and such connections occur by transport of heat and moisture by the atmosphere. The most prominent of these teleconnections link aberrations in sea surface temperatures in the equatorial Pacific, El Nino-Southern Oscillation (ENSO) variations, with warm and dry or cool and wet anomalies in extratropical climates. We show that in most cases early and middle Pliocene climate both in equatorial regions and in the extratropics differ from present-day climates with the same spatial pattern as that associated with ENSO. For instance, not only was Canada warmer during early Pliocene time than at present, as it is during El Nino, but the region surrounding the Gulf of Mexico appears to have been cooler and a bit wetter, as it commonly is during El Nino. A virtually permanent El Nino-like state appears to have characterized pre-Ice Age climates, suggesting that transport of heat by the atmosphere was the principal mechanism that maintained extratropical warmth. Accordingly, cooling and the growth of recurring ice sheets in the Northern Hemisphere resulted from the development of a strong Walker circulation and a weakening of the Hadley circulation.
Ou, H. W. and A. L. Gordon, 2002: Subduction along a midocean front and the generation of intrathermocline eddies: A theoretical study. Journal of Physical Oceanography, 32(6): 1975-1986.
Through an idealized model, the authors consider the dynamics of subduction along a midocean front and its linkage to the intrathermocline eddies (ITEs). The subduction is necessitated by advective-diffusive balance of potential vorticity (PV), with its flux mainly a function of the mixed layer depth over the normal range of the horizontal diffusivity. The mismatch of PV impedes the entry of the subducted water into the interior, resulting in an excess flux that peaks at some intermediate mixed layer depth. This mismatch also causes the generation of anticyclonic ITEs, whose radius contains no lower bound, and a maximum limited by the entrainment rate. Through entrainment cooling, ITEs may leave their imprints in the surface temperature, giving rise to a meandering appearance of the front, even in the absence of instability.
Robertson, R., M. Visbeck, A. L. Gordon and E. Fahrbach, 2002: Long-term temperature trends in the deep waters of the Weddell Sea. Deep-Sea Research Part II-Topical Studies in Oceanography, 49(21): 4791-4806.
Warming of the deep water in the Weddell Sea has important implications for Antarctic bottom water formation, melting of pack ice, and the regional ocean-atmosphere heat transfer. In order to evaluate warming trends in the Weddell Sea, a historical data set encompassing CTD and bottle data from 1912 to 2000 was analyzed for temporal trends in the deep water masses: warm deep water (WDW) and Weddell Sea deep water (WSDW). The coldest WDW temperatures were primarily associated with the Weddell Polynya of the mid-1970s. Subsequent warming occurred at a rate of similar to0.012+/-0.007degreesCyr(-1) from the 1970s to 1990s. This warming was comparable to the global, average surface water warming observed by Levitus et al. (Science 287 (2000) 2225), to the warming of the WSBW in the central Weddell Sea observed by Fahrbach et al. (Filchner-Ronne Ice Shelf Program, Report No. 12, Alfred-Wegener-Institut, Bremerhaven, Germany, 1998a, p.24), and to the surface ice temperature warming from 1970 to 1998 in the Weddell Sea observed by Comiso (J. Climate 13 (2000) 1674). The warming was not compensated by an increase in salinity, and thus the WDW became less dense. The location of the warmest temperature was displaced towards the surface by similar to200m from the 1970s to the 1990s. Although the average WSDW potential temperatures between 1500 and 3500m were warmer in the 1990s than in the 1970s, high variability in the data prevented identification of a well-defined temporal trend. (C) 2002 Elsevier Science Ltd. All rights reserved.
Schlosser, P., R. Newton, B. Ekwurzel, S. Khatiwala, R. Mortlock and R. Fairbanks, 2002: Decrease of river runoff in the upper waters of the Eurasian Basin, Arctic Ocean, between 1991 and 1996: Evidence from delta O-18 data. Geophysical Research Letters, 29(9): doi:10.1029/2001GL013135.
Measurements of the (H2O)-O-18/(H2O)-O-16 ratio of water from two sections crossing the Eurasian Basin in 1991 and 1996 show that the observed decrease in the freshwater contained in the upper waters of the Eurasian Basin during the 1990s is due to decrease in meteoric water (mainly river runoff). The decrease in meteoric water inventories between 1991 and 1996 calculated from balances of mass, salinity, delta(18)O, and PO4* is about 3 meters and accounts for basically the entire freshwater change inferred from salinity budgets. Climatological data are used to ensure that the two sections can be considered to belong to the same hydrographic regime. The data also suggest that in 96 the formation of sea ice from the upper waters in the Amundsen Basin was lower by about 1 meter (3 m in 1996 compared to 4 m in 1991).
Schorghofer, N., O. Aharonson and S. Khatiwala, 2002: Slope streaks on Mars: Correlations with surface properties and the potential role of water. Geophysical Research Letters, 29(23): doi:10.1029/2002GL015889.
The Mars Orbiter Camera on board the Mars Global Surveyor spacecraft has returned images of numerous dark streaks that are the result of down-slope mass movement occurring under present-day martian climatic conditions. We systematically analyze over 23,000 high-resolution images and demonstrate that slope streaks form exclusively in regions of low thermal inertia (confirming earlier results), steep slopes, and, remarkably, only where peak temperatures exceed 275 K. The northernmost streaks, which form in the coldest environment, form preferentially on warmer south-facing slopes. Repeat images of sites with slope streaks show changes only if the time interval between the two images includes the warm season. Surprisingly (in light of the theoretically short residence time of H2O close to the surface), the data support the possibility that small amounts of water are transiently present in low-latitude near-surface regions of Mars and undergo phase transitions at times of high insolation, triggering the observed mass movements.
Seager, R., D. S. Battisti, J. Yin, N. Gordon, N. H. Naik(Henderson), A. C. Clement and M. A. Cane, 2002: Is the Gulf Stream responsible for Europe's mild winters? Quarterly Journal of the Royal Meteorological Society, 128(586): 2563-2586.
Is the transport of heat northward by the Gulf Stream and North Atlantic Drift, and its subsequent release into the midlatitude westerlies, the reason why Europe's winters are so much milder than those of eastern North America and other places at the same latitude? Here, it is shown that the principal cause of this temperature difference is advection by the mean winds. South-westerlies bring warm maritime air into Europe and north-westerlies bring frigid continental air into north-eastern North America. Further, analysis of the ocean surface heat budget shows that the majority of the heat released during winter from the ocean to the atmosphere is accounted for by the seasonal release of heat previously absorbed and not by ocean heat-flux convergence. Therefore, the existence of the winter temperature contrast between western Europe and eastern North America does not require a dynamical ocean. Two experiments with an atmospheric general-circulation model coupled to an ocean mixed layer confirm this conclusion. The difference in winter temperatures across the North Atlantic, and the difference between western Europe and western North America, is essentially the same in these models whether or not the movement of heat by the ocean is accounted for. In an additional experiment with no mountains, the flow across the ocean is more zonal, western Europe is cooled, the trough east of the Rockies is weakened and the cold of north-eastern North America is ameliorated. In all experiments the west coast of Europe is warmer than the west coast of North America at the same latitude whether or not ocean heat transport is accounted for. In summary the deviations from zonal symmetry of winter temperatures in the northern hemisphere are fundamentally caused by the atmospheric circulation interacting with the oceanic mixed layer.
Shaman, J., J. F. Day and M. Stieglitz, 2002: Drought-induced amplification of Saint Louis encephalitis virus, Florida. Emerging Infectious Diseases, 8(6): 575-580.
We used a dynamic hydrology model to simulate water table depth (WTD) and quantify the relationship between Saint Louis encephalitis virus (SLEV) transmission and hydrologic conditions in Indian River County, Florida, from 1986 through 1991, a period with an SLEV epidemic. Virus transmission followed periods of modeled drought (specifically low WTDs 12 to 17 weeks before virus transmission, followed by a rising of the water table 1 to 2 weeks before virus transmission). Further evidence from collections of Culex nigripalpus (the major mosquito vector of SLEV in Florida) suggests that during extended spring droughts vector mosquitoes and nestling, juvenile, and adult wild birds congregate in selected refuges, facilitating epizootic amplification of SLEV. When the drought ends and habitat availability increases, the SLEV-infected Cx. nigripalpus and wild birds disperse, initiating an SLEV transmission cycle. These findings demonstrate a mechanism by which drought facilitates the amplification of SLEV and its subsequent transmission to humans.
Shaman, J., M. Stieglitz, C. Stark, S. LeBlancq and M. A. Cane, 2002: Using a dynamic hydrology model to predict mosquito abundances in flood and swamp water. Emerging Infectious Diseases, 8(1): 6-13.
We modeled surface wetness at high resolution, using a dynamic hydrology model, to predict flood and swamp water mosquito abundances. Historical meteorologic data, as well as topographic, soil, and vegetation data, were used to model surface wetness and identify potential fresh and swamp water breeding habitats in two northern New Jersey watersheds. Surface wetness was positively associated with the subsequent abundance of the dominant floodwater mosquito species, Aedes vexans, and the swamp water species, Anopheles walked. The subsequent abundance of Culex pipiens, a species that breeds in polluted, eutrophic waters, was negatively correlated with local modeled surface wetness. These associations permit real-time monitoring and forecasting of these floodwater and nonfloodwater species at high spatial and temporal resolution. These predictions will enable public health agencies to institute control measures before the mosquitoes emerge as adults, when their role as transmitters of disease comes into play.
Shaman, J., M. Stieglitz, V. C. Engel, R. D. Koster and C. Stark, 2002: Representation of subsurface storm flow and a more responsive water table in a TOPMODEL-based hydrology model. Water Resources Research, 38(8): doi:10.1029/2001WR000636.
 This study presents two new modeling strategies. First, a methodology for representing the physical process of subsurface storm flow within a TOPMODEL framework is developed. In using this approach, discharge at quick flow timescales is simulated, and a fuller depiction of hydrologic activity is brought about. Discharge of water from the vadose zone is permitted in a physically realistic manner without a priori assumption of the level within the soil column at which subsurface storm flow saturation can take place. Determination of the subsurface storm flow contribution to discharge is made using the equation for groundwater flow. No new parameters are needed. Instead, regions in excess of field capacity that develop during storm events, producing vertical recharge, are also allowed to contribute to soil zone discharge. These subsurface storm flow contributions to river runoff, as for groundwater flow contributions, are a function of catchment topography and hydraulic conductivity at the depth at which such regions in excess of field capacity occur. The second approach improves groundwater flow response through a reduction of porosity and field capacity with depth in the soil column. Large storm events are better captured and a more dynamic water table develops with application of this modified soil column profile (MSCP). The MSCP predominantly reflects soil depth differences in upland and lowland regions of a watershed. Combined, these two approaches, subsurface storm flow and the MSCP, provide a more accurate representation of the timescales at which discharge responds and a more complete depiction of hydrologic activity. Storm events large and small are better simulated, and some of the biases previously evident in TOPMODEL simulations are reduced.
Thurnherr, A. M., K. J. Richards, C. R. German, G. F. Lane-Serff and K. G. Speer, 2002: Flow and mixing in the rift valley of the Mid-Atlantic Ridge. Journal of Physical Oceanography, 32(6): 1763-1778.
High levels of diapycnal mixing and geothermal heating near midocean ridges contribute to the buoyancy fluxes that are required to close the global circulation. In topographically confined areas, such as the deep median valleys of slow-spreading ridges, these fluxes strongly influence the local hydrography and dynamics. Data from a segment-scale hydrographic survey of the rift valley of the Mid-Atlantic Ridge and from an array of current meters deployed there during an entire year are analyzed in order to characterize the dominant hydrographic patterns and dynamical processes. Comparison with historic hydrographic data indicates that the temporal variability during the last few decades has been small compared to the observed segment-scale gradients. The rift valley circulation is characterized by inflow from the eastern ridge flank and persistent unidirectional along-segment flow into a cul-de-sac. Therefore, most of the water flowing along the rift valley upwells within the segment with a mean vertical velocity >10(-5) m s(-1). The observed streamwise hydrographic gradients indicate that diapycnal mixing dominates the rift valley buoyancy fluxes by more than an order of magnitude, in spite of the presence of a large hydrothermal vent field supplying several gigawatts of heat to the water column. Hydrographic budgets in the rift valley yield diffusivity values of order 5x10(-3) m(2) s(-1), consistent with estimates derived from statically unstable overturns, the largest of which were observed downstream of topographic obstacles in the path of the along-segment flow. This suggests vertical shear associated with cross-sill flows as the dominant contributor to the mechanical mixing in the rift valley.
Visbeck, M., 2002: Deep velocity profiling using lowered acoustic Doppler current profilers: Bottom track and inverse solutions. Journal of Atmospheric and Oceanic Technology, 19(5): 794-807.
Lowered acoustic Doppler current profilers (LADCPs) have matured from an experimental instrument to an operational hydrographic tool to study ocean dynamics. The data processing, however, is still in a rather primitive state. First, a method to estimate bottom-track velocities using the standard water profile data was developed. Then inverse solutions are presented that enhance the standard data processing by adding external constraints such as bottom-referenced velocity profiles. Depending on the depth of the profile and the ADCP range the inclusion of bottom-track data can reduce the local velocity errors by a significant factor. The least squares framework also allows for simplified error analysis of the LADCP system and some of the trade-offs are discussed.
Vranes, K., A. L. Gordon and A. Ffield, 2002: The heat transport of the Indonesian Throughflow and implications for the Indian Ocean heat budget. Deep-Sea Research Part II-Topical Studies in Oceanography, 49(7-8): 1391-1410.
The Indonesian Throughflow (ITF) is considered central to the heat budgets of the Pacific and Indian Oceans. Temperature and ocean current time series obtained within the Makassar Strait from December 1996 to early July 1998 are used to calculate heat transport of the ITF and assess its influence on Indian Ocean heat divergence. Velocity and temperature values for the surface layer that were not directly measured are extrapolated from the shallowest measurement to the sea surface using a variety of model profiles. While a single temperature profile is used based on a linear interpolation from NCEP OI sea-surface temperatures to the top-most mooring temperature recorder, four different velocity profiles are employed. Heat transport is calculated as volume transport multiplied by temperature, density and specific heat, using reference temperatures between 0degreesC and 4degreesC. The mean heat transport averages 0.55 PW relative to 0 degrees C, and 0.41 PW relative to 4 degrees C for the two most reasonable velocity profiles. In comparison, model heat transport values are larger, between 0.6 and 1.15 PW. Heat transport varies with ENSO phase, lower during El Niño, higher during La Niña. As 1997 was a strong El Niño year, our heat transport estimate may be less than the climatic mean. The ITF water is advected towards Africa within the Indian Ocean South Equatorial Current, to eventually exit the Indian Ocean across 30 S, most likely within the Agulhas Current. For realistic consideration of the ITF component within the Agulhas Current, the heat flux divergence of ITF waters within the Indian Ocean north of 30degreesS is found to be insignificant. Our results provide support for model studies and hydrographic geostrophic inverse calculations that indicate the ITF heat, derived from the Pacific Ocean, is ultimately lost to the atmosphere in the southwest Indian Ocean. (C) 2002 Elsevier Science Ltd. All rights reserved.
Wang, Z. , D. Wu, D. Chen, H. Wu, X. Song and Z. Zhang, 2002: Critical Time Span and Nonlinear Action Structure Of Climatic Atmosphere and Ocean. Advances in Atmospheric Sciences, Vol.19: 741-756.
In this paper, we studied the critical time span and the approximate nonlinear action structure of climatic atmosphere and ocean. The critical time span of the climatic atmosphere and ocean may represent relative temporal scale of predictability, relating to the spatial resolution required, the strength of nonlinear action, and the calculation exactness. As far as the same characteristic spatial scale is concerned, the minimum critical time span of the ocean is about 9 times of that of atmosphere, several days or more. Usually, the stronger of the nonlinear action, the shorter the critical time span with smoothly changing external forces. The approximate structure of nonlinear action of climatic atmosphere and ocean is: usually the nonlinear action decreases with increasing latitude, which relates to the Coriolis force¡¯s role in fluid motion (forming geostrophic current); the nonlinear action changes with the anomalous cyclonic or anticyclonic circulation shear, for instance, when the strength of anomalous eastward zonal circulation equals to that of anomalous meridional circulation, the nonlinear action is the maximum; wind stress plus gradient forces enlarge the nonlinear action, etc..
Waple, A. M., J. H. Lawrimore, M. S. Halpert, G. D. Bell, W. Higgins, B. Lyon, M. J. Menne, K. L. Gleason, R. C. Schnell, J. R. Christy, W. Thiaw, W. J. Wright, M. J. Salinger, L. Alexander, R. S. Stone and S. J. Camargo, 2002: Climate Assessment for 2001. Bulletin of the American Meteorological Society, 83(6): S1-S62.
Global temperatures in 2001 were 0.51 degrees C (0.92 degrees F) above the long-term (1880-2000) average, which places 2001 as the second warmest year in the 122-year instrumental record. Land temperatures were 0.75degreesC (1.35 degrees F) above average and ocean temperatures were 0.40 degrees C (0.72 degrees F) above the 1880-2000 mean. This ranks them as the second and third warmest on record, respectively. The Northern Hemisphere temperature continued to average near record levels in 2001 at 0.60degreesC (1.08 degrees F) above the long-term average. The Southern Hemisphere also reflects the globally warmer conditions, with a positive anomaly of 0.43 degrees C (0.77 degrees F).
Warrach, K., M. Stieglitz, H. T. Mengelkamp and E. Raschke, 2002: Advantages of a topographically controlled runoff simulation in a soil-vegetation-atmosphere transfer model. Journal of Hydrometeorology, 3(2): 131-148.
Two methods to incorporate subgrid variability in soil moisture and runoff production into soil-vegetation-atmosphere transfer (SVAT) models are compared: 1) the variable infiltration capacity model approach (VIC), and 2) a modified "TOPMODEL'' approach. Because neither approach needs to track surface or subsurface flow within a catchment explicitly, they represent computationally efficient ways to represent hydrologic processes within the context of regional and global modeling. This study shows that, during low flow periods, the runoff simulation is superior when using the TOPMODEL-based equations, especially during the rising limb of the autumn hydrograph. A main drawback of the modified VIC-model approach, especially for regional and global application, is that, with five free parameters, considerably more model calibration is required. TOPMODEL, on the other hand, requires only the determination of one free parameter. However, a TOPMODEL approach does require extensive preprocessing of topographic data, and issues concerning resolution of the data used become relevant.
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