Surface Heat Budget Research Articles

Is the Gulf Stream responsible for Europe's mild winters?

AbstractIs 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. Copyright © 2002 Royal Meteorological Society.

Measurements near the Atmospheric Surface Flux Group tower at SHEBA: Near‐surface conditions and surface energy budget

Measurements at the Surface Heat Budget of the Arctic Ocean Experiment (SHEBA) Atmospheric Surface Flux Group (ASFG) tower site from October 1997 to October 1998 are used to describe the annual cycle of the near‐surface environment and the surface energy budget (SEB). Comparisons with historical data and climatological estimates suggest that the SHEBA site was 3–8°C warmer in March and April. The unique SHEBA profile measurements showed that the mean near‐surface environment is strongly stable during 6 winter months, and near neutral or weakly stable during the other months. However, one‐hour data show that neutral stratification does occur 25% of the time during the winter. The monthly mean flux profiles suggest that turbulent processes cool the near‐surface atmosphere during the winter and warm it during the summer, though the sign of the sensible heat flux is negative during both the winter and July. The SHEBA SEB calculation is unique in its nearly exclusive use of observed rather than derived values. The magnitude of the best estimate of the annual net observed surface energy surplus at SHEBA (8.2 W m−2) was consistent with the observed surface ice and snowmelt and was in reasonable agreement with most previous estimates of the net annual SEB over the Arctic pack ice. However, the partitioning of the various components of the SEB differed in the SHEBA data. The SHEBA site had unusually large incoming longwave radiation in the fall and spring, giving an annual mean that was larger by 10.4–19.3 W m−2. The site also had substantially less incoming solar radiation during most months than in previous estimates, producing a difference in the annual mean of 5.0–9.5 W m−2 when compared to these estimates. The observed magnitudes of the sensible (−2.2 W m−2) and latent (1.1 W m−2) heat fluxes at SHEBA were smaller than previous climatological estimates, as were the conductive flux estimates (2.4–5.0 W m−2) at this site. Estimates of the measurement errors suggest that they are not likely to alter the conclusions concerning the SEB terms presented here but will prevent us from conclusively determining the reasons for the net thinning of the ice observed during SHEBA.

Relating arctic pack ice stress and deformation under winter conditions

Together, thermodynamic and dynamic processes determine the thickness distribution of the ice cover on polar oceans, which governs the exchange of energy between the atmosphere and the ocean. Key to the dynamic processes is the mechanical behavior of the ice cover. During the Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment, we deployed sensors to measure the internal ice stress at several locations within a 15 × 15 km area. These measurements are combined with satellite‐derived ice motion and imagery products. The objective is to make a first step toward using these data sources for evaluating sea ice dynamics models by assessing whether the stress signal can be qualitatively linked to the regional‐scale (10–100 km) deformation activity. Four case studies are presented, each with distinguishing characteristics: consolidation of the seasonal ice zone against the Alaskan coast (5–7 December 1997); advancement of the consolidation zone into the perennial ice pack (11–13 December); extreme divergence (14–17 January); and consolidation of the pack against Wrangel Island and the Siberian coast (20–23 February). The results of this analysis (1) demonstrate that stress measurements are related to the regional deformation behavior of the ice cover, (2) confirm that regional‐scale ice dynamics is primarily a function of coastal geometry and sustained, large‐scale wind direction and magnitude, (3) provide continued evidence that the ice pack behaves as a granular hardening plastic, and (4) encourage pursuit of efforts to use direct measurements of ice stress and deformation in the formulation and development of sea ice dynamics models.

Sea ice kinematics and surface properties from RADARSAT synthetic aperture radar during the SHEBA drift

Satellite data are important for providing the large‐scale context of the Surface Heat Budget of the Arctic Ocean (SHEBA) station and for characterizing the spatial variability of the sea ice in its vicinity. The Canadian RADARSAT satellite collected 195 synthetic aperture radar (SAR) images of the SHEBA site over the course of the 1 year drift. The RADARSAT Geophysical Processor System (RGPS) used these images to compute the spatial pattern of ice motion within 100 km of the SHEBA station by tracking features in sequential images. From the ice motion data the divergence and shear of the pack ice are estimated. The divergence is large from November to January, followed by a gradual convergence from February through July. The character of the ice motion changes at the end of July, from piecewise rigid motion to free drift. The ice motion reverts to its winterlike character in late September. Thus the “kinematic” summer runs from late July to late September. The radar backscatter also goes through seasonal transitions, capturing the abrupt onset of melt (29 May) and freeze‐up (15 August). The concentration of multiyear ice is about 94% in the fall, and its backscatter signature remains stable through spring. Multiyear and first‐year ice cannot be distinguished during the summer melt season, when the mean backscatter is negatively correlated with the surface air temperature. The “thermodynamic” summer runs from late May to mid‐August.

An annual cycle of Arctic surface cloud forcing at SHEBA

We present an analysis of surface fluxes and cloud forcing from data obtained during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment, conducted in the Beaufort and Chuchki Seas and the Arctic Ocean from November 1997 to October 1998. The measurements used as part of this study include fluxes from optical radiometer sets, turbulent fluxes from an instrumented tower, cloud fraction from a depolarization lidar and ceilometer, and atmospheric temperature and humidity profiles from radiosondes. Clear‐sky radiative fluxes were modeled in order to estimate the cloud radiative forcing since direct observation of fluxes in cloud‐free conditions created large statistical sampling errors. This was particularly true during summer when cloud fractions were typically very high. A yearlong data set of measurements, obtained on a multiyear ice floe at the SHEBA camp, was processed in 20‐day blocks to produce the annual evolution of the surface cloud forcing components: upward, downward, and net longwave and shortwave radiative fluxes and turbulent (sensible and latent heat) fluxes. We found that clouds act to warm the Arctic surface for most of the annual cycle with a brief period of cooling in the middle of summer. Our best estimates for the annual average surface cloud forcings are −10 W m−2 for shortwave, 38 W m−2 for longwave, and −6 W m−2 for turbulent fluxes. Total cloud forcing (the sum of all components) is about 30 W m−2 for the fall, winter, and spring, dipping to a minimum of −4 W m−2 in early July. We compare the results of this study with satellite, model, and drifting station data.

Turbulent stress at the ice/ocean interface and bottom surface hydraulic roughness during the SHEBA drift

Upper ocean turbulence and mean current data from the 1997–1998 Surface Heat Budget of the Arctic Ocean (SHEBA) drift in the western Arctic Ocean were used to estimate turbulent shear stress at the ice/ocean interface and hydraulic roughness of the ice undersurface. Techniques for determining interfacial stress from velocity covariance measurements in the ice/ocean boundary layer (IOBL) are complicated by buoyancy flux and the heterogeneity of the ice undersurface, where protrusions corresponding to relatively small upper surface features become major obstacles when compared to the scale of the IOBL. In addition, ice deformation forced relocation of the main SHEBA oceanographic program about midway through the experiment. Hence, there were two different measurement sites to consider. Three different methods were used to compute the undersurface roughness characterizing the undeformed, multiyear floe occupied by the SHEBA project. The first was straightforward (naive) application of the “law of the wall” to turbulent stress and mean velocity measurements from the turbulence instrument cluster nearest to the interface, assuming a logarithmic velocity profile and constant stress. For the second method, local turbulence closure was used to model the entire IOBL in order to estimate the impact of Coriolis stress attenuation and buoyancy forces on stress and shear near the boundary. A third method, proposed here for the first time, estimated mixing length and eddy viscosity from a scale inversely proportional to the wave number at the peak of the weighted vertical velocity spectrum. The last method appears most robust, in that it shows no overall difference in z0 between the two sites and only minor seasonal and directional differences. The best estimate for the undersurface roughness of undeformed, multiyear ice at the SHEBA site is 0.0048 m < z0 < 0.007, i.e., about 6 mm. Specification of a regional “aggregate” under‐ice roughness requires additional consideration of the added drag from isolated pressure keels and floe edges, along with reduced drag from smoother, newly frozen ice and open water.

Characterization of springtime leads in the Beaufort/Chukchi Seas from airborne and satellite observations during FIRE/SHEBA

Airborne remote sensing observations in the vicinity of the Surface Heat Budget of the Arctic Ocean (SHEBA) camp in the Beaufort and Chukchi Seas during May 1998 are used to characterize leads. This characterization was accomplished using observations from a passive microwave radiometer, video camera, and infrared pyrometer. An automated methodology is presented to determine lead fraction, width, and orientation. Refrozen lead fraction decreased in the latter half of May, due in part to local convergence in the ice pack. Airborne passive microwave and video observations are combined to produce a lead width distribution for the SHEBA region. Narrow leads are most prevalent, with lead fraction decreasing exponentially with increasing lead width. Lead orientation showed a preference in a northwesterly direction, which is consistent with prevailing wind patterns and ocean circulation. The lead width distribution and lead orientation observed by the airborne sensors are similar to the characteristics derived from an advanced very high resolution radiometer (AVHRR) albedo image encompassing the Beaufort/Chukchi Seas during the same time period. The AVHRR albedos in the SHEBA vicinity are also comparable to the larger region. These similarities suggest that the area of study used by SHEBA investigators was representative of the Western Arctic during this time period for these surface characteristics.

Micrometeorological changes following establishment of artificially established artemisia vegetation on desertified sandy land in the Horqin sandy land, China and their implication on regional environmental change

Human-induced desertification in the Horqin sandy land in the north-eastern part of China has been reversed since the mid-1970s through re-vegetation. This land cover change affects surface energy and water transfer processes. We employed the Bowen ratio energy balance technique to examine micrometeorological changes following the establishment of artificially established artemisia vegetation on the severely desertified sandy land in Naiman, a county located in the Horqin. Re-vegetation on the desertified sandy land decreased the surface albedo and increased the surface roughness length, thereby resulting in considerable changes in both surface water and heat budget, and wind regimes. As compared with that (34%) before re-vegetation, albedo decreased by 15% as the sandy land was semi-fixed and decreased by 47% as the sandy land is entirely fixed. With change in albedo, partitioning of the available energy exhibited distinct patterns depending on vegetation cover, especially large increase in evapotranspiration, which may result in soil desiccation and thus further affecting temperature regime. Establishment of artificially established vegetation also affected wind regimes by altering surface roughness; consequently, erosion was avoided in the vegetated surfaces. These changes, if occurring in large spatial scale, may affect the local and regional climate according to the Charney theory.

Micrometeorological changes following establishment of artificially established artemisia vegetation on desertified sandy land in the Horqin sandy land, China and their implication on regional environmental change

Human-induced desertification in the Horqin sandy land in the north-eastern part of China has been reversed since the mid-1970s through re-vegetation. This land cover change affects surface energy and water transfer processes. We employed the Bowen ratio energy balance technique to examine micrometeorological changes following the establishment of artificially established artemisia vegetation on the severely desertified sandy land in Naiman, a county located in the Horqin. Re-vegetation on the desertified sandy land decreased the surface albedo and increased the surface roughness length, thereby resulting in considerable changes in both surface water and heat budget, and wind regimes. As compared with that (34%) before re-vegetation, albedo decreased by 15% as the sandy land was semi-fixed and decreased by 47% as the sandy land is entirely fixed. With change in albedo, partitioning of the available energy exhibited distinct patterns depending on vegetation cover, especially large increase in evapotranspiration, which may result in soil desiccation and thus further affecting temperature regime. Establishment of artificially established vegetation also affected wind regimes by altering surface roughness; consequently, erosion was avoided in the vegetated surfaces. These changes, if occurring in large spatial scale, may affect the local and regional climate according to the Charney theory.

Spatial distribution and radiative effects of soot in the snow and sea ice during the SHEBA experiment

Soot observations around the periphery of the Arctic Ocean indicate snowpack concentrations ranging from about 1 to more than 200 ng carbon/g snow (ngC/g), with typical values being near 40–50 ngC/g. Values of this magnitude would significantly affect not only the albedo and transmissivity of the ice cover but also surface melt rates and internal heat storage in the ice. During the Surface Heat Budget of the Arctic Ocean (SHEBA) drift, there was concern that soot emitted from the ship could adversely impact the heat and mass balance measurements, producing results that would not be representative of the region as a whole. To investigate this possibility, a series of soot measurements was carried out starting in the spring of 1998 during the time of maximum snowpack thickness. On the upwind side of the ship, where the heat and mass balance program was carried out, soot concentrations averaged over the depth of the snowpack spanned a range from 1 to 7 ngC/g, with average values of 4–5 ngC/g. On the downwind side, concentrations increased to 35 ngC/g and above. Measurements made up to 16 km from the ship yielded average background soot levels of approximately 4.4 ngC/g, with a standard deviation of 2.9 ngC/g evenly distributed throughout the different snow layers. These concentrations were not statistically distinguishable from the values measured in the observing areas on the upwind side of the ship. This indicates that soot concentrations in the central Arctic Basin are substantially lower than those reported for the coastal regions and are not sufficient to produce a significant decrease in the albedo. Although measurements of sea ice samples gave similarly low values, parameter studies show that the snow soot levels could be significant if the summer melt caused all the soot to be concentrated at the ice surface.

An annual cycle of Arctic cloud characteristics observed by radar and lidar at SHEBA

The temporal distributions of cloudiness, vertical distribution of cloud boundary heights, and occurrence of liquid phase in clouds are determined from radar and lidar data sets collected from October 1997 to October 1998 during the Surface Heat Budget of the Arctic Ocean (SHEBA) project. The radar/lidar combination was necessary for comprehensive cloud detection over a variety of physical conditions and is significantly more detailed (5–9 s temporal resolution, 30–40 m vertical resolution) than measurements made by surface observers or satellites. The combined measurements revealed that clouds were almost continuously present, with an annual average occurrence of 85%, and displayed an overall annual trend of a cloudier summer and clearer winter. A monthly averaged cloud occurrence maximum of 97% was observed in September and a minimum of 63% was observed in February. Monthly averaged lowest cloud base heights were between 0.25 and 1.0 km above ground level (agl) and monthly averaged highest cloud top heights were between 2.5 and 5.5 km agl, and displayed no significant seasonal variation. The number of cloud layers was typically 1 or 2, with the summer months tending to be multilayered. The lidar utilized depolarization ratios to detect liquid water; the percentage of lidar‐observed clouds containing liquid was 73% for the year. The least amount of liquid water phase was observed during December in 25% of the lidar‐detected clouds and the maximum was observed during July in 95% of the lidar‐detected clouds. Liquid was distributed in a combination of all‐liquid and mixed phase clouds, and was detected at altitudes as high as 6.5 km agl and at temperatures as low as −34°C.

Near‐surface water vapor over polar sea ice is always near ice saturation

During our yearlong participation in the Surface Heat Budget of the Arctic Ocean experiment (SHEBA), we found the measured relative humidity, figured for saturation with respect to ice, to almost always be near 100%. Often, multiple humidity sensors even showed supersaturation. Four months of observations over sea ice in the Antarctic showed the same behavior. These frequent, ubiquitous, and reproducible measurements are too compelling to discount. We hypothesize that the high relative humidity is a consequence of plentiful water vapor given up by leads and polynyas. We thus develop a simple time‐dependent vapor budget model that we solve analytically to assess the role of leads in supplying water vapor to the polar atmospheric boundary layer. The solution to that model shows that (1) because the polar marine boundary layer is generally thin, its timescale for reaching moisture equilibrium is much shorter than the timescale of the synoptic processes that tend to disrupt equilibrium, and (2) because they have relatively warm surfaces, open leads and polynyas supply water vapor more rapidly than the surrounding sea ice surface can remove it, despite an open water fractional area that may be only 5%. In concert, the two processes commonly lead to water vapor densities in the boundary layer over sea ice that are near the value for ice saturation.

Evaluation of data sets used to force sea ice models in the Arctic Ocean

Basin‐scale sea ice models are often run uncoupled to either an atmosphere or ocean model to evaluate the sea ice model, to compare different models, and to test changes in physical parameterizations. Such simulations require that the boundary forcing be specified. The specification of atmospheric forcing associated with the surface heat and freshwater fluxes has been done in various sea ice simulations using climatology, numerical weather prediction analyses, or and satellite data. However, the errors in the boundary forcing may be so large that it is difficult to determine whether discrepancies between simulated and observed properties of sea ice should be attributed to deficiencies in the sea ice model or to the boundary forcing. To assess the errors in boundary forcing, we use data from the Surface Heat Budget of the Arctic Ocean (SHEBA) to evaluate various data sets that have been used to provide boundary forcing for sea ice models that are associated with the surface heat and freshwater fluxes. The impact of errors in these data sets on a sea ice model is assessed by using a single‐column ice thickness distribution model, which is alternately forced with in situ measurements from SHEBA and output from large‐scale analyses. Substantial discrepancies are found among the data sets. The response of the sea ice model to the different forcing data sets was considerable.

The Retrieval of Stratus Cloud Droplet Effective Radius with Cloud Radars

In situ samples of cloud droplets by aircraft in Oklahoma in 1997, the Surface Heat Budget of the Arctic Ocean (SHEBA)/First ISCCP Regional Experiment (FIRE)-Arctic Cloud Experiment (ACE) in 1998, and various other locations around the world were used to evaluate a ground-based remote sensing technique for retrieving profiles of cloud droplet effective radius. The technique is based on vertically pointing measurements from high-sensitivity millimeter-wavelength radar and produces height-resolved estimates of cloud particle effective radius. Although most meteorological radars lack the sensitivity to detect small cloud droplets, millimeter-wavelength cloud radars provide opportunities for remotely monitoring the properties of nonprecipitating clouds. These high-sensitivity radars reveal detailed reflectivity structure of most clouds that are within several kilometers range. In order to turn reflectivity into usable microphysical quantities, relationships between the measured quantities and the desired quantities must be developed. This can be done through theoretical analysis, modeling, or empirical measurements. Then the uncertainty of each procedure must be determined in order to know which ones to use. In this study, two related techniques are examined for the retrieval of the effective radius. One method uses both radar reflectivity and integrated liquid water through the clouds obtained from a microwave radiometer; the second uses the radar reflectivity and an assumption that continental stratus clouds have a concentration of 200 drops per cubic centimeter and marine stratus 100 cm−3. Using in situ measurements of marine and continental stratus, the error analysis herein shows that the error in these techniques would be about 15%. In comparing the techniques with in situ aircraft measurements of effective radius, it is found that the radar radiometer retrieval was not quite as good as the technique using radar reflectivity alone. The radar reflectivity alone gave a 13% standard deviation with the in situ comparison, while the radar–radiometer retrieval gave a 19% standard deviation.

Estimates of ocean heat flux at SHEBA

Observations of sea ice mass balance and temperature made during the year‐long Surface HEat Budget of the Arctic Ocean (SHEBA) field experiment were used to calculate monthly estimates of the ocean heat flux for a variety of ice types. The ocean heat flux displayed a strong seasonal cycle, with values of a few W m−2 from October through June followed by a steady increase in June and July. By the end of July the the ocean heat flux for undeformed ice reached a peak value of about 33 W m−2 during a period of substantial ice motion. The annual average ocean heat flux for multiyear ice ranged from 7.5 W m−2 for undeformed ice to 10.4 W m−2 for a melt pond to 12.4 W m−2 for an old ridge. Annual averages measured at SHEBA were more than twice as large as values observed in 1975 during AIDJEX.

Surface Albedo over the Arctic Ocean Derived from AVHRR and Its Validation with SHEBA Data

A method is presented for retrieving the broadband albedo over the Arctic Ocean using advanced very high resolution radiometer (AVHRR) data obtained from NOAA polar-orbiting satellites. Visible and near-infrared albedos over snow and ice surfaces are retrieved from AVHRR channels 1 and 2, respectively, and the broadband shortwave albedo is derived through narrow-to-broadband conversion (NTBC). It is found that field measurements taken under different conditions yield different NTBC coefficients. Model simulations over snow and ice surfaces based on rigorous radiative transfer theory support this finding. The lack of a universal set of NTBC coefficients implies a 5%‐10% error in the retrieved broadband albedo. An empirical formula is derived for converting albedo values from AVHRR channels 1 and 2 into a broadband albedo under different snow and ice surface conditions. Uncertain calibration of AVHRR channels 1 and 2 is the largest source of uncertainty, and an error of 5% in satellite-measured radiance leads to an error of 5%‐10% in the retrieved albedo. NOAA-14 AVHRR data obtained over the Surface Heat Budget of the Arctic Ocean (SHEBA) ice camp are used to derive the seasonal variation of the surface albedo over the Arctic Ocean between April and August of 1998. Comparison with surface measurements of albedo by Perovich and others near the SHEBA ice camp shows very good agreement. On average, the retrieval error of albedo from AVHRR is 5%‐10%.

Surface heat budget over the Weddell Sea: Buoy results and model comparisons

The surface heat budget over the Weddell Sea ice cover in 1996 was studied on the basis of data from Argos buoys equipped with meteorological sensors. In addition, a thermodynamic sea ice model, satellite‐based data on the sea ice concentration, sonar results on ice thickness distribution, and output from large‐scale meteorological models were all utilized. Applying the buoy data, the sensible heat flux over sea ice was calculated by Monin‐Obukhov theory using the gradient method, and the latent heat flux was obtained by the bulk method. A second estimate for the surface fluxes was obtained from the thermodynamic sea ice model, which was forced by the buoy observations. The results showed a reasonable agreement. The dominating component in the heat budget over ice was the net longwave radiation, which had a mean annual cooling effect of −28 W m−2. This was balanced by the net shortwave radiation (annual mean 13 W m−2), the sensible (13 W m−2) and latent (−3 W m−2) heat fluxes, and the conductive heat flux through the ice (5 W m−2). The regional surface fluxes over the fractured ice cover were estimated using the buoy data and Special Sensor Microwave Imager (SSMI)‐derived ice concentrations. In winter the regional surface sensible heat flux was sensitive to the ice concentration and thickness distribution. The estimate for the area‐averaged formation rate of new ice in leads in winter varies from 0.05 to 0.21 m per month depending on the SSMI processing algorithm applied. Countergradient fluxes occurred 8–10% of the time. The buoy observations were compared with the operational analyses of the European Centre for Medium‐Range Weather Forecasts (ECMWF) and the reanalyses of the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR). The 2 m air temperature and surface temperature were 3.5° and 4.4°C too high, respectively, in the ECMWF and 3.2° and 3.0°C too low in the NCEP/NCAR fields, but the models reproduced the synoptic‐scale temperature variations well. The errors seem to be related to the cloud cover and the surface boundary conditions. Neither of the models recognizes leads in the ice pack, and the ice and snow thicknesses are often far from reality. The distribution of the cloud cover in the both models differed a lot from observations.

Surface Heat Budget of the Arctic Ocean

A summary is presented of the Surface Heat Budget of the Arctic Ocean (SHEBA) project, with a focus on the field experiment that was conducted from October 1997 to October 1998. The primary objective of the field work was to collect ocean, ice, and atmospheric datasets over a full annual cycle that could be used to understand the processes controlling surface heat exchanges—in particular, the ice–albedo feedback and cloud–radiation feedback. This information is being used to improve formulations of arctic ice–ocean–atmosphere processes in climate models and thereby improve simulations of present and future arctic climate. The experiment was deployed from an ice breaker that was frozen into the ice pack and allowed to drift for the duration of the experiment. This research platform allowed the use of an extensive suite of instruments that directly measured ocean, atmosphere, and ice properties from both the ship and the ice pack in the immediate vicinity of the ship. This summary describes the project goals, experimental design, instrumentation, and the resulting datasets. Examples of various data products available from the SHEBA project are presented.

Water properties on the west Antarctic Peninsula continental shelf: a model study of effects of surface fluxes and sea ice

Abstract A vertical- and time-dependent numerical mixed-layer and sea-ice model is used to analyze processes responsible for sea-ice and surface mixed-layer water properties on the continental shelf on the west side of the Antarctic Peninsula. Atmospheric observations from Faraday and Palmer stations along with satellite sea-ice observations and shipboard water observations (four hydrographic cruises between January 1993 to February 1994) are used for forcing and verification. The focus of this study is the year 1993 during which the best observations exist. However, a 16-year simulation is completed to analyze interannual variations of ice thickness and mixed-layer depth. This model study shows that surface waters of the west Antarctic Peninsula are heated in the summer by solar radiation and cooled in the winter by sensible heat losses. Diffusive-convection is important for upward heat flux across the pycnocline. Ice melt in the spring is due to solar warming of open water, which then melts ice; the direct melting for ice by solar heating is negligible. The near closure of surface heat and salt budgets over 1 year supports the minor importance, or at least the compensation, of near-surface lateral exchanges. Intrusion of Upper Circumpolar Deep water from the Antarctic Circumpolar Current onto the subpycnocline shelf is a critical element of both salt and heat budgets. A 16-year simulation (1978–1993) reproduces most high and low ice years as observed by satellite microwave measurements, thus supporting the major contribution of thermodynamic (local) processes in creating sea-ice and mixed-layer properties.

ＧＭＳ‐５ Ｓ‐ＶＩＳＳＲデータの高速高精度な幾何学的歪補正

Since the GMS-5 observes the earth very widely and frequently, its S-VISSR data are very useful not only for meteorology but also for sea surface and land surface temperature analysis, heat and water budget analysis and the various kinds of database generated from the S-VISSR data will contribute the understanding of earth environmental change. In order to process GMS-5 S-VISSR data immediately after reception and provide academic researchers the geometrically corrected data useful for the time series analysis, a high-speed and precise geometric correction method is described. For precise geometric correction, residual errors are acquired by matching the S-VISSR image pieces to their corresponding ground control point templates on image coordinate, and the affine coefficient is calculated using the errors. For fast computation, the output image of the map coordinate is divided into small blocks. Each latitude-longitude of four corners on a small window is converted to line-pixel in image coordinate by systematic geometric transformation and affine transformation is carried out toward the line-pixel for precise geometric correction. In the case of internal points excluding four corners in the small window, each correspondence of line-pixel and latitude-longitude is calculated by hi-linear interpolation using correspondences of the four corners for speeding up the geometric correction. As the result, the accuracy measured at low altitude points is about 0.5 pixels in average and within 2 pixels, and the processing time is about 6 minutes. The product is open for public use via the Internet.