Arctic Tropospheric Winds Derived from TOVS Satellite Retrievals

Abstract

Accurate three-dimensional wind fields are essential for diagnosing a variety of important climate processes in the Arctic, such as the advection and deposition of heat and moisture, changes in circulation features, and transport of trace constituents. In light of recent studies revealing significant biases in upperlevel winds over the Arctic Ocean from reanalyses, new daily wind fields are generated from 22.5 yr of satellite-retrieved thermal-wind profiles, corrected with a recently developed mass-conservation scheme. Compared to wind measurements from rawinsondes during the Surface Heat Budget of the Arctic (SHEBA) experiment, biases in satellite-retrieved winds are near zero in the meridional direction, versus biases of over 50% for reanalyses. Errors in the zonal component are smaller than those observed in reanalysis winds in the upper troposphere, while in the lower troposphere the effects of Greenland introduce uncertainty in the mass-conservation calculation. Further reduction in error may be achieved by incorporating winds retrieved from feature-tracking techniques using satellite imagers. Overall, satelliteretrieved winds are superior to reanalysis products over the data-sparse Arctic Ocean and provide increased accuracy for analyses requiring wind information.Trends and anomalies for the 22.5-yr record are calculated for both meridional and zonal winds at eight levels between the surface and 300 hPa. Annual mean trends are similar at varying levels, reflecting the relatively barotropic nature of the Arctic troposphere. Zonal winds are more westerly over Eurasia and the western Arctic Ocean, while westerlies have weakened over northern Canada. Combined with the corresponding pattern in meridional winds, these results suggest that the polar vortex has, on average, shifted toward northern Canada. Seasonal trends show that some changes persist throughout the year while others vary in magnitude and sign. Most striking are spring patterns, which differ markedly from the other seasons. Changes in meridional winds are consistent with observed trends in melt-onset date and sea ice concentration in the marginal seas. Anomalies in zonal wind profiles exhibit decadal-scale cyclicity in the eastern Arctic Ocean, while overall shifts in anomaly signs are evident and vary by region. The winter North Atlantic Oscillation (NAO) index correlates moderately with meridional wind anomalies in the Atlantic sector of the Arctic Ocean: positively (0.48) in the Barents Sea and negatively (Ϫ0.59) in the Lincoln Sea. These observed trends and anomalies are expected to translate to changes in advected heat and moisture into the Arctic basin, which are likely linked to trends in sea ice extent, melt onset, cloud properties, and surface temperature.

The Changing Climate of the Arctic

“…People in Paulatuk have also noticed a shift in the direction of the prevailing winds from the southwest to the west, affecting sea ice, water levels (through storm surges), and temperatures around the community (Communities et al, 2005), with an increase in frequency of storm surges around Tuktoyaktuk. These observations are consistent with changes in surface meridional winds shown in observational satellite data (Francis et al, 2005) and increases in storminess, or cyclonic activity, in the Beaufort Sea region (Macdonald et al, 2005). Shingle Point, a traditional beluga (Delphinapterus leucas) harvesting site for the community of Aklavik, had to be evacuated by helicopter on one occasion because of dangerous flooding conditions.…”

“…Scientific evidence for high-latitude climate change attests to changes in ocean currents, rising sea levels, increasing surface air temperature, decreasing sea-ice extent and thickness, and hemispheric-scale changes in atmospheric variability (Curry and Mauritzen, 2005;Francis et al, 2005;Meehl et al, 2005;Stroeve et al, 2005;Schiermeier, 2006). Investigation of changes in oceanographic, sea-ice, and atmospheric phenomena illustrates a collective response to global warming and increased levels of greenhouse gases.…”

Estimating the Sea Ice Compressive Strength from Satellite-Derived Sea Ice Drift and NCEP Reanalysis Data*

“…Errors in wind direction are also present. Francis and Hunter (2005) report 0.5 and 0 m s Ϫ1 errors in the zonal and meridional components of the surface winds. Given that all events analyzed in this study have a dominant meridional component (perpendicular to a coastline) and assuming a mean wind speed of 5 m s Ϫ1 in the Beaufort Sea [estimated using data from the Surface Heat Budget of the Arctic (SHEBA) experiment], this gives an error of about 5°in the wind direction, which amounts to an error of less than 1% in surface stresses.…”

A Comparison of Atmospheric Reanalysis Products for the Arctic Ocean and Implications for Uncertainties in Air–Sea Fluxes

“…Near-surface atmospheric state fields from five reanalysis products (NCEP-NCAR, ERA-Interim, JRA-25, CFSR, and MERRA) and one reanalysis-derived product (CORE2) are considered for evaluation against corresponding in situ and satellite-derived reference fields from the Global Precipitation Climatology Project (GPCP) (Adler et al 2003;Huffman et al 2009), the International Arctic Buoy Program/Polar Exchange at the Sea Surface (IABP/POLES) (Rigor et al 2000), the International Satellite Cloud Climatology Project (ISCCP) and its surface radiation budget (SRB) (Zhang et al 2004), the French Research Institute for Exploitation of the Sea (IFREMER) air-sea turbulent flux product (Bentamy et al 2008), and the Television Infrared Observation Satellite (TIROS)-N Operational Vertical Sounder (TOVS) Polar Pathfinder atmospheric winds for the Arctic (Francis et al 2005). A list of the products, with further details on resolution, available fields, and temporal coverage, is provided in Table 1.…”