Irina V. Gorodetskaya

The Influence of Cloud and Surface Properties on the Arctic Ocean Shortwave Radiation Budget in Coupled Models

Abstract The impact of Arctic sea ice concentrations, surface albedo, cloud fraction, and cloud ice and liquid water paths on the surface shortwave (SW) radiation budget is analyzed in the twentieth-century simulations of three coupled models participating in the Intergovernmental Panel on Climate Change Fourth Assessment Report. The models are the Goddard Institute for Space Studies Model E-R (GISS-ER), the Met Office Third Hadley Centre Coupled Ocean–Atmosphere GCM (UKMO HadCM3), and the National Center for Atmosphere Research Community Climate System Model, version 3 (NCAR CCSM3). In agreement with observations, the models all have high Arctic mean cloud fractions in summer; however, large differences are found in the cloud ice and liquid water contents. The simulated Arctic clouds of CCSM3 have the highest liquid water content, greatly exceeding the values observed during the Surface Heat Budget of the Arctic Ocean (SHEBA) campaign. Both GISS-ER and HadCM3 lack liquid water and have excessive ice amou...

The role of atmospheric rivers in anomalous snow accumulation in East Antarctica

Recent, heavy snow accumulation events over Dronning Maud Land (DML), East Antarctica, contributed significantly to the Antarctic ice sheet surface mass balance (SMB). Here we combine in situ accumulation measurements and radar-derived snowfall rates from Princess Elisabeth station (PE), located in the DML escarpment zone, along with the European Centre for Medium-range Weather Forecasts Interim reanalysis to investigate moisture transport patterns responsible for these events. In particular, two high-accumulation events in May 2009 and February 2011 showed an atmospheric river (AR) signature with enhanced integrated water vapor (IWV), concentrated in narrow long bands stretching from subtropical latitudes to the East Antarctic coast. Adapting IWV-based AR threshold criteria for Antarctica (by accounting for the much colder and drier environment), we find that it was four and five ARs reaching the coastal DML that contributed 74–80% of the outstanding SMB during 2009 and 2011 at PE. Therefore, accounting for ARs is crucial for understanding East Antarctic SMB.

How does the spaceborne radar blind zone affect derived surface snowfall statistics in polar regions

Global statistics of snowfall are currently only available from the CloudSat satellite. But CloudSat cannot provide observations of clouds and precipitation within the so-called blind zone, which is caused by ground-clutter contamination of the CloudSat radar and covers the last 1200 m above land/ice surface. In this study, the impact of the blind zone of CloudSat on derived snowfall statistics in polar regions is investigated by analyzing three 12 month data sets recorded by ground-based Micro Rain Radar (MRR) at the Belgian Princess Elisabeth station in East Antarctica and at Ny-Alesund and Longyearbyen in Svalbard, Norway. MRR radar reflectivity profiles are investigated in respect to vertical variability in the frequency distribution, changes in the number of observed snow events, and impacts on total precipitation. Results show that the blind zone leads to reflectivity being underestimated by up to 1 dB, the number of events being altered by ±5% and the precipitation amount being underestimated by 9 to 11 percentage points. Besides investigating a blind zone of 1200 m, the impacts of a reduced blind zone of 600 m are also analyzed. This analysis will help in assessing future missions with a smaller blind zone. The reduced blind zone leads to improved representation of mean reflectivity but does not improve the bias in event numbers and precipitation amount.

The effects of sea‐ice and land‐snow concentrations on planetary albedo from the earth radiation budget experiment

Abstract The high‐latitude ice/snow‐albedo feedback is a principal element in many paleoclimate theories and global warming scenarios. The strength of this feedback is determined by the ice/snow effects on the top‐of atmosphere (TOA) albedo, which is also strongly affected by clouds. Using currently available satellite observations, we estimate the radiative effectiveness (RE) of ice and snow with regards to the TOA albedo, which we define as the change in the TOA albedo corresponding to changes of 0% to 100% in the ice or snow cover. The REs of the northern hemisphere (NH) sea ice, land snow, and southern hemisphere (SH) sea ice are found to be 0.22, 0.23 and 0.16, respectively. This means that, for an incident solar flux of about 400 W m−2 reaching the TOA in the polar latitudes in summer, local reduction in ice/snow concentrations from 100% to 0% will result in a decrease in reflected short wave radiation of approximately 80 W m−2. These changes in the TOA albedo are significant, yet smaller than the associated changes in the surface albedo. Comparison of the TOA albedo values with available surface albedo observations helps to identify the role of clouds in the RE of ice/snow. The analysis is based on the whole time‐space domain where the sea ice and land snow appear, and reveals a remarkable similarity in the ice and snow RE in the areas with high sea‐ice and land‐snow cover variability, despite the varying nature of the surface cover, seasonality, and locations. These estimates provide a useful constraint to test current climate models.

Arctic Cloud Properties and Radiative Forcing from Observations and their Role in Sea Ice Decline Predicted by the NCAR CCSM3 Model During the 21st Century

Arctic sea ice is sensitive to changes in surface radiative fluxes. Clouds influence shortwave radiation primarily through their high albedo and longwave radiation by changing atmospheric emissivity and determining the height (temperature) of the layer of the highest emission. We review Arctic cloud properties affecting radiative fluxes, estimate sea ice effect on the top-of-atmosphere albedo, and discuss cloud response and contribution to the Arctic sea ice decline during the 21 st century predicted by the National Center for Atmospheric Research Community Climate System Model, version 3 (CCSM3). Over perennial sea ice, clouds decrease incoming shortwave flux at the surface compared to clear skies from zero in winter to ∼100 W m ―2 during the summer. On average over the Arctic Ocean, sea ice retreat decreases the shortwave radiation reflected at the top of the atmosphere within the same range for all-sky conditions. In addition, Arctic clouds warm the surface increasing the annual mean downwelling longwave flux by ∼40 W m ―2 . During the 21 st century, CCSM3 predicts a drastic sea ice decline accompanied by larger cloud cover and liquid water content, which increase both cloud cooling and warming effects at the surface. The surface albedo decrease caused by sea ice retreat is partly compensated but not canceled by stronger shortwave cloud cooling. Warming of the near-surface atmosphere is an additional factor increasing the downwelling longwave flux at the surface. The ultimate effect of cloud changes in this model is facilitating the sea ice decline.

An Ice-Free Arctic? Opportunities for Computational Science

The authors discuss modelings role in understanding the ice-ocean system, as well as its importance in predicting the future state of Arctic sea ice. In doing so, this article presents results from a hierarchy of models of different complexity, their strengths and weaknesses, and how they could help forecast the future state of the ice-ocean system.

Atmospheric Rivers Emerge as a Global Science and Applications Focus

California Department of Water Resources Scripps Institution of Oceanographys Center for Western Weather and Water Extremes