Takashi Yamanouchi

Abrupt changes in meteorological conditions observed at an inland Antarctic Station in association with wintertime blocking

Time evolution of a prominent wintertime blocking event over East Antarctica and the associated drastic changes in weather conditions observed at an inland station are documented. A strong blocking ridge was formed at the leading edge of a quasi-stationary Rossby wavetrain where a wave activity flux emanating from the subtropics was convergent. The ridge pumped up heat and moisture from lower latitudes into inland Antarctica with a strong poleward flow along its upstream flank. The station was situated under this flow just for two days, during which the normal condition with cold and clear weather was markedly disturbed. The flow climbing up the continental slope led to cloud formation above the inland station. Enhanced downward longwave radiation from the clouds and enhanced vertical mixing associated with the record-setting wind speeds resulted in a sudden, drastic increase in surface air temperature and the breakdown of the developed surface inversion layer.

Comparison of Radiation Budget at the TOA and Surface in the Antarctic from ERBE and Ground Surface Measurements

Abstract Radiative fluxes at the top of the atmosphere (TOA) and the surface were compared at two Antarctic stations, Syowa and the South Pole, using Earth Radiation Budget Experiment (ERBE) data and surface observations. Fluxes at both sites were plotted against cloud amounts derived from surface synoptic observations. Throughout the year over the snow- and ice-covered Antarctic, cloud radiation was found to heat the surface and cool the atmosphere; cloud longwave (LW) effects were greater than cloud shortwave (SW) effects. Clouds have a negligible effect on the absorption of SW by the atmosphere in the interior, and clouds slightly increase the absorption of SW by the atmosphere along the coast. At the TOA, the LW cloud effect was heating along the coast in summer and winter, heating in the interior during summer, and slight cooling in the interior during winter. This unique TOA cloud LW cooling was due to the extremely low surface temperature in the interior during winter. At the TOA, clouds induced SW...

Effects of clouds, ice sheet, and sea ice on the Earth radiation budget in the Antarctic

The effects of clouds, the continental ice sheet, and sea ice on the radiation budget in the Antarctic are examined by using Earth Radiation Budget Experiment, International Satellite Cloud Climatology Project, and special sensor microwave/imager data in 1987/1988. The continental ice sheet affects not only the albedo but also the surface temperature because of elevation and hence the outgoing longwave radiation (OLR). The high elevation of the Antarctic continent makes the radiation budget in both polar regions asymmetric. At elevations below 2 km the OLR is reduced at the rate of 5–10 W/m2/km; above 2 km the rate is about 20 W/m2/km. Sea ice, which is a critical climate feedback factor, appears to have less impact on radiation than do clouds. Between 60° and 65°S in October, sea ice increases the top of the atmosphere albedo by about 0.2 and reduces the OLR by 7–10 W/m2; this seems smaller than the formal cloud forcing, which increases the albedo by 0.3 and reduces the OLR by 30–40 W/m2. However, these numbers do not fully differentiate the independent effects of sea ice and cloudiness. A more detailed analysis shows that the independent effect of sea ice is as large as clouds, with clouds masking the radiative effect of sea ice by more than one half.

Seasonal Change of the Atmospheric Heat Budget over the Southern Ocean from ECMWF and ERBE Data

Abstract The seasonal variation of the zonally averaged atmospheric energy budget between 60° and 70°S was estimated. This region is predominantly within the seasonal sea ice zone of the Southern Ocean, including some parts of the Antarctic continent. In the Southern Ocean, seasonal sea ice extent exhibits large amplitudes and affects the surface heat exchange considerably. Seasonal variation of the energy budget and its relationship to the surface condition should be clarified as the basic variation. In spite of its importance, the data to estimate energy budgets are extremely sparse in this sea ice zone. Hence, the global objective analyses with forecasting models are mainly used as data for the present study. The surface energy flux is obtained as a remainder term in the energy budget of the total atmosphere, with the energy divergence and changes to the energy content of the atmospheric column derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) objective analyses, and with the ...

Cloud and ice detection using NOAA/AVHRR data

In the polar region, it is difficult to discriminate between clouds and the ground surface from satellite visible or infrared data, because of the high albedo and low surface temperature of snow and ice cover. In this paper, a method to classify cloud, sea ice and ground is proposed. This study is based upon analysis of the NOAA/AVHRR infrared images in Antarctica. The algorithm consists of two major approaches: extraction of image features and a classification algorithm. A minimum distance classifier was used to classify that region into one of three categories using five image features. To improve the classification accuracy, threshold boundaries for minimum distance classifier were changed. Both classified and misclassified areas were decreased with increasing the threshold levels.

Classification of MOS-1 VTIR images in the Antarctic, a case study

Abstract Several procedures are described for the automatic processing of data from the visible and thermal infrared radiometers of the MOS-I satellite during passes over the Antarctic. Under sunlight conditions it is possible to distinguish automatically between cloud free and cloudy surfaces by applying thresholds to the albedo, the brightness temperature and to the degree of homogeneity. Among the cloudy surfaces Stratus clouds above the Antarctic Continent are identified. The remaining clouds are classified according to their brightness temperatures and their albedos.

Detection of clouds from NOAA/AVHRR channel 4 in the Antarctic

Clouds were detected from NOAA/AVHRR channel 4 data received at Syowa Station in the Antarctic. First, the surface temperature of each pixel in the area was calculated. Then, these values were used as thresholds that were applied to each position. Thirty daily scenes received at daytime in November 1988 were analyzed. Almost all clouds could be detected correctly in these scenes.