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Itaru Okada and Takashi Yamanouchi

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 radiation budget at the top of the atmosphere estimated from the Earth Radiation Budget Experiment (ERBE) data.

The derived values of the surface flux are not seasonally symmetric. This differs from other latitude bands (e.g., 50°–60°S) where the variation is symmetric and is driven by shortwave radiation change. The monthly mean surface energy flux shows an immediate increase to the maximum of 116 W m−2 in May (heating of the atmosphere), and then gradually decreases to the minimum of −108 W m−2 in December (cooling of the atmosphere). It is suggested that the asymmetry at 60°–70°S is due to the effect of seasonal sea ice extent changes on the surface energy exchanges. A comparison of the derived values of the surface flux with the latent heat required for the change in sea ice extent provides some support for this suggestion. The rate of sea ice expansion shows a peak in May when the surface energy flux becomes maximum. The turbulent heat component of the surface energy flux is compared with other estimates of turbulent heat exchange over the Southern Ocean. Suppression of the turbulent heat exchange in late winter derived in the present study, in comparison with those values over open water area, suggests the effect of extended sea ice cover.

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Takashi Yamanouchi and Thomas P. Charlock

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 cooling in the interior and along the coast; sorting of pixel-scale ERBE data and surface cloud observations was needed to demonstrate this. The monthly averaged fluxes at the surface and TOA were compared, and the net radiative fluxes for the atmospheric column were estimated. The atmospheric column loses net radiant energy throughout the year with an asymmetrical seasonal variation. The loss of net radiant energy by the atmosphere is much larger than the loss by the surface.

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Yoshihiro Tomikawa, Masahiro Nomoto, Hiroaki Miura, Masaki Tsutsumi, Koji Nishimura, Takuji Nakamura, Hisao Yamagishi, Takashi Yamanouchi, Toru Sato, and Kaoru Sato

Abstract

Characteristically strong vertical wind disturbances (VWDs) with magnitudes larger than 1 m s−1 were observed in the Antarctic troposphere using a new mesosphere–stratosphere–troposphere (MST) radar called the Program of the Antarctic Syowa MST/incoherent scatter (IS) Radar (PANSY) during 15–19 June 2012 at Syowa Station (69.0°S, 39.6°E). In the same period, two synoptic-scale cyclones approached Syowa Station and caused a strong wind event (SWE) at the surface. The VWDs observed during the SWE at Syowa Station had a nearly standing (i.e., no phase tilt with height) phase structure up to the tropopause and a power spectrum proportional to the − power of frequency. On the other hand, the observed VWDs were not associated with systematic horizontal momentum fluxes. Meteorological fields around Syowa Station during the SWE were successfully simulated using the Nonhydrostatic Icosahedral Atmospheric Model (NICAM). A strong VWD was also simulated at the model grid of 70.0°S, 40.0°E in NICAM, which had a standing phase structure similar to the observed ones. An analysis based on the Froude number showed that the simulated VWD was likely due to a hydraulic jump leeward of the coastal mountain ridge. The Scorer parameter analysis indicated that the observed VWDs at Syowa Station during 16–17 June 2012 were likely due to the hydraulic jump similar to that in NICAM. On the other hand, a possibility of lee waves was also suggested for the VWD observed on 18 June 2012.

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Shinji Morimoto, Takashi Yamanouchi, Hideyuki Honda, Issei Iijima, Tetsuya Yoshida, Shuji Aoki, Takakiyo Nakazawa, Shigeyuki Ishidoya, and Satoshi Sugawara

Abstract

To collect stratospheric air samples for greenhouse gas measurements, a compact cryogenic air sampler has been developed using a cooling device called the Joule–Thomson (J–T) minicooler. The J–T minicooler can produce liquefied neon within 5 s from high pressure neon gas precooled by liquid nitrogen. The sampler employs liquid neon as a refrigerant to solidify or liquefy sampled atmospheric constituents. Laboratory experiments showed that the sampler is capable of collecting about 3 and more than 7 L STP of air at 25 and 120 hPa, respectively, which corresponds to about 25 and 15 km above ground within 240 s, respectively. The new balloon-borne sampling system, which was set up for Antarctic experiments, consists of the compact sampler, a 2-L high pressure neon gas cylinder, pneumatic and solenoid valves, a controller with a GPS receiver, a telemetry transmitter, and batteries. The size of the sampling system is 300 mm width × 300 mm depth × 950 mm height and it weighs about 22 kg (including liquid nitrogen). Two of these compact sampling systems (configured for sampling at altitudes 18 and 25 km) were launched from Syowa Station (69.0°S, 39.5°E), Antarctica, in January 2008 using 1000 or 2000 m3 plastic balloons. They were launched successfully and recovered without any problem on sea ice on the same day as their launch. The collected stratospheric air samples showed reasonable concentrations of the stratospheric greenhouse gases over the Antarctic region.

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