Characteristic feature in large-scale lower tropospheric structure over the traverse route on the East Antarctic ice sheet in the winter based upon a series of radiosonde observation in 2018

The Tenth Symposium on Polar Science/Ordinary sessions: [OM] Polar Meteorology and Glaciology, Wed. 4 Dec. / 2F Auditorium, National Institute of Polar Researc

Temperature dependence of brightness temperature difference of AVHRR infrared split window channels in the Antarctic

One method to identify clouds from NOAA/AVHRR data is to use the difference in brightness temperature of infrared split window channels in the 10μm region. Under the low temperature over the Antarctic continent in winter, it is necessary to detect a slight difference in brightness temperature. In this paper, we investigate the temperature dependence of the brightness temperature difference of channel 4 (10.8μm) brightness temperature (T4), and channel 5 (12 μm) brightness temperature (T5) (T4-T5) of a cloud free scene. T4-T5 is about 0°C at low temperature around -80°C, and gradually increases up to a high of 1°C at high temperature around 0°C. The rates of increase in T4-T5 were almost constant for T4 lower than -40°C. For T4 higher than -30°C, T4-T5 remains almost unchanged. For T4 between -40°C and -30°C, T4-T5 increases rapidly. In order to explain this temperature dependence, the contribution of water vapor and surface emissivity to the difference in brightness temperature was calculated from in situ data using the radiation code MODTRAN. The result is shown below. About the contribution of water vapor, at T4 lower than -25°C, T4-T5 was nearly zero. From about -25°C to 0°C of T4, T4-T5 increases up to near 0.6°C. On the other hand, when the surface emissivity difference between CH4 and CH5 was set to 0.01, T4-T5 increased in all temperature ranges. The rate of increase was almost constant. In the temperature range lower than -40°C, T4-T5 conformed to T4-T5 of satellite data

An examination of the humidity correction by Vaisala RS80-A radiosondes for experiments and measurements at an inland Antarctic station

The present paper examines the correction of humidity measurements by the Vaisala RS80-A radiosonde using data obtained at Dome Fuji Station, inland Antarctica. The correction method is based upon a procedure developed by L.M. Miloshevich et al.(J. Atmos. Oceanic Technol., 18, 135, 2001). In the present study, experiments in a snow cave below ground, where a state of ice saturation is assumed, show that Miloshevich\u27s coefficient is appropriate for temperatures warmer than -45 °C because the corrected humidity reflects the state of ice saturation. Below these temperatures a correction coefficient is needed. At -55 °C , for example, a factor of 1.2 is needed. An examination using surface humidity data obtained from a routine aerological observation concluded that the correction coefficient is larger than Miloshevich\u27s at temperatures colder than -50 °C , so that the multiplication factor(0.185968×exp((-0.0339)×T); T=temperature) is needed to apply Miloshevich\u27s coefficient. After the correction is performed, the relative humidity with respect to ice becomes 150 on average in the lower temperature range. Perpetual falling of ice crystals indicates at least an occurrence of ice saturation; this condition of high relative humidity is supported by downwelling of a large amount of water vapor in an intense temperature inversion layer and an extremely small number of ice nuclei, suggested by in-situ data. An improved correction applied to a vertical profile in the temperature inversion layer reveals that supersaturation with respect to ice appears at all levels. In the lowest layer, humidity increases with decreasing height, although observed data show steep dryness with decreasing height. This is considered a measurement error

Note on air temperature measurement by automatic weather stations in Antarctica

The Tenth Symposium on Polar Science/Ordinary sessions: [OM] Polar Meteorology and Glaciology, Wed. 4 Dec. / Entrance Hall (1st floor) , National Institute of Polar Researc

Seasonal variation of air transport in the Antarctic and Atmospheric Circulation in 1997

To better understand how present and past climates at Syowa Station, Antarctica relate to climate elsewhere, we analyzed the tropospheric air transport to Syowa Station for the year 1997 using a dataset from the European Centre for Medium Range Weather Forecasts(ECMWF). The five-day trajectories of the air parcels were estimated and analyzed. In the middle troposphere in winter, air parcels were usually from the lower troposphere over the Atlantic. However, in January, most of the air parcels came from latitudes higher than 60°S . The trajectories had little vertical motion and were associated with a low pressure system that forms along the coastal region of Antarctica only in summer. In the lower troposphere, trajectories could be classified as originating in one of three regions: the Southern Ocean, the continental interior, and the east coast. In contrast to the middle troposphere, air parcels from the Southern Ocean had the lowest frequency, irrespective of the time of year. This is partially due to a low pressure system that blocks air parcels from outside the continent. Most trajectories are affected by the drainage flow. An amplified quasi-stationary planetary wave for September to November and a blocking circulation in June make trajectories pass over Antarctica

Establishment of Unmanned aerial vehicle systems for Earth system sciences in the polar region

The Tenth Symposium on Polar Science/Special session: [S] Future plan of Antarctic research: Towards phase X of the Japanese Antarctic Research Project (2022-2028) and beyond, Tue. 3 Dec. / Entrance Hall (1st floor) at National Institute of Polar Research (NIPR

Meteorological characteristics of Antarctic inland station, Dome Fuji (scientific paper)

Surface meteorological observations were carried out during 1995 and 1997, and extended atmospheric science observations were carried out in 1997 as a sub program of "Atmospheric Circulation and Material Cycle in the Antarctic (1997-2001)" at Dome Fuji Station (77°19\u27S, 39°42\u27E) where deep ice core drilling was done. The annual mean surface air temperature was -54.4°C with the lowest record of -79.7°C. The mean wind speed was 5.8 m/s with no clear prevailing wind direction. From aerological soundings, temperature profiles are described; they are characterized by a strong surface inversion such as 25°C, on a normal winter day. Abrupt warming occurred several times a year; the largest showed 40 degree temperature increase within two days between 17 and 19 July 1997. The event was associated with the intrusion of an anticyclone, "a blocking high", and many drastic phenomena such as large accumulation of snow followed this event

ナンキョク ナイリクイキ ノ トウキ ノ ショウオン ゲンショウ ト タイリュウケン ノ ソウカン キボ ジュンカン

冬季の南極大陸の対流圏には成層圏から続く低温な極渦が形成される.総観規模の移動性擾乱の活動は強い傾圧性をもつ南極海上の極渦縁辺部で最も盛んで,南極内陸域に強い影響を及ぼすことは少ない.1997年にドームふじ基地(77゜S,40゜E)で行われた気象の強化観測では,極渦の低温に加え,その標高の高さと強い気温逆転層の影響も反映して,-70゜C以下の地上気温が観測されることが珍しくなかった.その中で冬季には,地上気温の変動が夏季に比べて大きくなった.6月には2日間で40゜Cにも及ぶ昇温現象があった(Hirasawa et al., 2000).この最も顕著だった昇温現象は,地上気圧上昇,地上風速増加,雲量増加を伴っていて,それらはブロッキングリッジに関連した総観規模大気循環に伴って暖湿大気がドームふじ基地上空へ移流したことにより引き起こされていた.このブロッキングリッジの形成にはロスビー波のエネルギー伝播が関係した.次に,1997年の冬季間(4-10月)について,ドームふじ基地の地上気温の時間変化から昇温現象を客観的に定義し,そこで抽出された17事例の特徴を調べた.多くの事例は地上気圧上昇,雲量増加を伴い,リッジ等の高気圧性大気循環の影響を受けていた.また,ブロッキングリッジに伴う6月の昇温現象が他の16事例に比べて,昇温の規模において突出していたことが示された.The atmosphere over the Antarctic interior is usually separated from the outside by circumpolar tight potential vorticity gradients, where surface transient eddies are embedded, at the Dome Fuji Station (77゜S, 40゜E) on the topographical ridge of the East Antarctic ice sheet, an intensive meteorological observation campaign was carried out in 1997, The daily surface air temperature at Dome Fuji Station in the winter was generally around -70゜C, influenced by a ground-based temperature inversion as well as lower temperature in the polar vortex, On the other hand, the air temperature varied with larger amplitude in winter than in summer, The most prominent fluctuation, which was warming to about -30゜C from -70゜C (approximately a 40゜C-warming for only 2 days), occurred in the second half of June (Hirasawa et al., 2000), The warming was accompanied with increments in surface pressure, surface wind speed, and cloud amount, They were induced by warm, moist air advection from outside of the continent, associated with a blocking ridge which was the leading edge of a quasi-stationary Rossby wave, The present research found 18 warming-events in the 1997 winter from April to October, including the one in June above, Most the warming-events were accompanied by increased surface pressure, surface wind speed, and cloud amount, and were associated with synoptic-scale anticyclonic circulations, respectively