Turbulent characteristics of the vertical wind velocity near the critical Richardson number

From analysis of the vertical wind velocity at two heights (3 and 30m) observed at Mizuho Station in Antarctica, intermittent turbulence was found under very stable conditions. In the range of gradient Richardson number from 0.2 up to about 2,wave-like flows with two groups of periods, in about the 10 and 20s, play a predominant role. Taking the behavior of such waves into account, the standard deviation and the skewness of the vertical wind velocity component were estimated

Climatological features of Mizuno Station in katabatic wind zone, East Antarctica

Climatological features of Mizuho Station are described using seasonal variations in, and frequency distributions of meteorological elements for individual months as well as the periodicities of the individual variations and cross-correlations obtained by spectral analyses on the basis of data collected in 1980. The findings follow : Air pressure obtained at Mizuho Station decreases and takes its minimum in winter. On the other hand, it keeps the almost constant value at Syowa Station during the year; therefore, the pressure difference between Mizuho and Syowa increases in winter. Air temperature shows a remarkable daily variation in summer. In winter this short-time periodic variation disappears and the semi-long periodicity of about five days comes about. A strong wind blows constantly almost throughout the year, the annual mean being about 11m/s. A significant cross-correlation is shown between air temperature at Mizuho and air pressure at Syowa in winter

Some Features of the Turbulent Transfer on the Bare Ice Field Near the Yamato Mountains, East Antarctica

Measurements were made of profiles of wind speed and air temperature on the bare ice surface on the lee of the Yamato Mountains from 1 to 7 December 1973. The vertical profile of air temperature was found unstable in the daytime when the wind speed decreased, as the bare ice surface was heated by solar radiation. Consequently, a mean eddy heat flux transported from the surface was 50ly/day. As for an energy budget, estimated latent heat flux was about 150ly/day which indicates the evaporation of 0.25cm/day in the summer. The observation of wind turbulence by the use of sonic anemometer showed a strong turbulence generated by nunataks. This strong turbulence contributes to the surface ablation of bare ice in the summer

ナンキョク ヤマト サンミャク シュウヘン ノ ラヒョウ ジョウ ニオケル セッチ キソウ ノ カンソク

やまと山脈周辺の裸氷原上で行った,高度約3.5mまでの接地気層の夏期間(12月)1週間の短かい観測結果から,次のことがわかった.1)風速分布から裸氷面の空気力学的粗度Z_0は,風速によらず一定で,0.085cmであった.これは裸氷表面のスプーンカットの深さ約2～3cmに対応している.2)Z_0が一定のため,摩擦速度U_*と1m高度の風速U_1との間には,U_*=0.057 U_1という直線的な関係がある.3)風が弱くなると,裸氷面の加熱のために大気は不安定になる傾向を示した.4)中立状態に近い時の渦拡散係数の値は,昭和基地周辺の雪で被われた海氷上の値よりも大きな値であった.The measurements of profiles of wind speed and air temperature in the atmospheric surface layer above bare ice surface in the circumference of the Yamato Mountains were carried out under neutral and unstable conditions in December, 1973. The results are summarized as follows: 1) The value of aerodynamic roughness parameter (Z_0) was constantly 0.085 cm independent on wind speed, and this value corresponded to the depth of spoon-cut features (2-3 cm) on the bare ice surface. 2) The relation between the friction velocity (U_*) and the wind speed at 1 m height (U_1) is expressed by U_*=0.057 U_1. 3) Atmosphere showed an unstable condition (negative Richardson number) with the decrease of wind speed, as the bare ice surface was heated by radiation. 4) Eddy diffusivity obtained on the bare ice surface in neutral condition was larger than that of sea ice around Syowa Station

Observations of an atmospheric gravity wave by shear instability in katabatic wind at Mizuho Station, East Antarctica

Measurements were made of vertical wind speed components, using two sonic anemothermometers on the snow surface at Mizuho Station in 1980 by the present authors who were members of the 21st Japanese Antarctic Research Expedition (JARE-21). The two anemothermometers were mounted at the fixed heights of 3m and 30m on a 30-m-high micrometeorological tower. The existence of shear instability (Kelvin-Helmholtz) waves with period of about 20s was revealed as a result. The maximum aplitude of the K-H waves was found when the surface layer had a local gradient Richardson number smaller than 0.25; the instability regime was in agreement with DRAZIN\u27s criterion (J. Fluid. Mech., 4,214,1958). Such gravity waves were observed when a strong surface inversion was progressing above the snow surface after the katabatic wind had been disturbed by a synoptic scale disturbance