南极特拉诺瓦湾下降风特征

南极罗斯海特拉诺瓦湾(Terra Nova Bay)是强下降风汇集区之一。采用高分辨率南极中尺度预报系统(Antarctic Mesoscale Prediction System,AMPS)资料和特拉诺瓦湾难言岛Manuela自动气象站实测数据,分析了特拉诺瓦湾及其附近地区的下降风特征。AMPS对难言岛地区风速和气温有较好的模拟能力,但风向比实测值偏西约30°。难言岛地区风速从1月开始迅速增大,4—9月风力平均为8级以上。难言岛夏季1月份的风速变化滞后气温变化约3 h;冬季7月份风向稳定为西至西南。特拉诺瓦湾及其附近地区下降风来自西岸海拔较高的冰盖,其风向的空间分布特征基本几乎不随季节而变化。下降风风速有显著的季节演变特征,11月至次年1月较小,3—9月风速较大。特拉诺瓦湾西岸等几处冰川地带在冬季是强风汇集区,难言岛处于Reeves冰川下降风汇集区中。该汇集区上边界和南北两侧均有清晰的分界线,风速较强区从地面延伸至650—800 m高处,风速最大值距离地面高度约为50—200 m。强下降风气流受难言岛地形阻挡,风速有所减弱,气流越过难言岛之后,风速再次加强。特拉诺瓦湾地区下降风流动过程中近地面气团位势温度变化幅度很小,表明下降风在从内陆高原到沿岸地区的流动是干绝热过程。

Characteristics of katabatic winds in Terra Nova Bay,Antarctica

Terra Nova Bay (TNB), Antarctica, is one of the confluence zones where strong katabatic winds are intense.In this paper, data from the high-resolution Antarctic mesoscale prediction system (AMPS) and automaticweather station (AWS) Manuela on Inexpressible Island in TNB are used to analyze the characteristicsof katabatic winds in these areas. The AMPS shows good capability in simulating wind speed and air temperatureat Inexpressible Island; however, the simulated wind direction is about 30° further westward thanmeasured. The wind speed at Inexpressible Island increases rapidly from January and it is maintained at ahigh level during April–September. Data from the Manuela AWS indicate the strongest winds lag the lowesttemperatures by about 3 h in January, and in winter, the measured wind direction is mostly west-southwest.Katabatic winds in TNB and the surrounding area are derived from the higher ice sheet to the west, and thespatial distribution of the wind direction rarely changes with season. The wind speed shows considerableseasonal variation; winds are generally a breeze during November–January, before increasing duringMarch–September. In winter, katabatic winds form confluence zones at several glaciers near the coast ofTNB, and Inexpressible Island is affected by katabatic winds from the Reeves Glacier. Boundaries are clearin the upper, northern, and southern sides of the katabatic winds areas of the Reeves Glacier. Strong katabaticwinds extend from the surface to 650–800 m above ground level (AGL), and the core of the maximumwind speed is located at about 50–200 m AGL. Strong katabatic winds can be weakened because of the terrainof Inexpressible Island. The surface potential temperature differs little from the inland plateau to thecoastal area near TNB, indicating a dry adiabatic process within the march of the katabatic winds in theseareas.