南极中山站风的长期变化特征及其可能原因

利用1989—2020年南极中山站地面气象观测数据和NCEP/NCAR再分析资料,分析了风的变化特征及其趋势,并对风速减小的原因进行了探讨。结果表明(1)中山站风速存在明显的季节差异,冬季风速最大,秋季次之,夏季最小,风速日变化呈单峰单谷型,峰值出现在凌晨5时,谷值出现在15时,春季和夏季风速具有明显的日变化特征,秋季和冬季风速日变化不明显;(2)中山站近31年的风速、下降风频数和大风日数均呈减小趋势,四季中夏季减小趋势最大,风矢量分解后显示,南风分量减小速率显著大于其他风分量,西风和北风变化趋势不显著,东风分量仅在夏季减小趋势显著;(3)中山站年平均风速的减小主要是由中大风和大风日数减少造成的。从大气环流的变化来看,中山站南部极地冷高压和北部南印度洋绕极低压带强度减弱,导致高、低压之间气压梯度减小,造成中山站风速减小。     

北极中央区经向水汽输送的主要通道

Atmospheric moisture transport plays an important role in latent heat release and hydrologic interactions in the Arctic. In recent years, with the rapid decline in sea ice, this transport has changed. Here, we calculated the vertically integrated atmospheric moisture meridional transport(AMTv) from two global reanalysis datasets, from1979–2015, and found moisture pathways into the central Arctic. Four stable pathways showed an occurrence frequency greater than 70%, and these pathways exhibited a perennial seasonal pattern in the atmosphere above the Laptev Sea Pathway(LSP), Canadian Arctic Archipelago Pathway(CAAP), both sides of the Greenland plateau. Another seasonal pathway appeared above the east of the Chukchi Sea(CSP) during the melting/freezing months(March to September). Through these pathways, AMTv contributed a total moisture exchange of60%–80%—averaged over a 75°N circle—and focused on the low troposphere. Transports across the LSP, CSP and CAAP pathways likely create an enclosed moisture route. Meridional moisture fluxes are intensified in the Pacific sector of Arctic(PSA), especially during melting/freezing months. AMTv interannual variabilities are illustrated mainly in the Laptev Sea and the east Greenland pathway. Results indicate that accompanying a tendency for a stronger Beaufort Sea High in this sea level pressure field, AMTv through PSA pathways, switched from output to input, and approximately 960 km~3 of equivalent liquid water was transferred into the central Arctic during each decade. The detrended AMTv increment is highly correlated with the rapid decline of old ice areas(correlation coefficient is –0.78) for their synchronous fluctuations in the 1980 s and the last decade.