北极涛动对青藏高原冬季变暖的影响

基于青藏高原地区1960-2010年高分辨率(0.5°×0.5°)的逐日地面气温格点资料以及 1960-2010年NCEP/NCAR全球月平均海平面气压场、高度场、风场的再分析格点资料(2.5°×2.5°), 通过计算青藏高原(74.75°~104.25° E, 26.75°~40.25° N)冬季地面温度平均值经标准化处理后得到的区域冬季气温强度指数, 分析了冬季北极涛动(AO)、西伯利亚高压与同期青藏高原地面气温的特征和关系. 结果表明: AO为负(正)相位时, 中高纬西风气流偏弱(强), 有(不)利于极地冷空气向南输送, 西伯利亚地区源地冬季风偏强(弱), 青藏高原冬季气温指数减小(增大), 地面气温偏低(高). 对AO作M-K突变分析, 发现其突变年份为1975年, 通过对突变年份前后高度场和风场作差值场分析, 结果显示: 冬季AO处于高指数时期, 500 hPa上, 欧洲东部槽变浅, 青藏高原北部的高压脊减弱, 环流呈纬向发展, 青藏高原上盛行偏南风, 气温偏高, 青藏高原地区为暖冬期; 200 hPa 上, 青藏高原东部的槽明显加深, 使得青藏高原地区对流层顶至平流层底的环流趋势以经向发展为主, 该区域主要受到偏北的急流控制, 易导致降温.

The Arctic Oscillation effect on winter warming over the Tibetan Plateau

Tibetan Plateau (TP), the study region of this paper, is defined as 74.75°~104.25° E, 26.75°~40.25° N. Based on the daily gridded surface air temperature data (0.5°×0.5°) and the data of the global monthly mean sea level pressure field, height field and wind field (2.5°×2.5°) from NCEP/NCAR reanalysis data from 1960 to 2010, the mean surface temperature in winter in the TP is calculated. The index of winter temperature in the TP is recognized as the standardized time series for the whole TP. The relationship between Arctic Oscillation (AO) in winter and the surface air temperature in the TP over the same period has been investigated. The results show that when the phase of AO is negative (positive), the westerly flow in the mid-high latitudes is weak (strong), which is conducive (not conducive) to drive the polar cold air southwards. It is shown that when the AO index is in low value period, the mean surface air temperature in winter in the TP is low also. M-K analysis on the AO mutation shows that the abrupt year was 1975. Significance tests at 500 hPa and 200 hPa height fields and wind field before and after the mutation year find that when the height field associates with high AO index in winter, at 500 hPa, the trough in the Eastern Europe shallows and the ridge in the northern TP weakens with zonal developing circulation, the north wind of middle troposphere is weak with higher air temperature, consistent with warm winter in the TP; at 200 hPa, the eastern trough over the east TP significantly deepens, resulting in meridional developing circulation between the tropopause and the end of the stratosphere.