青海高原冬季持续低温集中程度的气候特征及其成因

采用青海高原37个台站1961-2010年逐日气温数据, 着重讨论了持续3 d及以上低温过程集中程度的变化特征及其发生机制.结果表明: 低温集中度(LTCD)和集中期(LTCP)具有表征低温在时空场上非均匀性的较好分辨力; 近50 a青海高原冬季低温事件及其集中度均呈逐年明显减少趋势, 集中期明显提前; 利用REOF结合CAST方法分区并探讨了影响青海不同区域低温集中度的主要环流系统及因子, 发现影响柴达木盆地的主要系统为极涡和北大西洋涛动, 而青南牧区主要是由于局地气候反馈机制影响; 唐古拉地区的主要影响系统位于极区、 乌拉尔山地区及东部鄂霍次克海附近; 与东部农业区的相关体现为自西向东呈"+ - +"波列型分布, 反映冷空气不断东移过程中受东部高压阻塞, 在东部农业区堆积, 形成冷空气过程从而造成该地区集中度偏高.

Winter Persistence Low Temperature Concentration Degree over the Qinghai Plateau: Climatic Features and Causes

Based on 1961-2010 observed winter daily temperature data in the Qinghai Plateau, the climatic features and the mechanisms of low temperature concentration degree (LTCD), sustaining more than three days, are discussed. It is found that the LTCD and the low temperature concentration period (LTCP) are able to describe the spatial and temporal heterogeneity of the low temperature very well. The low temperature events and LTCD have been decreasing obviously in the last 50 years and the LTCP has appeared mainly ahead of schedule. The chief circulation system and factors affecting the LTCD in different areas of Qinghai Plateau are studied based on REOF and CAST. The mainly affecting system on Qaidam basin is polar vortex and North Atlantic Oscillation, but that on southern pastoral areas is the local climate feedback mechanism. The mainly affecting system on Tanggula area is located on Polar Regions, Ural Mountains and Eastern Okhotsk Sea. The system relating to eastern agricultural areas exhibits "+-+" wave shape, which can be explained by that the eastwards moving cold air is blocked by eastern high pressure, and then piled over the eastern agricultural areas, forming cold air course and leading to a higher LTCD.