青藏高原冬春积雪年际振荡成因分析

通过对高原冬春积雪异常年气温、降水和环流特征的分析,结果发现:从年际变化来讲,高原冬春积雪和冬春气温是明显的负相关,与降水呈正相关,高原冬春积雪的年际变化与前冬11月、12月高原降水的变化基本一致;1983年前,高原冬春积雪的偏多主要对应于高原冬春气温的偏低,积雪的偏少则主要对应于高原冬春降水的偏少;而自1984年后,高原冬春积雪的偏多主要对应于高原冬春降水的偏多,积雪的偏少则主要对应于高原冬春气温的偏高.多雪年前冬,副热带高压明显偏强,欧洲槽加深,乌山脊加强,东亚大槽从东北向西南明显倾斜,我国南海和阿拉伯海西岸各有一反气旋距平环流,而高原南部、印度半岛到孟加拉湾为一明显的气旋距平环流,有利于洋面暖湿气流抬升爬上高原;另一方面,从西伯利亚向我国出现北风距平,同时我国北方地区出现东风距平,这一形势使得西伯利亚冷空气多流向高原,冷暖空气在高原交汇,产生降雪.同时这种冷空气流保证了高原温度偏低,因而冬春高原多雪;少雪年前冬,副热带高压明显偏弱,欧洲槽变浅,乌山脊减弱,东亚大槽比较竖直,南海地区和阿拉伯海为气旋环流距平,而高原南侧为反气旋环流距平,西伯利亚为南风距平,形势基本与多雪年相反.

The Causes of the Interannual Variation of Snow Cover over the Tibetan Plateau

Analyzing the station snow, air temperature, precipitation and reanalyzed NECP/NCAR data demonstrates: The winter-spring snow in Tibetan Plateau has obvious negative correlation to the air temperature but positive correlation to the precipitation in the pre-winter (November and December) in Plateau according to its interannual variation. In the pre-winter of the rich (poor) winter-spring snow years in the plateau, the subtropical anticyclone is strong (weak), the polar vortex over Europe and Asia is strong (weak), and the trough over Europe is deep (shallow), the ridge over Ural is strong (weak), the trough line over East Asia inclines much (little) from northeast to southwest. Therefore, the warm and wet air from ocean flows easily (hard) to the plateau and the cold air from Siberia flows easily (hard) to the plateau, and the snowfall falls much (little) and the snow exists long (short).