青藏高原东部春季感热通量与我国东部气温的年际关系

Annual relationship between spring surface sensible heat flux over the East Qinghai-Tibet Plateau and air temperature in East China

利用ERA-Interim提供的地表感热、环流场资料和1979-2013年753站中国春季气温观测资料探讨了青藏高原(以下简称高原)东部春季感热通量与我国东部气温的关系。春季高原东部感热与我国东部气温在年际变化上存在密切的相关关系。去除9年滑动平均以后的SVD第一模态结果表明,当高原东部感热出现南弱(强)北强(弱)时,对应我国东北和华南地区的气温异常偏低(高)。当春季高原感热呈现南负北正的分布时,高层200hPa上,高纬东风异常减弱背景西风有利于冷空气的南下,加之副热带西风急流显著增强,有利于东北地区形成气旋性环流。中低层环流场上,我国北方地区上空为一深厚的东北冷涡所控制,从对流层低层到高层,均呈现较强的气旋式环流分布。一方面,它引导西伯利亚冷空气南下,造成我国东北地区气压异常减弱,气温异常偏低;另一方面,其西侧北风异常阻滞了华南地区上空的背景西南风,不利于暖气流的输送。进一步分析得出,与PC1相关的南北温度差值场上,东亚地区上空从低纬到高纬呈现"负-正-负"的分布形势,有利于副热带西风急流在我国上空的显著增强。气旋中心上暖下冷的结构,导致位涡显著发展并向低层伸展、侵入,增强了对流层中低层的气旋性环流。气旋中心整个对流层为深厚的异常干空气,湿度负值中心与冷中心相对应,表明干冷空气异常下传发展。干侵入使得冷涡加强发展,维持了异常气旋性环流,导致春季东北、华南地区的异常降温。虽然前冬Nino3.4区海温与春季感热相关较好,但其对我国东部春季气温影响并不显著。

Using surface sensible heat flux(SSHF)data and circulation data from ERA-Interim,and daily temperature data at springtime in 1979-2013 from 753 stations in China,the relationship between surface sensible heat flux over East Qinghai-Tibet Plateau and air temperature in East China at springtime is studied. The results show that the annual variation of spring air temperature in East China is closely related to the surface sensible heat flux over the Qinghai-Tibet Plateau. If there exits less(more)SSHF in the south of the East Qinghai-Tibet Plateau and more(less)SSHF in the north of the East Qinghai-Tibet Plateau,spring air temperature in Northeast and South China is much lower(higher). When SSHF anomalies are negative in the southeast East Qinghai-Tibet Plateau and positive in northeast East Qinghai-Tibet Plateau background westerlies are weakened by the easterly anomalies in high latitudes,which leads to cold air coming down from the north at 200 hPa,and the enhanced subtropical westerly jet favors for the formation of anomalous cyclonic circulation in Northeast China. At the middle and low troposphere,it is controlled by a deep northeast cold vortex in North China,indicating that it presents strong cyclonic circulation from the lower to higher layers. On the one hand,the cyclonic circulation leads strong cold air to south weakening the pressure with lower air temperature in Northeast China;on the other hand,background southeast winds are weakened by the anomalous north winds on the west side resulting in less transport of warm and humid air to South China. It is further found that the distribution of air temperature difference between south and north is‘negative-positive-negative’over the whole East Asia,making for the enhance of subtropical westerly jet. The warm air at upper layers and cold air at lower layers in the center of cyclone make contribution to the spread and invasion of potential vorticity to lower layers,enhancing the cyclonic circulation in middle and lower layers. It is deep dry through the whole troposphere in the center of cyclone and the center of negative specific humidity corresponds to cold center,indicating that dry and cold air develops and transfers to lower layer. It is dry intrusion inducing develop of cold vortex maintains the anomalous cyclone,and therefore causing the anomalous lower temperature over Northeast and South China. It is the strengthened cyclonic circulation at lower layers that leads to anomalous lower spring air temperature in Northeast and South China. Although SST in Nino3.4 region is closely related to SSHF in spring,it has no significant effect on air temperature in spring over East China.