冬季东亚大槽强度年际变化及其与中国气候联系的再分析

A further look at the interannual variations of East Asian trough intensity and their impacts on winter climate of China

中文关键词:  东亚大槽指数  年际变化  降水  气温  冬季

英文关键词:Fast Asian trough index  Interannual variability  Precipitation  Temperature  Winter

中文摘要:

      利用NCEP/NCAR再分析资料以及国家气象局整编的中国160站逐月降水和气温资料,定义了一个北半球冬季500hPa东亚大槽强度指数(I_EAT),并分析了该指数所反映的冬季东亚大槽强度的年际变化规律及其与同期中国冬季降水、气温的关系.结果表明:I_EAT指数反映了对流层中层冬季亚洲大陆高压脊与西北太平洋上空的低压槽系统之间的平均经向风强度,且能够较好地反映冬季东亚大槽的强度.东亚大槽的强度在20世纪80年代之前相对较弱,并存在2-3年和准4年的年际变化周期.冬季东亚大槽强弱变化可能与源自地中海地区的罗斯贝波动能量沿亚洲急流东传有关,且这种西风带中的扰动具有准正压结构.I_EAT指数与青藏高原东部地区的冬季降水和气温相关显着.当I_EAT指数为正(负),东亚大槽偏强(弱),对应着中国华中地区以及华东大部分地区冬季总降水量偏少(多),且华中地区冬季平均气温偏高(低).进一步研究发现,在东亚大槽偏强年,华中地区冬季平均气温异常升高主要是由于异常非绝热加热和下沉运动导致的异常动力增温所致.这些研究结果有助于更好地理解由于东亚大槽强度的变化而导致的中国冬季气候变化特征及其原因.

英文摘要:

      Using the NCEP/NCAR rcanalysis data and the observational precipitation and temperature data at the 160 stations of China, the interannual variations of the intensity of East Asian trough(EAT) along with their impacts on winter climate of China have been investigated.A new East Asian trough intensity index(I_EAT)at 500 hPa in boreal winter has been defined.The results show that the new index depicts the changes of intensity of EAT very well.This index integrates both the gcopotential height values of the trough area and the tonal pressure gradient in the western flank of the trough,making the I_EAT index a good indicator of the averaged meridional wind between the ridge of gcopotential height over Asian continent and the trough system over the western North Pacific in the middle troposphere.It is found that the intensity of EAT was relatively weaker before 1980's.The I_EAT changes with periodicitics of 2-3 years nd quasi-4 years.The variation of EAT intensity in winte may relate to the eastward propagation of the Rossby wave energy along the Asian jet from the Mediterranean region to East Asia.The disturbances in the westerlics have an equivalent barotropic structure.The I_EAT has significant corrclations with both the rainfall and temperatures in regions cast of the Tibet Plateau.When the index is positive(negative ),EAT is stronger(weaker),inducing the total winter precipitation in most part of East China to be less (more) than normal.Simultaneously, the winter time mean temperature over central China is to be higher(lower) than normal.It is found that the higher surface air temperatures in central China in strong EAT winters are resulted mostly from the diabatic heating anomalies and anomalous dynamic heating due to air subsidence.Thesc results are helpful to better understand why and how the winter climate of China along with the EAT intensity change.