中国西北5月和9月地表气温的年际变率机理及其预测

Mechanism and Seasonal Prediction of Interannual Variability of the Surface Air Temperature in May and September over Northwest China

本文基于1961~2016年中国西北地区逐日地表气温观测资料以及全球大气再分析资料,通过统计诊断和数值模拟的方法,揭示了西北地区5月和9月地表气温年际变率规律及其机理,并在此基础上分别构建了季节预测模型。结果表明:(1)西北5月和9月地表气温年际变率经验正交函数分解第一模态均为全区一致型空间分布,但具有不同的变率特征。(2)西北5月地表气温正异常与拉尼娜衰减型海表温度异常所对应的热带纬向三极型对流(降水)异常强迫有关,对流异常激发的热带外遥相关波列导致西北地区上空受反气旋(高压)异常控制,造成局地向下太阳短波辐射增多,从而使得西北地表气温增加;而西北9月地表气温正异常与拉尼娜发展型海表温度异常所对应的热带纬向偶极型对流(降水)异常强迫有关,偶极型对流强迫能够在西北地区东西两侧激发反气旋(高压)异常,导致西北地表气温正异常。(3)基于物理机制,分别利用拉尼娜衰减和发展型的相关海表温度异常预测因子,建立针对西北地区5月和9月地表气温年际变率的季节预测模型,独立预报期间(2007~2016年)预测技巧相关系数分别可达0.74和0.62,可为西北地表气温短期气候预测提供参考。

Based on the daily surface air temperature(SAT)gauge data and global reanalysis datasets from 1961 to 2016,this study revealed the interannual variability of the SAT over Northwest China(NWC)in May and September via observational diagnosis and numerical simulations,and constructed their corresponding seasonal prediction models.The results are as follows:(1)The first modes of the SAT over NWC during May and September are characterized by a similar homogenous spatial pattern but with different interannual variations.(2)The positive anomaly of the SAT over NWC in May is related to the tropical zonal tripole anomalous convection(precipitation),corresponding to the tropical sea surface temperature anomaly(SSTA)during the decaying phase of La Niña.The extratropical teleconnection wave train excited by tropical convection anomalies leads to a barotropic anticyclonic(high pressure)anomaly over NWC,which increases the downward solar shortwave radiation and causes an increased local SAT.In September,the tropical zonal dipole convection(precipitation)anomaly associated with the tropical SSTA during the developing phase of La Niña can trigger the barotropic anticyclonic(high pressure)anomaly on the east and west sides of NWC,leading to a positive SAT anomaly over NWC.(3)Based on the SSTA predictors associated with the decaying and developing phase of La Niña,the seasonal prediction model for the SAT over NWC in May and September was established.The prediction skill in terms of the correlation coefficient during the independent prediction period(2006–2016)can reach 0.74(0.62)in May(September),providing a reference for seasonal prediction of the SAT over NWC.