春夏季节转换前北亚平稳增温过程的热力学特征

Thermodynamic Characteristics of the Steady Warming Process over North Asia Before the Summer Onset

本文利用1958~2019年日本气象厅逐日再分析资料(JRA-55),基于热力学方程,详细研究了北亚地区春夏季节转换前(第19至28候)平稳增温过程的热力学特征。结果表明,气候温度平流和非绝热加热有相反的变化趋势,它们先后主导着北亚春夏季节转换前的温度变化。在第22候之前,绝热的气候温度平流主导着北亚地区的增暖过程。但随着欧亚大陆中高纬度上的非绝热加热逐步增强,气候温度平流逐渐变为冷平流,使得非绝热加热成为主导项。线性斜压模式结果表明,非绝热加热除直接加热局地大气外,它还会在北亚地区强迫出气旋式环流异常和上升运动,从而引导着原位于新地岛附近的低压系统向北亚地区移动,进而在水平和垂直方向上引起绝热的冷平流。该冷平流部分抵消了非绝热的加热作用,最终在北亚地区形成平稳的增温过程。

Thermodynamic characteristics of the warming process before the summer onset(from pentad 19 to pentad 28)over North Asia are studied based on the thermodynamic equation and the daily reanalysis data of the Japan Meteorological Agency(JRA55)from 1958 to 2019.Results show that the temperature advection and diabatic heating successively dominate the temperature tendency before the summer onset over North Asia.Interestingly,these two phenomenon show an opposite trend to each other.Before pentad 22,the adiabatic advection of the climatological mean temperature dominates the warming process over North Asia.However,after that,the diabatic heating enhances gradually,while the adiabatic advection process weakens gradually,making the diabatic heating dominant.Based on the linear baroclinic model,the numerical results reveal that the diabatic heating over mid-and high-latitude Eurasia can heat the local air masses aloft as well as force a cyclonic circulation and upward motion.Circulation responses are favorable for the southeastward movement of the low-pressure system,which is originally located around Novaya Zemlya toward North Asia,leading to the formation of cold advection in both horizontal and vertical directions.The cold advection partially counteracts the local diabatic heating,forming the steady warming process over North Asia.