冬季大气斜压性对黑潮延伸体年代际异常响应的维持机制研究

黑潮延伸体(Kuroshio Extension,KE)海域附近具有强烈的大气斜压性可显著影响北太平洋上空风暴轴异常,因而有必要研究KE海区附近斜压性的特征和维持机制.本文设计数值试验并结合高分辨率ERA-Interim资料研究了大气斜压性对KE年代际海温变率模态(KEDV-induced SSTA,Kuroshio Extension Decadal variability SSTA)中的中尺度海洋锋(KEDV-induced Meso-scale SST Front,KMSTF)的响应特征和维持机制.研究发现,表层斜压性对KMSTF的响应分布相对KMSTF经向梯度的分布偏南,平流过程的响应起主要作用.表层感热通量的响应相对KMSTF分布偏北,表层温度的响应分布与KMSTF分布的位相差异是导致其偏北分布的主要原因.积云对流过程、垂直热量输送和月内尺度扰动向极热量输送均可削弱表层斜压性,而感热通量加热可加强表层斜压性.研究对流层斜压性的特征发现,斜压大值随高度向北移动,极值在边界层顶附近,积云动量再分配影响的月内尺度扰动通量经向辐合有一定的贡献.同时,相对KMSTF暖海温异常偏南分布的低SLP(Surface Level Pressure)可引发经圈平面内次级环流,并将月内尺度扰动热量、水汽和动量向高纬度输送,从而引起斜压性随高度向北分布并增强斜压性.此外还发现,积云对流过程引发的非绝热加热通过扰动热力作用使高层急流向北偏移.

Response of atmospheric baroclinicity to Kuroshio Extension decadal variability in Winter

There is a strong atmospheric baroclinicity near the Kuroshio Extension (KE), which can significantly affect the storm tracks anomaly. Therefore, it is necessary to investigate the characteristics and maintenance process of baroclinicity near the KE. In this paper, numerical experiments are designed and high-resolution ERA-Interim data are used to study the response characteristics and maintenance of atmospheric baroclinicity to KE meso-scale SSTA Front (KMSTF) associated with KE decadal variability (KEDV-induced SSTA). The results suggest that the response of atmospheric surface baroclinicity to KMSTF is distributed southward due to advection process compared with distribution of KMSTF. The response of surface sensible heat flux is distributed to northward compared with distribution of KMSTF. The difference in the phase between atmospheric surface temperature and KMSTF is the main reason for its distribution to the northward. Cumulus convection, vertical heat transfer and submonthly fluctuations transferring the heat flux to polar weaken the surface baroclinicity, and sensible heat flux heating strengthen the surface baroclinicity. Studying the troposphere baroclinicity, it is found that the baroclinicity is distributed northward with height, and the large value is near the top of the boundary layer. Meridional convergence of fluctuations flux formed by cumulus momentum redistribution is the main contribution. The low SLP can trigger cumulus convection process, which causes the clockwise secondary circulation in altitude-latitude sections transfering heat, water vapor and momentum to polar. That is the main reason why the baroclinicity distribute to northward with height. In addition, it is also found that the diabatic heating induced by cumulus convection causes the upper jet to shift northward through fluctuations thermal effect.