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中纬度海洋热力状况异常影响大气主要通过两种途径:非绝热加热的直接强迫作用和大气瞬变涡旋反馈的间接强迫作用,而后者的作用并没有被很好地认识.为了进一步理解间接强迫作用的物理机制,本文利用观测资料分析和区域大气模式模拟,研究了伴随冬季北太平洋副热带海洋锋强度变化的中纬度大气场异常,特别是对流层中高层不同频率的涡旋扰动活动的异常.实际观测和数值试验结果均表明,当北太平洋副热带海表面温度锋偏强时,其上空的中纬度大气经向温度梯度增强;对应此时的大气斜压性增强,且中纬度大气西风急流整层加速;然而增强的大气斜压性并不对应一致性增强的大气涡旋扰动活动.中纬度大气的涡旋扰动根据其生命周期,进一步划分为高频(2~7天)和低频(10~90天)涡旋扰动.研究结果表明偏强的北太平洋副热带海洋锋对应着增强的中纬度大气高频涡旋扰动和减弱的低频涡旋扰动;其中,中纬度大气高频扰动活动的增强,将有利于削弱中纬度大气经向温度梯度,从而减弱中纬度大气斜压性;而高频扰动对纬向风倾向项的正贡献,有利于中纬度急流中心北侧及下游区域的西风加速,形成中纬度西风相当正压结构的增强;大气低频扰动的减弱,对中纬度大气纬向风倾向项产生负贡献,不利于急流的纬向均匀化,而其热力强迫异常则有利于维持中纬度对流层中层大气的经向温度梯度.
The mid-latitude ocean thermodynamic anomaly affect the atmosphere mainly through two ways: the indirect forcing of non-adiabatic heating and the indirect forcing of atmospheric transient vortex feedback, while the latter’s role is not well understood.In order to further understand the indirect coercion In this paper, we use the observation data analysis and regional atmospheric modeling to study the anomaly of the mid-latitude atmospheric anomalies along with the variation of winter North Pacific subtropical ocean frontal strength, especially the vorticity perturbations at different frequencies in the middle and upper troposphere. The results of observations and numerical experiments show that when the temperature front of the North Pacific subtropical surface is strong, the meridional warming gradient of the meridional atmosphere over the North Pacific increases, and the atmospheric baroclinic pressure increases at this time. At mid-latitudes, However, the enhanced atmospheric baroclinicity does not correspond to the enhanced atmospheric vortex perturbation activity. The mid-latitude atmospheric vortex perturbation is further divided into high frequency (2 ~ 7 days) and low frequency (10 ~ 90 days) vortex perturbation.The results show that the stronger North Pacific subtropical ocean front corresponds to the enhanced mid-latitude atmospheric high frequency The turbulence and turbulence of the low-frequency vortex disturbances in the mid-latitudes are enhanced by the enhancement of mid-latitude atmospheric turbulence, which will help weaken the mid-latitude meridional temperature gradient and weaken the mid-latitude atmospheric baroclinicity. The positive contribution of the wind tendencies favors the acceleration of the westerlies in the north and downstream regions of the middle latitude jet stream, resulting in the enhancement of the mid-latitude westerly relatively positive pressure structure. The weakening of atmospheric low-frequency disturbances has a negative effect on the zonal wind tendencies of mid-latitude Contribution is not conducive to the latitudinal uniformization of the jet stream, but its thermal forcing anomaly is conducive to maintaining the meridional temperature gradient of the mid-latitude tropospheric atmosphere.