南亚高压区Rossby波能量向上穿越对流层顶传播的特征与机制

夏季平流层盛行强东风,Rossby波能量难以从对流层向上传播至平流层,而冬季平流层盛行西风,Rossby波能量容易上传,因此以往对Rossby波能量向平流层传播的研究多考虑冬季的情况.而事实上,因为夏季高原上空南亚高压反气旋环流,并非只有强东风存在,所以Rossby波能量也可能在南亚高压区向上传播,从而影响平流层的温度、风场及大气成分等.因此,本文利用ERA-interim逐日再分析资料,分析了1979—2015年夏季南亚高压区Rossby波能量穿越对流层顶传播的特征与机制.结果表明:Rossby波能量可以从南亚高压西北部的窗口区上传至平流层,最高可到达平流层顶,而在南亚高压的其他部分,Rossby波能量均不能穿越对流层顶上传或穿越对流层顶后无法继续上传.南亚高压西北区Rossby波能量可以穿越对流层顶传播的原因是盛行西风,且西风急流出现的频率很小,同时涡动热量通量异常引起的垂直分量的第一项对其上传有很大贡献.南亚高压东北区也盛行西风,然而Rossby波能量不能向上穿越对流层顶的原因是强西风出现频率较高,且温度脊与高度脊位相相近,不利于上传.南亚高压南部均盛行东风,在平流层中下层均为稳定层结,因此Rossby波能量很难上传.南亚高压西南区在对流层位于青藏高原环流的伊朗高原下沉区附近,层结稳定,并且温度脊超前于高度脊,所以Rossby波能量很难上传.而南亚高压东南区在对流层位于南海-西太平洋热带幅合带,层结不稳定,存在Rossby波能量较弱的上传,达到对流层顶后无法继续上传,该区域温度脊落后于高度脊的温压场配置也为Rossby波能量在对流层内的传播提供了条件.

The characteristics and mechanism of Rossby-wave energy vertical propagation crossing tropopause in South Asia High region

Strong east wind prevails in the stratosphere in summer and Rossby wave energy is difficult to spread upwards from the troposphere to the stratosphere. Conversely, west wind prevails in the stratosphere in winter and Rossby wave energy is easy to propagate upwards. Therefore, the propagation of Rossby wave energy into the stratosphere in winter is considered most in the previous studies. In fact, because of the South Asia high (SAH) pressure anticyclonic circulation over the summer plateau which means strong east wind is not alone, Rossby wave energy may also propagate upwards in the SAH, thus affecting the temperature, wind field and atmospheric composition of the stratosphere. Therefore, using ERA-interim daily reanalysis data, the characteristics and mechanism of Rossby wave propagating energy crossing tropopause in the SAH in summer between 1979-2015 are studied. The results show that Rossby wave energy can only propagate to the stratosphere from the window area in northwestern SAH, and can reach the stratopause, but in other parts of the SAH, Rossby wave energy cannot transmit through the tropopause or cannot propagate upwards after transmitting through the tropopause. The reason why the energy of the Rossby wave can travel through the tropopause in northwest is because of the prevailing west wind and the frequency of westerly jet is small, and the first term of the vertical component caused by the vortex heat flux anomaly contributes greatly to its upward propagation. West wind also prevails in northeastern SAH. However, the reason why the Rossby wave energy cannot cross the tropopause upwards is that strong west wind occurs frequently and the temperature ridge is close to the height ridge, which is not conducive to its upward propagation. The south SAH is dominated by east wind and stable stratification in the middle and lower stratosphere, so it is difficult for Rossby wave energy to propagate upwards. The southwestern SAH region is located near the subsidence area of the Qinghai-Tibet plateau circulation in Iranian plateau in the troposphere, so the stratification is stable, in addition, the temperature ridge is ahead of the height ridge, so it is difficult for Rossby wave energy to propagate upwards. While the southeastern SAH is located in the tropical zone between the South China Sea and the western Pacific in the troposphere. So the stratification is unstable, and there is a weak upward propagation of Rossby wave energy that cannot continue to propagate upwards after reaching the tropopause. The temperature and pressure field configuration in this region, whose temperature ridge lagging behind the height ridge, also provides conditions for the propagation of Rossby wave energy in the troposphere.