平流层对热带臭氧浓度、对流及寒潮爆发的影响：平流层爆发性增温过程中位涡入侵和波动反射的作用

In the present proposal, we will mainly focus on three key aspects related to the stratospheric impact on tropospheric ozone (also water vapor, trace constituents) concentration, tropical deep convection and extreme cold air outbreaks in relation with SST anomalies and SSWs. .In phase 1, we investigate the long term changes in stratospheric PV intrusions (Rossby wave breaking events) and its impact on the concentration of ozone, water vapor and trace constituents across the tropical Pacific and Atlantic Oceans. The intrusions are mainly driven by the upper tropospheric zonal wind pattern (equatorial westerly & Sub tropical jet (STJ)) in the tropics. Zonal variation in SST in the Pacific ocean, characterized by gradual warming in the western Pacific–warm pool and cooling in the central–eastern Pacific, is associated with the strengthening of the Pacific Walker circulation and hence the equatorial westerly wind. On the other hand, the central-eastern Pacific cooling trend is linked to the weakening of the central–eastern Pacific Hadley circulation and so as the STJ. However, for Atlantic Ocean the conditions are quite different, which need to investigate here. .In phase 2, we will investigate the long term changes in tropical deep convection across the Pacific and Atlantic Ocean, due to stratospheric intrusions. The existing hypothesis for this connection between PV intrusions and convection proposes that the convection occurs as a result of decreased static stability and enhanced upward motion in the area of positive vorticity advection ahead of the intrusive trough. This decrease in the static stability, together with the translational motion of the anomaly itself, results in a vertical motion in low levels. However, the hypothesis needs to be tested in the present proposal. We further expect that, the latent heat released due to the convection (initiated by stratospheric intrusions) will act as a feedback (positive/negative) mechanism to the regional Hadley circulation and the impact will be different in the two phases on ENSO. Additionally, we will study the physical mechanism behind PV intrusions, stratosphere-troposphere coupling and the initiation of deep convection over the Indian Ocean, during the major SSW events..Finally in phase 3, we will focus on the intriguing aspects of planetary wave reflection from the stratosphere and its impact on cold air outbreaks in the troposphere. In the beginning, we will investigate whether the stratosphere needs to be preconditioned for the upward propagation of WN2 component, during the major SSW events. Next, the causative mechanism behind the reflection of planetary waves and the role of negative wind shear (formation of vertical reflecting surface and a meridional waveguide) need to be understood clearly. In general, when the planetary wave reflects back to the troposphere, it leads to a change in WN1 structure in the troposphere. The increase of the wave activity near the surface means increased thermal advection near the surface. This led to the advection of cold polar air southeastward, and it brought very cold weather to the subtropics. However, the above hypothesis and the physical mechanism need to be tested here with lot many cases, when stratospheric background is reflective. Moreover, the preferential geographical location for downward wave propagation and cold air outbreaks are not yet understood clearly. Furthermore, in our present proposal, we will try to increase the predictability skill for cold air outbreaks in a scale of few weeks, by analyzing the background informations from the stratosphere.

本项目将围绕由海温异常和平流层爆发性增温引起的平流层对对流层臭氧浓度、热带深对流以及寒潮爆发这三方面的影响开展。首先，我们将研究平流层位涡入侵的长期变化及其对热带太平洋和大西洋上空臭氧、水汽以及其他示踪物浓度的影响。其次，我们将分析太平洋和大西洋上空深对流活动的长期变化趋势。已有假说认为深对流是位涡入侵槽前的正涡度平流区域的静力稳定度的减弱和上升运动的增强引起。本研究将对该假设进行检验。此外，还将研究爆发性增温过程中位涡入侵、平流层对流层耦合以及印度洋上空深对流触发的物理机制。最后，将关注行星波反射的触发机制及其对寒潮爆发的影响:分析爆发性增温事件中二波上传在平流层是否存在先决条件；波动反射与纬向风负垂直切变之间的联系；以及行星波反射可能引发的极地冷空气向南爆发的区域和路径。通过本项目中这些对平流层背景信息的分析，我们希望能够在数周的时间尺度上提升对寒潮爆发的预报技巧。

在目前的提案中，我们调查了全球变暖和ENSO对太平洋潜在涡流（PV）入侵趋势增加的作用。其次，研究了高纬度和中纬度与平流层对对流层天气系统的影响。作为扩展的研究，我们调查（a） 导致北极扩大的因素和 （b） 印度夏末季风在喀拉拉邦开始，以及东亚的作用。为了达到结果，我们使用ECMWF/NCEP/JRA重新分析数据CMIP5模型仿真。我们确定了太平洋上200 hPa的光伏入侵事件，并估计了与ENSO不同阶段和全球平均气温上升相关的上升趋势。其次，进行了EOF分析，获得了200 hPa时季节性平均区域风的主导变异模式。我们计算发散风成分的变化，以研究沃克环流和区域哈德利环流的作用。最后，通过在所有模型中对变量进行平均计算，计算多模型组合 （MME）。泰勒图用于分析CMIP5模型在模拟任何变量的空间模式时的性能。研究的意义如下：.（a） 太平洋上亚热带光伏入侵事件的长期上升趋势是由于上对流层赤道西风管的加强和亚热带喷射的减弱。这些变化是由于沃克循环的加强和区域哈德利环流减弱，这与全球变暖是一应有之一的。增加的趋势可能会增加赤道的传输和臭氧和水蒸气在光伏入侵期间的向下混合。（b） 我们观察到，由于ENSO（厄尔尼诺/南方涛动），亚热带入侵频率具有很强的年际变异性，在拉尼娜现象期间发生的事件更多，在厄尔尼诺条件下发生的事件较少。我们的分析表明，对流层臭氧浓度和亚热带入侵占太平洋中部热带（10-25°N）外热带共变异性（低于5公里）的约65%，特别是在拉尼娜现象期间。（c） 巴伦支-卡拉海的海冰损失导致巴伦支-卡拉海温热异常，欧亚大陆上寒冷异常。研究结果对于了解北极扩增对欧亚大陆和中空地区地表天气条件的影响，以及加强乌拉尔在次冬的阻解，具有非常重要意义。（d） 我们确定了在夏季推动北极扩增的因素和物理机制。我们已经量化了，超过一半的变暖趋势在整个亚北极和80%的加拿大北部和东西伯利亚可以解释为增强的向下红外辐射（IR）。（e）在这里，我们强调了东亚在印度夏末季风开始中的作用，在东亚（东东TP，中国中东部）上发展低海平面压力。这加强了从BOB向东部TP和华南地区传输的低水平水分收敛。因此，相对较弱的 LLJ 和赤字低水平水分供应在东部 BOB 保持关键的作用，在调节季风在喀拉拉邦。