北半球冬季风暴轴与热带外海洋的相互作用

发布时间：2018-04-27 14:24

本文选题：中纬度海—气耦合 + 风暴轴　；参考：《中国海洋大学》2014年博士论文

【摘要】：风暴轴代表了强烈的中纬度天气尺度瞬变涡动活动，在中纬度天气和气候系统中具有十分重要的地位。不仅如此，从中纬度海-气相互作用的角度来讲，风暴轴对热带外海表面温度（SST）异常响应所产生的非线性反馈在大尺度海-气耦合过程中起着重要的调控作用。因此，认识和理解风暴轴在不同时间尺度上的变化及其与下垫面SST异常的关系对理解热带外气候变化及其可预测性具有重要的科学意义。然而，关于风暴轴异常与中纬度SST异常之间的耦合关系以及风暴轴的长期变化趋势，目前还缺乏清晰的认识。风暴轴的长期变化很可能在一定程度上预示中纬度海气耦合的变化。本文利用百年时间长度的海洋同化资料和20世纪大气再分析资料（20CRv2），，结合超前-滞后的最大协方差分析（MCA）等多种统计分析方法，阐明了北太平洋和北大西洋冬季风暴轴异常分别与其下垫面SST异常之间的季节和年际耦合关系。对于北太平洋而言：①在季节时间尺度上，秋季副极地海区的海盆尺度SST冷异常能够使早冬时期的风暴轴在30°N以北产生海盆尺度的正异常响应，从而使风暴轴活动向北加强。秋季这种海盆尺度SST冷异常实际上能够向北加强早冬大气的斜压性和斜压能量转换，这很可能导致相应的风暴轴活动加强。然而，风暴轴的这种响应模态与早冬风暴轴对SST的强迫模态完全不同，后者表现为：向南移动并加强的风暴轴能够在北太平洋中西部诱导产生SST冷异常，而在北美西海岸沿岸产生SST暖异常。②在年际时间尺度上，研究发现在冬季（DJF）中纬度海区，类似太平洋年代际振荡（PDO）模态的马蹄型SST异常（其中北太平洋中西部海区表现为SST暖异常）与40°N以北海盆尺度的风暴轴正异常之间存在相互加强的正反馈效应。该耦合模态具有显著的年代际变化特征。进一步分析发现：上述风暴轴异常响应与由SST异常变化引起的大气低层斜压性的增强密切相关；风暴轴的异常变化则主要通过引起异常的表面净热通量和Ekman平流输运来诱导产生SST异常。对于北大西洋而言：①在季节时间尺度上，早冬时期中纬度海区的经向偶极子型SST异常（冷异常中心位于纽芬兰外东南部；暖异常中心位于副热带海区西部）能够使早春时期的风暴轴活动显著增强。早冬时期的这种经向偶极子型SST异常实际上能够显著加强早春大气的斜压性和斜压能量转换，这很可能导致相应的风暴轴活动加强。然而与北太平洋不同的是，风暴轴的这种响应模态与早春风暴轴对SST的强迫模态非常类似。②在年际时间尺度上，研究发现在冬季（JFM）中纬度海区，单极子型的SST暖异常（异常中心位于纽芬兰以东和以南海区）与类似纬向偶极子型的风暴轴异常（以下游区域中的负异常为主导）之间存在相互加强的正反馈效应。该耦合模态具有显著的年代际变化特征。进一步研究发现：单极子型的SST暖异常能够使低层大气斜压性在40°N-50°N纬度带显著减弱，这很可能导致风暴轴活动减弱；风暴轴的异常变化则主要通过引起向下的异常净热通量和异常Ekman暖平流输运进而诱导产生单极子型的SST暖异常。基于20CRv2资料提供的56个集合样本数据集，本文还系统地揭示了北半球冬季风暴轴的百年变化趋势。研究发现，20世纪北半球冬季风暴轴在对流层高层和低层具有不同的百年变化趋势特征。在对流层高层，由天气尺度的瞬变涡动运动能（EKE）以及位势高度场标准差表征的北太平洋和北大西洋风暴轴均在其北部以及下游区域呈现出显著增强的趋势。这表明在20世纪后半叶，北半球冬季风暴轴显著向东北方向扩展。此外，在北太平洋以及美国上空的高层大气中，瞬变涡动对西风动量的经向输送也同样显著增强。然而，在对流层低层，风暴轴活动（尤其体现在EKE以及瞬变涡动对热量的经向输送）在北太平洋副极地海区的中西部上空以及北大西洋风暴轴上游地区呈现出显著减弱的趋势。进一步分析发现，在对流层高层（低层），风暴轴的增强（减弱）与大气斜压不稳定的增大（减小）密切相关。在上述分析基础上，我们以中纬度大气对黑潮-亲潮延伸体（KOE）区SST异常的响应为切入点，揭示了北太平洋中纬度海-气耦合在全球变暖背景下的变化。研究发现，早冬时期（NDJ）大气位势高度对KOE区SST暖异常的响应在阿留申低压区呈现出相当正压结构的脊响应特征。在20世纪中，这种暖SST-准正压脊响应具有显著增强的趋势，这很可能由全球变暖所致。IPCC-AR4多气候模式试验结果也进一步证实：在全球变暖场景下，暖SST-准正压脊响应显著增强。这表明全球变暖使早冬时期的北太平洋中纬度海-气耦合显著加强。
[Abstract]:The storm axis represents a strong mid latitude synoptic transient eddy activity, which is very important in mid latitude weather and climate systems. In addition, from the angle of mid latitude sea air interaction, the nonlinear feedback generated by the storm axis on the anomalous response of the tropical sea surface temperature (SST) is coupled with the large scale sea air coupling. Therefore, the understanding and understanding of the variation of the storm axis at different time scales and its relation to the SST anomaly of the underlying surface have important scientific significance for understanding the changes in the extratropical climate and its predictability. However, the coupling relationship between the anomaly of the storm axis and the anomaly of the mid latitude SST and the storm axis Long term change trend is still lacking in clear understanding. The long-term variation of storm axis is likely to predict the mid latitude air sea coupling to a certain extent.
In this paper, the seasonal and interannual coupling relationship between the anomalous winter storm axis in the North Pacific and the North Atlantic and its underlying surface SST anomalies in the North Pacific and North Atlantic is illustrated by using the oceanic assimilation data of a hundred years and the twentieth Century atmospheric reanalysis data (20CRv2) and the maximum covariance analysis (MCA). North Pacific: (1) on the seasonal time scale, the basin scale SST cold anomaly in the subpolar region of the autumn can cause the early winter storm axis to produce a positive abnormal response to the basin scale in the north of 30 N, so that the activity of the storm axis strengthens northward. In autumn, the basin scale SST cold anomaly can actually strengthen the early winter atmosphere in the north. However, this response mode of the storm axis is completely different from the forced mode of the early winter storm axis for SST, which shows that the Southward Moving and strengthened storm axis can induce SST cold anomalies in the Midwest of the North Pacific, while on the west coast of North America. On the interannual time scale, the study found that in winter (DJF) mid latitude sea area, the anomaly of horseshoe type SST similar to the Pacific interdecadal oscillation (PDO) mode (including the SST warm anomaly in the Midwest Pacific region of the North Pacific) and the positive feedback effect of 40 degree N to the positive anomaly of the wind storm axis of the Beihai basin scale. The coupling mode has significant interdecadal characteristics. Further analysis shows that the abnormal response of the storm axis is closely related to the enhancement of the low atmospheric baroclinic caused by the abnormal change of SST. The abnormal changes of the storm axis are mainly induced by the abnormal surface net heat flux and the Ekman advection transport to induce the SST anomaly.
For the North Atlantic: (1) on the seasonal time scale, the meridional dipole type SST anomalies in the mid latitudes of the early winter period (the cold anomaly center is located in the southeastern part of Newfoundland and the warm anomaly center in the west of the subtropical sea area) can significantly increase the activity of the storm axis in the early spring period. This meridional dipole type in early winter is different from that of the early winter. In fact, the baroclinic and baroclinic energy conversion in early spring can actually be significantly enhanced, which may lead to a corresponding enhancement of the corresponding storm axis activity. However, unlike the North Pacific, this response mode of the storm axis is very similar to the forced mode of the early spring storm axis for SST. There is a positive feedback effect between the latitude sea area, the monopole type SST warm anomaly (the anomaly center is located in the east of Newfoundland and the South China Sea) and the zonal dipole type storm axis anomaly (the negative anomaly in the downstream region). The coupling mode has the characteristic of the decadal variation. The SST warm abnormality of the polar subtype can weaken the low atmospheric baroclinic at 40 degrees N-50 degree N latitude, which may lead to the weakening of the activity of the storm axis, and the abnormal change of the storm axis is mainly induced by the downward anomalous net heat flux and the abnormal Ekman warm advection, which induces the SST warm anomaly of the monopole type.
Based on the 56 set sample data sets provided by the 20CRv2 data, this paper also systematically reveals the Centennial trend of the winter storm axis in the northern hemisphere. It is found that the winter storm axis in the northern hemisphere has a different Centennial trend in the upper troposphere and low layer in the northern hemisphere in twentieth Century. In the upper troposphere, the transient eddy motion energy of the synoptic scale (E KE) and the North Atlantic and North Atlantic storm axes, characterized by the standard deviation of the potential height field, showed a significant trend in the north and downstream regions. This indicates that the northern hemisphere winter storm axis expanded significantly in the northern hemisphere in the late twentieth Century. In addition, the transient vorticity in the North Pacific and the upper atmosphere over the United States. The meridional transport of the westerly momentum is also significantly enhanced. However, in the lower troposphere, the activity of the storm axis (especially the meridional transport of the EKE and the transient vortices) in the Midwest over the northern Pacific subpolar sea area and the upstream of the North Atlantic storm axis. The enhancement (weakening) of storm axis is closely related to the increase of atmospheric baroclinic instability.
On the basis of the above analysis, we take the response of the middle latitude atmosphere to the SST anomaly in the Kuroshio tidal extension (KOE) region as a breakthrough point, and reveal the changes of the mid latitude sea air coupling in the North Pacific under the global warming background. It is found that the response of the early winter (NDJ) atmospheric potential to the SST warm anomaly in the KOE region appears in the Aleutian low pressure region. In twentieth Century, this warm SST- quasi positive ridge response has a significant increasing trend in twentieth Century, which is likely to be further confirmed by the results of the.IPCC-AR4 multi climate model test caused by global warming: the warm SST- quasi positive pressure ridges should be significantly enhanced in the global warming scenario. This indicates that global warming makes early winter. The mid latitude Northern Pacific Ocean Atmosphere coupling is significantly enhanced.

【学位授予单位】：中国海洋大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：P732;P433

【参考文献】