类副热带印度洋偶极子影响低纬高原夏季降水的机理研究

发布时间：2018-06-23 10:54

本文选题：低纬高原 + 夏季降水　；参考：《云南大学》2016年博士论文

【摘要】：中国低纬高原位于中国西南部,南部濒临孟加拉湾和中国南海两大热带海洋,西北部是青藏高原,同时受到印度季风和东亚季风的影响,区内夏季降水的时空变化规律十分复杂,与中国其它地区存在明显区别。近年来低纬高原地区旱涝灾害频繁发生,给该区人民的生命财产造成了严重的影响,加强低纬高原地区夏季降水影响因子的研究,提高降水在短期气候尺度上的预测能力,对于防灾减灾具有十分重要的现实意义。本文基于低纬高原的降水资料、MERRA再分析资料、Hadley中心海温资料和NOAA的二十世纪再分析资料等,综合应用合成分析、经验正交函数分解、奇异值分解、线性回归分析方法和数值模拟方法,系统地研究了类副热带印度洋偶极子影响低纬高原夏季降水的物理机制。主要结论如下：(1)夏季为低纬高原降水的主汛期,月降水量在150mm以上。低纬高原区气候平均夏季降水量呈西南部和东南部降水量较多,中部及西北部降水较少的分布特征。低纬高原夏季降水演变的首要模态为全区一致变化型,且全区一致型的降水有微弱的减少趋势；次要模态为东西反向变化型,该模态在1985-2005年间存在2-5年的显著振荡周期。全区一致模态的合成分析表明,低纬高原附近西南风异常是影响低纬高原夏季降水异常的重要因素,当低纬高原西南侧出现异常西南风(东南风),暗示着低纬高原附近气候平均的西南风加强(减弱),加强的西南风将携带更多(更少)的水汽进入低纬高原,造成低纬高原降水异常偏多(偏少)。(2)通过对925hPa水平风场和海表温度联合场与低纬高原夏季降水的SVD分析发现,类副热带印度洋偶极子型海温异常与低纬高原夏季降水存在显著的关系,当副热带西南印度洋海表温度偏低(高),东南印度洋海表温度偏高(低)时,对应低纬高原夏季降水偏多(少)。进一步对海表温度与低纬高原区域平均夏季降水进行相关分析发现,在本研究中类副热带印度洋偶极子是影响低纬高原夏季降水的主要外部热力强迫因子之一,其影响强于其它类型的海气相互作用(如：ENSO)对低纬高原夏季降水的影响。(3)基于SVD分析第一模态SST和925hPa风场的时间系数,定义类副热带印度洋偶极子正、负异常年,通过合成分析揭示类副热带印度洋偶极子通过影响孟加拉湾北部的纬向风异常进而影响低纬高原夏季降水。当类副热带印度洋偶极子为正(负)异常年时,即西南印度洋海温偏高(低),东南印度洋海温偏低(高)时,会导致①印度半岛会产生气旋(反气旋)环流,其北部为东风(西风)异常；②热带印度洋低层气流辐散(辐合),阿拉伯海至印度半岛西北部低层气流辐合(辐散),孟加拉湾东海岸的散度风场中为东风(西风)异常；③热带印度洋的辐散风会导致在半球间形成异常的辐散环流：大气在热带印度洋上升(下沉),而在孟加拉湾下沉(上升)。以上三个因素均会导致孟加拉湾北部的东风(西风)异常,使得气候平均场中西南风减弱(增强),由西南风携带进入低纬高原区的水汽减少(增多),低纬高原区水汽辐散(辐合),从而使得低纬高原夏季降水减少(增加)。除此之外,印度半岛夏季降水异常对低纬高原夏季降水也具有一定程度的影响,印度半岛降水异常偏多(少),会加强孟加拉湾的气旋(反气旋)异常,使得孟加拉湾北部东风(西风)异常,进而影响低纬高原夏季降水偏少(多)。(4)类副热带印度洋偶极子的形成可追溯到前期冬季,并维持到夏季,特别是类副热带印度洋偶极子正异常年份。蒸发-风-海表温度(WES)反馈机制能够解释类副热带印度洋偶极子的维持机制,海洋的平流作用对类副热带印度洋偶极子的维持也有一定贡献。(5)大气环流模式的数值模拟结果表明：副热带西南印度洋相对暖(冷),而东南印度洋相对冷(暖)的海温异常分布型,确能强迫出低纬高原夏季降水偏少(多)。数值模式结果与第四章的诊断分析结论一致,比较好地验证低纬高原夏季降水对类副热带印度洋偶极子型海温异常的响应。海气耦合模式进一步证实了类副热带印度洋偶极子影响低纬高原夏季降水异常的物理机制,以及类副热带印度洋偶极子从前期冬季至夏季的维持机制。
[Abstract]:The low latitude plateau of China is located in the southwest of China. The south is on the two major tropical oceans in the bay of Bengal and the South China Sea. The northwest is the Qinghai Tibet Plateau. It is influenced by the India monsoon and the East Asian monsoon. The temporal and spatial variation of summer precipitation in the region is very complicated and distinct from other regions in China. In recent years, the drought and flood in the low latitude plateau area have been droughts and waterlogging. Frequent disasters have caused serious impact on the life and property of the people in the area. It is of great practical significance to strengthen the study on the influence factors of summer precipitation in the low latitude plateau area and improve the prediction ability of precipitation on the short-term climate scale. This paper is based on the precipitation data of low latitude plateau, MERRA reanalysis data, Ha Dley central sea temperature data and the reanalysis data of NOAA in twentieth Century, comprehensive application of synthetic analysis, empirical orthogonal function decomposition, singular value decomposition, linear regression analysis and numerical simulation, systematically studied the physical mechanism of the influence of the subtropical India Ocean Dipole on the low latitude Gao Yuanxia seasonal precipitation. The main conclusions are as follows: (1) summer In the main flood season of low latitude plateau precipitation, the monthly precipitation is above 150mm. The average summer precipitation in the low latitude plateau region is more precipitation in the southwest and Southeast, and the precipitation is less in the middle and northwestern regions. The first mode of the Summer Precipitation Evolution in the low latitude plateau is the uniform variation in the whole region, and the uniform precipitation in the whole region is weak. The trend is reduced; the secondary mode is the East-West reverse change type. The mode has a significant oscillation period of 2-5 years in 1985-2005 years. The analysis of the uniform mode in the whole region shows that the southwest wind anomaly near the low latitude plateau is an important factor affecting the summer precipitation anomaly in the low latitude plateau, and the southwest wind (east wind) appears in the southwest side of the low latitude plateau. It is suggested that the average southwest wind near the low latitude plateau is strengthened (weakened), and the strengthened southwest wind will carry more (less) water vapor into the low latitude plateau, causing the low latitude plateau precipitation anomaly (less). (2) through the SVD analysis of the 925hPa horizontal wind field and the sea surface temperature joint field and the low latitude plateau summer precipitation, the subtropical India is found. The oceanic dipole type SEA SST anomaly has a significant relationship with the summer precipitation in low latitude plateau. When the India ocean surface temperature in the sub tropical southwest is low (high) and the sea surface temperature in the Southeast India ocean is high (low), the summer precipitation in the low latitude plateau is much more (less). Further correlation analysis is found between the sea surface temperature and the low latitude plateau region average summer precipitation. In this study, the subtropical India Ocean dipole is one of the main external thermal forcing factors affecting the summer precipitation in low latitude plateau, and its influence is stronger than that of other types of sea air interaction (such as: ENSO) on the low latitude plateau summer precipitation. (3) based on the SVD analysis of the time coefficient of the first mode SST and 925hPa wind fields, the subtropics of the class is defined. The India Ocean dipole is positive and negative. Through the synthetic analysis, it is revealed that the subtropical India Ocean Dipole affects the Low Latitude Plateau Summer Precipitation in the north of the bay of Bengal. When the subtropical India Ocean dipole is a positive (negative) anomaly, the SST of the southwest India ocean is high (low) and the Southeast India ocean temperature is low (high). It will lead to the circulation of cyclone (anticyclone) in the India Peninsula, the north east wind (westerly) anomaly, and the divergence (convergence) of the low-level air flow in the tropical India ocean, the convergence (divergence) of the Arabia sea to the northwest of the India Peninsula, the easterly wind (westerly) in the east coast of the bay of Bengal, and the divergence of the tropical India ocean. It will lead to an anomalous radiant circulation between the hemispheres: the atmosphere rises in the tropical India ocean and sinks in the bay of Bengal. The above three factors will lead to the easterly wind (westerly wind) in the north of the bay of Bengal, which reduces the southwest wind in the average climate field and reduces the water vapor from the south wind into the low latitude plateau region. In addition, the summer precipitation anomaly in India Peninsula has a certain degree of influence on the low latitude plateau summer precipitation, and the anomaly of precipitation in the India peninsula is too much (less), which will strengthen the abnormality of the cyclone (anticyclone) in the bay of Bengal and make the bay of Bengal. The northern East Wind (west wind) is abnormal, which further affects the low Summer Precipitation in the low latitude plateau. (4) the formation of the subtropical India Ocean dipole can be traced back to the early winter and maintained to the summer, especially the subtropical India Ocean Dipole positive anomaly. The evaporative wind sea surface temperature (WES) feedback mechanism can explain the subtropical India Ocean Dipole The advection of the ocean has some contribution to the maintenance of the subtropical India Ocean dipole. (5) the numerical simulation results of the atmospheric circulation model show that the India ocean in the sub tropical southwest is relatively warm (cold), and the relatively cold (warm) SST in the Southeast India ocean is abnormally distributed, and the precipitation in the low latitude plateau can be forced to be less (more). The results of the value model are in agreement with the diagnostic analysis conclusions of the fourth chapter. The response of the summer precipitation in the low latitude plateau to the subtropical India Ocean Dipole SST anomaly is well verified. The sea air coupling model further confirms the physical mechanism of the subtropical India Ocean Dipole in the low latitude plateau in summer, and the subtropical India. The maintenance mechanism of ocean dipoles from early winter to summer.
【学位授予单位】：云南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P461.2

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