南海热带气旋引起的海表面温度变化特征分析

本文利用热带降雨测量卫星微波成像的微波遥感资料反演的高分辨率海表面温度(SST)资料,分别分析了南海4种典型热带气旋所引起的SST变化特征.结果表明,由于路径、移速和海面热力状况等方面的差异,这4种热带气旋在南海造成的海面降温具有不同的特征.热带气旋Imbudo(0308)属快速移动的西行路径型,在其路径的右侧造成了较大的降温区,降温中心离热带气旋中心约120km;热带气旋Chanchu(0601)为西行北翘型,在其路径两侧分别形成两个降温中心;打转型热带气旋很容易在其打转处形成降温中心,热带气旋Kai-Tak(0004)在海面造成了9.75°C的降温,在其打转处存在一个持续时间很长的冷涡;热带气旋Vongfong(0214)由于其左侧是南海西部夏季冷涡,混合层深度较浅,其作用使得冷涡加强,并在其路径的左侧造成大面积降温区.     

The Effect of Intensity： Typhoon-Induced SST Cooling on Typhoon The Case of Typhoon Chanchu （2006）

In order to investigate air-sea interactions during the life cycle of typhoons and the quantificational effects of typhoon-induced SST cooling on typhoon intensity, a mesoscale coupled air-sea model is developed based on the non-hydrostatic mesoscale model MM5 and the regional ocean model POM, which is used to simulate the life cycle of Typhoon Chanchu （2006） from a tropical depression to a typhoon followed by a steady weakening. The results show that improved intensity prediction is achieved after considering typhoon-induced SST cooling; the trend of the typhoon intensity change simulated by the coupled model is consistent with observations. The weakening stage of Typhoon Chanchu from 1200 UTC 15 May to 1800 UTC 16 May can be well reproduced, and it is the typhoon-induced SST cooling that makes Chanchu weaken during this period. Analysis reveals that the typhoon-induced SST cooling reduces the sensible and latent heat fluxes from the ocean to the typhoon＇s vortex, especially in the inner-core region. In this study, the average total heat flux in the inner-core region of the typhoon decrease by 57.2%, whereas typhoon intensity weakens by 46%. It is shown that incorporation of the typhoon-induced cooling, with an average value of 2.17℃, causes a 46-hPa weakening of the typhoon, which is about 20 hPa per 1℃ change in SST.     

ZONALLY SYMMETRICAL EKMAN-CISK MECHANISM AND 30—60-DAY LOW FREQUENCY OSCILLATION NEAR THE EQUATOR

Based on the baroclinic semi-geostrophic model,the effects of zonally symmetrical Ekman-CISK mechanism on the characteristics of 30—60-day low frequency oscillation(LFO)near theequator are investigated.It is found that the theoretical results are in good agreement with theobservational features of LFO.Besides,the planetary-scale LFO with the period of 30—60 d couldbe triggered by the Ekman-CISK mechanism,and the growth rate of perturbation with wavenumber 1 is in order of O (10~(-6)s~(-1)).The zonal propagation of LFO and the correspondinglongitudinal-height structure of physical quantities are also discussed in detail.     

地形对地转气流中重力惯性波稳定性影响的进一步研究

用一个带地形的2层均质流体线性模式，考虑了下层流体平均厚度不均匀性的影响，研究低空地转气流中波动的传播和稳定性。     

环台湾岛海域冬季水文要素的数值模拟

本文利用POM模式对环台湾岛海域冬季的水文要素进行了数值模拟,对有代表性的水平环流、温度场和上升流三个要素所进行的分析表明:模式再现了台湾岛东岸的高温高盐强流速区即黑潮,黑潮在冬季并无直接进入台湾海峡的分支存在;西岸的东北向流在冬季各个层次上都存在,台湾东北部的冷涡模拟与实况较为一致。温度场和上升流的分布与水平环流有很好的对应关系。本文还进一步验证了前人的一些研究成果,并对一些特殊物理现象的成因进行了定性解释。     

正则化方法在风海流Ekman模型资料同化中的应用

针对修正的风海流Ekman模型，采用变分同化技术结合反问题的正则化技巧，对模式的初始条件、边界条件和模式参数进行最优调整，使模式解与观测场能较好地符合。在对模式参数的估计过程中，引进正则化思想，在目标泛函中增加稳定泛函，从而克服在调整模式参数时造成的不适定。并通过数值试验进一步肯定正则化理论在资料同化中的作用。     

一次热带气旋过程对出梅影响的数值模拟研究

采用中尺度数值模式WRF对2001年江淮梅雨期热带气旋(Tropical Cyclone,TC)进行数值模拟,研究TC"飞燕"对梅雨结束过程的影响。结果表明,模式能够较好地模拟出"飞燕"的路径与强度演变,并能够较为精确地再现梅雨后期的降水强度和落区。对比分析消除"飞燕"影响的敏感性数值试验结果发现,"飞燕"影响梅雨的机制在于:随着其向东北向移动,西太平洋副热带高压北抬,东亚高、低空急流强度均有所减弱,低空切变辐合变弱,梅雨锋强度减弱,使得来自西南方向的水汽输送减少,造成假相当位温梯度和湿位涡倾斜项减小,垂直上升运动明显削弱,降水中断,导致梅雨结束。而消除"飞燕"影响后,梅雨后期降水仍然较多,梅雨期将有所延长。     

MECHANISM FOR THE SUSTAINING ATMOSPHERIC RESPONSE TO WARM WINTERTIME SEA SURFACE TEMPERATURE ANOMALY IN THE KUROSHIO EXTENSION

Sensitivity experiments with atmospheric general circulation model CAM3 have been performed to investigate the atmospheric response to warm wintertime sea surface temperature anomalies in the Kuroshio Extension (KE). Mechanism for the sustaining abnormal atmospheric response to sea surface temperature anomaly (SSTA) is revealed. It is found that the warm wintertime SSTA in KE leads to soil moisture changes across the Asia continent. The abnormal soil moisture may possibly be one of the reasons for the sustaining of abnormal atmospheric response intrigued by SSTA. Oscillations of perturbations intrigued by warm wintertime SSTA in KE, which have similar frequencies with that of intrinsic atmospheric oscillations, are superposed on the atmospheric oscillations and propagate with primary periodic oscillation of the atmosphere. These SSTA-intrigued oscillations are coupled with natural atmospheric oscillation and finally become parts of it. This is probably another reason for the sustaining of abnormal atmospheric response to SSTA in KE.     

西北太平洋热带气旋活动影响区域大尺度环流的数值模拟研究

本文利用"模式手术"方法研究了西北太平洋热带气旋(TC)对东亚—西北太平洋区域大尺度环流的影响.结果表明,夏季频繁的西北太平洋TC活动导致东亚夏季风增强,季风槽加深;西太平洋副热带高压东退,位置偏北;东亚副热带高空急流强度增强,北太平洋(东亚大陆)上急流轴偏北(偏南);热带地区(副热带地区)的对流层中低层出现异常上升气流(下沉气流),并且从低纬向高纬呈现异常上升气流和异常下沉气流交替分布特征.在中国东南沿海,TC降水导致夏季降水量明显增加;而在长江中下游和华北地区,TC活动引起的异常下沉气流使夏季降水量显著减少.因此,夏季西北太平洋TC活动对东亚—西北太平洋区域气候有显著影响.