西风爆发时赤道西太平洋热量平衡的诊断分析

西风爆发（ＷＷＢ）对赤道西太平洋暖池ＳＳＴ的影响是ＷＷＢ与ＥＮＳＯ相互作用的一个重要环节。作者运用 ＴＯＧＡ（Ｔｒｏｐｉｃａｌ Ｏｃｅａｎ－Ｇｌｏｂａｌ Ａｔｍｏｓｐｈｅｒｅ）－ＣＯＡＲＥ（Ｃｏｕｐｌｅ Ｏｃｅａｎ－Ａｔｍｏｓｐｈｅｒｅ Ｒｅｓｐｏｎｓｅ Ｅｘｐｅｒｉｍｅｎｔ）期间暖池海区 ８个浮标的观测资料，根据Ｓｔｅｎｖｅｎ和Ｎｉｉｌｅｒ的热量平衡诊断方法，从能量平衡角度分析了赤道１５６°Ｅ附近ＳＳＴ对１９９２年 ９月到 １９９３年 １月期间两次 ＷＷＢ事件的响应。两次 ＷＷＢ期间， ＳＳＴ都是在ＷＷＢ之前和其后升温，而在ＷＷＢ期间降温，升温和降温的幅度均为ｌ℃左右。热量平衡分析结果表明，季节内时间尺度上海表热通量是导致赤道西太平洋暖池混合层温度变化的主要因素。在海表热通量中，短波辐射和潜热是变化量最大的两项，决定着净通量的正负，其他项的变化则相对较小。水平平流项有时可以超过海表热通量的作用，其作用不可忽略、两次ＷＷＢ的过程中，季节变化造成的混合层的温盐结构和流场结构的差异是导致两次ＷＷＢ事件时上层海洋热量平衡差别的主要因素。另外，混合层的厚度也有明显的变化。

Is it possible to differentiate gastric GISTs from gastric leiomyomas by EUS?

AIM: To evaluate the ultrasonog raphy (EUS) features of gastric gastrointestinal stromal tumors (GISTs) as compared with gastric leiomyomas and then to determine the EUS features that could predict malignant GISTs.METHODS: We evaluated the endoscopic EUS features in 53 patients with gastric mesenchymal tumors conf irmed by histopathologic diagnosis. The GISTs were classif ied into benign and malignant groups according to the histological risk classif ication.RESULTS: Immunohistochemical analyses demon-strated 7 leiomyomas and 46 GISTs. Inhomogenicity, hyperechogenic spots, a marginal halo and higher echogenicity as compared with the surrounding muscle layer appeared more frequently in the GISTs than in the leiomyomas (P < 0.05). The presence of at least two of these four features had a sensitivity of 89.1% and a specifi city of 85.7% for predicting GISTs. Except for tumor size and irregularity of the border, most of the EUS features were not helpful for predicting the malignant potential of GISTs. On multivariate analysis, only the maximal diameter of the GISTs was an independent predictor. The optimal size for predicting malignant GISTs was 35 mm. The sensitivity and specificity using this value were 92.3% and 78.8%, respectively.CONCLUSION: EUS may help to differentiate gastric GISTs from gastric leiomyomas. Once GISTs are suspected, surgery should be considered if the size is greater than 3.5 cm.

THE DIAGNOSTIC ANALYSIS OF THE TRACK AND PRECIPITATION OF TYPHOON “RANANIM” AFTER LANDFALL

Over the past few years, landfall and track,intensity, sustaining mechanisms of tropical cyclones （hereafter TCs） and associated weather changes have become heated topics of research, From the viewpoints of energy transformation, moisture transfer, midlatitude baroclinic frontal zones and ambient wind fields, Chen et al.Le et al.and Zeng et al.studied the sustaining mechanism of TCs that have made landfall. Li et al.also pointed out that the intensification of TCs during transition was associated with the disturbance and downward transportation of high-level potential vortexes, low-level frontal zones and low-pressure circulation around TCs, after explaining the difference in TCs transition following the theory of wet potential vortexes. With large-scale diagnostic study of two types of TCs that unexpectedly weaken or enhance just before landfall in southern China, Hu et al.noted that enhancing TCs were usually to the southwest or south of the subtropical high with low levels featured by well-defined southwesterly inflow inside TCs and sufficient supply of water vapor. Liang et al.not only analyzed the changes in convective cloud bands, precipitation, track and temperature and humidity structure in the course of TC Vongfang landfall, but the effect of cold air and Southwest Monsoon on its intensity in particular. As also shown in numerical experiments conducted both at home and abroad and relevant studies,saturated humidity and large-sized bodies of water are favorable for the maintenance and enhancement of landfall TCs circulation. All of the above research achievements not only help broaden the understanding of the patterns by which TCs behave but are positive in improving the forecast of the track, winds and rains after landfall. It is.however, not much addressed in the field or evounon of landfall TCs when they are with special underlying surface and circulation background. TC Rananim （0414） was the most serious typhoon that ever affected Zhejiang province after landfall in the 48 years from 1956 to 2004, which was also the storm that caused heavy rains in the most widespread area in Jiangxi province in the past 20 years. There are two points about Rananim that stand out from the other storms. The first was the sudden westward turning of its track and the second the significant enhancement of precipitation after moving above the Boyang Lake.What kind of mechanism caused such remarkable change in the storm？ With 6-hourly 1×1°NECP global reanalysis data, real-time upper-level observations and TCs location reports by the Central Observatory, the above two points and possible causes are studied in terms large-scale circulation background, underlying surface, cold air and diagnosis of physical quantity fields. New understanding has been made about the behavioral pattern of landfall TCs and related results will offer effective help in operational forecast.

ON THE INTERACTIONS BETWEEN ENSO AND THE ASIAN MONSOON ON THE SCALE OF QUASI-BIENNIAL OSCILLATION

A diagnostic analysis is performed of the quasi-biennial oscillations during the ENSO cycle and the results are based to study the interactions between ENSO and the Asian monsoons. It shows that the Asian monsoons have significant influence on the ENSO cycle on the quasi-biennial scale. Materialized through the onset and southward progression of the winter monsoon, the influence appears in the tropical western Pacific to excite severe convection and to further affect the ENSO cycle. The phenomenon is not only reflected in the quasi-biennial mode but the annual variation of the Asian winter monsoon in reality.

DIAGNOSTIC ANALYSIS OF MEAN MERIDIONAL CIRCULATION ANOMALY IN LOW LATITUDES IN RELATION TO ZONAL MEAN SST ANOMALY

The mass stream function of zonal mean meridional circulation is calculated in terms of NCEP/NCAR monthly meridional wind speed and vertical velocity, and the climatic and anomalous features of zonal mean SST and meridional circulation are investigated. Results show that (1) a joint ascending branch of Northern and Southern Hadley circulation is on the side of the summer hemisphere near the equator ,being well consistent with the extremum of[]SST,and a strong descending by the winter-hemispheric side.(2)El Ni駉-related][SSTin low latitudes is an important outer-forcing source for anomaly meridional circulation, which is affected by seasonal variation of basic airflow and[]SST, and interannual and interdecadal changes of []SST.

Analysis of Large-scale Rainstorm Caused by Typhoon Nesat

Based on prediction data of T213 and ECMWF and historical information of tropical cyclone,the causes of long lasting and large scale rainstorm brought by Nesat in Guangxi were analyzed.Nesat,of high intensity,carried much vapor and energy and went through Beibu Gulf by subtropical high pressure.After Nesat made landfall,subtropical high pressure maintained high and gradient between typhoon circulation and subtropical high pressure increased;the typhoon was supported by abundant vapors and energies by powerful eastern flows.Furthermore,northern cold airs went downward and met southeast wind behind of the typhoon,resulting in shears and convective precipitation.Therefore,the rains brought by the typhoon itself,jet stream,and cold air contributed to long lasting rainfall under influence of Nesat.