STUDY ON THE MULTIVARIATE STATISTICAL ESTIMATION OF TROPICAL CYCLONE INTENSITY USING FY-3 MWRI BRIGHTNESS TEMPERATURE DATA

A technique for estimating tropical cyclone (TC) intensity over the Western North Pacific utilizing FY-3 Microwave Imager (MWRI) data is developed. As a first step, we investigated the relationship between the FY-3 MWRI brightness temperature (TB) parameters, which are computed in concentric circles or annuli of different radius in different MWRI frequencies, and the TC maximum wind speed (Vmax) from the TC best track data. We found that the parameters of lower frequency channels’ minimum TB, mean TB and ratio of pixels over the threshold TB with a radius of 1.0 or 1.5 degrees from the center give higher correlation. Then by applying principal components analysis (PCA) and multiple regression method, we established an estimation model and evaluated it using independent verification data, with the RMSE being 13 kt. The estimated Vmax is always stronger in the early stages of development, but slightly weaker toward the mature stage, and a reversal of positive and negative bias takes place with a boundary of around 70 kt. For the TC that has a larger error, we found that they are often with less organized and asymmetric cloud pattern, so the classification of TC cloud pattern will help improve the acuracy of the estimated TC intensity, and with the increase of statistical samples the accuracy of the estimated TC intensity will also be improved.     

1949—2015年北上热带气旋特征

利用1949—2015年CMA STI热带气旋(TC：Tropical Cyclone)最佳路径数据集、NCEP25°×25°再分析资料及常规资料,对北上TC特征进行研究。结果表明：1949—2015年进入北上定义区的TC共计91个,占西北太平洋（包含南海）TC总数41%,年平均14个;进入定义区最早5月,最晚9月,最多8月,但7月北上几率最大。依据TC运动形态特征将北上TC路径分为转向北上和直接北上两大类,其中转向北上TC转向之后路径与转向点密切联系,这对北上TC路径预报有重要意义。北上TC生成源地主要在8°~25°N,122°~155°E,不同路径北上TC源地纬度、经度分布有差异,源地偏北的TC未来转向点偏北和直接北上的可能性大。北上TC一般在定义区外20°N左右达到生命史最大强度,进入定义区后强度大多减弱为热带风暴,强度越强减弱速度越快;进入影响区后发生变性的TC明显增加。北上TC路径与西太平洋副热带高压的主体位置、形态和强度有关,副高西端高脊的引导气流决定北上TC未来路径是转向还是北上,西脊点的位置决定北上TC未来转向点的位置。不同路径北上TC暴雨和大风天气区分布存在差异,中纬转向、高纬转向和直接北上路径是造成北方强烈降水和大风的主要路径。     

Low-Level Westerly Winds,Topography, and Tropical Cyclogenesis of Arlene (2005): Observations and Model Simulations

The evolution process of the low-level westerly winds over the eastern North Pacific is investigated to understand the tropical cyclogenesis (TCG) of Tropical Storm Arlene (2005) over the Intra-Americas Sea (IAS). Also considered are the influences of the topography of the Central American mountain region interacting with the low-level westerly winds on Arlene's TCG by comparing results from a modified-topography simulation of Arlene's TCG with those from a simulation with the original topography in the Weather Research and Forecast (WRF) model. Interactions among large-scale circulations associated with subtropical highs in both hemispheres and an anticyclone over the warm eastern North Pacific produced low-level westerly winds into the IAS. WRF model experiments with a virtually elevated terrain filling in mountain passes in Central America resulted in the delayed and suppressed development of the incipient storm. The model experiments suggest that the low-level winds and moisture fluxes from the eastern North Pacific passing through the low-level mountain passes in Central America could play a critical role in the TCG process and perhaps also sustenance of storms over the western Caribbean.     

西北太平洋船舶避风暴分析

本文首先对远望二号船避９７０８号强热带风暴航行的情况作了简要回顾,对当时选择航线、悠入航线、徘徊、加速等一系列措施作了详细分析,还探讨了９７０８号强热带风暴的形成和路径预报问题;最后对远洋避风暴方法作了理论探讨。     

源自南海东北部海区热带气旋的若干统计特征

1949－1998年50a中，源自南海东北部海区的热带气旋共67个，其中有17a无热带气旋产生，45a无台风。该海区产生的热带气旋及其有关的统计特征与南海南部和热带西太平洋的热带气旋不同：平均个数是厄尔尼诺年较反厄尔尼诺年少；春季型的厄尔尼诺过程中热带气旋生成较多；1970－1990的的强厄尔尼诺过程中热带气旋个数当年较次年多，1990年后则相反，与历次厄尔尼诺过程比较，1997－1998年特强厄尔尼诺过程中的热带气旋生成较多、发展较快、其异常的气候特征为有史以来所罕见。     

福建出现秋台风前期几个物理因子特征

通过分析福建省出现秋台年与无秋台年夏季几个物理因子的变化，得出如下结论(1)有秋台年夏季东亚500hPa高度距平场呈现“－＋－”的分布特征，无秋台年东亚500hPa高度距平场呈“＋－＋”的分布.(2)有秋台年夏季副热带高压较活跃，北进南退的步伐较大，而无秋台年只在秋季的回跳速度快.(3)拉尼娜事件开始年份可能会出现秋台风，同时有秋台年夏、秋季海温距平分布是赤道中、东太平洋为负的海温距平，西、北太平洋为正海温距平，无秋台年份海温的分布形态与此刚好相反．     

登陆闽南地区的热带气旋对厦门天气的影响

根据1956～1990年的热带气旋资料,对登陆闽南地区的热带气旋进行气候统计及路径分型,共分北移Ⅰ型、北移Ⅱ型和偏西型三类,文中对上述不同路经类型的热带气旋对厦门降水和大风的影响分别进行了分析。     

Water circulation dynamics, water column nutrients and plankton productivity in a well-flushed tropical bay in Kenya

Water circulation, water column nutrients and plankton productivity were studied in a tropical bay with high rates of water exchange (60% to 90% per tide) and short residence times (3 to 4 h). The water circulation is predominantly affected by the semi-diurnal tides, which cause strong and reversing currents in the mangrove creeks (0.60 m·s⁻¹) and currents of low magnitude in the neighbouring seagrass and coral reef zones (< 0.30 m·s⁻¹). Tidal asymmetry, with relatively stronger ebb than flood flows in the mangrove creeks, promotes the net export of nutrients from the river mouth and of organic matter from the mangroves to the seagrass beds. The main sources of the dissolved inorganic nutrients are two rivers (the Kidogoweni and Mkurumuji) which discharge (up to 17.0 m³·s⁻¹) in the upper and lower regions of the bay. The increased input of nutrients did not cause eutrophic conditions since nutrients were rapidly flushed out of the bay. The mangrove biotope generated small amounts of dissolved nutrients which are likely to be used for primary production within the mangrove zone. The production of nutrients in the mangrove zone was masked by high rates of flushing, such that no appreciable nutrient signal was detected in the dry season when the influence of the rivers diminished. The rates of primary production were low in the mangrove, seagrass, and coral reef biotopes in the dry season. Primary production increased slightly during the rainy season. The level of chlorophyll a in the mangrove biotope increased during ebb tides and decreased during flood tides. The highest zooplankton densities, which could not be related directly to primary production in the water-column, occurred at the seagrass station during the wet season.     

海洋对热带气旋响应的一种改进模式

建立一个改进的二层非线性原始方程海洋模式，研究海洋对热带气旋的响应。采用湍流动能收支参数化风应力产生的垂直混合（夹卷），其中考虑了盐度对层结强度的影响。通过海洋对７００２号台风响应的数值模拟，结果表明，在引起海表温度下降的各热通量分量中，夹卷约占了８３％，余下的海表面热通量占了１７％。在台风路径转向的右侧，海洋出现强烈的降温，表现出明显的右偏性。降温的幅度、范围和形状均与观测结果较为一致。     

热带气旋移动研究近况综述

本文根据目前国内外近期的文献资料，总结介绍有关热带气旋移动的理论及现场试验研究方面的新成就和观点。可供科研、教学参考，亦可供业务预报中借鉴使用。