热带风场垂直结构的谐波分析方案

本文主要通过对傅里叶分析方案和模方分析方案谐波分析方案进行研究,给出这2种方案的详细说明,通过700h Pa这一层次的实例来说明此方法的优越性,并通过比较和分析,得出该方法用在各垂直层次中的分析状况,最终得出谐波分析方案是分析热带风场一种有效方法。

热带气旋风场对海浪分布特征的影响

设计了一系列理想的数值实验,利用高分辨率的WAVEWATCHIII海浪模式定量分析热带气旋移动速度、强度、最大风速半径和热带气旋移动时的转向等风场细节因素对热带气旋下表面海浪分布特征的影响。实验结果表明,热带气旋移动速度、最大风速半径和热带气旋移动时的转向会影响海浪的空间非对称分布。最大风速半径增大会使最大有效波高的位置向后移动,而移动速度增大会使最大有效波高位置向前移动。移动速度增大会使右侧象限内的有效波高增大,左侧象限内有效波高减小。最大风速半径增大和强度增强使各象限内有效波高均增高。热带气旋的转向使各象限内有效波高增高,除了右后象限。这些风场特征对各个象限内海浪的平均波长、平均周期、平均波向、和波峰方向都有很重要的影响,尤其以左后象限最为显著。

热带气候风场的傅立叶分析方案及试验

给出了热带气候风场V-的一个傅立叶分析方案。对热带(30°S^30°N)区域1月850hPa气候风场V-的试分析结果表明:V-具有低维、低阶特征,|m|=0,4的9个低波数分量共拟合了V-模方的92.4%。0波分量V-0最重要,拟合了V-模方的56.4%,它主要给出了纬向平均信风带结构特征。定常波(V-*)拟合了V-模方的43.6%,也具有低维、低阶特征,|m|=1,4的8个低波数分量拟合了V-*模方的82.6%,由它们构成的定常波合成风场V-4*与V-*的相似系数高达0.909,它给出了V-*的主要环流系统。因此,傅立叶分析方法是分析热带气候风场的一种有效方法。

热带月平均风场谱结构的傅立叶分析Ⅰ——气候风场分析

用风场傅立叶分析方案,分析了NCEP/NCAR再分析资料的热带(30°S^30°N)850、200 hPa气候风场V8 50、V2 00的谱结构,讨论热带风场定常波的成因,以弥补热带气候风场此类分析工作的空白。研究结果表明,(1)有低维、低阶特征,|m|=0,4-、0,3-波对月8 50、2 00的累积模方拟合率年均达90%、98%。(2)纬向平均分量0最重要,它对8 50、2 00的单波拟合率ρ0年均达52%、85%。850 hPa0主要由北、南半球的两支信风带构成,冬半球强、夏半球弱,轴线位置与所在半球Hadley环流中心对应;200 hPa0由强的外热带西风带和弱的内热带东风带构成。0的季节变化850 hPa层明显强于200 hPa,北半球明显强于南半球。(3)风场定常波的最大波分量全年两层均为|1|*,它对850*、200*的拟合率ρ|*1|年均达39%、55%;ρ|1|*作年双周振荡,北半球夏、冬季达极大,秋、春季达极小。次大波分量在北半球冬、夏季时同为3、2波,过渡季节也以3、2波为主(10—12月850*4波是例外)。(4)1、7月射出长波辐射定常波OLR*最大、次大波与同期V*相同,1月为1、3波,7月为1、2波;OLR*重要波分量上的极值区与*相应波分量散度场的垂直配置符合动力学原理。(5)7月青藏高原及以东以南的广阔区域,*的主要分量|1|*、|2|*同为下层辐合、上层辐散,1OLR*、2OLR*同为负值,是同纬度上最有利于降水和潜热释放的气候区。

热带异常风场序列的傅立叶分析方案及试验

给出了热带异常风场多年序列{V′(t)}的一个傅立叶分析方案。对热带(30°S^30°N)1月850 hPa等压面1948—2005年{V′(t)}的试分析表明:1){V′(t)}总模方S′中定常波异常{V′*(t)}的模方S′*远大于信风异常{[V′(t)]}的模方[S′],这与气候风场V-模方-S以信风为主的谱结构有显著差异。2){V′(t)}的谱结构具有低维、低阶的特征,|m|=0,6的13个低|m|分量共拟合了S′模方的87.2%。3)全域定常波异常的合成波模方S′*|m|随|m|增大递减,|m|=1、2的V′*|m|拟合了S′*的44.4%,是构成{V′*}的最主要的分量;φ纬定常波异常的累积模方拟合率P′*|m|(φ)存在纬际差异,赤道至10°S带是主要高值带,20°N及以北是另一个高值带。4)全域和φ纬度上t年定常波异常模方及|m|=1、2的分量模方和存在明显的年际变化,20世纪80年代以来它们的强异常与强ENSO事件密切相关。因此,傅立叶分析方法是研究热带异常风场时间序列时空结构的有效和有用的方法。

热带气旋风场动力释用技术的检验与评估

我国是受热带气旋,尤其是登陆热带气旋影响最为严重的国家之一,热带气旋造成的大风是主要的气象致灾因子和业务预报的主要对象,而目前数值预报是热带气旋风场预报的重要客观参考产品。当数值预报的热带气旋路径与强度等较主观预报出现较大偏差时,需要对数值模式预报的风场及时做出修正,而业务中对风场数值预报产品缺乏合理有效的修正手段,使得风场数值预报产品的可用性显著降低。本文采用“热带气旋风场动力释用技术”建立了台风精细化大风客观预报系统,并开展了主、客观的台风个例风场检验以及2020年的台风风场检验。检验评估表明:基于“热带气旋风场动力释用技术”的台风精细化大风客观预报系统对热带气旋风场数值预报产品表现出良好的释用效果,提高了预报员对相关数值预报产品的理解和应用水平,提升了风场预报的精细化程度,为气象预报和决策服务提供了重要参考和依据。

A DYNAMICAL INTERPRETATION OF THE WIND FIELD IN TROPICAL CYCLONES

Based on the primitive equations in polar coordinates and with the supposition that parcel velocity in tropical cyclones is in linear variation and that the distribution of surface pressure agrees with the Fujita formula, a set of equations are derived, which describe the impact of perturbations of central pressure, position of tropical cyclones, direction and velocity of movement of tropical cyclones on the wind field. It is proved that the second order approximation of the kinetic energy of tropical cyclones can be described by the equations under linear approximation. Typhoon Wipha (2007) is selected to verify the above interpretation method, and the results show that the interpretation method of the wind field could give very good results before the landfall of tropical cyclones, while making no apparent improvement after the landfall. The dynamical interpretation method in this paper is applicable to improving the forecasts of the wind field of tropical cyclones close to the coast.

Relationship of tropical cyclone size change rate with size and intensity over the western North Pacific

In this study,the relationship of tropical cyclone(TC)size change rate(SCR),within 24 hours,with size,intensity,and intensity change rate(ICR)are explored over the western North Pacific.TC size is defined as the azimuthally averaged radius of gale-force wind of 17 m s−1(R17)based on the Multiplatform Tropical Cyclone Surface Winds Analysis data.The majority of SCRs are mainly distributed in the range from−20 to 80 km d−1.The correlation coefficients between SCR and size(SCR-R17),intensity,and ICR(SCR-ICR)are−0.43,−0.12,and 0.25,respectively.The sensitivity of the SCR-R17 and SCR-ICR relationships to size,intensity,and evolution stage are further examined.Results show that the SCR-R17 relationship is more sensitive to variations of size and evolution stage than that of intensity.The relationship of SCR-ICR is largely modulated by the evolution stage.The correlation coefficient of SCR-ICR can increase from 0.25 to 0.40 when only considering the lifetime stages concurrently before and after the lifetime maximum size(LMS)and lifetime maximum intensity.This demonstrates that ICR is a potential factor in predicting SCR during these evolution stages.Besides,the TC size expansion(shrinkage)is more likely to occur for TCs with smaller(larger)size and weaker(stronger)intensity.The complexity of size change during a TC's lifetime can be attributed to the fact that shrinkage or expansion could occur both before and after LMS.

不同分布型La Nia事件及热带大气的响应特征对比

利用NCEP风场、HadISST海温及PREC降水数据,将1950年以来的14次LaNia事件分为东部型和中部型两类,并进一步研究了两类LaNia事件的海温发展演变特征以及热带大气响应特征的差异.LaNia事件的分类基于的是成熟期标准化的Nio3和Nio4指数及成熟期海温距平的空间分布特征.在东部型LaNia事件的成熟期,海温负距平绝对值的最大值主要分布在赤道东太平洋,而中部型LaNia事件达到成熟时海温负距平中心向西移动到赤道中太平洋日界线附近.中部型LaNia的强度比东部型强,并且赤道太平洋东西海温差异也较大.受中部型LaNia海温分布特征的影响,赤道东太平洋异常的下沉运动西移到日界线附近,低层异常辐散高层异常辐合的中心也相应西移,热带风场对两种分布类型LaNia的响应差异在对流层高层200hPa表现的更加显著.但是,两类LaNia成熟期热带降水异常的分布特征差异很小,只是中部型LaNia事件导致的赤道太平洋中部降水偏少和赤道东印度洋至西太平洋降水偏多的特征更明显.

RELATIONSHIP BETWEEN INTERANNUAL VARIATION OF MERIDIONAL WIND ANOMALIES IN TROPICAL PACIFIC AND SSTA

The Singular Spectrum Analysis (SSA) method is used to conduct studies of periodicity of the SST and meridional winds in tropical Pacific Ocean. The results show that the air-sea system for the Pacific varies on quasi-4-year, quasi-2-year and interannual scales, with the quasi-4-year scale having the highest variability. Depending on the scale, the wind field has a varying degree of association with the SST anomalies. Difference is also found in the evolution of phase. In addition, the work discusses the difference in SSTA resulted from wind fields for quasi-4-year and quasi-2-year components.

Estimation of tropical cyclone parameters and wind fields from SAR images

The traditional method of Synthetic Aperture Radar(SAR)wind field retrieval is based on an empirical relation between the near surface winds and the normalized radar backscatter cross section to estimate wind speeds,where this relation is called the geophysical model function(GMF).However,the accuracy rapidly decreases due to the impact of rainfall on the measurement of SAR and the saturation of backscattered intensity under the condition of tropical cyclone.Because of no available instrument synchronously monitoring rain rate on the satellite platform of SAR,we have to derive the precipitation of the SAR observation time from non-simultaneous passive microwave observations of rain in combination with geostationary IR images,and then use the model of rain correction to remove the impact of rain on SAR wind field measurements.For the saturation of radar backscatter cross section in high wind speed conditions,we develop an approach to estimate tropical cyclone parameters and wind fields based on the improved Holland model and the SAR image features of tropical cyclone.To retrieve the low-to-moderate wind speed,the wind direction of tropical cyclone is estimated from the SAR image using wavelet analysis.And then the maximum wind speed and the central pressure of tropical cyclone are calculated by a least square minimization of the difference between the improved Holland model and the low-to-moderate wind speed retrieved from SAR.In addition,wind fields are estimated from the improved Holland model using the above-mentioned parameters of tropical cyclone as input.To evaluate the accuracy of our approach,the SAR images of typhoon Aere,typhoon Khanun,and hurricane Ophelia are used to estimate tropical cyclone parameters and wind fields,which are compared with the best track data and reanalyzed wind fields of the Joint Typhoon Warning Center(JTWC)and the Hurricane Research Division(HRD).The results indicate that the tropical cyclone center,maximum wind speed,and central pressure are generally consistent with the best track data,and wind fields agree well with reanalyzed data from HRD.