浙江北部近海边界层风廓线特征分析

利用2010年12月至2014年5月宁波近海凉帽山370m高塔气象梯度风观测和浙江北部沿海自动气象站测风资料,对浙江北部近海风速垂直廓线进行分析,结果发现:受地形影响,偏南、偏北风时塔基风速一般比上一层风速大。不同天气系统影响下近地边界层风廓线不同,南风型320m以下风速基本遵从对数律。热带气旋影响型和北风型时风廓线可分为3段,常通量层内基本满足对数律,该层向上一段高度热带气旋影响型风速变化不大,北风型反而减小,再往上风速又继续增大。北风型风廓线的这种3段结构表现比热带气旋影响型更为清楚,约80~109m风速出现相对极大值,200~250m间存在风速极小值。满足对数律的近地边界层内小风比大风具有更好的拟合优度。浙江北部沿海自动气象站测风资料不同风型统计分析与高塔风廓线表现基本一致。     

登陆台风边界层风廓线特征的地基雷达观测

为了分析登陆台风边界层风廓线特征,利用2004—2013年中国东南沿海新一代多普勒天气雷达收集的17个登陆台风资料,采用飓风速度体积分析方法,反演登陆台风的边界层风场结构特征。与探空观测对比表明,利用雷达径向风场可以准确地反演登陆台风的边界层风场结构,其风速误差小于2 m/s,风向误差小于5°。所有登陆台风合成的边界层风廓线显示,在近地层(100 m)以上,边界层风廓线存在类似急流的最大切向风,其高度均在1 km以上,显著高于大西洋观测到的飓风边界层急流高度(低于1 km)。陆地边界层内低层入流强度也明显大于过去海上观测,这主要是由陆地上摩擦增大引起。越靠近台风中心,边界层风廓线离散度越大,其中,径向风廓线比全风速以及切向风廓线离散度更大。将风廓线相对台风移动方向分为4个象限,分析边界层风廓线非对称特征显示,台风移动前侧入流层明显高于移动后侧。最大切向风位于台风移动左后侧,而台风右后侧没有显著的急流特征,与过去理想模拟的海陆差异导致的台风非对称分布特征一致。     

延吉市边界层风场特征分析

利用风廓线雷达在延吉市开展了边界层风场的探测研究,根据2012年4个月逐日的边界层风场探测资料,分析了延吉市大气边界层风场的时空分布特征,得到了逐月的高空风廓线图。结果表明：1000m以下,水平风速和垂直风速随高度均呈现出增加的趋势,地面风速最小,750-1000m高度处存在明显的风切变层;2月和7月高空水平风速随高度的增加而增加,4月和10月高空水平风速变化呈单峰型的变化趋势;2月垂直风速随高度的增加逐渐增加,7月随高度的增加逐渐减少,4月和10月随高度呈双峰型的变化趋势;各月在1000～2000m高度垂直风速较小;各月水平风除个别高度外均以西风或偏西风为主导风向,垂直方向以下沉气流为主。     

丘陵地区大气边界层风廓线雷达适用性分析

本文利用2010年夏季福建省三明市开展的大气扩散实验资料,研究了大气边界层风廓线雷达在福建丘陵地区的适用性,并探讨了风廓线雷达探测的误差特征和修正方法。结果表明：大气边界层风廓线雷达水平风场的探测结果在300~2 000 m高度范围的偏差与高度和风速具有一定统计关系;通过与100 m气象铁塔水平风场资料对比,说明风廓线雷达对丘陵地区低层大气风场的探测具有一定局限性。经过修正的风廓线雷达探测结果可以较好地反映实验区域大气边界层水平风场的垂直结构。     

风廓线雷达资料在台风苏拉登陆过程中的应用初探

为了研究风廓线雷达在台风天气过程预报中的作用,对2012年8月2—4日在福建秦屿镇登陆的台风苏拉天气过程统计分析,结果表明：风廓线雷达在台风苏拉登陆期间4 km以上高空有效数据获取率明显提高,确定风廓线雷达的有效探测高度为4.8 km;通过信噪比和垂直速度数据统计分析出台风登陆前后带来间歇性的降雨,而台风眼登陆主要表现为无降水天气,仅有少量的降雨,这一结论进一步在小时降雨量统计中得到验证;通过水平风速数据统计分析出台风登陆前后在有效探测高度内水平风速在25 m·s-1左右,而台风眼登陆水平风速在0~3 m·s-1; 统计结果与台风登陆物理过程相吻合。     

青藏高原东南缘低层风场垂直结构与变化特征北大核心CSCD

为进一步认识青藏高原山地低层风场特征、长期变化规律,利用2008-2012年青藏高原东南缘云南大理站边界层铁塔和风廓线雷达的长期观测资料,初步分析了该地区低层风场垂直结构及其变化特征。结果表明：（1）从地面到高空,风速、风向频率分布随高度的增加而变化,2~400m高度风速基本为2级,盛行风向为偏东风,这说明边界层铁塔和风廓线雷达的风速、风向具有连续性。（2）从垂直高度上看,风速存在明显季节变化特征,冬季风速较大,夏季风速较小;日变化结构随高度的升高表现形式明显不同,20m以下为单峰型,100~1500m为双峰型,2000m以上日变化不明显;平均风速逐月变化,20m以下为单峰型,100~1000m为双峰型,1500m以上为单峰型。（3）纬向风600m以下出现东西风交替的日变化,经向风在2~20m高度全天为南风,100m高度以上午后至日落为南风、其余时段为北风,南风由高空向低层传递。     

青藏高原东南缘低层风场垂直结构与变化特征

为进一步认识青藏高原山地低层风场特征、长期变化规律,利用2008-2012年青藏高原东南缘云南大理站边界层铁塔和风廓线雷达的长期观测资料,初步分析了该地区低层风场垂直结构及其变化特征。结果表明:(1)从地面到高空,风速、风向频率分布随高度的增加而变化,2~400m高度风速基本为2级,盛行风向为偏东风,这说明边界层铁塔和风廓线雷达的风速、风向具有连续性。(2)从垂直高度上看,风速存在明显季节变化特征,冬季风速较大,夏季风速较小;日变化结构随高度的升高表现形式明显不同,20m以下为单峰型,100~1500m为双峰型,2000m以上日变化不明显;平均风速逐月变化,20m以下为单峰型,100~1000m为双峰型,1500m以上为单峰型。(3)纬向风600m以下出现东西风交替的日变化,经向风在2~20m高度全天为南风,100m高度以上午后至日落为南风、其余时段为北风,南风由高空向低层传递。     

强热带风暴“凤凰”（1416）登陆浙江后风场变化特征

基于宁波多普勒雷达、浙江省自动气象站、宁波凉帽山高塔梯度观测等资料,对1416号强热带风暴“凤凰”登陆浙江后的风场时空变化进行分析。结果表明:“凤凰”结构不对称,8级以上风速带主要位于风暴中心前进方向的前侧和右侧。前侧最大风速半径一直维持在60 km左右,最大风速带宽度约为50 km;其右侧最大风速半径为80~120 km,随中心北移有增大趋势,最大风速带宽度约100 km;其前侧和右侧最大风速半径在垂直方向上变化不大。“凤凰”前侧TREC（Tracking Radar Echoes by Correlation）风速在1 km高度最强,其上则随高度的增大而减小,其右侧1~3 km高度TREC风速的垂直变化明显小于前侧。宁波凉帽山高塔处TREC风和梯度观测表明:“凤凰”影响期间,高塔上空159 m和2~4 km高度出现多个风速高值中心;常通量层高度约为159 m;常通量层内风廓线遵从对数率,当高塔位于“凤凰”右前侧时塔层阵风系数随高度增大而减小,当高塔位于“凤凰”中心附近和右后侧时阵风系数明显增大,且层次差异减小;常通量层以上159~318 m的塔层风廓线不满足指数率或对数率,阵风系数上下差异不大。      

"派比安"在阳江不同地区的风场特征及防风问题

利用阳江海岸线上不同下垫面梯度风观测塔在“派比安”过程中所取得的资料,探讨登陆热带气旋在不同下垫面的垂直风场特点以及防台措施。分析发现,平原地区各层风速较稳定,随“派比安”的移近而增大,远离而减小,风随高度成指数增长,在v<20 m/s时,80 m的10 m in平均风速与10 m的最大风速相当;背风面风速扰动大,很有可能在热带气旋靠近时出现风速减小现象;迎风坡出现大风时间长,最大风速比背风面和平原地区都大。迎风坡和背风面在台风环状下沉运动带影响时,高层和地面10 m in平均风速相差较小,而平原地区并没有这一特征。根据弗洛斯特(Frost)风速随高度变化的经验公式,近地层风速垂直切变指数n在平原地区稳定,风随高度的对应关系好。台风登陆前所有下垫面的n都出现突增现象。阵风系数受下垫面和周围环境影响大。     

2015年热带气旋“彩虹”的高分辨率数值模拟与风场诊断分析

利用WRF模式,对热带气旋“彩虹”（1522）登陆过程开展了高分辨率数值模拟,模拟验证表明:模式较成功地模拟出了“彩虹”的移动路径、强度变化和降水分布。利用高分辨率模拟资料,分析了“彩虹”登陆期间的大风分布以及热、动力结构特征,结合切向风动量方程开展了模拟诊断,结果表明:切向风动量方程各项在近地面层和边界层顶代表高度上的平面结构诊断分析显示,近地面（0.4 km）层上,VVOR（角动量径向平流项）和VPGF（切向气压梯度项）是切向风变化的最大贡献项;边界层顶（1.3 km）附近,VPGF和VVA（切向动量垂直平流项）对切向风起到正加速作用,而VVOR则根据入流（出流）特征,起到正（负）加速作用。切向风动量方程各项的轴对称平均结构诊断分析显示,“彩虹”登陆前,VVA和VVOR是决定切向风变化的主要贡献项。     

Dynamic Impact of the Vertical Shear of Gradient Wind on the Tropical Cyclone Boundary Layer Wind Field

This work studies the impact of the vertical shear of gradient wind （VSGW） in the free atmosphere on the tropical cyclone boundary layer （TCBL）. A new TCBL model is established, which relies on five- force balance including the pressure gradient force, Coriolis force, centrifugal force, turbulent friction, and inertial deviation force. This model is then employed to idealize tropical cyclones （TCs） produced by DeMaria＇s model, under different VSGW conditions （non-VSGW, positive VSGW, negative VSGW, and VSGW increase/decrease along the radial direction）. The results show that the free-atmosphere VSGW is particularly important to the intensity of TC. For negative VSGW, the total horizontal velocity in the TCBL is somewhat suppressed. However, with the maximum radial inflow displaced upward and outward, the radial velocity notably intensifies. Consequently, the convergence is enhanced throughout the TCBL, giving rise to a stronger vertical pumping at the TCBL top. In contrast, for positive VSGW, the radial inflow is significantly suppressed, even with divergent outflow in the middle-upper TCBL. For varying VSGW along the radial direction, the results indicate that the sign and value of VSGW is more important than its radial distribution, and the negative VSGW induces stronger convergence and Ekman pumping in the TCBL. which favors the formation and intensification of TC.     

Boundary-Layer Wind Structure in a Landfalling Tropical Cyclone

In this study, a slab boundary layer model with a constant depth is used to analyze the boundary-layer wind structure in a landfalling tropical cyclone. Asymmetry is found in both the tangential and radial components of horizontal wind in the tropical cyclone boundary layer at landfall. For a steady tropical cyclone on a straight coastline at landfall, the magnitude of the radial component is greater in the offshoreflow side and the tangential component is greater over the sea, slightly offshore, therefore the greater total wind speed occurs in the offshore-flow side over the sea. The budget analysis suggests that： （1） a greater surface friction over land produces a greater inflow and the nonlinear effect advects the maximum inflow downstream, and （2） a smaller surface friction over the sea makes the decrease of the tangential wind component less than that over land. Moreover, the boundary layer wind structures in a tropical cyclone are related to the locations of the tropical cyclone relative to the coastline due to the different surface frictions. During tropical cyclone landfall, the impact of rough terrain on the cyclone increases, so the magnitude of the radial component of wind speed increases in the offshore-flow side and the tangential component outside the radius of maximum wind speed decreases gradually.     

Effects of a Dry-Mass Conserving Dynamical Core on the Simulation of Tropical Cyclones

The accurate forecasting of tropical cyclones(TCs) is a challenging task. The purpose of this study was to investigate the effects of a dry-mass conserving(DMC) hydrostatic global spectral dynamical core on TC simulation. Experiments were conducted with DMC and total(moist) mass conserving(TMC) dynamical cores. The TC forecast performance was first evaluated considering 20 TCs in the West Pacific region observed during the 2020 typhoon season. The impacts of the DMC dynamical core on forecasts o...     

IMPACT OF SEA SPRAY ON TROPICAL CYCLONE STRUCTURE AND INTENSITY CHANGE

In this paper,the effects of sea spray on tropical cyclone(TC)structure and intensity variation are evaluated through numerical simulations using an advanced sea-spray parameterization from the National Oceanic and Atmospheric Administration/Earth System Research Laboratory(NOAA/ESRL),which is incorporated in the idealized Advanced Research version of the Weather Research and Forecast (WRF-ARW)model.The effect of sea spray on TC boundary-layer structure is also analyzed.The results show that there is a significant increase in TC intensity when its boundary-layer wind includes the radial and tangential winds,their structure change,and the total surface wind speed change.Diagnosis of the vorticity budget shows that an increase of convergence in TC boundary layer enhances TC vorticity due to the dynamic effect of sea spay.The main kinematic effect of the friction velocity reduction by sea spray produces an increment of large-scale convergence in the TC boundary layer,while the radial and tangential winds significantly increase with an increment of the horizontal gradient maximum of the radial wind, resulting in a final increase in the simulated TC intensity.The surface enthalpy flux enlarges TC intensity and reduces storm structure change to some degree,which results in a secondary thermodynamic impact on TC intensification.Implications of the new interpretation of sea-spray effects on TC intensification are also discussed.     

Insight into the Role of Lower-Layer Vertical Wind Shear in Tropical Cyclone Intensification over the Western North Pacific

Vertical wind shear fundamentally influences changes in tropical cyclone (TC) intensity. The effects of vertical wind shear on tropical cyclogenesis and evolution in the western North Pacific basin are not well understood. We present a new statistical study of all named TCs in this region during the period 2000-2006 using a second-generation partial least squares (PLS) regression technique. The results show that the lower-layer (between 850 hPa and 10 m above the sea surface) wind shear is more important than the commonly analyzed deep-layer shear (between 200 and 850 hPa) for changes in TC intensity during the TC intensification period. This relationship is particularly strong for westerly low-level shear. Downdrafts induced by the lower-layer shear bring low θ e air into the boundary layer from above, significantly reducing values of θ e in the TC inflow layer and weakening the TC. Large values of deep-layer shear over the ocean to the east of the Philippine Islands inhibit TC formation, while large values of lower-layer shear over the central and western North Pacific inhibit TC intensification. The critical value of deep-layer shear for TC formation is approximately 10 ms-1 , and the critical value of lower-layer shear for TC intensification is approximately ±1.5 ms-1 .     

Reexamination of the Relationship between Tropical Cyclone Size and Intensity over the Western North Pacific

This study reexamines the correlation between the size and intensity of tropical cyclones (TCs) over the western North Pacific from the perspective of individual TCs, rather than the previous large-sample framework mixing up all TC records. Statistics show that the positive size-intensity correlation based on individual TCs is relatively high. However, this correlation is obscured by mixing large samples. The weakened correlation based on all TC records is primarily due to the diversity in the size change relative to the same intensity change among TCs, which can be quantitatively measured by the linear regression coefficient (RC) of size against intensity. To further explore the factors that cause the variability in RCs that weakens the size-intensity correlation when considering all TC records, the TCs from 2001 to 2020 are classified into two groups according to their RC magnitudes, within which the high-RC TCs have a larger size expansion than the low-RC TCs given the same intensity change. Two key mechanisms responsible for the RC differences are proposed. First, the high-RC TCs are generally located at higher latitudes than the low-RC TCs, resulting in higher planetary vorticity and thus higher planetary angular momentum import at low levels. Second, the high-RC TCs are susceptible to stronger environmental vertical wind shear, leading to more prolific outer convection than the low-RC TCs. The positive feedback between outer diabatic heating and boundary layer inflow favors the inward import of absolute angular momentum in the outer region, thereby contributing to a larger size expansion in the high-RC TCs.     

登陆广东热带气旋特征及其与副热带高压的关系

2004年登陆广东的热带气旋只有2个,个数明显偏少,粤西无热带气旋登陆;登陆广东的初台偏迟,终台结束早,登陆时间集中于7月;热带气旋移速快,强度弱(为热带风暴),对广东影响利大于弊。对1951~2004年7~9月登陆广东的热带气旋进行统计分析,发现各月登陆广东的热带气旋次数差异较大,最多时一个月有5个,最少时没有。登陆广东的热带气旋个数与西北太平洋副热带高压位置、强度有密切关系,可以将有利于和不利于热带气旋登陆广东的副热带高压各分为3种环流形势。     

基于MTCSWA风场资料对西北太平洋热带气旋风场结构的气候统计特征研究

基于多平台热带气旋表面风场资料（MTCSWA）,研究了2007～2016年6～11月西北太平洋上不同尺度热带气旋（TC）的气候统计特征,TC各级风圈半径在不同象限的变化特征、风场结构的对称度及二者与强度变化之间的相关性。利用7级风圈半径与TC近中心最大持续风速（MSW）来定义TC的尺度和强度。结果表明,西北太平洋上TC的平均尺度为221.9 km,其中小TC平均尺度为96.4 km,大TC平均尺度为346.4 km。大TC活动位置的空间分布较小TC更为集中,整体活动范围较小TC偏北。TC尺度的峰值出现在8月和10月。在TC的风场结构中,7级、10级、12级风圈的平均半径分别为221.9、121.0、77.4 km。TC风圈的对称度的统计结果表明7级风圈的对称度最低,12级风圈的对称度最高。相关分析表明,在TC的生命史中,各级风圈半径与其强度存在一定的正相关关系,其中12级风圈半径与强度的相关性最低;对于同一风圈而言,在TC的不同发展阶段中,不同象限的风圈半径与强度的相关性不同。在TC的风场结构中,风圈的对称度与TC强度的相关性随着风圈强度的增强而减弱,只有7级风圈的对称度在TC的整个生命周期中表现出与TC强度之间的弱的正相关关系。     

沿海风工程设计风速中泊松-耿贝尔法的应用

每年西北太平洋热带气旋(TC)发生的次数、移动路径和强度都是随机的,我国东南沿海各地每年受TC影响的次数便构成了某种离散型分布,而TC影响下的最大风速则可以构成某种连续型分布。该文采用上海台风研究所提供的1961—2006年TC中心风速和TC影响期间各台站大风资料,利用泊松-耿贝尔联合极值风速计算方法,计算了沿海各气象站TC影响大风的多年一遇风工程设计最大风速。结果表明:当观测资料样本序列较短,特别是像TC这样随机性很强的天气事件,泊松-耿贝尔联合极值算法更具优势;我国沿海地区有53.9%的台站50年一遇最大风速在25 m/s以下,最大风速大于42.5 m/s以上的台站分布于浙江的大陈岛、嵊山、石浦,福建的北茭和台山,广东的遮浪、上川岛和海南的西沙岛,在这些地区进行风电开发风险较大,应引起足够重视。     

Sensitivity of tropical cyclone intensity and structure to vertical resolution in WRF

In this paper the impacts of vertical resolution on the simulations of Typhoon Talim (2005) are examined using the Weather Research and Forecasting (WRF) model, with cumulus parameterization scheme representing the cumulus convection implicitly. It is shown that the tropical cyclone (TC) track has little sensitivity to vertical resolution, whereas the TC intensity and structure are highly sensitive to vertical resolution. It is partly determined by the sensitivity of the planetary boundary layer (and the surface layer) and the cumulus convection processes to vertical resolution. Increasing vertical resolution in the lower layer could strengthen the TC effectively. Increasing vertical resolution in the upper layer is also beneficial for the storm intensification, but to a lesser degree. In contrast, improving the midlevel resolution may cause the convergence of environmental air, which inhibits the TC intensification. The results also show that the impacts of vertical resolution on features of the TC structure, such as the tangential winds, secondary circulations and the evolution of the warm-core structure, are consistent with the impacts on the TC intensity. It is suggested that in the simulations of TCs, the vertical levels should be distributed properly rather than the more the better, with higher vertical resolution being expected both in the lower and upper layer, while the middle layer should not hold too many levels.