Impacts of Horizontal and Vertical Resolutions on the Microphysical Structure and Boundary Layer Fluxes of Typhoon Hato(2017)

We set four sets of simulation experiments to explore the impacts of horizontal resolution(HR) and vertical resolution(VR) on the microphysical structure and boundary layer fluxes of tropical cyclone(TC) Hato(2017). The study shows that higher HR tends to strengthen TC. Increasing VR in the upper layers tends to weaken TC, while increasing VR in the lower layers tends to strengthen TC. Simulated amounts of all hydrometeors were larger with higher HR. Increasing VR at the upper level enhanced the mixing ratios of cloud ice and cloud snow,while increasing VR at the lower level elevated the mixing ratios of graupel and rainwater. HR has greater impact on the distributions of hydrometeors. Higher HR has a more complete ring structure of the eyewall and more concentrated hydrometeors along the cloud wall. Increasing VR at the lower level has little impact on the distribution of TC hydrometeors, while increasing VR at the upper level enhances the cloud thickness of the eyewall area.Surface latent heat flux(SLHF) is influenced greatly by resolution. Higher HR leads to larger water vapor fluxes and larger latent heat, which would result in a stronger TC. A large amount of false latent heat was generated when HR was too high, leading to an extremely strong TC, VR has a smaller impact on SLHF than HR. But increasing VR at the upper-level reduces the SLHF and weakens TC, and elevating VR at the lower-level increases the SLHF and strengthens TC. The changes in surface water vapor flux and SLHF were practically identical and the simulation results were improved when HR and VR were more coordinated. The friction velocity was greater with higher VR.Enhancing VR at the lower level increased the friction velocity, while increasing VR at the upper level reduced it.     

WRF模式不同云微物理参数化方案及水平分辨率对降水预报效果的影响

利用WRF模式和GFS资料对一次大尺度天气系统作用下的暴雨过程进行了回报,分析了WRF模式不同降水方案和3种不同的水平分辨率（45km,15km和5km）对降水预报效果的影响。结果表明：①对于大尺度强迫作用较强的暴雨,尤其是层状云降水为主的暴雨,云微物理过程方案对降水的影响远大于积云参数化方案对降水的影响。②WRF模式不同的微物理过程方案对各等级降水量的预报效果差别较大。其中Kessler方案的TS评分明显随降水量级的增加而减小,其他6个方案的TS评分都呈现＂两头大,中间小＂的特点,即小雨和暴雨的TS评分较高,而中雨和大雨的TS评分较低。③对于小雨量级的降水,Lin方案的预报效果最好;对于中雨和大雨量级的降水,WSM 3方案的预报效果最好;对于暴雨量级的降水,WSM 5方案的预报效果最好;整体预报效果最好的是WSM 3方案,其次是WSM 5方案,Kessler方案最差。④WRF模式的降水预报效果并不总是随水平分辨率的提高而提高。模式水平分辨率的提高存在明显的阈值（15km左右）,当模式的水平分辨率提高到超过这一阈值以后,预报效果开始转差。     

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.     

Impacts of Randomly Distributed Small-Scale Vortices on Typhoon Tracks

Impacts of small-scale vortices on typhoon or tropical cyclone(TC) tracks in a system of three components (an idealized subtropical high ridge,a TC,and small-scale vortices) were examined numerically using a barotropic primitive equation model and idealized initial fields.Two small-scale vorticity fields were generated stochastically,where the number of initial small-scale vortices is 100.In the two fields,the number, size,structure as well as the total kinetic energy of the small-scale vortices were all...     

WRF模式分辨率对新疆异常降雨天气要素模拟的影响

利用新一代中尺度气候数值模式WRF对中国西北干旱典型地区——新疆2000年10月的异常降雨事件进行模拟,主要研究了不同水平分辨率、垂直分辨率以及不同积云参数化过程对气温、降雨和土壤温度模拟的影响。结果表明：不同分辨率的模拟基本上均模拟出了地面气温的分布特征,且随着水平分辨率的提高,模式模拟能力显著提高,对地面气温值、分布范围的模拟渐趋合理,同时模式对于地形引起的温度分布变化的模拟更加趋近实际。水平分辨率、垂直分辨率的提高同样改善了模式对降水的模拟能力,分辨率的提高不仅改进了模式对降雨分布区模拟的精度,也增强了对于地形引起的降雨变异的模拟能力。在土壤温度模拟上,不同分辨率的试验均能模拟出土壤温度的分布特征,较高水平分辨率有利于描述土壤温度分布细节,但更容易出现“数值点风暴”现象。     

对流非对称台风\

2020年第7号台风“海高斯”在广东省造成大风、暴雨灾害,细致研究其多尺度能量分布及转化特征有助于更好地认识和防御类似的台风灾害。运用WRF模式对台风“海高斯”进行了数值模拟,使用Barnes滤波方法将模拟结果分离为大尺度背景场（> 2 000 km）、α中尺度系统（200~2 000 km）、β中小尺度系统（< 200 km）等三个尺度分量,分别计算三个尺度动能、有效位能的分布及变化。结果表明：（1）台风“海高斯”活跃期内,大尺度背景场动能先增加后稳定,α中尺度动能先增加后减少,β中小尺度动能变化不明显。动能的主要来源是有效位能的转化及气压梯度力做功,主要去向是水平输送及跨尺度转化。三种尺度动能主要分布于对流层低层。（2）大尺度背景场有效位能有两次先增加后减少的过程,α中尺度和β中小尺度有效位能先增加后减少。有效位能的主要来源是非绝热加热,主要去向是转化为动能和水平输送及跨尺度转化。三种尺度有效位能主要分布于对流层高层。（3）台风“海高斯”能量转化区域主要为距台风中心200 km以内台风眼壁及中心密集云盖区域对流层上层、距台风中心200—700 km台风外围区域对流层上层、距台风中心400 km以内对流层低层。

     

Impacts of a Large-scale Adaptive Blending Scheme for CMA-MESO on Regional Forecasts-A Case Study of Typhoon Haima

Large-scale atmospheric information plays an important role in the regional model for the forecasts of weather such as tropical cyclone (TC). However, it is difficult to be fully represented in regional models due to domain size and a lack of observation data, particularly at sea used in regional data assimilation. Blending analysis has been developed and implemented in regional models to reintroduce large-scale information from global model to regional analysis. Research of the impact of this large-scale blending scheme for the Global / Regional Assimilation and PrEdiction System (CMA-MESO) regional model on TC forecasting is limited and this study attempts to further progress by examining the adaptivity of the blending scheme using the two-dimensional Discrete Cosine Transform (2D-DCT) filter on the model forecast of Typhoon Haima over Shenzhen, China in 2016 and considering various cut-off wavelengths. Results showed that the error of the 24-hour typhoon track forecast can be reduced to less than 25 km by applying the scale-dependent blending scheme, indicating that the blending analysis is effectively able to minimise the large-scale bias for the initial fields. The improvement of the wind forecast is more evident for u-wind component according to the reduced root mean square errors (RMSEs) by comparing the experiments with and without blending analysis. Furthermore, the higher equitable threat score (ETS) provided implications that the precipitation prediction skills were increased in the 24h forecast by improving the representation of the large-scale feature in the CMA-MESO analysis. Furthermore, significant differences of the track error forecast were found by applying the blending analysis with different cut-off wavelengths from 400 km to 1200 km and the track error can be reduced less than by 10 km with 400 km cut-off wavelength in the first 6h forecast. It highlighted that the blending scheme with dynamic cut-off wavelengths adapted to the development of different TC systems is necessary in order to optimally introduce and ingest the large-scale information from global model to the regional model for improving the TC forecast. In this paper, the methods and data applied in this study will be firstly introduced, before discussion of the results regarding the performance of the blending analysis and its impacts on the wind and precipitation forecast correspondingly, followed by the discussion of the effects of different blending scheme on TC forecasts and the conclusion section.     

大涡模式水平分辨率对边界层夹卷过程及示踪物垂直传输的影响

利用敦煌干旱区野外加密观测资料,结合大涡模式模拟研究模式水平分辨率对边界层对流、夹卷过程及示踪物垂直传输的影响。结果表明:模式水平分辨率越高,模拟的边界层对流泡个数越多,尺度越小,且对流强度越强;提高模式水平分辨率,夹卷层位温方差增大,水平速度方差减小,垂直速度方差增大,且上升冷气流对夹卷层热通量的贡献最大。模式水平分辨率越高,垂直速度、位温及示踪物绝对质量浓度概率密度函数分布变化范围相对越广,且模拟的细微变化特征越清晰。另外,提高模式水平分辨率,模拟的示踪物空间分布特征更加细致,示踪物传输高度也较高。综合考虑到分辨率越高在模拟过程中产生的噪音越大且计算时间越久等问题,认为采用200 m水平分辨率时,模式既能较好地模拟出边界层对流的平均结构,又能模拟出边界层湍流的较细微分布特征,是较为理想的选择。     

The Uncertainty of Tropical Cyclone Intensity and Structure Based on Different Parameterization Schemes of Planetary Boundary Layer

Based on different parameterization schemes of planetary boundary layer (PBL), the uncertainty of intensity and structure of the Super-strong Typhoon Rammasun (1409) is investigated using the WRF model (v3.4) with six PBL parameterization schemes. Results indicate that PBL uncertainty leads to the uncertainty in tropical cyclone (TC) prediction, which increases with forecast time. The uncertainty in TC prediction is mainly reflected in the uncertainty in TC intensity, with significant differences in the TC intensity forecasts using various PBL schemes. The uncertainty in TC prediction is also reflected in the uncertainty in TC structures. Greater intensity is accompanied by smaller vortex width, tighter vortex structure, stronger wind in the near-surface layer and middle and lower troposphere, stronger inflow (outflow) wind at the lower (upper) levels, stronger vertical upward wind, smaller thickness of the eye wall, smaller outward extension of the eye wall, and warmer warm core at the upper levels of eye. PBL height, surface upward heat flux and water vapor flux are important factors that cause the uncertainty in TC intensity and structure. The more surface upward heat flux and water vapor flux and the lower PBL height, the faster TC development and the stronger TC intensity.     

Effects of Microphysical Latent Heating on the Rapid Intensification of Typhoon Hato(2017)

A 72-h cloud-resolving numerical simulation of Typhoon Hato(2017)is performed by using the Weather Research and Forecasting(WRF)model with the Advanced Research WRF(ARW)core(V3.8.1)on a horizontal resolution of2 km.To enhance the background tropical cyclone structure and intensity,a vortex dynamic initialization scheme with a terrain-filtering algorithm is utilized.The model reproduces reasonably well the track,structure,and intensity change of Typhoon Hato.More specifically,the change trend of simulated maximum wind speed is consistent with that of best-track analysis,and the simulated maximum wind of 49 ms^-1 is close to that(52 ms^-1)of the best-track analysis,indicating that the model has successfully captured the rapid intensification(RI)of Typhoon Hato(2017).Analyses of the model outputs reveal that the total microphysical latent heating of the inner-core region associated with enhanced vertical upward motion reaches its maximum at 9-km height in the upper troposphere during the RI stage.The dominant microphysical processes with positive latent heat contributions(i.e.,heating effect)are water vapor condensation into cloud water(67.6%),depositional growth of ice(12.9%),and generation(nucleation)of ice from vapor(7.9%).Those with negative latent heat contributions(cooling effect)are evaporation of rain(47.6%),melting of snow(27.7%),and melting of graupel(9.8%).Sensitivity experiments further show that the intensification speed and peak intensity of this typhoon are highly correlated to the dominant heating effect.A significant increase in graupel over 5-10-km height and snow at 10-14-km height in the inner-core region of Typhoon Hato corresponds well with its RI stage,and the latent heating from nucleation and depositional growth is crucial to the RI of simulated Hato.     

边缘区域扰动演变对台风结构的影响

在台风环流边缘区域给出不稳定模态的扰动四波分布作为初始场，用准地转正压模式实施四组数值积分，研究了边缘区域扰动演变及其对台风非对称结构及外区流型的影响。结果表明:线性平流对于外缘区域扰动的发展起主要作用。β项导致一个气旋—反气旋涡旋对和非对称结构的形成。非线性平流则使外缘区域较小尺度的涡旋破碎，形成更小尺度的涡旋。在线性平流、β项和非线性平流的共同作用下，台风结构与外区形成象螺旋云系的分布。外缘区域扰动引起的结构变化，进而能影响到台风的移动路径。     

Systematic Vertical Variation of Mesoscale Fluxes in the Nocturnal Boundary Layer

The vertical mesoscale flux in the nocturnal boundary layer is generally considered to be difficult to estimate because of the small mesoscale vertical velocities and the large random variation of the mesoscale fluxes. However, the mesoscale vertical flux of heat, computed from FLOSSII data, varies quasi-systematically with height, stability and time scale. Such systematic variation requires correction for sonic misalignment and averaging over a large quantity of data. The relation of the mesoscale heat flux to the vertical structure of the nocturnal boundary layer is examined. For the most common conditions, the vertical convergence of the mesoscale heat flux acts to reduce the nocturnal cooling rate. Important uncertainties are discussed as well as the need for improved observations.     

Precipitation Microphysical Characteristics of Typhoon Ewiniar (2018) before and after Its Final Landfall over Southern China

In this paper, the evolution of the microphysical characteristics in different regions(eyewall, inner core, and outer rainbands) and different quadrants [downshear left(DL), downshear right(DR), upshear left(UL), and upshear right(UR)]during the final landfall of Typhoon Ewiniar(2018) is analyzed using two-dimensional video disdrometer and S-band polarimetric radar data collected in Guangdong, China. Due to the different types of underlying surfaces, the periods before landfall(mainly dominated ...     

Numerical Study on the Impacts of the Bogus Data Assimilation and Sea Spray Parameterization on Typhoon Ducts

The Weather Research and Forecasting model version 3.2 (WRF v3.2) was used with the bogus data assimilation (BDA) scheme and sea spray parameterization (SSP), and experiments were conducted to assess the impacts of the BDA and SSP on prediction of the typhoon ducting process induced by Typhoon Mindule (2004). The global positioning system (GPS) dropsonde observations were used for comparison. The results show that typhoon ducts are likely to form in every direction around the typhoon center, with the main type of ducts being elevated duct. With the BDA scheme included in the model initialization, the model has a better performance in predicting the existence, distribution, and strength of typhoon ducts. This improvement is attributed to the positive effect of the BDA scheme on the typhoon’s ambient boundary layer structure. Sea spray affects typhoon ducts mainly by changing the latent heat (LH) flux at the air-sea interface beyond 270 km from the typhoon center. The strength of the typhoon duct is enhanced when the boundary layer under this duct is cooled and moistened by the sea spray; otherwise, the typhoon duct is weakened. The sea spray induced changes in the air-sea sensible heat (SH) flux and LH flux are concentrated in the maximum wind speed area near the typhoon center, and the changes are significantly weakened with the increase of the radial range.     

数值模式垂直分辨率对台风大涡模拟的影响

随着计算能力的提升,台风数值模拟大量采用了大涡尺度模拟,其水平分辨率已达到数10 m的量级,而垂直分辨率提升不大,其问题是数值模式的垂直分辨率对台风大涡模拟的影响如何?因此,本文利用WRF(Weather Research and Forecasting)模式开展理想台风模拟,在不同的模式垂直层次(42,69和90层)...     

Evaluation of the Ocean Feedback on Height Characteristics of the Tropical Cyclone Boundary Layer

In this study, the interaction between the tropical cyclone（TC） and the underlying ocean is reproduced by using a coupled atmosphere-ocean model. Based on the simulation results, characteristics of the TC boundary layer depth are investigated in terms of three commonly used definitions, i.e., the height of the mixed layer depth（HVTH）, the height of the maximum tangential winds（HTAN）, and the inflow layer depth（HRAD）. The symmetric height of the boundary layer is shown to be cut down by the ocean response, with the decrease of HVTH slightly smaller than that of HTAN and HRAD. The ocean feedback also leads to evident changes in asymmetric features of the boundary layer depth. The HVTH in the right rear of the TC is significantly diminished due to presence of the cold wake, while the changes of HVTH in other regions are rather small. The decreased surface virtual potential temperature by the cold wake is identified to be dominant in the asymmetric changes in HVTH. The impacts of ocean response on the asymmetric distributions of HTAN are nonetheless not distinct, which is attributed to the highly axisymmetric property of tangential winds. The HRAD possesses remarkable asymmetric features and the inflow layer does not exist in all regions, an indication of the inadequacy of the definition based on symmetric inflow layer depth. Under influences of the cold wake, the peak inflow area rotates counterclockwise distinctly. As a consequence, the HRAD becomes deeper in the east while shallower in the west of the TC.     

地形和边界层摩擦对登陆热带气旋路径和强度影响的研究

采用准地转的正压模式, 研究了无非绝热加热时地形和边界层摩擦对登陆热带气旋路径和强度的影响.结果表明: 地形作用对登陆热带气旋西北移动路径的影响比较明显, 而对登陆热带气旋强度的影响不明显; 边界层摩擦可以通过改变热带气旋X方向上和Y方向上的移动速度以及改变热带气旋水平环流结构对登陆热带气旋西北移动路径产生一定的影响, 边界层摩擦对登陆热带气旋强度的影响非常明显, 其中摩擦是造成登陆热带气旋强度迅速减弱的一个重要因素.     

A Statistical Analysis on the E ect of Vertical Wind Shear on Tropical Cyclone Development

Using tropical cyclone (TC) best track and intensity of the western North Pacific data from the Joint TyphoonWarning Center (JTWC) of the United States and the NCEP/NCAR reanalysis data for the period of 1992-2002, the effects of vertical wind shear on TC intensity are examined. The samples were limited to the westward or northwestward moving TCs between 5°N and 20°N in order to minimize thermodynamic effects. It is found that the effect of vertical wind shear between 200 and 500 hPa on TC intensity change is larger than that of the shear between 500 and 850 hPa, while similar to that of the shear between 200 and 850 hPa. Vertical wind shear may have a threshold value, which tends to decrease as TC intensifies. As the intensifying rate of TC weakens, the average shear increases. The large shear has the obvious trend of inhibiting TC development. The average shear of TC which can develop into typhoon (tropical depression or tropical storm) is below 7 m s-1 (above 8 m s-1).     

Effects of Microphysical Latent Heating on the Rapid Intensification of Typhoon Hato (2017)

Journal of Meteorological Research - A 72-h cloud-resolving numerical simulation of Typhoon Hato (2017) is performed by using the Weather Research and Forecasting (WRF) model with the Advanced...     

A Statistical Analysis on the Effect of Vertical Wind Shear on Tropical Cyclone Development

Using tropical cyclone (TC) best track and intensity of the western North Pacific data from the Joint Typhoon Warning Center (JTWC) of the United States and the NCEP/NCAR reanalysis data for the period of 1992-2002, the effects of vertical wind shear on TC intensity are examined. The samples were limited to the westward or northwestward moving TCs between 5°N and 20°N in order to minimize thermodynamic effects. It is found that the effect of vertical wind shear between 200 and 500 hPa on TC intensity change is larger than that of the shear between 500 and 850 hPa, while similar to that of the shear between 200 and 850 hPa. Vertical wind shear may have a threshold value, which tends to decrease as TC intensifies. As the intensifying rate of TC weakens, the average shear increases. The large shear has the obvious trend of inhibiting TC development. The average shear of TC which can develop into typhoon (tropical depression or tropical storm) is below 7 m s-1 (above 8 m s-1).