Using real-time correction technology for typhoons, this paper discusses real-time correction for forecasting the track of four typhoons during 2009 and 2010 in Japan, Beijing, Guangzhou, and Shanghai. It was determined that the short-time forecast effect was better than the original objective mode. By selecting four types of integration schemes after multiple mode path integration for those four objective modes, the forecast effect of the multi-mode path integration is better, on average, than any single model. Moreover, multi-mode ensemble forecasting has obvious advantages during the initial 36 h.
Forecasts of tropical cyclone(TC)tracks from six global models during 2010 and 2012 were assessed to study the current capability of track forecast guidance over the western North Pacific.To measure the performance of the global model forecasts,a series of statistical evaluations of track forecasts up to 120 h were carried out,including the mean,median,percentile distribution,regional distribution,relative position,correlation analysis,and binned analysis.Results showed that certain improvements have been made for the six global models in their prediction accuracy and stability in the past three years.Remarkably,stepped decreases in the values of each quantile were found at all lead time levels from 2010 to 2012 for NCEP-GFS.An analysis of the regional distribution of position errors showed that a high-latitude region,low-latitude region(which covers mostly the TC genesis region)and the South China Sea are the three main areas within which large errors tend to concentrate.The majority of the models show their own respective characteristics of systematic bias at each lead time,as established through the relative position analysis results.Only the results of NCEP-GFS and CMA-T639 did not show any obvious systematic bias in the three-year study period.Binned analyses indicated that the prediction accuracy and stability of most of the models were better for strong TCs than for weak TCs at short lead time levels.It was also found that the models tend to perform better for initially large TCs,or for those with weak vertical wind shear at lead times shorter than 48 h.The results demonstrate the heavy reliance of forecast errors upon the initial characteristics of a TC or its environmental conditions.
基于CWRF模式(Climate Extension of Weather Research and Forecast Model)结果,探讨了8种云微物理参数化方案对1986—2015年间东亚近海热带气旋的空间分布、频数及强度模拟的影响。结果发现:CWRF模式中各云微物理参数化方案模拟的热带气旋频数普遍较观测偏少,其模拟的强度相比观测也偏弱;热带气旋的空间分布和频数对云微物理参数化方案的选择较为敏感,而云微物理方案的选择对热带气旋强度的模拟影响不大;Morrison方案和Morrison-a方案模拟的热带气旋空间分布更接近于观测,但对热带气旋频数及强度的年际变化趋势模拟得较差,而GSFCGCE方案的TS评分及强度、频数的相关系数均较其他方案偏高。综合来看,采用GSFCGCE方案模拟热带气旋活动总体最优。进一步分析发现,相较于Morrison方案和Thompson方案,考虑气溶胶影响的Thompson-a和Morrison-a方案不仅可以有效提高对热带气旋频数及空间分布的模拟能力,还对热带气旋频数及强度年际变化趋势的模拟能力也有所提升。
The mean kinematic and thermodynamic structures of tropical cyclones(TCs) making landfall in China's Mainland are examined by using sounding data from 1998 to 2009. It is found that TC landfall is usually accompanied with a decrease in low-level wind speed, an expansion of the radius of strong wind, weakening of the upper-level warm core, and drying of the mid-tropospheric air. On average, the warm core of the TCs dissipates 24 h after landfall. The height of the maximum low-level wind and the base of the stable layer both increase with the increased distance to the TC center; however, the former is always higher than the latter. In particular, an asymmetric structure of the TC after landfall is found. The kinematic and thermodynamic structures across various areas of TC circulation differ, especially over the left-front and right-rear quadrants(relative to the direction of TC motion). In the left-front quadrant, strong winds locate at a smaller radius, the upper-level temperature is warmer with the warm core extending into a deep layer,while the wet air occupies a shallow layer. In the right-rear quadrant, strong wind and wet air dwell in an area that is broader and deeper, and the warmest air is situated farther away from the TC center.
We use the WRF(V3.4) model as the experimental model and select three horizontal resolutions of 15, 9,and 3 km to research the influence of the model's horizontal resolution on the intensity and structure of the super-strong typhoon Rammasun(1409) in 2014. The results indicate that the horizontal resolution has a very large impact on the intensity and structure of Rammasun. The Rammasun intensity increases as the horizontal resolution increases. When the horizontal resolution increases from 9 km to 3 km, the enhancement of intensity is more obvious, but the strongest intensity simulated by 3 km horizontal resolution is still weaker than the observed strongest intensity. Along with the increase of horizontal resolution, the horizontal scale of the Rammasun vortex decreases, and the vortex gradually contracts toward its center. The vortex structure changes from loose to compact and deep. The maximum wind radius,thickness of the eye wall, and outward inclination of the eye wall with height decrease, and the wind in the inner core region, updraft motion along the eye wall, and strength of the warm core become stronger. Additionally, the pressure gradient and temperature gradient of the eye wall region increase, and the vortex intensity becomes stronger. When the horizontal resolution increases from 9 km to 3 km, the change in the Rammasun structure is much larger than the change when the horizontal resolution increases from 15 km to 9 km. When the model does not employ the method of convection parameterization, the Rammasun intensity simulated with 3 km horizontal resolution is slightly weaker than the intensity simulated with 3 km horizontal resolution when the Kain-Fritsch(KF) convection parameterization scheme is adopted, while the intensity simulated with 9 km horizontal resolution is much weaker than the intensity simulated with 9 km horizontal resolution when the KF scheme is adopted. The influence of the horizontal resolution on the intensity and structure of Rammasun is larger than the influence when the KF s
利用WRF(Weather Research and Forecasting)模式,在理想岛屿地形条件下设计了云的微物理冰相过程中水凝物中有霰和无霰的两个对比试验,考察了台风登陆时复杂冰相和简单冰相对台风移动路径、强度和降水增幅的影响。结果表明:1)云微物理过程中有霰的复杂冰相过程时,具有更强烈的云“播撒”效应,因而对台风降水具有明显增幅作用。2)当台风受到理想地形作用时,地形对云“播撒”效应引起的增幅作用具有放大作用,此时台风眼墙非绝热加热量形成明显增强中心,使得台风降水增幅明显。3)当台风登陆时,云微物理冰相过程使得台风越山时存在向西北指向的涡度变化倾向。
Tropical cyclones(TCs)forecasts from seven global models in 2013 were assessed to study the current capability of track and intensity forecast guidance over the western North Pacific.Analysis of along-and cross-track error revealed stepped decreases in the values of each quantile at each lead time level by showing the annual track error distribution from 2010 to 2013,particularly in the ECMWF-IFS,NCEP-GFS and UKMO-Met UM models.The TC propagation direction was much easier to handle for most of the global models;however,the propagation speed seemed to be more closely linked to the inner-core dynamics and thus processes that take place at smaller spatial scales.A new model evaluation tool,‘track error rose’,was used to analyze the models’systematic error in the track forecast using the same concepts as the‘wind rose’.The results showed that as the lead time increased,most of the global models forecast a TC moving speed that was slower than observations and the largest track error often appeared around the rear direction of the observation position.Another new model evaluation tool,the Taylor diagram,was used to evaluate the intensity predictions from the global models.A Taylor diagram provides a way of plotting standard deviation,centered root mean square,and the correlation coefficient on a two-dimensional graph,indicating how closely a predicted TC intensity matches observations.This made it easy to distinguish the intensity forecast performance of the seven global models and determine which models were in relatively good agreement with observations.Furthermore,it also provided a statistical measure of the correlation between modeled and observed TC intensity,offering a practical way of assessing and summarizing model capability.
In daily typhoon operation, identifying the intensity of typhoons is always a contentious problem, which can be attributed to the absence of direct observational data when typhoons are present on the ocean. When typhoons move to the offshore region, where many automatic weather stations(AWSs) are present, utilizing automatic observations in non-standard conditions is a good way of identifying the intensity or wind of a typhoon. Before identification, AWS data should be conversed or revised based on statistical experiences from a multilayer wind tower. In this study, the intensity of Haikui(1211) at the landing stage(from 08071200 UTC to 08071920 UTC) is revised carefully. Calculating the wind conversion coefficient between different heights from a 300 m multilayer tower observation, the wind data caught by two offshore AWSs were converted to the standard wind of 10 meters and used to identify the intensity of the landing Haikui. The maximum surface wind of Haikui in the landing period was about 45 m/s to 48 m/s and then reduced to 40 m/s to 42 m/s approximately just before landing.On the basis of the discussion in this study, the AWS data in a non-standard environment can be utilized to determine the surface wind at 10 m height by arithmetic conversion. This implies that we should pay more attention and patient to the wind data observed in offshore island AWSs during typhoon identification.
The operational track and intensity forecast errors of tropical cyclones(TCs) over the western North Pacific in 2015 were evaluated on the basis of RSMC-Tokyo's "best-track" dataset. The results showed that position errors for each official agency were under 80 km, 130 km, 180 km, 260 km and 370 km at 24, 48, 72, 96 and 120 hr lead time. Stepped decreases in the values of each quantile were made at every lead times and have been made by global models from 2010 to 2015, especially for long lead time. The results of the Track Forecast Integral Deviation(TFID) show a clearly decreasing trend for most global models, indicating that the TC forecast tracks became increasingly similar to the observations. In 2015, the intensity forecast skill scores for both global and regional models were almost negative. However, the skill of EPSs' intensity forecasting has made significant progress in the past year.
Guomin ChenXiaotu LEIXiping ZHANGPeiyan CHENHui YURijin WAN
