2017 Vol. 23, No. 3

THE INFLUENCE OF INHOMOGENEOUS WIND DISTRIBUTION ON DATA QUALITY FOR WIND PROFILING RADAR
RUAN Zheng, LIU Rui-ting, GAO Zhu-yu, GE Run-sheng
2017, 23(3): 237-244. doi: 10.16555/j.1006-8775.2017.03.001
Abstract:
Horizontal wind measured by wind profiling radar (WPR) is based on uniform wind assumption in volume of lateral beam. However, this assumption cannot completely meet in the real atmosphere. The subject of this work is to analyze the influence of atmospheric inhomogeneities for wind measurement. Five-beam WPR can measure two groups of horizontal wind components U and V independently, using the difference of horizontal wind components U and V can evaluate the influence of the inhomogeneity of the atmospheric motion on wind measurement. The influences can be divided into both inhomogeneous distribution of horizontal motion and vertical motion. Based on wind measurements and meteorological background information, a new means of coordinate rotation the two kinds of inhomogeneous factor was separated, and the impact in different weather background was discussed. From analysis of the wind measured by type of PB-II WPR (445MHz) during 2012 at Yanqing of Beijing, it is shown that the inhomogeneity of horizontal motion is nearly the same in U and V direction. Both the inhomogeneities of horizontal motion and vertical motion have influence on wind measurement, and the degrees of both influences are associated with changes of wind speed. In clear air, inhomogeneity of horizontal motion is the main influence on wind measurement because of small vertical velocity. In precipitation, the two influences are larger than that in clear air.
STRUCTURE FEATURES AND COMPOSITE ANALYSIS OF CONVECTIVE CELLS IN A WARM SECTOR HEAVY RAINFALL EVENT OVER SOUTHERN CHINA
QIAN Lei, DING Zhi-ying, ZHAO Xiang-jun, XIA Fan
2017, 23(3): 245-258. doi: 10.16555/j.1006-8775.2017.03.002
Abstract:
This paper uses the ARW-WRF model to carry out a numerical simulation of a warm-sector heavy rainfall event over southern China on the 22–C23 May, 2014. A composite analysis method was used to analyze the evolution process and structural features of the convective cells on a convection line during this rainfall event. This analysis identified three stages: (1) Stage of activation: the equivalent potential temperature surfaces as lower layers start to bulge and form warm cells and weak vertical convective cloud towers which are subject to the impact of low-level warm moist updrafts in the rainfall sector; (2) Stage of development: the warm cells continue to bulge and form warm air columns and the convective cloud towers develop upwards becoming stronger as they rise; (3) Stage of maturity: the warm air columns start to connect with the stable layer in the upper air; the convective cloud tower will bend and tilt westward with each increasing in height, and the convection cell is characterized by a “crescent-shaped echo” above the 700hPa plane. During this stage the internal temperature of the cell is higher than the ambient temperature and the dynamic structural field is manifested as intensive vertical upward movement. The large-value centers of the northerly and westerly winds in the middle layer correspond to the warm moist center in the cells and the relatively cold center south of the warm air column. Further analysis shows that the formation of the “crescent-shaped” convective cell is associated with horizontal vorticity. Horizontal vorticity in the center and west of the warm cell experiences stronger cyclonic and anticyclonic shear transformation over time; this not only causes the original suborbicular cell echo shape to develop into a crescent-like shape, but also makes a convection line consisting of cells that develop to the northwest.
A MODELING STUDY OF PARAMETERIZATION SCHEMES FOR DEPOSITIONAL GROWTH OF ICE CRYSTAL: FOUR RAINFALL CASES OVER TROPICS AND MIDLATITUDES
XIN Jin, LI Xiao-fan
2017, 23(3): 259-268. doi: 10.16555/j.1006-8775.2017.03.003
Abstract:
Depositional growth of ice crystal is one of the major processes for development of precipitation systems and can be represented by depositional growth of cloud ice from cloud water (PIDW) and depositional growth of snow from cloud ice (PSFI) in cloud-resolving model. Four parameterization schemes are analyzed in the cloud-resolving model simulations of four rainfall cases over the tropics and midlatitudes. The comparison of time and model domain mean data shows that Shen’s scheme produces the closest rainfall simulation to the observation. Compared to Zeng’s scheme, Shen’s scheme improves the mean rain-rate simulation significantly through the dramatic decrease in depositional growth of cloud ice from cloud water. Compared to other schemes, Shen’s scheme produces the better rainfall simulation via the reduction in the mean rain rate associated with the enhanced gain of cloud water and ice.
NUMERICAL SIMULATION STUDY ON THE RAPID INTENSIFICATION OF TYPHOON HAIKUI (1211) OFF THE SHORE OF CHINA
ZHANG Sheng-jun, QIAN Yan-zhen, HUANG Yi-wu, GUO Jian-min
2017, 23(3): 269-280. doi: 10.16555/j.1006-8775.2017.03.004
Abstract:
Forecasting the rapid intensification of tropical cyclones over offshore areas remains difficult. In this article, the Weather Research and Forecast (WRF) model was used to study the rapid intensification of Typhoon Haikui (1211) off the shore of China. After successful simulation of the intensity change and track of the typhoon, the model output was further analyzed to determine the mechanism of the rapid change in intensity. The results indicated that a remarkable increase in low-level moisture transportation toward the inner core, favorable large-scale background field with low-level convergence, and high-level divergence played key roles in the rapid intensification of Typhoon Haikui in which high-level divergence could be used as an indicator for the rapid intensity change of Typhoon Haikui approximately 6 h in advance. An analysis of the typhoon structure revealed that Typhoon Haikui was structurally symmetric during the rapid intensification and the range of the eyewall was small in the low level but extended outward in the high level. In addition, the vertically ascending motion, the radial and tangential along wind speeds increased with increasing typhoon intensity, especially during the process of rapid intensification. Furthermore, the intensity of the warm core of the typhoon increased during the intensification process with the warm core extending outward and toward the lower layer. All of the above structural changes contributed to the maintenance and development of typhoon intensity.
COMPARISONS OF THE CHARACTERISTICS OF TROPICAL CYCLONES EXPERIENCING EXTRATROPICAL TRANSITION IN THE WESTERN NORTH PACIFIC BASED ON DIFFERENT DATASETS
SUN Hong-mei, LEI Xiao-tu, TANG Jie, YAO Cai, LUO Xiao-li
2017, 23(3): 281-291. doi: 10.16555/j.1006-8775.2017.03.005
Abstract:
The differences in the climatology of extratropical transition (ET) of western North Pacific tropical cyclones (TCs) were investigated in this study using the TCs best-track datasets of China Meteorological Administration (CMA), Japan Meteorological Agency (JMA) and the Joint Typhoon Warning Center (JTWC). The results show that the ET identification, ET completion time, and post-ET duration reported in the JTWC dataset are greatly different from those in CMA and JMA datasets during 2004–C2010. However, the key differences between the CMA and JMA datasets from 1951 to 2010 are the ET identification and the post-ET duration, because of inconsistent objective ET criteria used in the centers. Further analysis indicates that annual ET percentage of CMA was lower than that of JMA, and exhibited an interannual decreasing trend, while that of JMA was an unchanged trend. The western North Pacific ET events occurred mainly during the period June to November. The latitude of ET occurrence shifted northward from February to August, followed by a southward shift. Most of ET events were observed between 35° N and 45° N. From a regional perspective, TCs tended to undergo ET in Japan and the ocean east to it. It is found that TCs which experienced the ET process at higher latitudes were generally more intense at the ET completion time. TCs completing the ET overland or offshore were weaker than those finishing the ET over the ocean. Most of the TCs weakened 24 h before the completion of ET. In contrast, 21% (27%) of the TCs showed an intensification process based on the CMA (JMA) dataset during the post-ET period. The results presented in this study indicate that consistent ET determination criteria are needed to reduce the uncertainty involved in ET identification among the centers.
COMPARATIVE ANALYSIS OF VARIOUS DATA OF AIR-CSEA TEMPERATURE DIFFERENCE AND ITS VARIATION ACROSS SOUTH CHINA SEA IN THE PAST 35 YEARS
XU Feng, XIA Tian-zhu, WANG Hui, LIU Ke-xiu
2017, 23(3): 292-301. doi: 10.16555/j.1006-8775.2017.03.006
Abstract:
Using the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) and ERA-Interim data, spatial distributions of air–Csea temperature difference (ASTD) in the South China Sea (SCS) for the past 35 years are compared, and variations of spatial and temporal distributions of ASTD in this region are addressed using empirical orthogonal function decomposition and wavelet analysis methods. The results indicate that both ICOADS and ERA-Interim data can reflect actual distribution characteristics of ASTD in the SCS, but values of ASTD from the ERA-Interim data are smaller than those of the ICOADS data in the same region. In addition, the ASTD characteristics from the ERA-Interim data are not obvious inshore. A seesaw-type, north–Csouth distribution of ASTD is dominant in the SCS; i.e., a positive peak in the south is associated with a negative peak in the north in November, and a negative peak in the south is accompanied by a positive peak in the north during April and May. Interannual ASTD variations in summer or autumn are decreasing. There is a seesaw-type distribution of ASTD between Beibu Bay and most of the SCS in summer, and the center of large values is in the Nansha Islands area in autumn. The ASTD in the SCS has a strong quasi-3a oscillation period in all seasons, and a quasi-11a period in winter and spring. The ASTD is positively correlated with the Niño3.4 index in summer and autumn but negatively correlated in spring and winter.
ROLE OF A WARM AND WET TRANSPORT CONVEYOR OF ASIAN SUMMER MONSOON IN A BEIJING HEAVY RAINSTORM ON JULY 21, 2012
LIU Yan-ju, DING Yi-hui, ZHANG Ying-xian, SONG Ya-fang
2017, 23(3): 302-313. doi: 10.16555/j.1006-8775.2017.03.007
Abstract:
A heavy rainstorm named Beijing “7.21” heavy rainstorm hit Beijing on 21 to 22 July 2012, which is recorded as the most severe rainstorm since 1951. The daily precipitation amount in many stations in Beijing has broken the history record. Based on the NCAR/NCEP reanalysis data and precipitation observation,the large-scale conditions which caused the “7.21” heavy rainstorm are investigated, with the emphasis on the relationship between it and an equatorial convergence zone, Asian summer monsoon as well as the tropical cyclone over the ocean from the Philippines to the South China Sea (SCS). The results indicated that a great deal of southerly warm and wet moisture carried by northward migrating Asian summer monsoon provided plenty of moisture supplying for the “7.21” heavy rainstorm. When the warm and wet moisture met with the strong cold temperature advection induced by cold troughs or vortexes, an obviously unstable stratification formed, thus leading to the occurrence of heavy precipitation. Without this kind of intense moisture transport, the rainstorm only relying on the role of the cold air from mid- and higher- latitudes could not reach the record-breaking intensity. Further research suggested that the northward movement of an Asian monsoonal warm and wet moisture transport conveyor (MWWTC) was closely related with the active phase of a 30-60 day intra-seasonal oscillation of the Asian summer monsoon. During this time, the monsoon surge triggered and maintained the northward movement of the MWWTC. In addition, compared with another heavy rainstorm named “63.8” heavy rainstorm, which occurred over the Huaihe River Basin in the mid-August 1963 and seriously affected North China, a similar MWWTC was also observed. It was just the intense interaction of the MWWTC with strong cold air from the north that caused this severe rain storm.
A PRELIMINARY STUDY ON THE 3DVAR ASSIMILATION OF THE AMSU-A DATA IN SPACE-TIME MULTISCALE ANALYSIS SYSTEM
LIU Rui-xia, XIE Yuan-fu, LIU Jie
2017, 23(3): 314-322. doi: 10.16555/j.1006-8775.2017.03.008
Abstract:
Assimilating satellite radiances into Numerical Weather Prediction (NWP) models has become an important approach to increase the accuracy of numerical weather forecasting. In this study, the assimilation technique scheme was employed in NOAA’s STMAS (Space-Time Multiscale Analysis System) to assimilate AMSU-A radiances data. Channel selection sensitivity experiments were conducted on assimilated satellite data in the first place. Then, real case analysis of AMSU-A data assimilation was performed. The analysis results showed that, following assimilating of AMSU-A channels 5–C11 in STMAS, the objective function quickly converged, and the channel vertical response was consistent with the AMSU-A weighting function distribution, which suggests that the channels can be used in the assimilation of satellite data in STMAS. With the case of the Typhoon Morakot in Taiwan Island in August 2009 as an example, experiments on assimilated and unassimilated AMSU-A radiances data were designed to analyze the impact of the assimilation of satellite data on STMAS. The results demonstrated that assimilation of AMSU-A data provided more accurate prediction of the precipitation region and intensity, and especially, it improved the 0–C6h precipitation forecast significantly.
THE ABRUPT CHANGE OF TROPICAL CYCLONE NUMBER OVER THE WESTERN NORTH PACIFIC IN THE MID-1990s
LI De-lin, XIAO Zi-niu, XIN Fei, ZHOU Xiu-hua
2017, 23(3): 323-333. doi: 10.16555/j.1006-8775.2017.03.009
Abstract:
Based on the CMA tropical cyclone (TC) best track data as well as the reanalysis datasets from the NCEP/NCAR and NOAA, the variation characteristics of TC number from 1949 to 2013 over the western North Pacific (including the South China Sea) are examined. Notably, the time series of TC number exhibits a significant abrupt change from more to less around 1995. Comparative analysis indicates that the environmental factors necessary to TC formation also change significantly around the mid-1990s. After 1995, accompanying with anomalous warm sea surface temperature (SST) in western equatorial Pacific, a La Niña-like pattern in tropical Pacific appears obviously. However, compared with the period before 1995, the vertical upward movement decreases, vertical shear of tropospheric zonal wind increases, and sea level pressure (SLP) rises, all of which are unfavorable to TC formation and work together to make TC number reduce markedly after 1995. Furthermore, when the typical interannual more and less TCs years are selected in the two separate stages before and after 1995, the relative importance of oceanic and atmospheric environments in interannual TC generation is also investigated respectively. The results imply that the SST over the tropical Pacific exerts relatively important influence on TC formation before 1995 whereas the atmospheric circulation plays a more prominent role in the generation of TC after 1995.
INTEGRATED RISK ASSESSMENT OF MAJOR METEOROLOGICAL DISASTERS WITH PAPRIKA PEPPER IN HAINAN PROVINCE
ZHANG Lei, HUO Zhi-guo, ZHANG Li-zhen, HUANG Da-peng
2017, 23(3): 334-344. doi: 10.16555/j.1006-8775.2017.03.010
Abstract:
Paprika pepper, as one of the main vegetable crops, is originated in the tropics and now widely planted in the world for its dietary therapy and medicinal functions. For its typical physiological properties referring to low tolerances to flood, drought and cold, paprika pepper often suffers from one or several disasters during its growing period, especially under tropical climate. Paprika pepper in Hainan, as a typical region of tropical climate in China, sustains flood, chilling and drought disaster risks induced by varied weather systems. This study was to develop and employ appropriate indices to assess hazard, sensitivity, vulnerability and prevention capability for major disasters during paprika pepper growth period, using long-term meteorological data from 1998 to 2011, actual disasters record from 1999 to 2011, production and socioeconomic statistics from 2002 to 2011 at 18 weather stations. Based on the Analytic Hierarchy Process and Entropy method, the combined weight was given to each disaster factor, thus an integrated disaster risk assessment model was developed and applied at regional level. High flood hazard mainly occurred in eastern Hainan, high chilling hazard in north and central mountain areas, and high drought hazard in the western part of Hainan. Drought and chilling sensitivity had a similar spatial distribution which decreased from central to coastal regions while flood sensitivity was the opposite. High vulnerability of the disasters mainly occurred in central regions, similar to low prevention capability. Eastern Hainan suffered from high integrated damage risk. The predicted damage occurrence showed a good agreement with the occurrence of actual disasters. We concluded that an integrated damage risk assessment model could provide a new tool to assess major meteorological disasters and help farmers and policy makers to alleviate the risks of major meteorological disasters for paprika pepper, which seems also suitable for other crops.