ON THE RELATIONSHIPS BETWEEN THE UNUSUAL TRACK OF TYPHOON MORAKOT(0908)AND THE UPPER WESTERLY TROUGH

In this paper,by carrying out sensitivity tests of initial conditions and diagnostic analysis of physical fields,the impact factors and the physical mechanism of the unusual track of Morakot in the Taiwan Strait are discussed and examined based on the potential vorticity(PV)inversion.The diagnostic results of NCEP data showed that Morakot's track was mainly steered by the subtropical high.The breaking of a high-pressure zone was the main cause for the northward turn of Morakot.A sensitivity test of initial conditions showed that the existence of upper-level trough was the leading factor for the breaking of the high-pressure zone.When the intensity was strengthened of the upper-level trough at initial time,the high-pressure zone would break ahead of time,leading to the early northward turn of Morakot.Conversely,when the intensity was weakened,the breaking of the high-pressure zone would be delayed.Especially,when the intensity was weakened to a certain extent,the high-pressure zone would not break.The typhoon,steered by the easterly flow to the south of the high-pressure zone,would keep moving westward,with no turn in the test.The diagnostic analysis of the physical fields based on the sensitivity test revealed that positive vorticity advection and cold advection associated with the upper-level trough weakened the intensity of the high-pressure zone.The upper-level trough affected typhoon's track indirectly by influencing the high-pressure zone.

Role of the Subtropical Westerly Jet Waveguide in a Southern China Heavy Rainstorm in December 2013

An extreme rainstorm hit southern China during 13–17 December 2013, with a record-breaking daily rainfall rate, large spatial extent, and unusually long persistence. We examined what induced this heavy rainfall process, based on observed rainfall data and NCEP–NCAR reanalysis data through composite and diagnostic methods. The results showed that a Rossby waveguide within the subtropical westerly jet caused the event. The Rossby wave originated from strong cold air intrusion into the subtropical westerly jet over the eastern Mediterranean. With the enhancement and northward shift of the Middle East westerly jet, the Rossby wave propagated slowly eastward and deepened the India–Burma trough, which transported a large amount of moisture from the Bay of Bengal and South China Sea to southern China. Strong divergence in the upper troposphere, caused by the enhancement of the East Asian westerly jet, also favored the heavy rainfall process over Southeast China. In addition, the Rossby wave was associated with a negative-to-positive phase shift and enhancement of the North Atlantic Oscillation, but convergence in the eastern Mediterranean played the key role in the eastward propagation of the Rossby wave within the subtropical westerly jet.

Analysis of the Regional Heavy Rainfall in Shenyang City

The analysis of '09.08.19' regional rainstorm weather in Shenyang showed that the circulation situation of the rainfall was the typical subtropical high pressure with westerly trough.Surface cyclone development in cooperation with the convergence and the role of the front of the uplift produced by the heavy rains trigger mechanism.The coupling configuration of low-level jet created favorable conditions for the development of convection,while the two rapids provided a steady stream of water vapor transport for the heavy rainfall.K exponential distribution,500 hPa,700 hPa temperature field and the total pseudo-equivalent potential temperature for the precipitation forecasts have a certain direction meaning.Japan fax map and MM5 grasped the precipitation forecasts better.

Predecessor Rain Events in the Yangtze River Delta Region Associated with South China Sea and Northwest Pacific Ocean(SCS-WNPO)Tropical Cyclones

Predecessor rain events(PREs) in the Yangtze River Delta(YRD) region associated with the South China Sea and Northwest Pacific Ocean(SCS-WNPO) tropical cyclones(TCs) are investigated during the period from 2010 to 2019.Results indicate that approximately 10% of TCs making landfall in China produce PREs over the YRD region;however,they are seldom forecasted. PREs often occur over the YRD region when TCs begin to be active in the SCS-WNPO with westward paths, whilst the cold air is still existing or beginning to be present. PREs are more likely to peak in June and September. The distances between the PRE centers and the parent TC range from 900 to 1700 km. The median value of rain amounts and the median lifetime of PREs is approximately 200 mm and 24 h, respectively. Composite results suggest that PREs form in the equatorward jet-entrance region of the upper-level westerly jet(WJ), where a 925-hPa equivalent potential temperature ridge is located east of a 500-hPa trough. Deep moisture is transported from the TC vicinity to the remote PREs region. The ascent of this deep moist air in front of the 500-hPa trough and frontogenesis beneath the equatorward entrance region of the WJ is advantageous for the occurrence of PREs in the YRD region. The upper-level WJ may be affected by the subtropical high and westerly trough in the Northwest Pacific Ocean, and the occurrence of PREs may favor the maintenance of the upper-level WJ. The upper-level outflow of TCs in the SCS plays a secondary role.

THE STRONG DRAGON BOAT RACE PRECIPITATION OF GUANGDONG IN 2008 AND QUASI-10-DAY OSCILLATION

Guangdong suffered from the most serious precipitation of its corresponding time during the dragon-boat race of 2008 since 1951.The relationship between the strong dragon-boat precipitation in 2008 and atmospheric low-frequency oscillation was analyzed with the methods of wavelet analysis,correlation and Lanczos filter.Results showed that the daily rainfall exhibits a significant 7 to 12-day quasi-periodic oscillation(namely quasi-10-day oscillation) during the precipitation,the daily 500 hPa height over Guangdong exhibits a significant 8 to 13-day quasi-periodic oscillation,and the daily 850 hPa zonal wind averaged over the north of the South China Sea presents a significant quasi-12-day periodic oscillation.The Guangdong rainfall during the annually first rainy season is most closely correlated with monsoon over the north of South China Sea,and less closely with an upper-level trough at 500 hPa affecting Guangdong.Strong monsoon surges induced two heavy rainfall processes in 2008.The monsoon surges joined with a westward-propagating quasi-10-day oscillation that originated from the central Pacific and was enhanced in a strong convective region east of the Philippines and a northward-propagating monsoon that originated from the southern South China Sea was enhanced.With composite analysis of typical phases,the common evolution characteristics of atmospheric circulation of the two heavy rainfall processes were analyzed for different phases.These features can be used as reference for medium prediction of heavy rainfall processes in Guangdong.

A Study of Extratropical Transition and Re-Intensification of Typhoon Mindulle(2004)

In this study,the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) is used to simulate Typhoon Mindulle (2004) at high resolution (3-km grid size).The data from measurements show that in the upper atmosphere the existence of an upper jet is important to the transition cyclone.When Mindulle moved to the area of the upper jet entrance,where high-altitude divergence existed, the pumping of the high-altitude divergence would enhance the vertical motion and low-level cyclone convergence. The enhanced vertical motion was confirmed by the simulation results and indicated that the existence of upper divergence enhanced the vertical motion which was favorable for the maintenance of Typhoon Mindulle.The process of extratropical transition (ET) and re-intensification always accompanies the process of cold air invasion. This process enhances the baroclinicity of the atmosphere and the formation of front at high altitudes, which converts baroclinic potential energy into kinetic energy and strengthens the cyclone vortex.The distributions of equivalent potential temperature (θe) and temperature anomalies show that the warm-core of the typhoon at the tropopause aids the re-intensification of the system. As the typhoon reenters the ocean, latent heat flux (LHF) increases in the north and west and the strong reflectivity and vertical motion occur in the east and southeast,and the west.With the re-intensification of the typhoon the wind field evolves from an oval to a circle at the lower atmosphere, the area coverage by high winds increases, and the distribution of the tangential wind shows an asymmetric pattern.

DEVELOPING AND NON-DEVELOPING TROPICAL CYCLONES AS REVEALED BY HIGH DENSITY CLOUD MOTION WINDS

An algorithm for computation of cloud motion winds has been developed at the National Satellite Meteorological Center in China. Since 1997, it has been applied to calculate the cloud motion winds for a 1.25 lat. ×1.25 long. mesh over the northwest Pacific region with the satellite data from GMS-5. The development of the tropical cyclones is studied. It shows that the tropical cyclone is usually intrigued by the westerly jet streams at the upper levels of the troposphere, which may be caused by mid-latitude troughs well extending into the tropics. During the prime season of summer, the westerly flowing equatorward of the TUTT may also be a cause for the generation of typhoons.

SUBTROPICAL HIGH, LATENT HEATING BY CONVECTION AND ASSOCIATION WITH DISSIPATION AND MAINTENANCE OF SOUTH CHINA SEA TYPHOONS

Numerical modeling and experiments are conducted for the South China Sea typhoons Helen (1995) and Willie (1996) with an auto-adaptive mesh model. It is shown that durating the stage of dissipation the typhoons are mainly related with the subtropical high rather than the topography. The high is sensitive to the intensity change of the typhoon so that the former weakens as the latter strengthens and vice versa. Maintaining the typhoon as a main factor, the release of latent heat is in reversed proportion with the subtropical high in terms of the intensity. It is found that the storm tends to be maintained if it moves close to the westerly trough after landfall.

Analysis on the Genesis and the Omission of a Torrential Rain over Linqu on 9 July 2012

In order to further study the drop zone of torrential rain in Weifang and summarize the experience of forecasting torrential rain in the future,a special diagnosis analysis was made on the process of the torrential rain.The meteorological information comprehensive analysis and processing system（MICAPS） 3.1 was used to carry out the analysis of profile and sounding to the conventional meteorological data,and finally numerical weather prediction was tested,which got the reason of production and omission of torrential rain.The results showed that one of the important reason of the torrential rain was caused by the combined effects of the dry cold air brought by the middle latitude shortwave trough and the southwest warm wet airflow brought by the jet flow,and the terrain influence caused by the Yishan in southern Liju County and the water evaporation in Mihe River was also an important reason.The main reason for the omission of the rain was caused by the over dependent on the rainfall forecast of numerical products and neglected the evolution of small scale process as well as analysis of the physical quantity field.Therefore,it was very important to monitor the actual weather situation and analyze all kinds of physical quantities for forecasting torrential rain.Besides,the forecaster should improve their ability in revising the numerical weather prediction.

Analysis of Formation Mechanism of Two Successive Heavy Rainfall Processes on the Edge of the Subtropical High

Based on sounding and ground observation data,GPS/MET and FY-2 E satellite data,NCEP/NCAR reanalysis data（ 1°× 1°）,the formation mechanisms of two successive heavy rainfall processes on the edge of the subtropical high were analyzed. The results showed that the two heavy rainfall processes were caused by weak westerly troughs on the edge of the subtropical high at 500 h Pa,and there was strong southwest jet stream at 850-700 h Pa. As the low-level southwest jet stream intensified and moved northwards,heavy rainfall began. When the jet stream weakened,heavy rainfall ended. The heavy rainfall areas had good consistency with the high-value areas of CAPE,the high-value tongue of low-level water vapor flux,water vapor convergence center and warm advection center. Water vapor monitoring by GPS/MET had certain denotative meaning to the short-term prediction of heavy rainfall. The minimum TBB of convective cloud clusters was between-62 and-78 ℃,and the corresponding hourly maximum precipitation was 40-90 mm. In the heavy rainfall process,mesoscale vortexes occurred at 850 h Pa and below,but the scale was small,with weak low pressure but significant cyclonic circulation. The most intense rainfall was generated at the center of warm advection in the southeast of the vortex center at 925 h Pa. In the first heavy rainfall process,the mesoscale vortexes moved less,while strong rainfall was induced by strong upward movement in the southeast of the vortexes. In the second heavy rainfall process,low-level cold air invaded from the northwest into the vortexes to form cyclones and moved northeastwards. Heavy rainfall happened in the warm zone in front of cold front,and convective instability energy was high. Rainfall intensity was high,and rainfall range was large.

数值产品在2001年主汛期暴雨过程中的释用

利用天气学暴雨天气形势概念模式,根据ECMWF数值预报产品,提前2天预报出7月22和30日的暴雨过程;日本传真图预报的降水量和物理量,也满足多年使用日本传真图总结出的强降水指标。

Interdecadal Variations of Precipitation and Temperature in China Around the Abrupt Change of Atmospheric Circulation in 1976

The interdecadal characteristics of rainfall and temperature in China before and after the abrupt change of the general circulation in 1976 are analyzed using the global 2.5°×2.5° monthly mean reanalysis data from the National Centers for Environmental Prediction of US and the precipitation and temperature data at the 743 stations of China from the National Climate Center of China. The results show that after 1976, springtime precipitation and temperature were anomalously enhanced and reduced respectively in South China, while the reverse was true in the western Yangtze River basin. In summer, precipitation was anomalously less in South China, more in the Yangtze River basin, less again in North China and more again in Northeast China, showing a distribution pattern alternating with negative and positive anomalies （＂ , ＋, -, ＋＂）. Meanwhile, temperature shows a distribution of warming in South China, cooling in the Yangtze and Huaihe River basins, and warming again in northern China. In autumn, precipitation tended to decrease and temperature tended to increase in in South China and warming was most parts of the country. In winter, the trend across all parts of China. precipitation increased moderately The interdecadal decline of mean temperature in spring and summer in China was mainly due to the daily maximum temperature variation, while the interdecadal increase was mainly the result of the minimum temperature change. The overall warming in autumn （winter） was mostly influenced by the minimum （maximum） temperature variation. These changes were closely related to the north-south shifts of the ascending and descending branches of the Hadley cell, the strengthening and north-south progression of the westerly jet stream, and the atmospheric stratification and water vapor transport conditions.

Comparison of the Multi-Scale Features in Two Persistent Heavy Rainfall Events in the Middle and Lower Reaches of Yangtze River

Two persistent heavy rainfall（PHR） events in the middle and lower reaches of Yangtze River（MLYR）occurring in June 1982 and 1998 are studied in this paper.Though both events happened in the Meiyu season,their large-scale background and developing processes were quite different.During the PHR event in 1982,the Lake Baikal area was occupied by a strong westerly trough and the western Pacific subtropical high（WPSH） was stronger and more westward-extending than the normal years.Under such a condition,the cold dry air and warm moist air were continuously transported to the MLYR and favored the PHR there.For the event in 1998,the WPSH was similar to that in 1982,while the westerly trough in the Lake Baikal area was comparatively weak and a shortwave trough situating in East China contributed to advect cold dry air to the MLYR.It is found that the high-latitude trough was closely related to the 1030-day low-frequency oscillation while the anomaly of WPSH was linked with the combined effect of both30 60- and 10 30-day low-frequency oscillations in the PHR event in 1982.By contrast,the 60-day low-pass perturbation demonstrated positive impact on the westward extension of WPSH and development of the Baikal trough while the 30 60-day oscillation played a role in strengthening the shortwave trough in East China and the WPSH in the case of 1998.Though the low-latitude 30 60-day oscillations contributed to the intensification and westward extension of the WPSH in both PHR events,their evolution exhibited evident differences.In the 1982 case,the 30 60-day anomalies originated from the western Indian Ocean were much more like the Madden Julian Oscillation,while its counterpart in the 1998 case was much more similar to the first mode of the boreal summer intraseasonal oscillation.