Finescale spiral rainbands associated with Typhoon Rananim （2004） with the band length ranging from 10 to nearly 100 km and band width varying from 5 to 15 km are simulated using the Fifth-Generation NCAR/Penn State...Finescale spiral rainbands associated with Typhoon Rananim （2004） with the band length ranging from 10 to nearly 100 km and band width varying from 5 to 15 km are simulated using the Fifth-Generation NCAR/Penn State Mesoscale Model （MM5）. The finescale rainbands have two types： one intersecting the eyewall and causing damaging wind streaks, and the other distributed azimuthally along the inner edge of the eyewall with a relatively short lifetime. The formation of the high-velocity wind streaks results from the interaction of the azimuthal flow with the banded vertical vorticity structure triggered by tilting of the horizontal vorticity. The vertical advection of azimuthal momentum also leads to acceleration of tangential flow at a relatively high Mtitude. The evolution and structures of the bands are also examined in this study. Further investigation suggests that the boundary inflection points are related tightly to the development of the finescale rainbands, consistent with previous findings using simple symmetric models. In particular; the presence of the level of inflow reversal in the boundary layer is a crucial factor controlling the formation of these bands. The near-surface wavy peaks of vertical vorticity always follow the inflection points in radial flow. The mesoscale vortices and associated convective updrafts in the eyewall are considered to strengthen the activity of finescale bands, and the updrafts can trigger the formation of the bands as they reside in the environment with inflow reversal in the boundary layer.展开更多
Over the past few years, landfall and track,intensity, sustaining mechanisms of tropical cyclones （hereafter TCs） and associated weather changes have become heated topics of research, From the viewpoints of energy t...Over the past few years, landfall and track,intensity, sustaining mechanisms of tropical cyclones （hereafter TCs） and associated weather changes have become heated topics of research, From the viewpoints of energy transformation, moisture transfer, midlatitude baroclinic frontal zones and ambient wind fields, Chen et al.Le et al.and Zeng et al.studied the sustaining mechanism of TCs that have made landfall. Li et al.also pointed out that the intensification of TCs during transition was associated with the disturbance and downward transportation of high-level potential vortexes, low-level frontal zones and low-pressure circulation around TCs, after explaining the difference in TCs transition following the theory of wet potential vortexes. With large-scale diagnostic study of two types of TCs that unexpectedly weaken or enhance just before landfall in southern China, Hu et al.noted that enhancing TCs were usually to the southwest or south of the subtropical high with low levels featured by well-defined southwesterly inflow inside TCs and sufficient supply of water vapor. Liang et al.not only analyzed the changes in convective cloud bands, precipitation, track and temperature and humidity structure in the course of TC Vongfang landfall, but the effect of cold air and Southwest Monsoon on its intensity in particular. As also shown in numerical experiments conducted both at home and abroad and relevant studies,saturated humidity and large-sized bodies of water are favorable for the maintenance and enhancement of landfall TCs circulation. All of the above research achievements not only help broaden the understanding of the patterns by which TCs behave but are positive in improving the forecast of the track, winds and rains after landfall. It is.however, not much addressed in the field or evounon of landfall TCs when they are with special underlying surface and circulation background. TC Rananim （0414） was the most serious typhoon that ever affected Zhejiang province after landfall in the 48 years from 1956 to 2004, which was also the storm that caused heavy rains in the most widespread area in Jiangxi province in the past 20 years. There are two points about Rananim that stand out from the other storms. The first was the sudden westward turning of its track and the second the significant enhancement of precipitation after moving above the Boyang Lake.What kind of mechanism caused such remarkable change in the storm？ With 6-hourly 1×1°NECP global reanalysis data, real-time upper-level observations and TCs location reports by the Central Observatory, the above two points and possible causes are studied in terms large-scale circulation background, underlying surface, cold air and diagnosis of physical quantity fields. New understanding has been made about the behavioral pattern of landfall TCs and related results will offer effective help in operational forecast.展开更多
Using the high-resolution non-hydrostatic model ARPS （Advanced Regional Prediction System）, the Typhoon Rananim （0414） was simulated by using the CINRAD Doppler radar data. The results before and after typhoon lan...Using the high-resolution non-hydrostatic model ARPS （Advanced Regional Prediction System）, the Typhoon Rananim （0414） was simulated by using the CINRAD Doppler radar data. The results before and after typhoon landfall show that model ARPS performs well to simulate the track, the variation of center pressure, as well as severe heavy rain of Rananim. Meanwhile, the simulated composite reflectivity was compared with the observed radar composite reflectivity. The numerical results reveal that the asymmetrical structure of Rananim plays an important role in its westward deflecting after landfall. The sensitivity simulation experiments of terrain effects on Rananim （0414） were also investigated, and the terrain of the southeastern China has important effects on Rananim turning right slightly of its track and increasing its intensity obviously, but when typhoon is far away from the coastline, the terrain only impacts slightly on the storm intensity during its landfall. The results show that topographic lifting contributes greatly to precipitation enhancement, and makes the distribution of precipitation more uneven.展开更多
基金supported by the National Basic Research Program of China (2009CB421505)the National Natural Science Foundation of China under Grants Nos.40730948+5 种基金the National Natural Science Foundation of China under Grants Nos.40575030the National Natural Science Foundation of China under Grants Nos.40705024the Shanghai Typhoon Foundation (2009ST09)supported by the National Nature Science Foundation of China under the Grant No.40675060the program of the Ministry of Science and Technology of the People's Republic of China (2006AA09Z151)the program of China Meteorological Administration(GYHY200706031)
文摘Finescale spiral rainbands associated with Typhoon Rananim （2004） with the band length ranging from 10 to nearly 100 km and band width varying from 5 to 15 km are simulated using the Fifth-Generation NCAR/Penn State Mesoscale Model （MM5）. The finescale rainbands have two types： one intersecting the eyewall and causing damaging wind streaks, and the other distributed azimuthally along the inner edge of the eyewall with a relatively short lifetime. The formation of the high-velocity wind streaks results from the interaction of the azimuthal flow with the banded vertical vorticity structure triggered by tilting of the horizontal vorticity. The vertical advection of azimuthal momentum also leads to acceleration of tangential flow at a relatively high Mtitude. The evolution and structures of the bands are also examined in this study. Further investigation suggests that the boundary inflection points are related tightly to the development of the finescale rainbands, consistent with previous findings using simple symmetric models. In particular; the presence of the level of inflow reversal in the boundary layer is a crucial factor controlling the formation of these bands. The near-surface wavy peaks of vertical vorticity always follow the inflection points in radial flow. The mesoscale vortices and associated convective updrafts in the eyewall are considered to strengthen the activity of finescale bands, and the updrafts can trigger the formation of the bands as they reside in the environment with inflow reversal in the boundary layer.
文摘Over the past few years, landfall and track,intensity, sustaining mechanisms of tropical cyclones （hereafter TCs） and associated weather changes have become heated topics of research, From the viewpoints of energy transformation, moisture transfer, midlatitude baroclinic frontal zones and ambient wind fields, Chen et al.Le et al.and Zeng et al.studied the sustaining mechanism of TCs that have made landfall. Li et al.also pointed out that the intensification of TCs during transition was associated with the disturbance and downward transportation of high-level potential vortexes, low-level frontal zones and low-pressure circulation around TCs, after explaining the difference in TCs transition following the theory of wet potential vortexes. With large-scale diagnostic study of two types of TCs that unexpectedly weaken or enhance just before landfall in southern China, Hu et al.noted that enhancing TCs were usually to the southwest or south of the subtropical high with low levels featured by well-defined southwesterly inflow inside TCs and sufficient supply of water vapor. Liang et al.not only analyzed the changes in convective cloud bands, precipitation, track and temperature and humidity structure in the course of TC Vongfang landfall, but the effect of cold air and Southwest Monsoon on its intensity in particular. As also shown in numerical experiments conducted both at home and abroad and relevant studies,saturated humidity and large-sized bodies of water are favorable for the maintenance and enhancement of landfall TCs circulation. All of the above research achievements not only help broaden the understanding of the patterns by which TCs behave but are positive in improving the forecast of the track, winds and rains after landfall. It is.however, not much addressed in the field or evounon of landfall TCs when they are with special underlying surface and circulation background. TC Rananim （0414） was the most serious typhoon that ever affected Zhejiang province after landfall in the 48 years from 1956 to 2004, which was also the storm that caused heavy rains in the most widespread area in Jiangxi province in the past 20 years. There are two points about Rananim that stand out from the other storms. The first was the sudden westward turning of its track and the second the significant enhancement of precipitation after moving above the Boyang Lake.What kind of mechanism caused such remarkable change in the storm？ With 6-hourly 1×1°NECP global reanalysis data, real-time upper-level observations and TCs location reports by the Central Observatory, the above two points and possible causes are studied in terms large-scale circulation background, underlying surface, cold air and diagnosis of physical quantity fields. New understanding has been made about the behavioral pattern of landfall TCs and related results will offer effective help in operational forecast.
基金Supported by the Meteorology Gathers Capital Plan Key Project of Zhejiang Province under Grant Nos.2004ZD03,2004ZD05,and the Technical Plan Key Project of Wenzhou under Grant No.S2003A011.
文摘Using the high-resolution non-hydrostatic model ARPS （Advanced Regional Prediction System）, the Typhoon Rananim （0414） was simulated by using the CINRAD Doppler radar data. The results before and after typhoon landfall show that model ARPS performs well to simulate the track, the variation of center pressure, as well as severe heavy rain of Rananim. Meanwhile, the simulated composite reflectivity was compared with the observed radar composite reflectivity. The numerical results reveal that the asymmetrical structure of Rananim plays an important role in its westward deflecting after landfall. The sensitivity simulation experiments of terrain effects on Rananim （0414） were also investigated, and the terrain of the southeastern China has important effects on Rananim turning right slightly of its track and increasing its intensity obviously, but when typhoon is far away from the coastline, the terrain only impacts slightly on the storm intensity during its landfall. The results show that topographic lifting contributes greatly to precipitation enhancement, and makes the distribution of precipitation more uneven.
