Application Of Radar And Satellites Imagery In Forecast Of Typhoon Landing In Fujian

With Doppler radar images,water vapor images from FY2 geostationary meteorological satellite and AMSU images from NOAA polar orbiting satellite,the typhoons landing in Fujian province are studied on their major features of the tracks and the wind and precipitation distributions.The primary conclusions are as follows:1.At first,the tracks of typhoons landing in Fujian province and the associated climatology characteristics are analyzed.The tracks can be divided into 4 types:â‘ landing in Fujian directly after crossing the Bashi Channel from the western Pacific,â‘¡landing in Taiwan province and then landing in Fujian,â‘¢landing in Guangdong and then moving into Fujian in land,â‘£landing in the northern part of Fujian directly through the Eastern China sea.Wherein,the type of landing in Fujian directly(â‘ ) has the most risk in causing disaster,and the south Fujian and east Guangdong regions suffered the most seriously and frequently by severe typhoons in the history. Each year in the average,there is one typhoon landing those regions after crossing the Bashi Channel from the western Pacific.Among the typhoons landing in Fujian, around 60%typhoons land on Taiwan firstly and then landing in Fujian about 18 hours later.The typhoons landing in Fujian may cause heavy rainstorm there usually. In addition,the effect of Daiyun Mountains on typhoon-caused rainstorm is analyzed, and the reasons why the typhoon-caused rainstorm frequently appears along the band of Dehua,Anxi,Nan'an and Yongchun are also discussed.2.Asymmetric structures of typhoons landing in Fujian province can exert great impacts on typhoon track and its weather associated.At the time when Typhoon AERE(2004)was moving towards southwest,Doppler radar wind field distribution was associated with an asymmetry character with wave number one whose wave peak was located at the northwest quadrant.Such asymmetry might be caused by both the environmental wind field and the structure of Typhoon AERE itself,and was favorable to AERE at maintaining its southwestward movement.As to Typhoon CHANCHU(2006),which was detected by radar at the lower elevation around the core radius of typhoon,the negative radial velocity on the left side of its track was larger than the positive velocity on the right side.It was expected that this type of radial velocity distribution was caused by the intruding cold air with northeast wind in the northern quadrant below 3Km height.However,when detected by radar at higher elevation,the positive velocity was larger than the negative velocity obviously with differences 14m/s.This indicated that the southwestward movement of CHANCHU was leaded by the southwest wind aloft.And the intruding cold air at the lower atmosphere produced ascending motion,enhanced the release of the instability energy,and finally triggered the heavy precipitation. 3.A method of extracting information from real-time radar observed radial wind was induced to judge the typhoon track changes.With Rankin model,Doppler velocity characteristics for a pure cyclone rotation are simulated,and furthermore,the impacts of different environmental wind direction and divergence wind blowing to the typhoon center on the Doppler velocity characteristics are simulated,too.Based on the above results,typhoon wind velocity characteristics between the radar observations and simulations with different environmental wind directions are compared,and the method of extracting information of related environmental wind is proposed,which can be used to judge the typhoon track change more sensitively. Indeed,this method works very well in practice,especially during the key time period when typhoon track is going to change.It is also meaningful that the environmental wind direction change comes ahead of the typhoon track change,usually by about 1-2 hours.4.Application of NOAA satellite AMSU data in the typhoon structure is studied. Among the 5 channels of AMSU-B,the bright temperature in Channel 2(Ch2) reflects the depth of ice crystal layer in the spiral rain band of tropical cyclone,thus the intensity of the spiral rain band can be inferred.By using the AMSU-A temperature inversion data,the warm core of tropical cyclone is revealed,and there exist good correlation between the maximum of AMSU temperature anomaly and both the surface wind velocity and the central pressure of tropical cyclone.According to the vertical cross section of AMSU temperature,a warm core above the center of tropical cyclone is found at the mid-higher troposphere,which becomes wider along the height,reaching its maximum for both width and warm temperature at about 250hPa.In addition,there exists a cold core at the lower troposphere above the center of tropical cyclone,and the negative temperature anomaly at the lower troposphere revealed by AMSU data can be used to orient the precipitation and analyze the precipitation intensity.5.With FY-2 satellite water vapor imageries and AMVs,issues on typhoon movement are studied.Water vapor imageries and AMVs for 4 typhoon processes from 2005 to 2006 are analyzed.It is found that before the track turning of both Typhoons CHANCHU and SHANSHAN(2006),a process of either base-surge or darkness expanding occurs at the east side by 17/13 longitude degrees away from the typhoon center.The base surge represents the southward movement of cold surge in the mid-latitude,which may be clearly traced by satellite water vapor images combined with AMVs.The tracks of both Typhoons LONGWANG(2005)and SAOMAI(2006)are relatively stable,and the satellite water vapor images show grey color without the base-surge and darkness expanding at the eastern side of the typhoon in the distance of 17/13 longitude degrees.It is expected that warm air arises inside typhoon whereas cold air sinks in the dry regions,and both ascending and descending movements may produce a kind of vertical circulation.Therefore,the lower inflow and upper outflow may result in enhanced southerly wind(leading wind current)at the mid-lower troposphere over there.Actually,the base-surge region east to the typhoon corresponds to the high pressure at the mid-lower troposphere,and its development favor the strengthening of southerly wind at the mid-lower troposphere at the same side of typhoon.Thus,the base-surge or darkness expanding is probably an indicator for the turning motion of typhoon track.Interestingly,this indicator leads the actually turning of typhoon track by 15-20 hours at least.