1997 Vol. 3, No. 2
1997, 3(2): 113-120.
Abstract:
Based on the definition of cool summer and warm summer, statistical characteristics of severe tropical cyclones are studied over East China Sea using 1951-1994 typhoon and temperature data. It is foundthat the frequency, tracks, intensity and moving speed of the tropical cyclone between cold summer andwarm summer were much different. The backgtound features of the difference were also discussed incontrast.
Based on the definition of cool summer and warm summer, statistical characteristics of severe tropical cyclones are studied over East China Sea using 1951-1994 typhoon and temperature data. It is foundthat the frequency, tracks, intensity and moving speed of the tropical cyclone between cold summer andwarm summer were much different. The backgtound features of the difference were also discussed incontrast.
1997, 3(2): 122-127.
Abstract:
By using the WKB method and slowly-varying wave packet theory the maincause for the sisechange in tropical cyclones is analyzed. It is shown that the size change in tropical cyclones is mainly determined by the inner factors. In general case the angular frequencies of inertio-gravity waves are positive, thus provided that both stratification and inertia are stable, when the parameters of inertial andstatic stabilities increase with the distance from the centre, the sise gets larger; when the parameters of inertial and static stabilities decrease with the distance from the centre, the size gets smaller. The for mer may be called the "expanding" of tropical cyclones and the latter may be called the "shrinking" of tropical cyclones.
By using the WKB method and slowly-varying wave packet theory the maincause for the sisechange in tropical cyclones is analyzed. It is shown that the size change in tropical cyclones is mainly determined by the inner factors. In general case the angular frequencies of inertio-gravity waves are positive, thus provided that both stratification and inertia are stable, when the parameters of inertial andstatic stabilities increase with the distance from the centre, the sise gets larger; when the parameters of inertial and static stabilities decrease with the distance from the centre, the size gets smaller. The for mer may be called the "expanding" of tropical cyclones and the latter may be called the "shrinking" of tropical cyclones.
1997, 3(2): 128-138.
Abstract:
With the use of analyzed TCM-90 data,Typhoon Dot(1990)and complex evolutions are successfullyreproduced in numerical sboulation as it travels over the island of Taiwan. The simulation includes theformation of secondary highs in both circulation and geopotential fields, trajectory jumps during mergence with main centers, anomalous northward movement of a low center west of Taiwan, evolutionalprocess of a low-level jet over the Taiwan Straits and significant deviations of circulation center fromgeopotentia1 center between upper and lower levels. By examining ev0lutions of 3-h interval simulatedresults, detailed processes of changes in structure and track before and after Dot's passage of Taiwanis given, whose evolutional images are otherwise impossible with conventionai observations at intervalsof 6 h. A number of control experboents are conducted in the end of the work for understanding causesand mechanisms behind various properties.
With the use of analyzed TCM-90 data,Typhoon Dot(1990)and complex evolutions are successfullyreproduced in numerical sboulation as it travels over the island of Taiwan. The simulation includes theformation of secondary highs in both circulation and geopotential fields, trajectory jumps during mergence with main centers, anomalous northward movement of a low center west of Taiwan, evolutionalprocess of a low-level jet over the Taiwan Straits and significant deviations of circulation center fromgeopotentia1 center between upper and lower levels. By examining ev0lutions of 3-h interval simulatedresults, detailed processes of changes in structure and track before and after Dot's passage of Taiwanis given, whose evolutional images are otherwise impossible with conventionai observations at intervalsof 6 h. A number of control experboents are conducted in the end of the work for understanding causesand mechanisms behind various properties.
1997, 3(2): 140-151.
Abstract:
A predictive model for 24-120 h track of the tropical cyclone over the South ChinaSea is set upusing the predictors of CLIPER and with reference to those of EOF and CCA. This EOF-and CCA-basedmodel is compared with dependent and independent samples in veritring forecasts'Analpees appltwg themethods to 500-hPa geopotential heights have shown that the CCA method is able toconcentrate moreoriginal information of variable fleld that has the best global correlation withtropical cyclone track andthus reduces more efficiently error arisen in forecast,despite that can0nicaldistribution of weighted vari-able coefficients derived by it is less well-defined or smoothed of a spacialpattern as is done by eigenvec-tor in the EOF method. The verification indicates a certain degree of skill in both track predictive model,though better results are yielded in the CCA-based one, whose mean vector errorare 159.27, 314.84,524.12, 813.03, and 987.12 km, respectively for periods of 24, 48, 72, 96, and 120 h. The modelmakes an objective approach for prediction of short-and medium-range track of tropical cyclone in theSouth China Sea.
A predictive model for 24-120 h track of the tropical cyclone over the South ChinaSea is set upusing the predictors of CLIPER and with reference to those of EOF and CCA. This EOF-and CCA-basedmodel is compared with dependent and independent samples in veritring forecasts'Analpees appltwg themethods to 500-hPa geopotential heights have shown that the CCA method is able toconcentrate moreoriginal information of variable fleld that has the best global correlation withtropical cyclone track andthus reduces more efficiently error arisen in forecast,despite that can0nicaldistribution of weighted vari-able coefficients derived by it is less well-defined or smoothed of a spacialpattern as is done by eigenvec-tor in the EOF method. The verification indicates a certain degree of skill in both track predictive model,though better results are yielded in the CCA-based one, whose mean vector errorare 159.27, 314.84,524.12, 813.03, and 987.12 km, respectively for periods of 24, 48, 72, 96, and 120 h. The modelmakes an objective approach for prediction of short-and medium-range track of tropical cyclone in theSouth China Sea.
1997, 3(2): 152-158.
Abstract:
In this paper, a statistical interpretation composite forecast model for typhoon track is set up by using numerical forecast products and several forecast schemes. Tested in 1994 typhoon season, its forecastperformance is much better than that of a previous statistical forecast model. The test shows that it is aneffective method that sufficiently Anproves objective forecast of typhoon track using the numerical forecast output products obtained in forecast and adopting several schemes in composition.
In this paper, a statistical interpretation composite forecast model for typhoon track is set up by using numerical forecast products and several forecast schemes. Tested in 1994 typhoon season, its forecastperformance is much better than that of a previous statistical forecast model. The test shows that it is aneffective method that sufficiently Anproves objective forecast of typhoon track using the numerical forecast output products obtained in forecast and adopting several schemes in composition.
1997, 3(2): 159-167.
Abstract:
Five prediction experiments are carried out with two typhoons in 1992 using a limitedarca primitiveequations and two-way interactive model in a movable,nested mesh. The result indicates good agreementin terms of motion between the prediction and observation. Studying the asymmetric structure in the cases selected, a close link is uncovered between the temporal evolutions of the structure and the track of motion in a tropical cyclone. Understanding of real asymmetric structure will help to improve the skill offorecasting tropical cyclones.
Five prediction experiments are carried out with two typhoons in 1992 using a limitedarca primitiveequations and two-way interactive model in a movable,nested mesh. The result indicates good agreementin terms of motion between the prediction and observation. Studying the asymmetric structure in the cases selected, a close link is uncovered between the temporal evolutions of the structure and the track of motion in a tropical cyclone. Understanding of real asymmetric structure will help to improve the skill offorecasting tropical cyclones.
1997, 3(2): 168-176.
Abstract:
Using IAP-AGCM, a model developed by the institute of atmospheric research, Academia Sinica,controlled numerital expertrients on SST and east Asian circulation have been performed and some conclusions have been reached as follows. The abnomality of subtropical high has a two-month remote lagging response to SSTA of the western tropical Pacific, the South China Sea and the Bay of Bengal. Theabnormality always appears in pair for the western Pacific subtrphal high and the eastern Pacific subtropical high, with the latter beginning earlier than the former. When the SST of the western trophal Pacific, South China Sea and Bay of Bengal anomalously decreases(increases), the subtropical high iskept anomalously more to the south(north),consistently so is the location at which two zonal geopotential waves meet in the subtropical western Pacific. Under the action of the SSTA above and when ablocking pattern over east Asia continent appears, the assembling location of the joinin8 waves for thewestern Pacific is closely related to that of the blocking high, which is especially important to consistentabnormality of the subtropical high.
Using IAP-AGCM, a model developed by the institute of atmospheric research, Academia Sinica,controlled numerital expertrients on SST and east Asian circulation have been performed and some conclusions have been reached as follows. The abnomality of subtropical high has a two-month remote lagging response to SSTA of the western tropical Pacific, the South China Sea and the Bay of Bengal. Theabnormality always appears in pair for the western Pacific subtrphal high and the eastern Pacific subtropical high, with the latter beginning earlier than the former. When the SST of the western trophal Pacific, South China Sea and Bay of Bengal anomalously decreases(increases), the subtropical high iskept anomalously more to the south(north),consistently so is the location at which two zonal geopotential waves meet in the subtropical western Pacific. Under the action of the SSTA above and when ablocking pattern over east Asia continent appears, the assembling location of the joinin8 waves for thewestern Pacific is closely related to that of the blocking high, which is especially important to consistentabnormality of the subtropical high.
1997, 3(2): 177-191.
Abstract:
During the "8th Five-Year Plan"(1991～1995), a new operational mesoscale numerical predictionsystem is developed, which is called the "Regional Enhanced Numerical Prediction System". The system possesses higher resolution(45 km grid sise in horizontal, 10 layers in vertital), as well as fullphysical processes, and can be run operationally in the Guangzhou Regional Meteorological Centre(GRMC). A plenty of experiments indicate its better performance in predicting various weather systemsaffecting the south of China, especially the typhoon and heavy rain in the "early floods stage"(annuallyspeaking). Verification of the prediction of all typhoon cases affecting the region in 1993～1995 indicatethat rainfall prediction scores of the system are obviously higher than those of the LAFS in the NationalMeteorological Centre, and track prediction error is no larger than those of NWPs in main world centressuch as the National Hurrieane Center of NOAA and the JMA. The aim of the paper is to give a generalized introduction and analysis to the system and its performance.
During the "8th Five-Year Plan"(1991～1995), a new operational mesoscale numerical predictionsystem is developed, which is called the "Regional Enhanced Numerical Prediction System". The system possesses higher resolution(45 km grid sise in horizontal, 10 layers in vertital), as well as fullphysical processes, and can be run operationally in the Guangzhou Regional Meteorological Centre(GRMC). A plenty of experiments indicate its better performance in predicting various weather systemsaffecting the south of China, especially the typhoon and heavy rain in the "early floods stage"(annuallyspeaking). Verification of the prediction of all typhoon cases affecting the region in 1993～1995 indicatethat rainfall prediction scores of the system are obviously higher than those of the LAFS in the NationalMeteorological Centre, and track prediction error is no larger than those of NWPs in main world centressuch as the National Hurrieane Center of NOAA and the JMA. The aim of the paper is to give a generalized introduction and analysis to the system and its performance.
1997, 3(2): 192-201.
Abstract:
It is very important to locate and track weather systems which cause severe calamity,such as severeconvective clouds(SCC),in nowcasting. In this paper the recognition and tracking of SCC is studied with GMS IR images using computer image techniques. As an IR image preprocessing, a SCC futerlng algorithm is put forward that combines a segment smoothing filtering and a removal procedure by thresholds. To the filtered SCCs the T algorithm and IP algorithm of contour coding method are applied to extract the contour line and its initial point. The description of SCCs includes four characteristic quantities, i. e. center of gravity, cloud size, moment invariant M and R-shaped descriptor. Pattern recosnitionand pattern matching techniques are used to track the SCCs. Two procedures of rough and fine matchingare given. The former procedure include the setting of searching area and recognition of area and the latter is composed by the matching of shape descriptor R and moment invariant M and the analysis of correlative brightness temperature analysis.
It is very important to locate and track weather systems which cause severe calamity,such as severeconvective clouds(SCC),in nowcasting. In this paper the recognition and tracking of SCC is studied with GMS IR images using computer image techniques. As an IR image preprocessing, a SCC futerlng algorithm is put forward that combines a segment smoothing filtering and a removal procedure by thresholds. To the filtered SCCs the T algorithm and IP algorithm of contour coding method are applied to extract the contour line and its initial point. The description of SCCs includes four characteristic quantities, i. e. center of gravity, cloud size, moment invariant M and R-shaped descriptor. Pattern recosnitionand pattern matching techniques are used to track the SCCs. Two procedures of rough and fine matchingare given. The former procedure include the setting of searching area and recognition of area and the latter is composed by the matching of shape descriptor R and moment invariant M and the analysis of correlative brightness temperature analysis.
1997, 3(2): 202-206.
Abstract:
This paper suggests a method to eompute the verticaI velocity at the top of PBL Jn low latitude areas by use of the wind data on(sea)surfaca and some characteristics of the vcrtical velocity are shownThe results show the important rolcs played by the incrtial forces and β effect
This paper suggests a method to eompute the verticaI velocity at the top of PBL Jn low latitude areas by use of the wind data on(sea)surfaca and some characteristics of the vcrtical velocity are shownThe results show the important rolcs played by the incrtial forces and β effect
1997, 3(2): 208-214.
Abstract:
As shown in a statistical analysis of the relationship between environmental fields at varied timeand tropical cyclone motion, the forecasting ability of the initisl environmental field predictors for tropical cyclone motion decreases with the increase of valid time period of forecast;it is higher with these predictors at a fUture time than at an initial time. The work also indicates that for the tropical cyclone motion over a given period of valid forecast, better predictors appear at times mostly differing from thevalid periods; for periods at 48-120 h the environmental predictors at 48-72 h are more capable of forecasting. With statistical interpretation of NWP products, a predictive model for tropical cyclone motionis superior in performance over a statistical forecasting model that employes predictors of the initial field in the basic framework. The concluding remarks can be used as reference in the construction of an objective prediction model for tropical cyclone motion.
As shown in a statistical analysis of the relationship between environmental fields at varied timeand tropical cyclone motion, the forecasting ability of the initisl environmental field predictors for tropical cyclone motion decreases with the increase of valid time period of forecast;it is higher with these predictors at a fUture time than at an initial time. The work also indicates that for the tropical cyclone motion over a given period of valid forecast, better predictors appear at times mostly differing from thevalid periods; for periods at 48-120 h the environmental predictors at 48-72 h are more capable of forecasting. With statistical interpretation of NWP products, a predictive model for tropical cyclone motionis superior in performance over a statistical forecasting model that employes predictors of the initial field in the basic framework. The concluding remarks can be used as reference in the construction of an objective prediction model for tropical cyclone motion.
1997, 3(2): 215-224.
Abstract:
In this paper satellite-derived radiative energy budget such as shortwave radiative heating,longwaveradiative heating and net radiation balance have been studied for the onset phase of summer monsoon1979. Since cloud play an important role in determining diabatic heating field as well as being a reflectionof status of the monsoon itself, the day to day evolution of clouds from TIROS-N satellite has beenmade. Satellite-derived radiative heating rates from surface to 100 hPa were computed for each 100 hPathickness layer. These heating rates were then compared with the observed latitudinal distribution of total radintive heating rates over the domain of the study. From the results of our study it was found thatthe characteristic features such as net radiative heating rates of the order of 0.2℃/day at upper tropospheric level(100-200 hPa)and cooling throughout the lower tropospheric layers with relatively lesscooling between 500-700 hPa layer observed.in a case of satellitexierived radiative energy budget agreewell with the characteristic features of observational radiative energy budget over the domain of thestudy. Therefore, it is suggested that radiative energy budget derived from satellite observati0ns be usedwith great potential and confidence for the evolution of complete life cycle of monsoon over the Indianregion for different years.
In this paper satellite-derived radiative energy budget such as shortwave radiative heating,longwaveradiative heating and net radiation balance have been studied for the onset phase of summer monsoon1979. Since cloud play an important role in determining diabatic heating field as well as being a reflectionof status of the monsoon itself, the day to day evolution of clouds from TIROS-N satellite has beenmade. Satellite-derived radiative heating rates from surface to 100 hPa were computed for each 100 hPathickness layer. These heating rates were then compared with the observed latitudinal distribution of total radintive heating rates over the domain of the study. From the results of our study it was found thatthe characteristic features such as net radiative heating rates of the order of 0.2℃/day at upper tropospheric level(100-200 hPa)and cooling throughout the lower tropospheric layers with relatively lesscooling between 500-700 hPa layer observed.in a case of satellitexierived radiative energy budget agreewell with the characteristic features of observational radiative energy budget over the domain of thestudy. Therefore, it is suggested that radiative energy budget derived from satellite observati0ns be usedwith great potential and confidence for the evolution of complete life cycle of monsoon over the Indianregion for different years.
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