This paper describes the results of an analysis of extreme rainfall events in the central plateau of Iran. To study the extreme events, daily records of eighteen stations’ rainfalls in the region for different initia...This paper describes the results of an analysis of extreme rainfall events in the central plateau of Iran. To study the extreme events, daily records of eighteen stations’ rainfalls in the region for different initial dates up to 2005 gathered from the bureau of meteorology. Then, the extreme rainfall threshold was calculated for each individual station using the statistical index of Gamble type I. Lastly, 22 mm was determined as the extreme rainfall value for the entire stations, and eventually 17 out of 169 extreme precipitation events were extracted in accordance with three factors including a) days with precipitation in not less than 50% of the stations, b) maximum rainfall is 22 mm or more in at least one of the stations, and c) mean precipitation of the basin is more than 3 mm. In the next step to analyze the synoptic features, the relevant meteorological data i.e. relative vorticity, geopotential height, sea level pressure, u and v wind components, relative humidity, vertical velocity, and precipitable water content at multiple levels of the atmosphere were examined from the NCEP/NCAR reanalysis dataset. The synoptic findings indicate that two patterns of deep trough and high ridge of the eastern Mediterranean were responsible for making the heavy precipitation events over the central plateau of Iran. The most and severest rainfall events occurred via deep tough pattern, which covered 76% of days with extreme precipitations during the examined period. Furthermore, the results suggest that the main moisture resources, which identified by HYSPLIT model’s outputs and moisture convergence/divergence zones for the rainy systems in the first pattern (deep trough) including Persian Gulf, Oman Sea, Indian Ocean, and Red Sea, while for the second pattern (high ridge) Persian Gulf and Red Sea play a significant role in feeding the storms in the central regions of Iran. Moreover, the southward movement of Polar Vortex is also considered as those important factors to produce extreme precipitation events over the central plateau of Iran. In general, the HYSPLIT trajectories model’s outputs confirmed the observed synoptic features in particular for the systems’ moisture feeding discussed in the patterns.展开更多
In this paper, an objective technique for estimating the tropical cyclone （TC） precipitation from station observations is proposed. Based on a comparison between the Original Objective Method （OOM） and the Expert ...In this paper, an objective technique for estimating the tropical cyclone （TC） precipitation from station observations is proposed. Based on a comparison between the Original Objective Method （OOM） and the Expert Subjective Method （ESM）, the Objective Synoptic Analysis Technique （OSAT） for partitioning TC precipitation was developed by analyzing the western North Pacific （WNP） TC historical track and the daily precipitation datasets. Being an objective way of the ESM, OSAT overcomes the main problems in OOM, by changing two fixed parameters in OOM, the thresholds for the distance of the absolute TC precipitation （D0） and the TC size （D1）, into variable parameters.Case verification for OSAT was also carried out by applying CMORPH （Climate Prediction Center MORPHing technique） daily precipitation measurements, which is NOAA＇s combined satellite precipitation measurement system. This indicates that OSAT is capable of distinguishing simultaneous TC precipitation rain-belts from those associated with different TCs or with middle-latitude weather systems.展开更多
The heavy rainfall in Beijing on 21 July 2012 was a high impact event. First, a synoptic overview of this event is presented based on the ECMWF reanalysis and forecast data, together with observations of hourly precip...The heavy rainfall in Beijing on 21 July 2012 was a high impact event. First, a synoptic overview of this event is presented based on the ECMWF reanalysis and forecast data, together with observations of hourly precipitation. It is found that an east to northeastward moving ＂low-level northwest vortex＂ caused this event. The vortex was formed under favorable circulation patterns and intensified by low-level dry intrusions. The source regions of the large volume of moisture necessary to sustain the intense rainfall are diagnosed by back-trajectory analysis. Approximately 77% of the moisture was transported from the Bay of Bengal （BOB）. The transport processes, including vertical profiles, mean humidity variations, and relative importance of the rain-paths, are further quantified by the back-trajectory analysis and cluster analysis. The results highlight the importance of the southwestern path in transporting moisture to northern China, which accounts for 88.4% of the moisture from the BoB, and 68% of the total of the ＂7.21＂ heavy rainfall event.展开更多
The momentum advection vorticity equation in the form of cross multiplication is introduced, in which the divergence term in the classic vorticity equation does not appear explicitly. This equation includes the rotati...The momentum advection vorticity equation in the form of cross multiplication is introduced, in which the divergence term in the classic vorticity equation does not appear explicitly. This equation includes the rotation effect of the horizontal wind advection, which are not explicitly included in the classic vortieity equation. The vorticity and its tendency of Typhoon Fung-Wong （0808） that occurred in July 2008 are analyzed. The computed results show that the rotation effect of the advection of the horizontal wind is a leading factor in determining the change of vertical vorticity for Fung-Wong during its life cycle, especially in the period leading up to landfall. The advection term represents the tendency variation of the vertical vortieity, and the positive-value region of the vertical vorticity tendency is almost in accord with the track of Fung-Wong, which may be taken as a factor to locate the key observational region of Fung-Wong. The equation provides a supplementary diagnostic tool for the systems related with strong advection of horizontal wind.展开更多
[Objective] The research aimed to study the influence of typhoon Usagi on Shaoyang in 2013. [Method] By using synoptic analysis, physical quantity diagnosis and Doppler radar, a rainstorm process caused by typhoon Usa...[Objective] The research aimed to study the influence of typhoon Usagi on Shaoyang in 2013. [Method] By using synoptic analysis, physical quantity diagnosis and Doppler radar, a rainstorm process caused by typhoon Usagi was analyzed. [ Result] Sufficient water vaper and strong ascending motion caused by high-altitude divergence were favorable conditions for rainstorm generation in Shaoyang. Uplifting effect of the terrain in Shaoyang was also one of favorable conditions for rainstorm generation in Shaoyang. [Conclusion] The research could provide reference for flood prevention and disaster reduction in Shaoyang area.展开更多
Both of Typhoon Winnie (9711) and Matsa (0509) underwent an extratropical transition (ET) process when they moved northward after landfall and affected Liaodong Peninsula. However, Matsa produced half as much rainfall...Both of Typhoon Winnie (9711) and Matsa (0509) underwent an extratropical transition (ET) process when they moved northward after landfall and affected Liaodong Peninsula. However, Matsa produced half as much rainfall as Winnie, although it struck Liaodong Peninsula directly while Winnie passed through the Bohai Sea. The relations between the ET processes and the precipitation over Liaodong Peninsula are examined. The result shows that the precipitation difference between Winnie and Matsa was closely related to the interactions between the westerly systems and typhoons during their ET processes. Winnie was captured by the upper westerly trough and then coupled with it when moving to the mid-latitudes, and the positive anomaly of moist potential vorticity (MPV) was transported downward from the upper troposphere over the remnant circulation of the tropical cyclone (TC). It was favorable to the interaction between tropical warm and wet air and westerly cold air, causing convective cloud clusters to form and develop. The rain belt composed of several meso-β cloud clusters over the Liaodong Peninsula, resulting in heavy rainfall. On the other hand, Matsa did not couple with any upper trough during its ET process and the positive anomaly of MPV in the upper troposphere and its downward transfer were weak. Only one meso-β cloud cluster occurred in Matsa’s rain belt during its ET process that tended to lessen rainfall over Liaodong Peninsula.展开更多
South China suffered an extremely severe disaster caused by low-temperature and ice-snow during the last 20 days of January 2008. The freezing rain and snow are climatologically related to the South China quasistation...South China suffered an extremely severe disaster caused by low-temperature and ice-snow during the last 20 days of January 2008. The freezing rain and snow are climatologically related to the South China quasistationary front （SCQSF） in mid winter. The three-dimensional structure of the SCQSF was examined based on the weather charts, the sounding profiles, and the vertical cross-sections using the method of classical synoptic analysis.展开更多
文摘This paper describes the results of an analysis of extreme rainfall events in the central plateau of Iran. To study the extreme events, daily records of eighteen stations’ rainfalls in the region for different initial dates up to 2005 gathered from the bureau of meteorology. Then, the extreme rainfall threshold was calculated for each individual station using the statistical index of Gamble type I. Lastly, 22 mm was determined as the extreme rainfall value for the entire stations, and eventually 17 out of 169 extreme precipitation events were extracted in accordance with three factors including a) days with precipitation in not less than 50% of the stations, b) maximum rainfall is 22 mm or more in at least one of the stations, and c) mean precipitation of the basin is more than 3 mm. In the next step to analyze the synoptic features, the relevant meteorological data i.e. relative vorticity, geopotential height, sea level pressure, u and v wind components, relative humidity, vertical velocity, and precipitable water content at multiple levels of the atmosphere were examined from the NCEP/NCAR reanalysis dataset. The synoptic findings indicate that two patterns of deep trough and high ridge of the eastern Mediterranean were responsible for making the heavy precipitation events over the central plateau of Iran. The most and severest rainfall events occurred via deep tough pattern, which covered 76% of days with extreme precipitations during the examined period. Furthermore, the results suggest that the main moisture resources, which identified by HYSPLIT model’s outputs and moisture convergence/divergence zones for the rainy systems in the first pattern (deep trough) including Persian Gulf, Oman Sea, Indian Ocean, and Red Sea, while for the second pattern (high ridge) Persian Gulf and Red Sea play a significant role in feeding the storms in the central regions of Iran. Moreover, the southward movement of Polar Vortex is also considered as those important factors to produce extreme precipitation events over the central plateau of Iran. In general, the HYSPLIT trajectories model’s outputs confirmed the observed synoptic features in particular for the systems’ moisture feeding discussed in the patterns.
文摘In this paper, an objective technique for estimating the tropical cyclone （TC） precipitation from station observations is proposed. Based on a comparison between the Original Objective Method （OOM） and the Expert Subjective Method （ESM）, the Objective Synoptic Analysis Technique （OSAT） for partitioning TC precipitation was developed by analyzing the western North Pacific （WNP） TC historical track and the daily precipitation datasets. Being an objective way of the ESM, OSAT overcomes the main problems in OOM, by changing two fixed parameters in OOM, the thresholds for the distance of the absolute TC precipitation （D0） and the TC size （D1）, into variable parameters.Case verification for OSAT was also carried out by applying CMORPH （Climate Prediction Center MORPHing technique） daily precipitation measurements, which is NOAA＇s combined satellite precipitation measurement system. This indicates that OSAT is capable of distinguishing simultaneous TC precipitation rain-belts from those associated with different TCs or with middle-latitude weather systems.
基金Supported by the Joint Scientific Thematic Research Programme(JSTP)International Cooperation Program of the Ministry of Science and Technology of China(2011DFG23440)State Scholarship Fund of China Scholarship Council(CSC)
文摘The heavy rainfall in Beijing on 21 July 2012 was a high impact event. First, a synoptic overview of this event is presented based on the ECMWF reanalysis and forecast data, together with observations of hourly precipitation. It is found that an east to northeastward moving ＂low-level northwest vortex＂ caused this event. The vortex was formed under favorable circulation patterns and intensified by low-level dry intrusions. The source regions of the large volume of moisture necessary to sustain the intense rainfall are diagnosed by back-trajectory analysis. Approximately 77% of the moisture was transported from the Bay of Bengal （BOB）. The transport processes, including vertical profiles, mean humidity variations, and relative importance of the rain-paths, are further quantified by the back-trajectory analysis and cluster analysis. The results highlight the importance of the southwestern path in transporting moisture to northern China, which accounts for 88.4% of the moisture from the BoB, and 68% of the total of the ＂7.21＂ heavy rainfall event.
基金projects of the Ministry of Sciences and Technology of the People’s Republic of China (GYHY200906004 GYHY200706020)+1 种基金project of the Natural Science Foundation of China (40975034)project of State Key Laboratory of Severe Weather (2008LASW-A01)
文摘The momentum advection vorticity equation in the form of cross multiplication is introduced, in which the divergence term in the classic vorticity equation does not appear explicitly. This equation includes the rotation effect of the horizontal wind advection, which are not explicitly included in the classic vortieity equation. The vorticity and its tendency of Typhoon Fung-Wong （0808） that occurred in July 2008 are analyzed. The computed results show that the rotation effect of the advection of the horizontal wind is a leading factor in determining the change of vertical vorticity for Fung-Wong during its life cycle, especially in the period leading up to landfall. The advection term represents the tendency variation of the vertical vortieity, and the positive-value region of the vertical vorticity tendency is almost in accord with the track of Fung-Wong, which may be taken as a factor to locate the key observational region of Fung-Wong. The equation provides a supplementary diagnostic tool for the systems related with strong advection of horizontal wind.
文摘[Objective] The research aimed to study the influence of typhoon Usagi on Shaoyang in 2013. [Method] By using synoptic analysis, physical quantity diagnosis and Doppler radar, a rainstorm process caused by typhoon Usagi was analyzed. [ Result] Sufficient water vaper and strong ascending motion caused by high-altitude divergence were favorable conditions for rainstorm generation in Shaoyang. Uplifting effect of the terrain in Shaoyang was also one of favorable conditions for rainstorm generation in Shaoyang. [Conclusion] The research could provide reference for flood prevention and disaster reduction in Shaoyang area.
基金National Key Fundamental Project for Research Development and Plan (2004CB418301)Natural Science Foundation of China (40575018, 40675033)
文摘Both of Typhoon Winnie (9711) and Matsa (0509) underwent an extratropical transition (ET) process when they moved northward after landfall and affected Liaodong Peninsula. However, Matsa produced half as much rainfall as Winnie, although it struck Liaodong Peninsula directly while Winnie passed through the Bohai Sea. The relations between the ET processes and the precipitation over Liaodong Peninsula are examined. The result shows that the precipitation difference between Winnie and Matsa was closely related to the interactions between the westerly systems and typhoons during their ET processes. Winnie was captured by the upper westerly trough and then coupled with it when moving to the mid-latitudes, and the positive anomaly of moist potential vorticity (MPV) was transported downward from the upper troposphere over the remnant circulation of the tropical cyclone (TC). It was favorable to the interaction between tropical warm and wet air and westerly cold air, causing convective cloud clusters to form and develop. The rain belt composed of several meso-β cloud clusters over the Liaodong Peninsula, resulting in heavy rainfall. On the other hand, Matsa did not couple with any upper trough during its ET process and the positive anomaly of MPV in the upper troposphere and its downward transfer were weak. Only one meso-β cloud cluster occurred in Matsa’s rain belt during its ET process that tended to lessen rainfall over Liaodong Peninsula.
基金the Key Project of the National Scientific and Technological Supporting Program of the 11th Five-Year Plan of China and the Open Project of the State Key Laboratory of Severe Weather of Chinese Academy of Meteorological Sciences in 2007.
文摘South China suffered an extremely severe disaster caused by low-temperature and ice-snow during the last 20 days of January 2008. The freezing rain and snow are climatologically related to the South China quasistationary front （SCQSF） in mid winter. The three-dimensional structure of the SCQSF was examined based on the weather charts, the sounding profiles, and the vertical cross-sections using the method of classical synoptic analysis.
