Monsoon gyres have been identified as one of the important large-scale circulation patterns associated with tropical cyclone （TC） formation in the western North Pacific.A recent observational analysis indicated that...Monsoon gyres have been identified as one of the important large-scale circulation patterns associated with tropical cyclone （TC） formation in the western North Pacific.A recent observational analysis indicated that most TCs form near the center of monsoon gyres or at the northeast end of the enhanced low-level southwesterly flows on the southeast-east periphery of monsoon gyres.In the present reported study,idealized numerical experiments were conducted to examine the tropical cyclogenesis associated with Rossby wave energy dispersion with an initial idealized monsoon gyre.The numerical simulations showed that the development of the low-level enhanced southwesterly flows on the southeasteast periphery of monsoon gyres can be induced by Rossby wave energy dispersion.Mesoscale convective systems emerged from the northeast end of the enhanced southwesterly flows with mid-level maximum relative vorticity.The simulated TC formed in the northeast of the monsoon gyre and moved westward towards the center of the monsoon gyre.The numerical experiment with a relatively smaller sized initial monsoon gyre showed the TC forming near the center of the initial monsoon gyre.The results of the present study suggest that Rossby wave energy dispersion can play an important role in TC formation in the presence of monsoon gyres.展开更多
A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding.The simulations are performed for two clouds that differ in their initial wind shear.Results show that,although cloud see...A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding.The simulations are performed for two clouds that differ in their initial wind shear.Results show that,although cloud seeding with an ice concentration of 1000 Lin a regime that has relatively high supercooled liquid water can obtain a positive effect,the rainfall enhancement seems more pronounced when the cloud develops in a wind shear environment.In no-shear environment,the change in the microphysical thermodynamic field after seeding shows that,although more graupel is produced via riming and this can increase the surface rainfall intensity,the larger drag force and cooling of melting graupel is unfavorable for the development of cloud.On the contrary,when the cloud develops in a wind shear environment,since the main downdraft is behind the direction of movement of the cloud,its negative effect on precipitation is much weaker.展开更多
Recent observational and numerical studies have revealed the dependence of the intensification rate on the inner-core size of tropical cyclones(TCs). In this study, with the initial inner-core size(i.e., the radius of...Recent observational and numerical studies have revealed the dependence of the intensification rate on the inner-core size of tropical cyclones(TCs). In this study, with the initial inner-core size(i.e., the radius of maximum wind—RMW)varied from 20–180 km in idealized simulations using two different numerical models, we found a nonmonotonic dependence of the lifetime maximum intensification rate(LMIR) on the inner-core size. Namely, there is an optimal innercore size for the LMIR of a TC. Tangential wind budget analysis shows that, compared to large TCs, small TCs have large inward flux of absolute vorticity due to large absolute vorticity inside the RMW. However, small TCs also suffer from strong lateral diffusion across the eyewall, which partly offsets the positive contribution from large inward flux of absolute vorticity. These two competing processes ultimately lead to the TC with an intermediate initial inner-core size having the largest LMIR. Results from sensitivity experiments show that the optimal size varies in the range of 40–120 km and increases with higher sea surface temperature, lower latitude, larger horizontal mixing length, and weaker initial TC intensity. The 40–120 km RMW corresponds to the inner-core size most commonly found for intensifying TCs in observations, suggesting the natural selection of initial TC size for intensification. This study highlights the importance of accurate representation of TC inner-core size to TC intensity forecasts by numerical weather prediction models.展开更多
The aim of this study is to examine the difference in tropical cyclone （TC） formation in different cyclonic circulation locations using a mesoscale model on a beta plane. A weak initial vortex is imposed at differen...The aim of this study is to examine the difference in tropical cyclone （TC） formation in different cyclonic circulation locations using a mesoscale model on a beta plane. A weak initial vortex is imposed at different positions in a cyclonic circulation. Numerical experiments indicate that the tropical disturbances located in the center and northeastern parts of the cyclonic circulation are favorable to TC formation, while those located in the south of the cyclonic circulation are unfavorable. Since the asymmetric circulation induced by the beta effect peaks in the northeastern quadrant of the vortex, when the initial vortex is placed in the southern part of the cyclonic circulation, the vortex begins to develop in the south due to the effect of the westerly wind of the cyclonic circulation. The westerly wind of the cyclonic circulation gradually decreases and the vortex is contributed mainly by the beta effect afterwards. Thus, establishment of the convection circulation-moisture positive feedback is delayed, unfavorable to TC rapid development. On the contrary, when the initial vortex is placed in the northern part of the cyclonic circulation, the superposition of the beta gyres and easterly wind of the cyclonic circulation induces stronger wavenumber-1 wind in the northeastern part of the vortex. The greater asymmetric wind is closely associated with the symmetric wind through energy conversion, thus accelerating a positive feedback and facilitating vortex development into a stronger TC. Meanwhile, when the initial vortex is placed in the center and eastern parts of the cyclonic circulation, the vortex develops a little slower than when it is placed in the northern part, but stronger than when placed in the southern part.展开更多
In this article,the approach of simulating ideal tarp scene was proposed to determine the MTF for CCD camera on CBERS-02.The MTF acquired from this technique was compared to those from some common methods.MTFs achieve...In this article,the approach of simulating ideal tarp scene was proposed to determine the MTF for CCD camera on CBERS-02.The MTF acquired from this technique was compared to those from some common methods.MTFs achieved from different approaches were employed to compensate the CCD images based on three restoration algorithms:the iterative method,the Wiener filter and the modified inverse filter(MIF).The two-dimensional MTF was established with the value at frequency 0.5 for 45°directional MTF as the value at its four corners.This article addressed the variations of the restored CCD images with different techniques of constructing two-dimensional MTF,restoring algorithms and determining the in-flight MTFs.Results showed images restored with the MTF determined from the technique of simulating ideal tarp scene represent the real scene best.And the restoration technique based on the MIF would produce better restored images than the other two techniques.This research also demonstrated that the two-dimensional MTF used for restoration should be interpolated under the control of the MTF for 45°axis,rather than by multiplying the cross-orbit MTF with along-orbit MTF.展开更多
基金supported by the typhoon research project (Grant No. 2009CB421503) of the National Basic Research Program of Chinathe National Natural Science Foundation of China (Grant No. 41275093)+2 种基金the social commonwealth research program of the Ministry of ScienceTechnology of the People’s Republic of China (Grant No. GYHY200806009)the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘Monsoon gyres have been identified as one of the important large-scale circulation patterns associated with tropical cyclone （TC） formation in the western North Pacific.A recent observational analysis indicated that most TCs form near the center of monsoon gyres or at the northeast end of the enhanced low-level southwesterly flows on the southeast-east periphery of monsoon gyres.In the present reported study,idealized numerical experiments were conducted to examine the tropical cyclogenesis associated with Rossby wave energy dispersion with an initial idealized monsoon gyre.The numerical simulations showed that the development of the low-level enhanced southwesterly flows on the southeasteast periphery of monsoon gyres can be induced by Rossby wave energy dispersion.Mesoscale convective systems emerged from the northeast end of the enhanced southwesterly flows with mid-level maximum relative vorticity.The simulated TC formed in the northeast of the monsoon gyre and moved westward towards the center of the monsoon gyre.The numerical experiment with a relatively smaller sized initial monsoon gyre showed the TC forming near the center of the initial monsoon gyre.The results of the present study suggest that Rossby wave energy dispersion can play an important role in TC formation in the presence of monsoon gyres.
基金This study was jointly supported by the National Key Research and Development Program of China[grant number 2018YFC1507900]the National Natural Science Foundation of China[grant numbers 41875172 and 42075192].
文摘A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding.The simulations are performed for two clouds that differ in their initial wind shear.Results show that,although cloud seeding with an ice concentration of 1000 Lin a regime that has relatively high supercooled liquid water can obtain a positive effect,the rainfall enhancement seems more pronounced when the cloud develops in a wind shear environment.In no-shear environment,the change in the microphysical thermodynamic field after seeding shows that,although more graupel is produced via riming and this can increase the surface rainfall intensity,the larger drag force and cooling of melting graupel is unfavorable for the development of cloud.On the contrary,when the cloud develops in a wind shear environment,since the main downdraft is behind the direction of movement of the cloud,its negative effect on precipitation is much weaker.
基金supported by the National Natural Science Foundation of China (Grant No.41730960)Wuxi University Research Start-up Fund for Introduced Talents (2024r037)Yuqing WANG was supported by the NSF (Grant No. AGS-1834300)。
文摘Recent observational and numerical studies have revealed the dependence of the intensification rate on the inner-core size of tropical cyclones(TCs). In this study, with the initial inner-core size(i.e., the radius of maximum wind—RMW)varied from 20–180 km in idealized simulations using two different numerical models, we found a nonmonotonic dependence of the lifetime maximum intensification rate(LMIR) on the inner-core size. Namely, there is an optimal innercore size for the LMIR of a TC. Tangential wind budget analysis shows that, compared to large TCs, small TCs have large inward flux of absolute vorticity due to large absolute vorticity inside the RMW. However, small TCs also suffer from strong lateral diffusion across the eyewall, which partly offsets the positive contribution from large inward flux of absolute vorticity. These two competing processes ultimately lead to the TC with an intermediate initial inner-core size having the largest LMIR. Results from sensitivity experiments show that the optimal size varies in the range of 40–120 km and increases with higher sea surface temperature, lower latitude, larger horizontal mixing length, and weaker initial TC intensity. The 40–120 km RMW corresponds to the inner-core size most commonly found for intensifying TCs in observations, suggesting the natural selection of initial TC size for intensification. This study highlights the importance of accurate representation of TC inner-core size to TC intensity forecasts by numerical weather prediction models.
基金Supported by the National Basic ResearchDevelopment(973)Program of China(2014CB953902)+1 种基金National Natural Science Foundation of China(41505048,41461164005,41275001,and 41475074)LASW State Key Laboratory Special Fund(2015LASW-B04)
文摘The aim of this study is to examine the difference in tropical cyclone （TC） formation in different cyclonic circulation locations using a mesoscale model on a beta plane. A weak initial vortex is imposed at different positions in a cyclonic circulation. Numerical experiments indicate that the tropical disturbances located in the center and northeastern parts of the cyclonic circulation are favorable to TC formation, while those located in the south of the cyclonic circulation are unfavorable. Since the asymmetric circulation induced by the beta effect peaks in the northeastern quadrant of the vortex, when the initial vortex is placed in the southern part of the cyclonic circulation, the vortex begins to develop in the south due to the effect of the westerly wind of the cyclonic circulation. The westerly wind of the cyclonic circulation gradually decreases and the vortex is contributed mainly by the beta effect afterwards. Thus, establishment of the convection circulation-moisture positive feedback is delayed, unfavorable to TC rapid development. On the contrary, when the initial vortex is placed in the northern part of the cyclonic circulation, the superposition of the beta gyres and easterly wind of the cyclonic circulation induces stronger wavenumber-1 wind in the northeastern part of the vortex. The greater asymmetric wind is closely associated with the symmetric wind through energy conversion, thus accelerating a positive feedback and facilitating vortex development into a stronger TC. Meanwhile, when the initial vortex is placed in the center and eastern parts of the cyclonic circulation, the vortex develops a little slower than when it is placed in the northern part, but stronger than when placed in the southern part.
基金supported by the Hundred Talents Program of the Chinese Academy of Sciences(Grant No.KZCX0415)the Scientific Research Foundation for the Returned Overseas Chinese Scholars+1 种基金the Ministry of Education(Grant No.HX040013)the fund from Commission of Science Technology and Industry for National Defense(KJSX0401).
文摘In this article,the approach of simulating ideal tarp scene was proposed to determine the MTF for CCD camera on CBERS-02.The MTF acquired from this technique was compared to those from some common methods.MTFs achieved from different approaches were employed to compensate the CCD images based on three restoration algorithms:the iterative method,the Wiener filter and the modified inverse filter(MIF).The two-dimensional MTF was established with the value at frequency 0.5 for 45°directional MTF as the value at its four corners.This article addressed the variations of the restored CCD images with different techniques of constructing two-dimensional MTF,restoring algorithms and determining the in-flight MTFs.Results showed images restored with the MTF determined from the technique of simulating ideal tarp scene represent the real scene best.And the restoration technique based on the MIF would produce better restored images than the other two techniques.This research also demonstrated that the two-dimensional MTF used for restoration should be interpolated under the control of the MTF for 45°axis,rather than by multiplying the cross-orbit MTF with along-orbit MTF.
