A nondivergent barotropic model （Model 1） and a barotropic primitive equation vortex model （Model 2） are linearized respectively in this paper. Then their perturbation wave spectrums are computed with a normal mod...A nondivergent barotropic model （Model 1） and a barotropic primitive equation vortex model （Model 2） are linearized respectively in this paper. Then their perturbation wave spectrums are computed with a normal mode approach to study the instability problem on an appointed tropical cyclone （TC）-like vortex, thereby, the dynamic instability properties of spiral cloud bands of TCs are discussed. The results show that the unstable mode of both models exhibits a spiral band-like structure that propagates away from the vortex outside the radius of maximum winds. The discrete modal instability of the pure vortex Rossby wave can account for the generation of the eyewall and the inner spiral band. The unstable mode in Model 2 has three parts, i.e., eyewall, inner and outer spiral bands. This mode can be interpreted as a mixed vortex Rossby-inertia gravitational wave. The unbalanced property of the wave outside the stagnation radius of the vortex Rossby wave is one of the important reasons for the formation of the outer spiral band in TCs. Accordingly, the outer spiral band can be identified to possess properties of an inertial-gravitational wave. When the formation of unstable inner and outer spiral bands is studied, a barotropic vortex model shall be used. In this model, the most unstable perturbation bears the attributes of either the vortex Rossby wave or the inertial-gravitational wave, depending on the vortex radius. So such perturbations shall be viewed as an unbalanced and unstable mixed wave of these two kinds of waves.展开更多
This paper describes the characteristics of the Special Sensor Microwave/Imager (SSM/I) onboard the Defense Meteorological Satellite Program (DMSP),analyzes absorbing,re-emitting and scattering effects of the atmosphe...This paper describes the characteristics of the Special Sensor Microwave/Imager (SSM/I) onboard the Defense Meteorological Satellite Program (DMSP),analyzes absorbing,re-emitting and scattering effects of the atmospheric particles (especially cloud particles and rain drops).The inner physical cause of typhoon's representative form on microwave images is revealed.An index of particle size is then induced as such:Symmetrically inverse channel 85H's (85H is an abbreviation for channel 85.5 GHz in horizontal polarization,see Table 1 in the text.) absorption segment and put it into the extension of the scattering segment.The precipitation index was formed as the average of three elements:normalized 19H,normalized 37H,and inversed normalized 85H.It is approved that the image of particle size index overcomes some shortcomings of the single raw channel,such as:37H is not sensitive to large rain drops,85H is not sensitive to mid-size rain drops and can reveal typhoon's spiral structure more clearly.展开更多
This study of the general features of occurrence frequencies, spatial distribution of locations, life time and cloud patterns of polar lows over the Japan Sea and the neighboring Northwestern Pacific in winter of 1995...This study of the general features of occurrence frequencies, spatial distribution of locations, life time and cloud patterns of polar lows over the Japan Sea and the neighboring Northwestern Pacific in winter of 1995/1996 based on observation and satellite data showed that polar lows develop most frequently in mid winter over the Japan Sea (35-45°N ) and the Northwestern Pacific (30-50°N). They rarely form over the Eurasian Continent. Polar lows over the Northwestern Pacific are usually long lived (2-3 days). But polar lows over the Japan Sea are relatively short lived (1-2 days), because the east west width of the Japan Sea is relatively narrow and polar lows tend to decay after their passing over the Japan Islands. Generally speaking, polar lows over the Japan Sea are characterized by tight, spiral (or comma) cloud patterns on satellite images. It was observed that polar lows over the Japan Sea have a typically spiral cloud band with clear “eye” at their mature stage. In winter, because of the effect of the warm Tsushima Current, the annual mean SST of the Japan Sea is 5-9℃ higher than that of the same latitude oceans. The large sea air temperature difference sustained over the Japan Sea provides favorable condition for polar low formation. The general features of polar lows over the Japan Sea are compared with those of other areas where polar lows often occur.展开更多
An explicit simulation of the tropical cyclone Winnie （1997） was conducted by use of a triply-nested 3-D nonhydrostatic mesoscale model MM5, before and after its landfall. The simulated results show that the model c...An explicit simulation of the tropical cyclone Winnie （1997） was conducted by use of a triply-nested 3-D nonhydrostatic mesoscale model MM5, before and after its landfall. The simulated results show that the model can well reproduce the track of Winnie （1997） with a BOGUS storm-like vortex inserted in the large-scale first-guess field at the initial model time. The mean track error in a 6 h interval is 54.5 km, which is much less than that obtained with the operational prediction. Comparisons between simulation and observation near the landfall place show that the main temporal variation features of sea level pressure and surface wind speed can also be successfully captured. The characteristics of the eyewall, the spiral cloud band and the corresponding precipitation were disclosed, and the applications of the model outputs were also discussed.展开更多
基金Supported by the Typhoon Research Fund of Shanghai Typhoon Institute, China Meteorological Administration, under GrantNo. 2008ST06the National Natural Science Foundation of China under Grant No. 40575023
文摘A nondivergent barotropic model （Model 1） and a barotropic primitive equation vortex model （Model 2） are linearized respectively in this paper. Then their perturbation wave spectrums are computed with a normal mode approach to study the instability problem on an appointed tropical cyclone （TC）-like vortex, thereby, the dynamic instability properties of spiral cloud bands of TCs are discussed. The results show that the unstable mode of both models exhibits a spiral band-like structure that propagates away from the vortex outside the radius of maximum winds. The discrete modal instability of the pure vortex Rossby wave can account for the generation of the eyewall and the inner spiral band. The unstable mode in Model 2 has three parts, i.e., eyewall, inner and outer spiral bands. This mode can be interpreted as a mixed vortex Rossby-inertia gravitational wave. The unbalanced property of the wave outside the stagnation radius of the vortex Rossby wave is one of the important reasons for the formation of the outer spiral band in TCs. Accordingly, the outer spiral band can be identified to possess properties of an inertial-gravitational wave. When the formation of unstable inner and outer spiral bands is studied, a barotropic vortex model shall be used. In this model, the most unstable perturbation bears the attributes of either the vortex Rossby wave or the inertial-gravitational wave, depending on the vortex radius. So such perturbations shall be viewed as an unbalanced and unstable mixed wave of these two kinds of waves.
文摘This paper describes the characteristics of the Special Sensor Microwave/Imager (SSM/I) onboard the Defense Meteorological Satellite Program (DMSP),analyzes absorbing,re-emitting and scattering effects of the atmospheric particles (especially cloud particles and rain drops).The inner physical cause of typhoon's representative form on microwave images is revealed.An index of particle size is then induced as such:Symmetrically inverse channel 85H's (85H is an abbreviation for channel 85.5 GHz in horizontal polarization,see Table 1 in the text.) absorption segment and put it into the extension of the scattering segment.The precipitation index was formed as the average of three elements:normalized 19H,normalized 37H,and inversed normalized 85H.It is approved that the image of particle size index overcomes some shortcomings of the single raw channel,such as:37H is not sensitive to large rain drops,85H is not sensitive to mid-size rain drops and can reveal typhoon's spiral structure more clearly.
文摘This study of the general features of occurrence frequencies, spatial distribution of locations, life time and cloud patterns of polar lows over the Japan Sea and the neighboring Northwestern Pacific in winter of 1995/1996 based on observation and satellite data showed that polar lows develop most frequently in mid winter over the Japan Sea (35-45°N ) and the Northwestern Pacific (30-50°N). They rarely form over the Eurasian Continent. Polar lows over the Northwestern Pacific are usually long lived (2-3 days). But polar lows over the Japan Sea are relatively short lived (1-2 days), because the east west width of the Japan Sea is relatively narrow and polar lows tend to decay after their passing over the Japan Islands. Generally speaking, polar lows over the Japan Sea are characterized by tight, spiral (or comma) cloud patterns on satellite images. It was observed that polar lows over the Japan Sea have a typically spiral cloud band with clear “eye” at their mature stage. In winter, because of the effect of the warm Tsushima Current, the annual mean SST of the Japan Sea is 5-9℃ higher than that of the same latitude oceans. The large sea air temperature difference sustained over the Japan Sea provides favorable condition for polar low formation. The general features of polar lows over the Japan Sea are compared with those of other areas where polar lows often occur.
基金Project supported by the R and D Infrastructure and Facility Development Program (Grant No: 2000DIB20096) of Ministry of Science and Technology of China and the National Natural Science Foundation of China (Grant Nos: 40333026 and 40333025)
文摘An explicit simulation of the tropical cyclone Winnie （1997） was conducted by use of a triply-nested 3-D nonhydrostatic mesoscale model MM5, before and after its landfall. The simulated results show that the model can well reproduce the track of Winnie （1997） with a BOGUS storm-like vortex inserted in the large-scale first-guess field at the initial model time. The mean track error in a 6 h interval is 54.5 km, which is much less than that obtained with the operational prediction. Comparisons between simulation and observation near the landfall place show that the main temporal variation features of sea level pressure and surface wind speed can also be successfully captured. The characteristics of the eyewall, the spiral cloud band and the corresponding precipitation were disclosed, and the applications of the model outputs were also discussed.
