A new tangential wind profile for simulating strong tropical cyclones is put forward and planted into the NCAR- AFWA tropical cyclone bogussing scheme in MM5. The scheme for the new profile can make full use of the in...A new tangential wind profile for simulating strong tropical cyclones is put forward and planted into the NCAR- AFWA tropical cyclone bogussing scheme in MM5. The scheme for the new profile can make full use of the information from routine typhoon reports, including not only the maximum wind, but also the additional information of the wind speeds of 25.7 and 15.4 ms-1 and their corresponding radii, which are usually provided for strong cyclones. Thus, the new profile can be used to describe the outer structure of cyclones more accurately than by using the earlier scheme of MM5 in which on- ly the maximum wind speed is considered. Numerical experimental forecasts of two strong tropical cyclones are performed to examine the new profile. Results show that by using the new profile the prediction of both cyclones’ intensity can be obvi- ously improved, but the effects on the track prediction of the two cyclones are different. It seems that the new profile might be more suitable for strong cyclones with shifted tracks. However, the conclusion is drawn from only two typhoon cases, so more cases are needed to evaluate the new profile.展开更多
This study examines the impact of atmospheric and oceanic conditions during May–August of 2004 and 2010 on the frequency and genesis location of tropical cyclones over the western North Pacific. Using the WRF model, ...This study examines the impact of atmospheric and oceanic conditions during May–August of 2004 and 2010 on the frequency and genesis location of tropical cyclones over the western North Pacific. Using the WRF model, four numerical experiments were carried out based on different atmospheric conditions and SST forcing. The numerical experiments indicated that changes in atmospheric and oceanic conditions greatly affect tropical cyclone activity, and the roles of atmospheric conditions are slightly greater than oceanic conditions. Specifically, the total number of tropical cyclones was found to be mostly affected by atmospheric conditions, while the distribution of tropical cyclone genesis locations was mainly related to oceanic conditions, especially the distribution of SST. In 2010, a warmer SST occurred west of 140°E, with a colder SST east of 140°E. On the one hand, the easterly flow was enhanced through the effect of the increase in the zonal SST gradient.The strengthened easterly flow led to an anomalous boundary layer divergence over the region to the east of 140°E, which suppressed the formation of tropical cyclones over this region. On the other hand, the colder SST over the region to the east of 140°E led to a colder low-level air temperature, which resulted in decreased CAPE and static instability energy. The decrease in thermodynamic energy restricted the generation of tropical cyclones over the same region.展开更多
The latest version of sea spray flux parameterization scheme developed by Andreas is coupled with the PSU/NCAR model MM5 in this paper. A western Pacific tropical cyclone named Nabi in 2005 is simulated using this cou...The latest version of sea spray flux parameterization scheme developed by Andreas is coupled with the PSU/NCAR model MM5 in this paper. A western Pacific tropical cyclone named Nabi in 2005 is simulated using this coupled air-sea spray modeling system to study the impacts of sea spray evaporation on the evolution of tropical cyclones. The results demonstrate that sea spray can lead to a significant increase of heat fluxes in the air-sea interface, especially the latent heat flux, the maximum of which can increase by up to about 35% - 80% The latent heat flux seems to be more important than the sensible heat flux for the evolution of tropical cyclones. Regardless of whether sea spray fluxes have been considered, the model can always simulate the track of Nabi well, which seems to indicate that sea spray has little impact on the movement of tropical cyclones. However, with sea spray fluxes taken into account in the model, the intensity of a simulated tropical cyclone can have significant increase. Due to the enhancement of water vapor and heat from the sea surface to the air caused by sea spray, the warm core structure is better-defined, the minimum sea level pressure decreases and the vertical speed is stronger around the eye in the experiments, which is propitious to the development and evolution of tropical cyclones.展开更多
This study concerns the precipitation induced by a tropical cyclone （TC） before the TC arrives, which will be referred to as TC remote precipitation （TRP）. Based on the distribution characteristics of the non-rota...This study concerns the precipitation induced by a tropical cyclone （TC） before the TC arrives, which will be referred to as TC remote precipitation （TRP）. Based on the distribution characteristics of the non-rotational wind and the divergent-wind vertical circulation related to TC, the subtropical high, and TRP of 45 TRP events during June, July, and August of 2000-2009, the relationships among these three entities （TC, subtropical high, and TRP） can be categorized into four patterns. The first pattern accounts for the highest proportion of the TRP events （59%）, and a conceptual model is then provided for this pattern. The primary characteristics of this model are as follows： TC, the subtropical high, and TRP can interact with each other through the divergent-wind secondary circulation at both sides of the ridge line of the subtropical high （between the subtropical high and TC, and between the subtropical high and TRP）. At the upper level （150 or 200 hPa）, the northward non-rotational wind from the TC converged toward the subtropical high ridge line and subsided, and at 950 hPa the divergent wind from the ridge line of the subtropical high converged toward TC; these constructed the secondary circulation between TC and the subtropical high. In the meantime, the southward non- rotational wind at the upper level （150 or 200hPa） from TRP and the divergent wind at 950hPa from the subtropical high ridge line toward TRP constructed the secondary circulation between TRP and the subtropical high. As TC and TRP interacted with each other, the subtropical high ridge line was usually under the down- draft area of the whole atmosphere. The other three patterns are different from the first pattern mainly in terms of the intensity and position of the non-rotational-wind secondary circulation. The numerical simulation of the Beijing 7.21 rainstorm confirmed the relationship amongTC, the subtropical high, and TRP, indicating that when the interaction weakened, the TRP also weakened.展开更多
文摘A new tangential wind profile for simulating strong tropical cyclones is put forward and planted into the NCAR- AFWA tropical cyclone bogussing scheme in MM5. The scheme for the new profile can make full use of the information from routine typhoon reports, including not only the maximum wind, but also the additional information of the wind speeds of 25.7 and 15.4 ms-1 and their corresponding radii, which are usually provided for strong cyclones. Thus, the new profile can be used to describe the outer structure of cyclones more accurately than by using the earlier scheme of MM5 in which on- ly the maximum wind speed is considered. Numerical experimental forecasts of two strong tropical cyclones are performed to examine the new profile. Results show that by using the new profile the prediction of both cyclones’ intensity can be obvi- ously improved, but the effects on the track prediction of the two cyclones are different. It seems that the new profile might be more suitable for strong cyclones with shifted tracks. However, the conclusion is drawn from only two typhoon cases, so more cases are needed to evaluate the new profile.
基金supported by the Chinese Academy of Sciences’Project“Western Pacific Ocean System:Structure,Dynamics and Consequences”(Grant No.XDA10010405)the National High Technology Research and Development Program of China(863 program)(Grant No.2012AA091801)+1 种基金the National Natural Science Foundation of China(Grant Nos.41205044 and 41205075)the Natural Science Foundation of Jiangsu Province(Grant No.BK2012062)
文摘This study examines the impact of atmospheric and oceanic conditions during May–August of 2004 and 2010 on the frequency and genesis location of tropical cyclones over the western North Pacific. Using the WRF model, four numerical experiments were carried out based on different atmospheric conditions and SST forcing. The numerical experiments indicated that changes in atmospheric and oceanic conditions greatly affect tropical cyclone activity, and the roles of atmospheric conditions are slightly greater than oceanic conditions. Specifically, the total number of tropical cyclones was found to be mostly affected by atmospheric conditions, while the distribution of tropical cyclone genesis locations was mainly related to oceanic conditions, especially the distribution of SST. In 2010, a warmer SST occurred west of 140°E, with a colder SST east of 140°E. On the one hand, the easterly flow was enhanced through the effect of the increase in the zonal SST gradient.The strengthened easterly flow led to an anomalous boundary layer divergence over the region to the east of 140°E, which suppressed the formation of tropical cyclones over this region. On the other hand, the colder SST over the region to the east of 140°E led to a colder low-level air temperature, which resulted in decreased CAPE and static instability energy. The decrease in thermodynamic energy restricted the generation of tropical cyclones over the same region.
基金Key Program of National Natural Science Foundation of China (40830235, 40333025)State Key Development Program of Basic Research (973 Program) of China (2004CB418301)
文摘The latest version of sea spray flux parameterization scheme developed by Andreas is coupled with the PSU/NCAR model MM5 in this paper. A western Pacific tropical cyclone named Nabi in 2005 is simulated using this coupled air-sea spray modeling system to study the impacts of sea spray evaporation on the evolution of tropical cyclones. The results demonstrate that sea spray can lead to a significant increase of heat fluxes in the air-sea interface, especially the latent heat flux, the maximum of which can increase by up to about 35% - 80% The latent heat flux seems to be more important than the sensible heat flux for the evolution of tropical cyclones. Regardless of whether sea spray fluxes have been considered, the model can always simulate the track of Nabi well, which seems to indicate that sea spray has little impact on the movement of tropical cyclones. However, with sea spray fluxes taken into account in the model, the intensity of a simulated tropical cyclone can have significant increase. Due to the enhancement of water vapor and heat from the sea surface to the air caused by sea spray, the warm core structure is better-defined, the minimum sea level pressure decreases and the vertical speed is stronger around the eye in the experiments, which is propitious to the development and evolution of tropical cyclones.
基金This research was jointly supported by the National Basic Research Program of China （Nos. 2009CB421503 and 2013CB430103） and the National Natural Science Foundation of China （Grant Nos. 40975037 and 41375058）.
文摘This study concerns the precipitation induced by a tropical cyclone （TC） before the TC arrives, which will be referred to as TC remote precipitation （TRP）. Based on the distribution characteristics of the non-rotational wind and the divergent-wind vertical circulation related to TC, the subtropical high, and TRP of 45 TRP events during June, July, and August of 2000-2009, the relationships among these three entities （TC, subtropical high, and TRP） can be categorized into four patterns. The first pattern accounts for the highest proportion of the TRP events （59%）, and a conceptual model is then provided for this pattern. The primary characteristics of this model are as follows： TC, the subtropical high, and TRP can interact with each other through the divergent-wind secondary circulation at both sides of the ridge line of the subtropical high （between the subtropical high and TC, and between the subtropical high and TRP）. At the upper level （150 or 200 hPa）, the northward non-rotational wind from the TC converged toward the subtropical high ridge line and subsided, and at 950 hPa the divergent wind from the ridge line of the subtropical high converged toward TC; these constructed the secondary circulation between TC and the subtropical high. In the meantime, the southward non- rotational wind at the upper level （150 or 200hPa） from TRP and the divergent wind at 950hPa from the subtropical high ridge line toward TRP constructed the secondary circulation between TRP and the subtropical high. As TC and TRP interacted with each other, the subtropical high ridge line was usually under the down- draft area of the whole atmosphere. The other three patterns are different from the first pattern mainly in terms of the intensity and position of the non-rotational-wind secondary circulation. The numerical simulation of the Beijing 7.21 rainstorm confirmed the relationship amongTC, the subtropical high, and TRP, indicating that when the interaction weakened, the TRP also weakened.
