2011 Vol. 17, No. 1
2011, 17(1): 1-10.
Abstract:
With multiple meteorological data, including precipitation from automatic weather stations, integrated satellite-based precipitation (CMORPH), brightness temperature (TBB), radar echoes and NCEP reanalysis, a rainstorm event, which occurred on May 26, 2007 over South China, is analyzed with the focus on the evolution characteristics of associated mesoscale-β convective systems (Mβcss). Results are shown as follows. (1) The rainstorm presents itself as a typical warm-sector event, for it occurs within a surface inverted trough and on the left side of a southwesterly low-level jet (LLJ), which shows no obvious features of baroclinicity. (2) The heavy rainfall event is directly related to at least three bodies of Mβcss with peak precipitation corresponding well to their mature stages. (3) The Mβcss manifest a backward propagation, which is marked with a new form of downstream convection different from the more usual type of forward propagation over South China, i.e., new convective systems mainly form at the rear part of older Mβcss. (4) Rainstorm-causing Mβcss form near the convergence region on the left side of an 850-hPa southwesterly LLJ, over which there are dominantly divergent air flows at 200 hPa. Different from the typical flow pattern of outward divergence off the east side of South Asia High, which is usually found to be over zones of heavy rains during the annually first rainy season of South China, this warm-sector heavy rain is below the divergence region formed between the easterly and southerly flows west of the South Asian High that is moving out to sea. (5) The LLJ transports abundant amount of warm and moist air to the heavy rainfall area, providing advantageous conditions for highly unstable energy to generate and store at middle and high levels, where corresponding low-level warm advection may be playing a more direct role in the development of Mβcss. As a triggering mechanism for organized convective systems, the effect of low-level warm advection deserves more of our attention. Based on the analysis of surface mesoscale airflow in the article, possible triggering mechanisms for Mβcss are also discussed.
With multiple meteorological data, including precipitation from automatic weather stations, integrated satellite-based precipitation (CMORPH), brightness temperature (TBB), radar echoes and NCEP reanalysis, a rainstorm event, which occurred on May 26, 2007 over South China, is analyzed with the focus on the evolution characteristics of associated mesoscale-β convective systems (Mβcss). Results are shown as follows. (1) The rainstorm presents itself as a typical warm-sector event, for it occurs within a surface inverted trough and on the left side of a southwesterly low-level jet (LLJ), which shows no obvious features of baroclinicity. (2) The heavy rainfall event is directly related to at least three bodies of Mβcss with peak precipitation corresponding well to their mature stages. (3) The Mβcss manifest a backward propagation, which is marked with a new form of downstream convection different from the more usual type of forward propagation over South China, i.e., new convective systems mainly form at the rear part of older Mβcss. (4) Rainstorm-causing Mβcss form near the convergence region on the left side of an 850-hPa southwesterly LLJ, over which there are dominantly divergent air flows at 200 hPa. Different from the typical flow pattern of outward divergence off the east side of South Asia High, which is usually found to be over zones of heavy rains during the annually first rainy season of South China, this warm-sector heavy rain is below the divergence region formed between the easterly and southerly flows west of the South Asian High that is moving out to sea. (5) The LLJ transports abundant amount of warm and moist air to the heavy rainfall area, providing advantageous conditions for highly unstable energy to generate and store at middle and high levels, where corresponding low-level warm advection may be playing a more direct role in the development of Mβcss. As a triggering mechanism for organized convective systems, the effect of low-level warm advection deserves more of our attention. Based on the analysis of surface mesoscale airflow in the article, possible triggering mechanisms for Mβcss are also discussed.
2011, 17(1): 11-17.
Abstract:
Based on consideration of both thermodynamic and kinetic features of the subtropical summer monsoon in East Asia, a new index is defined by the moist potential vorticity (MPV) for this monsoon. Variation features of the subtropical summer monsoon over 60 years are analyzed using National Centers for Environmental Prediction/National Center for Atmospheric Research (USA) data from 1948 to 2007. Results show that the new index can well reflect the seasonal, interannual, and interdecadal variations of the East Asian subtropical summer monsoon. Correlation analysis of the new index and precipitation data from 160 stations in China shows that in high-index years, the summer monsoon is strong, and more rain falls in eastern North China, southwestern China, and along the coast of South China and less rain falls in the Yangtze-Huaihe R. basin. In low-index years, the opposite occurs. Lastly, the new index is compared with four established monsoon indices. The new index is found to have an advantage in representing summer rainfall in the Yangtze-Huaihe R. basin.
Based on consideration of both thermodynamic and kinetic features of the subtropical summer monsoon in East Asia, a new index is defined by the moist potential vorticity (MPV) for this monsoon. Variation features of the subtropical summer monsoon over 60 years are analyzed using National Centers for Environmental Prediction/National Center for Atmospheric Research (USA) data from 1948 to 2007. Results show that the new index can well reflect the seasonal, interannual, and interdecadal variations of the East Asian subtropical summer monsoon. Correlation analysis of the new index and precipitation data from 160 stations in China shows that in high-index years, the summer monsoon is strong, and more rain falls in eastern North China, southwestern China, and along the coast of South China and less rain falls in the Yangtze-Huaihe R. basin. In low-index years, the opposite occurs. Lastly, the new index is compared with four established monsoon indices. The new index is found to have an advantage in representing summer rainfall in the Yangtze-Huaihe R. basin.
2011, 17(1): 18-26.
Abstract:
The impact of anomalous sea surface temperature (SST) warming in the Kuroshio Extension in the previous winter on the East Asian summer monsoon (EASM) was investigated by performing simulation tests using NCAR CAM3. The results show that anomalous SST warming in the Kuroshio Extension in winter causes the enhancement and northward movement of the EASM. The monsoon indexes for East Asian summer monsoon and land-sea thermal difference, which characterize the intensity of the EASM, show an obvious increase during the onset period of the EASM. Moreover, the land-sea thermal difference is more sensitive to warmer SST. Low-level southwesterly monsoon is clearly strengthened meanwhile westerly flows north (south) of the subtropical westerly jet axis are strengthened (weakened) in northern China, South China Sea, and the Western Pacific Ocean to the east of the Philippines. While there is an obvious decrease in precipitation over the Japanese archipelago and adjacent oceans and over the area from the south of the Yangtze River in eastern China to the Qinling Mountains in southern China, precipitation increases notably in northern China, the South China Sea, the East China Sea, the Yellow Sea, and the Western Pacific to the east of the Philippines. North China is the key area where the response of the EASM to the SST anomalous warming in the Kuroshio Extension is prominent. The surface air temperature shows a warming trend. The warming in the entire troposphere between 30oN and 50oN increases the land-sea thermal contrast, which plays an important role in the enhancement of the EASM. Atmospheric circulation and precipitation anomalies in China and its adjacent regions have a close relationship with the enhancement of the Western Pacific subtropical high and its northward extension.
The impact of anomalous sea surface temperature (SST) warming in the Kuroshio Extension in the previous winter on the East Asian summer monsoon (EASM) was investigated by performing simulation tests using NCAR CAM3. The results show that anomalous SST warming in the Kuroshio Extension in winter causes the enhancement and northward movement of the EASM. The monsoon indexes for East Asian summer monsoon and land-sea thermal difference, which characterize the intensity of the EASM, show an obvious increase during the onset period of the EASM. Moreover, the land-sea thermal difference is more sensitive to warmer SST. Low-level southwesterly monsoon is clearly strengthened meanwhile westerly flows north (south) of the subtropical westerly jet axis are strengthened (weakened) in northern China, South China Sea, and the Western Pacific Ocean to the east of the Philippines. While there is an obvious decrease in precipitation over the Japanese archipelago and adjacent oceans and over the area from the south of the Yangtze River in eastern China to the Qinling Mountains in southern China, precipitation increases notably in northern China, the South China Sea, the East China Sea, the Yellow Sea, and the Western Pacific to the east of the Philippines. North China is the key area where the response of the EASM to the SST anomalous warming in the Kuroshio Extension is prominent. The surface air temperature shows a warming trend. The warming in the entire troposphere between 30oN and 50oN increases the land-sea thermal contrast, which plays an important role in the enhancement of the EASM. Atmospheric circulation and precipitation anomalies in China and its adjacent regions have a close relationship with the enhancement of the Western Pacific subtropical high and its northward extension.
2011, 17(1): 27-35.
Abstract:
Based on monthly mean wind, geopotential height, specific humidity, and surface pressure of NCAR/NCEP reanalysis, NOAA-reconstructed sea surface temperature (SST) of the Indian Ocean, and daily precipitation data at 97 meteorological stations over the eastern NW China in the past 47 years, the threshold values for extreme precipitation events (EPE) are defined using the percentile method. Singular Value Decomposition and synthetic analysis methods are used to analyze the relationship between summer EPE in the eastern NW China and SSTA in the preceding fall, winter, spring, and the concurrent summer. The result shows that preceding spring SST anomalies (SSTA) in the Indian Ocean are clear indicators for the forecast of summer EPE in the eastern NW China, and a key area of impact is located in the equatorial Indian Ocean. When spring SST is anomalously high in the equatorial Indian Ocean, the meridional circulation averaged over 100°E–C110°E will be anomalously ascending near the equator but anomalously descending near 30°N in the middle and upper troposphere from the concurrent to the subsequent summer. In the meantime, the Southwest Monsoon from the Indian Ocean will be anomalously weak and there will be no anomalous water vapor transport to the eastern NW China, resulting in a lack of EPE in the subsequent summer, and vice versa. In addition, in response to anomalously high SST in the equatorial Indian Ocean in spring, the South Asia high pressure tends to be strong in the subsequent summer and more to the west. In the anomalously low SST year, however, the South Asia high tends to be weak in the subsequent summer and more to the east. This is another possible cause of the variation of summer EPE in the eastern NW China.
Based on monthly mean wind, geopotential height, specific humidity, and surface pressure of NCAR/NCEP reanalysis, NOAA-reconstructed sea surface temperature (SST) of the Indian Ocean, and daily precipitation data at 97 meteorological stations over the eastern NW China in the past 47 years, the threshold values for extreme precipitation events (EPE) are defined using the percentile method. Singular Value Decomposition and synthetic analysis methods are used to analyze the relationship between summer EPE in the eastern NW China and SSTA in the preceding fall, winter, spring, and the concurrent summer. The result shows that preceding spring SST anomalies (SSTA) in the Indian Ocean are clear indicators for the forecast of summer EPE in the eastern NW China, and a key area of impact is located in the equatorial Indian Ocean. When spring SST is anomalously high in the equatorial Indian Ocean, the meridional circulation averaged over 100°E–C110°E will be anomalously ascending near the equator but anomalously descending near 30°N in the middle and upper troposphere from the concurrent to the subsequent summer. In the meantime, the Southwest Monsoon from the Indian Ocean will be anomalously weak and there will be no anomalous water vapor transport to the eastern NW China, resulting in a lack of EPE in the subsequent summer, and vice versa. In addition, in response to anomalously high SST in the equatorial Indian Ocean in spring, the South Asia high pressure tends to be strong in the subsequent summer and more to the west. In the anomalously low SST year, however, the South Asia high tends to be weak in the subsequent summer and more to the east. This is another possible cause of the variation of summer EPE in the eastern NW China.
A Method of Initial Vortex Relocation and Numerical Simulation Experiments on Tropical Cyclone Track
2011, 17(1): 36-42.
Abstract:
Using the technique of smooth filtering and cylindrical filtering, the initial vortex circulation and large-scale environmental field were separated from the background field. Then the separated initial vortex circulation was translated and reinserted in the location where it was observed. This led to the determination of a method of initial vortex relocation. For seven tropical cyclones at 23 points of measurement time in the years of 2006 and 2007, two schemes, either directly adding a tropical cyclone bogus model in the background or adding it after the relocation of the initial vortex in the background field, were employed. Simulation experiments were compared. The results showed that the mean errors of the simulated tropical cyclone tracks at 24 and 48 hours were both smaller with the scheme of adding tropical cyclone bogus model after the relocation of the initial vortex in the background field. The relocation method of the initial vortex decreases the error caused by the deviation of the initial tropical cyclone location in tropical cyclone models. The relocation method is conducive to improving the track forecast of tropical cyclone models and has a good perspective for operational application.
Using the technique of smooth filtering and cylindrical filtering, the initial vortex circulation and large-scale environmental field were separated from the background field. Then the separated initial vortex circulation was translated and reinserted in the location where it was observed. This led to the determination of a method of initial vortex relocation. For seven tropical cyclones at 23 points of measurement time in the years of 2006 and 2007, two schemes, either directly adding a tropical cyclone bogus model in the background or adding it after the relocation of the initial vortex in the background field, were employed. Simulation experiments were compared. The results showed that the mean errors of the simulated tropical cyclone tracks at 24 and 48 hours were both smaller with the scheme of adding tropical cyclone bogus model after the relocation of the initial vortex in the background field. The relocation method of the initial vortex decreases the error caused by the deviation of the initial tropical cyclone location in tropical cyclone models. The relocation method is conducive to improving the track forecast of tropical cyclone models and has a good perspective for operational application.
2011, 17(1): 43-49.
Abstract:
In this paper we investigate the impact of the Atmospheric Infra-Red Sounder (AIRS) temperature retrievals on data assimilation and the resulting forecasts using the four-dimensional Local Ensemble Transform Kalman Filter (LETKF) data assimilation scheme and a reduced resolution version of the NCEP Global Forecast System (GFS). Our results indicate that the AIRS temperature retrievals have a significant and consistent positive impact in the Southern Hemispheric extratropics on both analyses and forecasts, which is found not only in the temperature field but also in other variables. In tropics and the Northern Hemispheric extratropics these impacts are smaller, but are still generally positive or neutral.
In this paper we investigate the impact of the Atmospheric Infra-Red Sounder (AIRS) temperature retrievals on data assimilation and the resulting forecasts using the four-dimensional Local Ensemble Transform Kalman Filter (LETKF) data assimilation scheme and a reduced resolution version of the NCEP Global Forecast System (GFS). Our results indicate that the AIRS temperature retrievals have a significant and consistent positive impact in the Southern Hemispheric extratropics on both analyses and forecasts, which is found not only in the temperature field but also in other variables. In tropics and the Northern Hemispheric extratropics these impacts are smaller, but are still generally positive or neutral.
2011, 17(1): 50-57.
Abstract:
Based on the high-resolution datasets collected in a sea fog field experiment at the northern coast of South China Sea, the variations of liquid water content (LWC) and net longwave radiation flux (NLRF) during two sea fog events on 16th-17th and 18th-19th March, 2008 are exaimeed by wavelet analysis, and the cooling mechanisms for fog formation and persistence are also investigated. The main results are shown as follows. (1) Sea fog may develop and persist whether it is cloudy or not aloft. However, when there is cloud aloft the LWC is less and wind speed in sea fog is higher than that in the clear sky. (2) The quasi-periodic oscillations (QPOs) of NLRF are observed in the formation stage of the two fogs. QPOs of LWC are only found in the developing stage no matter with cloudless or cloudy condition. (3) It is likely that sea fog forms by the cooling effects of longwave radiation and develops through the vertical mixing induced by the radiative cooling at the upper level. (4) During sea fog development and persistence, other mechanisms could also play important roles in fog-layer cooling, such as turbulent heat transport and radiation transport between air-sea interfaces.
Based on the high-resolution datasets collected in a sea fog field experiment at the northern coast of South China Sea, the variations of liquid water content (LWC) and net longwave radiation flux (NLRF) during two sea fog events on 16th-17th and 18th-19th March, 2008 are exaimeed by wavelet analysis, and the cooling mechanisms for fog formation and persistence are also investigated. The main results are shown as follows. (1) Sea fog may develop and persist whether it is cloudy or not aloft. However, when there is cloud aloft the LWC is less and wind speed in sea fog is higher than that in the clear sky. (2) The quasi-periodic oscillations (QPOs) of NLRF are observed in the formation stage of the two fogs. QPOs of LWC are only found in the developing stage no matter with cloudless or cloudy condition. (3) It is likely that sea fog forms by the cooling effects of longwave radiation and develops through the vertical mixing induced by the radiative cooling at the upper level. (4) During sea fog development and persistence, other mechanisms could also play important roles in fog-layer cooling, such as turbulent heat transport and radiation transport between air-sea interfaces.
2011, 17(1): 58-63.
Abstract:
Based on the 1951–C2007 thunderstorms in Jiangsu, a study is conducted for their climate trends, periodicity, spatiotemporal patterns, and the distributions of the first and last days of the thunderstorms at different guarantee rates (GRs) using climate tendency rate, wavelet analysis, and GR for diagnosis. Results suggest that the inter-annual number of thunderstorm days (TSDs) exhibits a decreasing trend in this province. The trend is displayed mainly in the decreasing TSD number in summer and autumn except in spring, when the variation is not significant in the study period. In this province, the TSD number declines by ~2 days per 10 years. On an inter-annual basis, the pronounced positive departures of the number take place chiefly in the early 1960s, the late 1960s to the early-mid-1970s, the late 1980s, and the late 1990s compared with the negative anomalies dominant in the late 1970s to the mid-1980s, the mid-to-late-1990s, and the late 1990s to 2007. There are vast differences in the initial and ending days at diverse GRs in different areas of the province. At 50% GR, the earliest (last) days occur from mid-March to early April (early to late September) while at 80% GR, the initial (last) days are from late March to early May (early to late October). For the distribution of periods, the periods >8–C10 years are relatively stable for the entire province. Based on 1951–C2007 period analysis, the region north (south) of the Huaihe River experiences TSDs less (more) than normal days in recent years.
Based on the 1951–C2007 thunderstorms in Jiangsu, a study is conducted for their climate trends, periodicity, spatiotemporal patterns, and the distributions of the first and last days of the thunderstorms at different guarantee rates (GRs) using climate tendency rate, wavelet analysis, and GR for diagnosis. Results suggest that the inter-annual number of thunderstorm days (TSDs) exhibits a decreasing trend in this province. The trend is displayed mainly in the decreasing TSD number in summer and autumn except in spring, when the variation is not significant in the study period. In this province, the TSD number declines by ~2 days per 10 years. On an inter-annual basis, the pronounced positive departures of the number take place chiefly in the early 1960s, the late 1960s to the early-mid-1970s, the late 1980s, and the late 1990s compared with the negative anomalies dominant in the late 1970s to the mid-1980s, the mid-to-late-1990s, and the late 1990s to 2007. There are vast differences in the initial and ending days at diverse GRs in different areas of the province. At 50% GR, the earliest (last) days occur from mid-March to early April (early to late September) while at 80% GR, the initial (last) days are from late March to early May (early to late October). For the distribution of periods, the periods >8–C10 years are relatively stable for the entire province. Based on 1951–C2007 period analysis, the region north (south) of the Huaihe River experiences TSDs less (more) than normal days in recent years.
2011, 17(1): 64-72.
Abstract:
Modified refractivity (M) profile is an important parameter to describe the atmospheric refraction environment, as well as a key factor in uniquely evaluating electromagnetic propagation effects. In order to improve the model-derived M profile in stable (especially very stable) conditions, three nonlinear similarity functions, namely BH91, CB05, SHEBA07, are introduced in this paper to improve the original Babin_V25 model, and the performances of these modified models are verified based on the hydrometeorological observations from tower platforms, which are finally compared with the original Babin_V25 model and Local_HYQ92 model. Results show that introducing nonlinear similarity functions can significantly improve the model-derived M profile; especially, the newly developed SHEBA07 functions manage to reduce the predicted root mean square (rms) differences of M and M slope (for both 0–C5 m and 5–C40 m) by 64.5%, 16.6%, and 60.4%, respectively in stable conditions. Unfortunately, this improved method reacts little on the evaporation duct height; in contrast, Local_HYQ92 model is capable of reducing the predicted rms differences of M, M slope (for both 0–C5 m and 5–C40 m), and evaporation duct height by 76.7%, 40.2%, 83.7%, and 58.0% respectively. Finally, a new recommendation is made to apply Local_HYQ92 and Babin_SHEBA07 in very stable conditions considering that M slope is more important than evaporation duct height and absolute M value in uniquely determining electromagnetic propagation effects.
Modified refractivity (M) profile is an important parameter to describe the atmospheric refraction environment, as well as a key factor in uniquely evaluating electromagnetic propagation effects. In order to improve the model-derived M profile in stable (especially very stable) conditions, three nonlinear similarity functions, namely BH91, CB05, SHEBA07, are introduced in this paper to improve the original Babin_V25 model, and the performances of these modified models are verified based on the hydrometeorological observations from tower platforms, which are finally compared with the original Babin_V25 model and Local_HYQ92 model. Results show that introducing nonlinear similarity functions can significantly improve the model-derived M profile; especially, the newly developed SHEBA07 functions manage to reduce the predicted root mean square (rms) differences of M and M slope (for both 0–C5 m and 5–C40 m) by 64.5%, 16.6%, and 60.4%, respectively in stable conditions. Unfortunately, this improved method reacts little on the evaporation duct height; in contrast, Local_HYQ92 model is capable of reducing the predicted rms differences of M, M slope (for both 0–C5 m and 5–C40 m), and evaporation duct height by 76.7%, 40.2%, 83.7%, and 58.0% respectively. Finally, a new recommendation is made to apply Local_HYQ92 and Babin_SHEBA07 in very stable conditions considering that M slope is more important than evaporation duct height and absolute M value in uniquely determining electromagnetic propagation effects.
2011, 17(1): 73-78.
Abstract:
The South China Sea summer monsoon is an important system affecting the weather and climate in China; its outbreak and evolution vary from year to year. Using the reanalysis data from the U.S. National Centers for Environmental Prediction (NCEP) and outgoing longwave radiation (OLR) data from the National Oceanic and Atmospheric Administration (NOAA), USA, we analyze the circulation pattern, precipitation distribution, convection, temperature, and humidity around the monsoon outbreaks in 2004 and 2008. Results show that the monsoon had a late onset in 2004 (May 19) but an early outbreak in 2008 (May 4). Prior to the monsoon outbreak in 2008, cross-equatorial flows in Somalia were weaker than in 2004, subtropical precipitation did not arrive in southern China as it did in 2004, and the strongest convection was located more southward than in 2004. The results also indicate that accumulated rainfall in the Indochina Peninsula was about 61% of that in 2004 during a period of 25 days leading up to the monsoon outbreak, causing differences in land surface processes and then different activity levels for the summer monsoon. Post-onset warm and humid conditions in 2008 (2004) maintained through the end of October (mid-September), while the summer monsoon lasted longer in 2008 than in 2004.
The South China Sea summer monsoon is an important system affecting the weather and climate in China; its outbreak and evolution vary from year to year. Using the reanalysis data from the U.S. National Centers for Environmental Prediction (NCEP) and outgoing longwave radiation (OLR) data from the National Oceanic and Atmospheric Administration (NOAA), USA, we analyze the circulation pattern, precipitation distribution, convection, temperature, and humidity around the monsoon outbreaks in 2004 and 2008. Results show that the monsoon had a late onset in 2004 (May 19) but an early outbreak in 2008 (May 4). Prior to the monsoon outbreak in 2008, cross-equatorial flows in Somalia were weaker than in 2004, subtropical precipitation did not arrive in southern China as it did in 2004, and the strongest convection was located more southward than in 2004. The results also indicate that accumulated rainfall in the Indochina Peninsula was about 61% of that in 2004 during a period of 25 days leading up to the monsoon outbreak, causing differences in land surface processes and then different activity levels for the summer monsoon. Post-onset warm and humid conditions in 2008 (2004) maintained through the end of October (mid-September), while the summer monsoon lasted longer in 2008 than in 2004.
2011, 17(1): 79-86.
Abstract:
This paper presents a study on potential instability and spiral structure of unstable rain clusters. First, we develop a linearized non-axisymmetrical mathematic model for rain clusters in circular cylindrical coordinates and acquire its analytic solution. Second, we discuss the potential instability of non-axisymmetrical rain clusters. Finally, we conclude that spiral structures can exist in rain clusters. Our analysis indicates that potential instability occurs when humid stratification coefficient is less than zero. Unstable growth rate increases with the increase of the absolute value for humid stratification coefficient. The simpler the vertical structure of perturbation, the thicker the inversion layer; additionally, the smaller the radius of the rain clusters, the larger the unstable growth rate. Simulation results agree well with those from observation and forecast. The spiral structure simulated by our model is similar to a radar echo, suggesting that rain clusters with spiral structures can occur in the atmosphere. In addition, they are generally close to the model solution in this work.
This paper presents a study on potential instability and spiral structure of unstable rain clusters. First, we develop a linearized non-axisymmetrical mathematic model for rain clusters in circular cylindrical coordinates and acquire its analytic solution. Second, we discuss the potential instability of non-axisymmetrical rain clusters. Finally, we conclude that spiral structures can exist in rain clusters. Our analysis indicates that potential instability occurs when humid stratification coefficient is less than zero. Unstable growth rate increases with the increase of the absolute value for humid stratification coefficient. The simpler the vertical structure of perturbation, the thicker the inversion layer; additionally, the smaller the radius of the rain clusters, the larger the unstable growth rate. Simulation results agree well with those from observation and forecast. The spiral structure simulated by our model is similar to a radar echo, suggesting that rain clusters with spiral structures can occur in the atmosphere. In addition, they are generally close to the model solution in this work.
2011, 17(1): 87-92.
Abstract:
In this work, the results of a coupled experiment and an uncoupled experiment conducted in one of our former works are used to analyze the impact of air-sea interactions on the structure of typhoons. Results reveal that typhoon-induced SST decreases to reduce the latent heat fluxes transporting from the ocean to the atmosphere and cause the flux of sensible heat to transfer downward from the atmosphere to the ocean. Such SST reduction also has remarkable impacts on the typhoon structure by making the typhoon more axisymmetric, especially in the middle and high levels. This study also analyzes the basic characteristics of symmetric typhoon structure.
In this work, the results of a coupled experiment and an uncoupled experiment conducted in one of our former works are used to analyze the impact of air-sea interactions on the structure of typhoons. Results reveal that typhoon-induced SST decreases to reduce the latent heat fluxes transporting from the ocean to the atmosphere and cause the flux of sensible heat to transfer downward from the atmosphere to the ocean. Such SST reduction also has remarkable impacts on the typhoon structure by making the typhoon more axisymmetric, especially in the middle and high levels. This study also analyzes the basic characteristics of symmetric typhoon structure.
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