2013 Vol. 19, No. 3
2013, 19(3): 197-213.
Abstract:
Cloud resolving Weather Research and Forecasting (WRF) model simulations are used to investigate tropical cyclone (TC) genesis efficiency in an environment with a near bottom vortex (EBV) and an environment with a mid-level vortex (EMV). Sensitivity experiments show that the genesis timing depends greatly on initial vorticity vertical profiles. The larger the initial column integrated absolute vorticity, the greater the genesis efficiency is. Given the same column integrated absolute vorticity, a bottom vortex has higher genesis efficiency than a mid-level vortex. A common feature among these experiments is the formation of a mid-level vorticity maximum prior to TC genesis irrespective where the initial vorticity maximum locates. Both the EMV and EBV scenarios share the following development characteristics: 1) a transition from non-organized cumulus-scale (~5 km) convective cells into an organized meso-vortex-scale (~50 to 100 km) system through upscale cascade processes, 2) the establishment of a nearly saturated air column prior to a rapid drop of the central minimum pressure, and 3) a multiple convective-stratiform phase transition. A genesis efficiency index (GEI) is formulated that includes the following factors: initial column integrated absolute vorticity, vorticity at top of the boundary layer and vertically integrated relative humidity. The calculated GEI reflects well the simulated genesis efficiency and thus may be used to estimate how fast a tropical disturbance develops into a TC.
Cloud resolving Weather Research and Forecasting (WRF) model simulations are used to investigate tropical cyclone (TC) genesis efficiency in an environment with a near bottom vortex (EBV) and an environment with a mid-level vortex (EMV). Sensitivity experiments show that the genesis timing depends greatly on initial vorticity vertical profiles. The larger the initial column integrated absolute vorticity, the greater the genesis efficiency is. Given the same column integrated absolute vorticity, a bottom vortex has higher genesis efficiency than a mid-level vortex. A common feature among these experiments is the formation of a mid-level vorticity maximum prior to TC genesis irrespective where the initial vorticity maximum locates. Both the EMV and EBV scenarios share the following development characteristics: 1) a transition from non-organized cumulus-scale (~5 km) convective cells into an organized meso-vortex-scale (~50 to 100 km) system through upscale cascade processes, 2) the establishment of a nearly saturated air column prior to a rapid drop of the central minimum pressure, and 3) a multiple convective-stratiform phase transition. A genesis efficiency index (GEI) is formulated that includes the following factors: initial column integrated absolute vorticity, vorticity at top of the boundary layer and vertically integrated relative humidity. The calculated GEI reflects well the simulated genesis efficiency and thus may be used to estimate how fast a tropical disturbance develops into a TC.
2013, 19(3): 214-222.
Abstract:
Phase composite analyses are conducted to investigate the possible effect of the Madden-Julian oscillation (MJO) on the spring rainfall anomalies in East China by using the Real-time Multivariate MJO (RMM) index from Australian Meteorological Bureau. The results show that the rainfall anomalies over the mid- and lower-valley of Yangtze River are positive when the MJO shifts eastward to the mid- and eastern-Indian Ocean, and anomalous precipitation over South China are positive when the MJO moves further eastward to the maritime continent, whereas spring rainfall anomalies over East China are negative in the other MJO episodes. The MJO impacts on the precipitation over East China result from the changes in large-scale atmospheric circulation as well as vorticity and water vapor transportation in the mid- and lower-troposphere.
Phase composite analyses are conducted to investigate the possible effect of the Madden-Julian oscillation (MJO) on the spring rainfall anomalies in East China by using the Real-time Multivariate MJO (RMM) index from Australian Meteorological Bureau. The results show that the rainfall anomalies over the mid- and lower-valley of Yangtze River are positive when the MJO shifts eastward to the mid- and eastern-Indian Ocean, and anomalous precipitation over South China are positive when the MJO moves further eastward to the maritime continent, whereas spring rainfall anomalies over East China are negative in the other MJO episodes. The MJO impacts on the precipitation over East China result from the changes in large-scale atmospheric circulation as well as vorticity and water vapor transportation in the mid- and lower-troposphere.
2013, 19(3): 223-232.
Abstract:
Impacts of regional sea surface temperature (SST) anomalies on the interdecadal variation of the cross-equatorial flows (CEFs) in Eastern Hemisphere are studied using numerical simulations with a global atmospheric circulation model (NCAR CAM3) driven with 1950-2000 monthly SSTs in different marine areas (the globe, extratropics, tropics, tropical Indian Ocean-Pacific, and tropical Pacific) and ERA-40 reanalysis data. Results show that all simulations, except the one driven with extratropical SSTs, can simulate the interdecadal strengthening of CEFs around Somali, 120oE, and 150oE that occurred in the midand late-1970s. Among those simulated CEFs, the interdecadal variability in Somali and its interdecadal relationship with the East Asian summer monsoon are in better agreement with the observations, suggesting that changes in the SSTs of tropical oceans, especially the tropical Pacific, play a crucial role in the interdecadal variability of CEFs in Somali. The interdecadal change of CEFs in Somali is highly associated with the interdecadal variation of tropical Pacific SST. As the interdecadal warmer (colder) SST happens in the tropical Pacific, a "sandwich" pattern of SST anomalies, i.e. "+, -, +" ("-, +, -"), will occur in the eastern tropical Pacific from north to south with a pair of anomalous anticyclone (cyclone) at the lower troposphere; the pair links to another pair of anomalous cyclone (anticyclone) in the tropical Indian Ocean through an atmospheric bridge, and thus strengthens (weakens) the CEFs in Somali.
Impacts of regional sea surface temperature (SST) anomalies on the interdecadal variation of the cross-equatorial flows (CEFs) in Eastern Hemisphere are studied using numerical simulations with a global atmospheric circulation model (NCAR CAM3) driven with 1950-2000 monthly SSTs in different marine areas (the globe, extratropics, tropics, tropical Indian Ocean-Pacific, and tropical Pacific) and ERA-40 reanalysis data. Results show that all simulations, except the one driven with extratropical SSTs, can simulate the interdecadal strengthening of CEFs around Somali, 120oE, and 150oE that occurred in the midand late-1970s. Among those simulated CEFs, the interdecadal variability in Somali and its interdecadal relationship with the East Asian summer monsoon are in better agreement with the observations, suggesting that changes in the SSTs of tropical oceans, especially the tropical Pacific, play a crucial role in the interdecadal variability of CEFs in Somali. The interdecadal change of CEFs in Somali is highly associated with the interdecadal variation of tropical Pacific SST. As the interdecadal warmer (colder) SST happens in the tropical Pacific, a "sandwich" pattern of SST anomalies, i.e. "+, -, +" ("-, +, -"), will occur in the eastern tropical Pacific from north to south with a pair of anomalous anticyclone (cyclone) at the lower troposphere; the pair links to another pair of anomalous cyclone (anticyclone) in the tropical Indian Ocean through an atmospheric bridge, and thus strengthens (weakens) the CEFs in Somali.
2013, 19(3): 233-241.
Abstract:
Possible relationships between MJO and the severe rain-snow weather in Eastern China during November of 2009 are analyzed and results show that a strong MJO process is one of the strong impact factors. MJO is very active over the Indian Ocean in November 2009. Especially, it maintains 9 days in MJO phase 3, just corresponding to the two strongest rain-snow processes. Composites of MJO events show that when the MJO convective center is located over the Indian Ocean, the probability of rainfall is significantly increased and the temperature is lower than normal in eastern China, which is consistent with the situation in November of 2009. Atmospheric circulation anomalies of mid- and higher-latitudes can be influenced by the tropical MJO convection forcing and this influence could be realized by teleconnection. When the MJO is over the Indian Ocean, it is favorable for the maintenance of a circulation pattern of two ridges versus one trough at mid- and higher-latitudes. Meanwhile, the western Pacific subtropical high is stronger and more westward than normal, and a significant convective belt appears over eastern East Asia. All these circulation anomalies shown in the composite result also appeared in the observations in November 2009, which indicates the general features of relationships between the MJO and the circulation anomalies over the extratropics. Besides the zonal circulation anomalies, the MJO convection can also lead to meridional circulation anomalies. When the MJO convection is located over the Indian Ocean, the western Pacific is dominated by anomalous descending motion, and the eastern East Asia is controlled by strong convergence and ascending motion. Therefore, an anomalous meridional circulation is formed between the tropics and middle latitudes, enhancing the northward transportation of low-level moisture. It is potentially helpful to understanding and even forecasting such kind of rain-snow weather anomalies as that in November 2009 using MJO.
Possible relationships between MJO and the severe rain-snow weather in Eastern China during November of 2009 are analyzed and results show that a strong MJO process is one of the strong impact factors. MJO is very active over the Indian Ocean in November 2009. Especially, it maintains 9 days in MJO phase 3, just corresponding to the two strongest rain-snow processes. Composites of MJO events show that when the MJO convective center is located over the Indian Ocean, the probability of rainfall is significantly increased and the temperature is lower than normal in eastern China, which is consistent with the situation in November of 2009. Atmospheric circulation anomalies of mid- and higher-latitudes can be influenced by the tropical MJO convection forcing and this influence could be realized by teleconnection. When the MJO is over the Indian Ocean, it is favorable for the maintenance of a circulation pattern of two ridges versus one trough at mid- and higher-latitudes. Meanwhile, the western Pacific subtropical high is stronger and more westward than normal, and a significant convective belt appears over eastern East Asia. All these circulation anomalies shown in the composite result also appeared in the observations in November 2009, which indicates the general features of relationships between the MJO and the circulation anomalies over the extratropics. Besides the zonal circulation anomalies, the MJO convection can also lead to meridional circulation anomalies. When the MJO convection is located over the Indian Ocean, the western Pacific is dominated by anomalous descending motion, and the eastern East Asia is controlled by strong convergence and ascending motion. Therefore, an anomalous meridional circulation is formed between the tropics and middle latitudes, enhancing the northward transportation of low-level moisture. It is potentially helpful to understanding and even forecasting such kind of rain-snow weather anomalies as that in November 2009 using MJO.
2013, 19(3): 242-252.
Abstract:
Based on the newly developed Weather Research and Forecasting model (WRF) and its three-dimensional variational data assimilation (3DVAR) system, this study constructed twelve experiments to explore the impact of direct assimilation of different ATOVS radiance on the intensity and track simulation of super-typhoon Fanapi (2010) using a data assimilation cycle method. The result indicates that the assimilation of ATOVS radiance could improve typhoon intensity effectively. The average bias of the central sea level pressure (CSLP) drops to 18 hPa, compared to 42 hPa in the experiment without data assimilation. However, the influence due to different radiance data is not significant, which is less than 6 hPa on average, implying limited improvement from sole assimilation of ATOVS radiance. The track issue is studied in the following steps. First, the radiance from the same sensor of different satellites could produce different effect. For the AMSU-A, NOAA-15 and NOAA-18, they produce equivalent improvement, whereas NOAA-16 produces slightly poor effect. And for the AMSU-B, NOAA-15 and NOAA-16, they produce equivalent and more positive effect than that provided by the AMSU-A. Second, the assimilation radiance from different sensors of the identical satellites could also produce different effect. The assimilation of AMSU-B produces the largest improvement, while the ameliorating effect of HIRS/3 assimilation is inferior to that of AMSU-B assimilation, while the AMSU-A assimilation exhibits the poorest improvement. Moreover, the simultaneous assimilation of different radiance could not produce further improvement. Finally, the experiments of simultaneous assimilation radiance from multiple satellites indicate that such assimilation may lead to negative effect due to accumulative bias when adding various radiance data into the data assimilation system. Thus the assimilation of ATOVS radiance from a single satellite may perform better than that from two or three satellites.
Based on the newly developed Weather Research and Forecasting model (WRF) and its three-dimensional variational data assimilation (3DVAR) system, this study constructed twelve experiments to explore the impact of direct assimilation of different ATOVS radiance on the intensity and track simulation of super-typhoon Fanapi (2010) using a data assimilation cycle method. The result indicates that the assimilation of ATOVS radiance could improve typhoon intensity effectively. The average bias of the central sea level pressure (CSLP) drops to 18 hPa, compared to 42 hPa in the experiment without data assimilation. However, the influence due to different radiance data is not significant, which is less than 6 hPa on average, implying limited improvement from sole assimilation of ATOVS radiance. The track issue is studied in the following steps. First, the radiance from the same sensor of different satellites could produce different effect. For the AMSU-A, NOAA-15 and NOAA-18, they produce equivalent improvement, whereas NOAA-16 produces slightly poor effect. And for the AMSU-B, NOAA-15 and NOAA-16, they produce equivalent and more positive effect than that provided by the AMSU-A. Second, the assimilation radiance from different sensors of the identical satellites could also produce different effect. The assimilation of AMSU-B produces the largest improvement, while the ameliorating effect of HIRS/3 assimilation is inferior to that of AMSU-B assimilation, while the AMSU-A assimilation exhibits the poorest improvement. Moreover, the simultaneous assimilation of different radiance could not produce further improvement. Finally, the experiments of simultaneous assimilation radiance from multiple satellites indicate that such assimilation may lead to negative effect due to accumulative bias when adding various radiance data into the data assimilation system. Thus the assimilation of ATOVS radiance from a single satellite may perform better than that from two or three satellites.
2013, 19(3): 253-263.
Abstract:
In this study, we investigate the decadal variability of subsurface ocean temperature anomaly (SOTA) in the tropical Pacific and associated anomalous atmospheric circulation over Asia-North Pacific-North America by analyzing 50 years of atmosphere-ocean data from the National Center for Environmental Prediction (NCEP) reanalysis project and Simple Ocean Data Assimilation (SODA). Relationship between the ENSO-Like variability and climate of China is also revealed. The results show that the decadal variability of tropical Pacific SOTA has two dominant ENSO-like modes: the primary mode is an ENSO-Like mature phase pattern, and the second mode is associated with the ENSO-like transition (developing or decaying) phase. These two modes consist of a cycle of ENSO-Like variability, which exhibits a quasi-40a fluctuation, superimposed with an oscillation of a 13a period. The ENSO-Like variability in the tropical Pacific influences the atmosphere system at the mid- and higher-latitudes and subtropical regions, resulting in decadal variability of south wind over North China, the East Asian monsoon and climate of China. During the mature phase of El Niño-Like variability, the anomalous north wind prevails over the north part of China and the East Asian monsoon weakens, with little rain in North China but much rain in the middle- and lower-reaches of the Yangtze River. With El Niño-Like decaying (La Niña-Like developing), anomalous northerly wind also prevails over North China, then the East Asian monsoon weakens with drought occurring in North China. The situation during the La Niña-Like variability is the opposite. The pattern of anomalous climate of China is primarily dominated by the first ENSO-like variability, while the second mode can modulate the contribution of the first one, depending on whether its phase agrees with that of the first mode. The climate shift in China around 1978 and successive occurrence of drought for more than 20 years in North China are primarily induced by the first two ENSO-like variabilities. The latest La Niña-Like phase starts from 1998 and will presumably end around 2018. It is expected that more rainfall would be in North China and less rainfall would appear in the middle- and lower-reaches of the Yangtze River valley during this period.
In this study, we investigate the decadal variability of subsurface ocean temperature anomaly (SOTA) in the tropical Pacific and associated anomalous atmospheric circulation over Asia-North Pacific-North America by analyzing 50 years of atmosphere-ocean data from the National Center for Environmental Prediction (NCEP) reanalysis project and Simple Ocean Data Assimilation (SODA). Relationship between the ENSO-Like variability and climate of China is also revealed. The results show that the decadal variability of tropical Pacific SOTA has two dominant ENSO-like modes: the primary mode is an ENSO-Like mature phase pattern, and the second mode is associated with the ENSO-like transition (developing or decaying) phase. These two modes consist of a cycle of ENSO-Like variability, which exhibits a quasi-40a fluctuation, superimposed with an oscillation of a 13a period. The ENSO-Like variability in the tropical Pacific influences the atmosphere system at the mid- and higher-latitudes and subtropical regions, resulting in decadal variability of south wind over North China, the East Asian monsoon and climate of China. During the mature phase of El Niño-Like variability, the anomalous north wind prevails over the north part of China and the East Asian monsoon weakens, with little rain in North China but much rain in the middle- and lower-reaches of the Yangtze River. With El Niño-Like decaying (La Niña-Like developing), anomalous northerly wind also prevails over North China, then the East Asian monsoon weakens with drought occurring in North China. The situation during the La Niña-Like variability is the opposite. The pattern of anomalous climate of China is primarily dominated by the first ENSO-like variability, while the second mode can modulate the contribution of the first one, depending on whether its phase agrees with that of the first mode. The climate shift in China around 1978 and successive occurrence of drought for more than 20 years in North China are primarily induced by the first two ENSO-like variabilities. The latest La Niña-Like phase starts from 1998 and will presumably end around 2018. It is expected that more rainfall would be in North China and less rainfall would appear in the middle- and lower-reaches of the Yangtze River valley during this period.
2013, 19(3): 264-275.
Abstract:
Based on the daily regional mean rainfall, the Z-index method is used to identify persistent flood and drought events lasting for at least 10 days over a region where Dongting Lake and Poyang Lake sit (referred to as the "two-lake region" hereafter). The National Centers for Environmental Prediction (NCEP) reanalysis data are then utilized to perform a preliminary diagnostic analysis on these events. The results indicate that the composite standardized geopotential height at 500 hPa presents two different meridional wave trains from north to south over the East Asian-Pacific region, i.e., a "-+-" pattern for the droughts and a "+-+" pattern for the floods, respectively. The developing, maintaining and decaying phases in the drought and flood events are closely related to the intensity and location of a subtropical high and an extra-tropical blocking high. It is shown that the East Asian summer monsoon is strong (weak) with the occurrence of persistent drought (flood) events. Droughts (floods) are accompanied by a weak (strong) tropical convergent system and a strong (weak) subtropical convergent system. Furthermore, the persistent drought (flood) events are associated with a divergence (convergence) of vertically integrated water vapor flux. In the vertical profile of water vapor flux, divergence (convergence) in the mid- and lower-levels and convergence (divergence) in the higher levels are evident in the droughts (floods). Both the divergence in the droughts and the convergence in floods are strongest at 850 hPa.
Based on the daily regional mean rainfall, the Z-index method is used to identify persistent flood and drought events lasting for at least 10 days over a region where Dongting Lake and Poyang Lake sit (referred to as the "two-lake region" hereafter). The National Centers for Environmental Prediction (NCEP) reanalysis data are then utilized to perform a preliminary diagnostic analysis on these events. The results indicate that the composite standardized geopotential height at 500 hPa presents two different meridional wave trains from north to south over the East Asian-Pacific region, i.e., a "-+-" pattern for the droughts and a "+-+" pattern for the floods, respectively. The developing, maintaining and decaying phases in the drought and flood events are closely related to the intensity and location of a subtropical high and an extra-tropical blocking high. It is shown that the East Asian summer monsoon is strong (weak) with the occurrence of persistent drought (flood) events. Droughts (floods) are accompanied by a weak (strong) tropical convergent system and a strong (weak) subtropical convergent system. Furthermore, the persistent drought (flood) events are associated with a divergence (convergence) of vertically integrated water vapor flux. In the vertical profile of water vapor flux, divergence (convergence) in the mid- and lower-levels and convergence (divergence) in the higher levels are evident in the droughts (floods). Both the divergence in the droughts and the convergence in floods are strongest at 850 hPa.
2013, 19(3): 276-283.
Abstract:
The locations (longitudes and latitudes) of the tropical cyclones (TCs) making landfall on the Chinese mainland from 1949 to 2008 are investigated in detail by using ArcGis and FORTRAN routine. The southeast coastline [110 to 122°E) with most landfall TCs was selected as the key region, which was divided into 12 subsections with 1° intervals of longitude. The study period was from July to September in each year. The result showed that the average sustaining time of TCs making landfall on the subsections east of 118°E is longer than those west of 118°E. Before landfall, the averaged TC intensity in the subsections east of 118°E is stronger than that west of it. After landfall, however, the difference between the west and east is not significant. The index of destructive potential for the period before/after landfall was defined as TDP1/TDP2. The maximum of TDP1/TDP2 occurred in the subsection of [119, 120°E)/[110, 111°E). The ENSO impact on the frequency and average location of landfall TC over the whole region at 110 to 122°E is not obvious, but the effect varies with specific subsections. There is little differences of averaged TDP1 in the subsections between different phases of ENSO events, but the averaged TDP2 is larger in the warm events than that in the cold events. The rainstorm days of each station caused by TCs in different subsections were counted respectively. The results suggested that the rainstorm days of the subsections east of 118 °E are much more than those west of 118°E. The larger values are primarily distributed at the subsections of [119, 120°E) and [110, 111°E).
The locations (longitudes and latitudes) of the tropical cyclones (TCs) making landfall on the Chinese mainland from 1949 to 2008 are investigated in detail by using ArcGis and FORTRAN routine. The southeast coastline [110 to 122°E) with most landfall TCs was selected as the key region, which was divided into 12 subsections with 1° intervals of longitude. The study period was from July to September in each year. The result showed that the average sustaining time of TCs making landfall on the subsections east of 118°E is longer than those west of 118°E. Before landfall, the averaged TC intensity in the subsections east of 118°E is stronger than that west of it. After landfall, however, the difference between the west and east is not significant. The index of destructive potential for the period before/after landfall was defined as TDP1/TDP2. The maximum of TDP1/TDP2 occurred in the subsection of [119, 120°E)/[110, 111°E). The ENSO impact on the frequency and average location of landfall TC over the whole region at 110 to 122°E is not obvious, but the effect varies with specific subsections. There is little differences of averaged TDP1 in the subsections between different phases of ENSO events, but the averaged TDP2 is larger in the warm events than that in the cold events. The rainstorm days of each station caused by TCs in different subsections were counted respectively. The results suggested that the rainstorm days of the subsections east of 118 °E are much more than those west of 118°E. The larger values are primarily distributed at the subsections of [119, 120°E) and [110, 111°E).
2013, 19(3): 284-296.
Abstract:
In this study, the super typhoon KROSA (2007) was simulated using a mesoscale numerical model Global and Regional Assimilation and Prediction System (GRAPES) with a two-moment mixed-phase microphysics scheme. Local rainfall observations, radar and satellite data were also used to analyze the precipitation structure and microphysical features. It was shown that low-level jets and unstable temperature stratification provided this precipitation process with favorable weather condition. Heavy rainfall centers were located in the north and east part of KROSA with the maxima of 6-hourly total rainfall during the simulation more than 100 mm. The quantities of column solid water and column liquid water were generally equivalent, indicating the important role of ice phase in precipitation formation. Results of CloudSat showed that strong convection occurred in the eyewall around the cyclonic center. According to the simulation results, heavy precipitation in the northeast part of the typhoon was mainly triggered by convective clouds, accompanied by the strongest updraft under the melting level. In the southwest part of KROSA, precipitation intensity was rather homogeneous. The ascending center occurred in high-level cold clouds, favoring the formation and growth of ice particles.
In this study, the super typhoon KROSA (2007) was simulated using a mesoscale numerical model Global and Regional Assimilation and Prediction System (GRAPES) with a two-moment mixed-phase microphysics scheme. Local rainfall observations, radar and satellite data were also used to analyze the precipitation structure and microphysical features. It was shown that low-level jets and unstable temperature stratification provided this precipitation process with favorable weather condition. Heavy rainfall centers were located in the north and east part of KROSA with the maxima of 6-hourly total rainfall during the simulation more than 100 mm. The quantities of column solid water and column liquid water were generally equivalent, indicating the important role of ice phase in precipitation formation. Results of CloudSat showed that strong convection occurred in the eyewall around the cyclonic center. According to the simulation results, heavy precipitation in the northeast part of the typhoon was mainly triggered by convective clouds, accompanied by the strongest updraft under the melting level. In the southwest part of KROSA, precipitation intensity was rather homogeneous. The ascending center occurred in high-level cold clouds, favoring the formation and growth of ice particles.
2013, 19(3): 297-304.
Abstract:
China's new generation of polar-orbiting meteorological satellite FY-3A was successfully launched on May 26, 2008, carrying microwave sounding devices which had similar performance to ATOVS of NOAA series. In order to study the application of microwave sounding data in numerical prediction of typhoons and to improve typhoon forecasting, we assimilated data directly for numerical forecasting of the track and intensity of the 2009 typhoon Morakot (0908) based on the WRF-3DVar system. Results showed that the initial fields of the numerical model due to direct assimilation of FY-3A microwave sounding data was improved much more than that due to assimilation of conventional observations alone, and the improvement was especially significant over the ocean, which is always without conventional observations. The model initial fields were more reasonable in reflecting the initial situation of typhoon circulation as well as temperature and humidity conditions, and typhoon central position at sea was also adjusted. Through direct 3DVar assimilation of FY-3A microwave data, the regional mesoscale model improves the forecasting of typhoon track. Therefore, the FY-3A microwave data could efficiently improve the numerical prediction of typhoons.
China's new generation of polar-orbiting meteorological satellite FY-3A was successfully launched on May 26, 2008, carrying microwave sounding devices which had similar performance to ATOVS of NOAA series. In order to study the application of microwave sounding data in numerical prediction of typhoons and to improve typhoon forecasting, we assimilated data directly for numerical forecasting of the track and intensity of the 2009 typhoon Morakot (0908) based on the WRF-3DVar system. Results showed that the initial fields of the numerical model due to direct assimilation of FY-3A microwave sounding data was improved much more than that due to assimilation of conventional observations alone, and the improvement was especially significant over the ocean, which is always without conventional observations. The model initial fields were more reasonable in reflecting the initial situation of typhoon circulation as well as temperature and humidity conditions, and typhoon central position at sea was also adjusted. Through direct 3DVar assimilation of FY-3A microwave data, the regional mesoscale model improves the forecasting of typhoon track. Therefore, the FY-3A microwave data could efficiently improve the numerical prediction of typhoons.
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