Rain cells or convective rain,the dominant form of rain in the tropics and subtropics,can be easy detected by satellite Synthetic Aperture Radar（SAR） images with high horizontal resolution.The footprints of rain cel...Rain cells or convective rain,the dominant form of rain in the tropics and subtropics,can be easy detected by satellite Synthetic Aperture Radar（SAR） images with high horizontal resolution.The footprints of rain cells on SAR images are caused by the scattering and attenuation of the rain drops,as well as the downward airflow.In this study,we extract sea surface wind field and its structure caused by rain cells by using a RADARSAT-2 SAR image with a spatial resolution of 100 m for case study.We extract the sea surface wind speeds from SAR image by using CMOD4 geophysical model function with outside wind directions of NCEP final operational global analysis data,Advance Scatterometer（ASCAT） onboard European Met Op-A satellite and microwave scatterometer onboard Chinese HY-2 satellite,respectively.The root-mean-square errors（RMSE） of these SAR wind speeds,validated against NCEP,ASCAT and HY-2,are 1.48 m/s,1.64 m/s and 2.14 m/s,respectively.Circular signature patterns with brighter on one side and darker on the opposite side on SAR image are interpreted as the sea surface wind speed（or sea surface roughness） variety caused by downdraft associated with rain cells.The wind speeds taken from the transect profile which superposes to the wind ambient vectors and goes through the center of the circular footprint of rain cell can be fitted as a cosine or sine curve in high linear correlation with the values of no less than 0.80.The background wind speed,the wind speed caused by rain cell and the diameter of footprint of the rain cell with kilometers or tens of kilometers can be acquired by fitting curve.Eight cases interpreted and analyzed in this study all show the same conclusion.展开更多
As an approach to the technological problem that the wind data of QuikSCAT scatterometer cannot accurately describe the zone of typhoon-level strong wind speed, some objective factors such as the typhoon moving speed,...As an approach to the technological problem that the wind data of QuikSCAT scatterometer cannot accurately describe the zone of typhoon-level strong wind speed, some objective factors such as the typhoon moving speed, direction and friction are introduced in this study to construct the asymmetric strengthening of the QuikSCAT wind field. Then by adopting a technology of four-dimensional data assimilation, an experiment that includes both the assimilation and forecasting phases is designed to simulate Typhoon Rananim numerically. The results show that with model constraints and adjustment, this technology can incorporate the QuikSCAT wind data to the entire column of the model atmosphere, improve greatly the simulating effects of the whole-column wind, pressure field and the track as well as the simulated typhoon intensity covered by the forecast phase, and work positively for the forecasting of landfall locations.展开更多
This paper presents results from a statistical validation of the hindcasts of surface wind by a high-resolution-mesoscale atmospheric numerical model Advanced Research WRF(ARW3.3), which is set up to force the operati...This paper presents results from a statistical validation of the hindcasts of surface wind by a high-resolution-mesoscale atmospheric numerical model Advanced Research WRF(ARW3.3), which is set up to force the operational coastal ocean forecast system at Indian National Centre for Ocean Information Services(INCOIS). Evaluation is carried out based on comparisons of day-3 forecasts of surface wind with in situ and remote-sensing data. The results show that the model predicts the surface wind fields fairly accurately over the west coast of India, with high skill in predicting the surface wind during the pre-monsoon season. The model predicts the diurnal variability of the surface wind with reasonable accuracy. The model simulates the land-sea breeze cycle in the coastal region realistically, which is very clearly observed during the northeast monsoon and pre-monsoon season and is less prominent during the southwest monsoon season.展开更多
Sea surface wind(SSW)observations from a newly developed“Black Pearl”wave glider,the Chinese-French Oceanography Satellite(CFOSAT),the HY-2A microwave scatterometer,and a recently released high-resolution atmospheri...Sea surface wind(SSW)observations from a newly developed“Black Pearl”wave glider,the Chinese-French Oceanography Satellite(CFOSAT),the HY-2A microwave scatterometer,and a recently released high-resolution atmospheric reanalysis(ERA5)are evaluated with respect to in-situ buoy observations(115.46°E,19.85°N)from the South China Sea.Buoy observations from June to November 2019 are used to evaluate the wind estimates from the different platforms.The comparisons show that the HY-2A and CFOSAT scatterometer wind speeds have mean root mean square errors(RMSEs)of approximately 1.6 and 1.6 m/s,respectively,and the corresponding mean wind direction RMSEs are approximately 19°and 17°,which indicates that these satellite retrievals meet the requirements of design engineering missions.The wind speed and wind direction RMSEs of ERA5 are approximately 1.9 m/s and 33°,respectively.The correlation coefficients between the HY-2A,CFOSAT,and ERA5 wind speeds and the buoy observations are 0.86,0.85,and 0.84,respectively,and the corresponding coefficients of the wind direction are 0.98,0.98,and 0.93,respectively,at a 95%confidence level.However,the wind sensor in the wave glider provides relatively poor-quality observations compared with the buoy measurements and has higher wind speed and wind direction RMSEs of 2.9 m/s and 50.1°,respectively.Taylor diagrams are utilized to illustrate comprehensive wind comparisons between the multiplatform observations and buoy observations.The results help identify the basic biases in SSWs among different products and enhance confidence in the future use of SSW data for studies of upper ocean dynamics and climate analysis.Suggestions are also off ered to help improve the design of next-generation wave gliders.展开更多
With the advances of numerical weather simulation and reduced data assimilation updating cycle,surface observation data assimilation becomes more and more important in data assimilation systems.It is widely accepted t...With the advances of numerical weather simulation and reduced data assimilation updating cycle,surface observation data assimilation becomes more and more important in data assimilation systems.It is widely accepted that a better data assimilation system should contain the restriction of thermodynamic processes in the surface layer.Therefore,in this paper,a new surface wind observation operator is utilized in Global and Regional Assimilation PrEdiction System_3D-Variance(GRAPES_3D-Var),with the restriction of thermodynamic process in the planetary boundary layer(PBL).In order to research the ability of this new surface wind observation operator in assimilation and forecasting,a series of experiments are operated by using the GRAPES model.The main results indicate that this new method of surface wind observation operator has positive impact on the forecast with the GRAPES model.展开更多
The study investigated the impacts of tropical cyclone (TC) Fantala (11<sup>th</sup> to 27<sup>th</sup> April, 2016) to the coastal areas of Tanzania, Zanzibar in particular. Daily reanalysis d...The study investigated the impacts of tropical cyclone (TC) Fantala (11<sup>th</sup> to 27<sup>th</sup> April, 2016) to the coastal areas of Tanzania, Zanzibar in particular. Daily reanalysis data consisting of wind speed, sea level pressure (SLP), sea surface temperatures (SSTs) anomaly, and relative humidity from the National Centres for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) were used to analyze the variation in strength of Fantala as it was approaching the Tanzania coastal line. In addition observed rainfall from Tanzania Meteorological Authority (TMA) at Zanzibar office, Global Forecasting System (GFS) rainfall estimates and satellite images were used to visualize the impacts of tropical cyclone Fantala to Zanzibar. The results revealed that, TC Fantala was associated with deepening/decreasing in SLP (from 1012 - 1010 mb) around the north-western Madagascar and coastal Tanzania, whereas the mean SSTs was greater than 28<span style="white-space:nowrap;">°</span>C and an SSTs anomaly ranged from 0 to 2.3<span style="white-space:nowrap;">°</span>C. The vertical wind shear which ridged at Mozambican Channel and over north-eastern Madagascar was high enough (12 - 15 ms<sup>-1</sup>) to support the intensifying of Fantala. The thermodynamic and dynamic conditions of Fantala influenced heavy rainfall of greater than 170 mm over most stations in Zanzibar. Moreover, Fantala disrupted the temporal variability of 2016 March to May (MAM) seasonal rainfall. Besides, more than 420 people were homeless, at least 3330 houses were destroyed, and about 2 people died. As for mainland Tanzania Fantala resulted in a death of 12 people in Kilimanjaro and Arusha, more than 315 houses were washed away by flooding leading to 13,933 people being homeless. Conclusively the study calls for an extensive research work based on examining and forecasting the TCs rainfall impacts and their contribution during the two rainfall seasons of OND and MAM in Tanzania.展开更多
A complex weather process at Shanghai Pudong International Airport during April 8-9 in 2017 was analyzed deeply to study the causes of low clouds and convective weather and how to provide services for control in the c...A complex weather process at Shanghai Pudong International Airport during April 8-9 in 2017 was analyzed deeply to study the causes of low clouds and convective weather and how to provide services for control in the complex weather situation. The results showed that when clouds and visibility were low,the situation of wind fields should be analyzed carefully to forecast the weather more accurately. The actual situation of the weather was in line with the numerical forecast on the day,and numerical forecast had certain reference value for convection forecast. The prediction of cloud height was not as perfect as expected on the day,but corresponding services were provided to the regulatory agencies 3 h early,and they had sufficient time to make decisions. The meteorological services have also been well received by the regulatory authorities,which further explains the importance of forecast in advance.展开更多
基金The Joint Foundation of National Natural Science Foundation of China and the Marine Science Center of Shandong Province under contract No.U1406404the National Natural Science Foundation of China under contract Nos 41506206,41306186 and41476152+1 种基金the Global Change and Air-Sea Interaction Project of China under contract No.GASI-03-03-01-01the Open funds of State Key Laboratory of Satellite Ocean Environment Dynamics under contract No.SOED1411
文摘Rain cells or convective rain,the dominant form of rain in the tropics and subtropics,can be easy detected by satellite Synthetic Aperture Radar（SAR） images with high horizontal resolution.The footprints of rain cells on SAR images are caused by the scattering and attenuation of the rain drops,as well as the downward airflow.In this study,we extract sea surface wind field and its structure caused by rain cells by using a RADARSAT-2 SAR image with a spatial resolution of 100 m for case study.We extract the sea surface wind speeds from SAR image by using CMOD4 geophysical model function with outside wind directions of NCEP final operational global analysis data,Advance Scatterometer（ASCAT） onboard European Met Op-A satellite and microwave scatterometer onboard Chinese HY-2 satellite,respectively.The root-mean-square errors（RMSE） of these SAR wind speeds,validated against NCEP,ASCAT and HY-2,are 1.48 m/s,1.64 m/s and 2.14 m/s,respectively.Circular signature patterns with brighter on one side and darker on the opposite side on SAR image are interpreted as the sea surface wind speed（or sea surface roughness） variety caused by downdraft associated with rain cells.The wind speeds taken from the transect profile which superposes to the wind ambient vectors and goes through the center of the circular footprint of rain cell can be fitted as a cosine or sine curve in high linear correlation with the values of no less than 0.80.The background wind speed,the wind speed caused by rain cell and the diameter of footprint of the rain cell with kilometers or tens of kilometers can be acquired by fitting curve.Eight cases interpreted and analyzed in this study all show the same conclusion.
基金National Key Fundamental Research and Development Plan of China (2004CB418301)Natural Science Foundation of China (40830958)
文摘As an approach to the technological problem that the wind data of QuikSCAT scatterometer cannot accurately describe the zone of typhoon-level strong wind speed, some objective factors such as the typhoon moving speed, direction and friction are introduced in this study to construct the asymmetric strengthening of the QuikSCAT wind field. Then by adopting a technology of four-dimensional data assimilation, an experiment that includes both the assimilation and forecasting phases is designed to simulate Typhoon Rananim numerically. The results show that with model constraints and adjustment, this technology can incorporate the QuikSCAT wind data to the entire column of the model atmosphere, improve greatly the simulating effects of the whole-column wind, pressure field and the track as well as the simulated typhoon intensity covered by the forecast phase, and work positively for the forecasting of landfall locations.
基金University Grants Commission (UGC) for funding to pursue this work
文摘This paper presents results from a statistical validation of the hindcasts of surface wind by a high-resolution-mesoscale atmospheric numerical model Advanced Research WRF(ARW3.3), which is set up to force the operational coastal ocean forecast system at Indian National Centre for Ocean Information Services(INCOIS). Evaluation is carried out based on comparisons of day-3 forecasts of surface wind with in situ and remote-sensing data. The results show that the model predicts the surface wind fields fairly accurately over the west coast of India, with high skill in predicting the surface wind during the pre-monsoon season. The model predicts the diurnal variability of the surface wind with reasonable accuracy. The model simulates the land-sea breeze cycle in the coastal region realistically, which is very clearly observed during the northeast monsoon and pre-monsoon season and is less prominent during the southwest monsoon season.
基金Supported by the National Natural Science Foundation of China(No.42076016)the Fundamental Research Funds for the Central Universities(No.2019B02814)the National Key Research and Development Program of China(No.2018YFC0213104)。
文摘Sea surface wind(SSW)observations from a newly developed“Black Pearl”wave glider,the Chinese-French Oceanography Satellite(CFOSAT),the HY-2A microwave scatterometer,and a recently released high-resolution atmospheric reanalysis(ERA5)are evaluated with respect to in-situ buoy observations(115.46°E,19.85°N)from the South China Sea.Buoy observations from June to November 2019 are used to evaluate the wind estimates from the different platforms.The comparisons show that the HY-2A and CFOSAT scatterometer wind speeds have mean root mean square errors(RMSEs)of approximately 1.6 and 1.6 m/s,respectively,and the corresponding mean wind direction RMSEs are approximately 19°and 17°,which indicates that these satellite retrievals meet the requirements of design engineering missions.The wind speed and wind direction RMSEs of ERA5 are approximately 1.9 m/s and 33°,respectively.The correlation coefficients between the HY-2A,CFOSAT,and ERA5 wind speeds and the buoy observations are 0.86,0.85,and 0.84,respectively,and the corresponding coefficients of the wind direction are 0.98,0.98,and 0.93,respectively,at a 95%confidence level.However,the wind sensor in the wave glider provides relatively poor-quality observations compared with the buoy measurements and has higher wind speed and wind direction RMSEs of 2.9 m/s and 50.1°,respectively.Taylor diagrams are utilized to illustrate comprehensive wind comparisons between the multiplatform observations and buoy observations.The results help identify the basic biases in SSWs among different products and enhance confidence in the future use of SSW data for studies of upper ocean dynamics and climate analysis.Suggestions are also off ered to help improve the design of next-generation wave gliders.
基金National Natural Science Foundation of China (40675064)
文摘With the advances of numerical weather simulation and reduced data assimilation updating cycle,surface observation data assimilation becomes more and more important in data assimilation systems.It is widely accepted that a better data assimilation system should contain the restriction of thermodynamic processes in the surface layer.Therefore,in this paper,a new surface wind observation operator is utilized in Global and Regional Assimilation PrEdiction System_3D-Variance(GRAPES_3D-Var),with the restriction of thermodynamic process in the planetary boundary layer(PBL).In order to research the ability of this new surface wind observation operator in assimilation and forecasting,a series of experiments are operated by using the GRAPES model.The main results indicate that this new method of surface wind observation operator has positive impact on the forecast with the GRAPES model.
文摘The study investigated the impacts of tropical cyclone (TC) Fantala (11<sup>th</sup> to 27<sup>th</sup> April, 2016) to the coastal areas of Tanzania, Zanzibar in particular. Daily reanalysis data consisting of wind speed, sea level pressure (SLP), sea surface temperatures (SSTs) anomaly, and relative humidity from the National Centres for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) were used to analyze the variation in strength of Fantala as it was approaching the Tanzania coastal line. In addition observed rainfall from Tanzania Meteorological Authority (TMA) at Zanzibar office, Global Forecasting System (GFS) rainfall estimates and satellite images were used to visualize the impacts of tropical cyclone Fantala to Zanzibar. The results revealed that, TC Fantala was associated with deepening/decreasing in SLP (from 1012 - 1010 mb) around the north-western Madagascar and coastal Tanzania, whereas the mean SSTs was greater than 28<span style="white-space:nowrap;">°</span>C and an SSTs anomaly ranged from 0 to 2.3<span style="white-space:nowrap;">°</span>C. The vertical wind shear which ridged at Mozambican Channel and over north-eastern Madagascar was high enough (12 - 15 ms<sup>-1</sup>) to support the intensifying of Fantala. The thermodynamic and dynamic conditions of Fantala influenced heavy rainfall of greater than 170 mm over most stations in Zanzibar. Moreover, Fantala disrupted the temporal variability of 2016 March to May (MAM) seasonal rainfall. Besides, more than 420 people were homeless, at least 3330 houses were destroyed, and about 2 people died. As for mainland Tanzania Fantala resulted in a death of 12 people in Kilimanjaro and Arusha, more than 315 houses were washed away by flooding leading to 13,933 people being homeless. Conclusively the study calls for an extensive research work based on examining and forecasting the TCs rainfall impacts and their contribution during the two rainfall seasons of OND and MAM in Tanzania.
文摘A complex weather process at Shanghai Pudong International Airport during April 8-9 in 2017 was analyzed deeply to study the causes of low clouds and convective weather and how to provide services for control in the complex weather situation. The results showed that when clouds and visibility were low,the situation of wind fields should be analyzed carefully to forecast the weather more accurately. The actual situation of the weather was in line with the numerical forecast on the day,and numerical forecast had certain reference value for convection forecast. The prediction of cloud height was not as perfect as expected on the day,but corresponding services were provided to the regulatory agencies 3 h early,and they had sufficient time to make decisions. The meteorological services have also been well received by the regulatory authorities,which further explains the importance of forecast in advance.
