There is an urgent need for the development of a method that can undertake rapid, effective, and accurate monitoring and identification of fog by satellite remote sensing, since heavy fog can cause enormous disasters ...There is an urgent need for the development of a method that can undertake rapid, effective, and accurate monitoring and identification of fog by satellite remote sensing, since heavy fog can cause enormous disasters to China’s national economy and people's lives and property in the urban and coastal areas. In this paper, the correlative relationship between the reflectivity of land surface and clouds in different time phases is found, based on the analysis of the radiative and satellite-based spectral characteristics of fog. Through calculation and analyses of the relative variability of the reflectivity in the images, the threshold to identify quasi-fog areas is generated automatically. Furthermore, using the technique of quick image run-length encoding, and in combination with such practical methods as analyzing texture and shape fractures, smoothness, and template characteristics, the automatic identification of fog and fog-cloud separation using meteorological satellite remote sensing images are studied, with good results in application.展开更多
Mesoscale convective systems (MCSs) are severe disaster-producing weather systems. Previous attempts of MCS census are made by examining infrared satellite imageries artificially, with subjectivity involved in the pro...Mesoscale convective systems (MCSs) are severe disaster-producing weather systems. Previous attempts of MCS census are made by examining infrared satellite imageries artificially, with subjectivity involved in the process unavoidably. This method is also inefficient and time-consuming. The disadvantages make it impossible to do MCS census over Asia and western Pacific region (AWPR) with an extended span of time, which is not favorable for gaining a deeper insight into these systems. In this paper, a fire-new automatic MCS identification (AMI) method is used to capture four categories of MCSs with different sizes and shapes from numerical satellite infrared data. 47,468 MCSs are identified over Asia and western Pacific region during the warm season (May to October) from 1995 to 2008. Based on this database, MCS characteristics such as shape, size, duration, velocity, geographical distribution, intermonthly variation, and lifecycle are studied. Results indicate that the number of linear MCSs is 2.5 times that of circular MCSs. The former is of a larger size while the latter is of a longer duration. The 500 hPa steering flow plays an important role in the MCS movement. MCSs tend to move faster after they reach the maximum extent. Four categories of MCS have similar characteristics of geographical distribution and intermonthly variation. Basically, MCSs are zonally distributed, with three zones weakening from south to north. The intermonthly variation of MCSs is related to the seasonal adjustment of the large-scale circulation. As to the MCSs over China, they have different lifecycle characteristics over different areas. MCSs over plateaus and hill areas, with only one peak in their lifecycle curves, tend to form in the afternoon, mature at nightfall, and dissipate at night. On the other hand, MCSs over plains, which have several peaks in their lifecycle curves, may form either in the afternoon or at night, whereas MCSs over the oceans tend to form at midnight. Affected by the sea-land breeze circulation, MCSs over coastal areas of Guangdong and Guangxi always come into being at about 1500 or 1600 (local time), while MCSs over the Sichuan Basin, affected by the mountain-valley breeze circulation, generally initiate nocturnally.展开更多
Mesoscale convective systems （MCSs） are severe disaster-producing weather systems. Radar data and infrared satellite image are useful tools in MCS surveillance. The previous method of MCS census is to look through t...Mesoscale convective systems （MCSs） are severe disaster-producing weather systems. Radar data and infrared satellite image are useful tools in MCS surveillance. The previous method of MCS census is to look through the printed infrared imagery manually. This method is not only subjective and inaccurate, but also inefficient. Different from previous studies, a new automatic MCS identification （AMI） method, which overcomes the above disadvantages, is used in the present study. The AMI method takes three steps： searching potential MCS profiles, tracking the MCS, and assessing the MCS, so as to capture MCSs from infrared satellite images. Finally, 47468 MCSs are identified over Asia and the western Pacific region during the warm seasons （May-October） from 1995 to 2008. From this database, the geographical distribution and diurnal variation of MCSs are analyzed. The results show that different types of MCSs have similar geographical distributions. Latitude is the main control factor for MCS distribution. MCSs are most frequent over the central Tibetan Plateau; meanwhile, this area also has the highest hail frequency according to previous studies. ~rther, it is found that the diurnal variation of MCSs has little to do with MCSs＇ size or shape; MCSs in different areas have their own particular diurnal variation patterns. Based on the diurnal variation characteristics, MCSs are classified into four categories： the whole-day occurring MCSs in low latitude, the whole-day occurring MCSs in high latitude, the nocturnal MCSs, and the postmeridian MCSs. MCSs over most places of China's Mainland are postmeridian; but MCSs over the Sichuan basin and its vicinity are nocturnal. This conclusion is coincidental with the hail climatology of China.展开更多
基金Key research project "Research of Shanghai City and Costal Heavy Fog Remote Sensing Detecting and Warning System" of Science and Technology Commission of Shanghai Municipality (075115011)
文摘There is an urgent need for the development of a method that can undertake rapid, effective, and accurate monitoring and identification of fog by satellite remote sensing, since heavy fog can cause enormous disasters to China’s national economy and people's lives and property in the urban and coastal areas. In this paper, the correlative relationship between the reflectivity of land surface and clouds in different time phases is found, based on the analysis of the radiative and satellite-based spectral characteristics of fog. Through calculation and analyses of the relative variability of the reflectivity in the images, the threshold to identify quasi-fog areas is generated automatically. Furthermore, using the technique of quick image run-length encoding, and in combination with such practical methods as analyzing texture and shape fractures, smoothness, and template characteristics, the automatic identification of fog and fog-cloud separation using meteorological satellite remote sensing images are studied, with good results in application.
基金National Natural Science Founds of China (40875028)Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Mesoscale convective systems (MCSs) are severe disaster-producing weather systems. Previous attempts of MCS census are made by examining infrared satellite imageries artificially, with subjectivity involved in the process unavoidably. This method is also inefficient and time-consuming. The disadvantages make it impossible to do MCS census over Asia and western Pacific region (AWPR) with an extended span of time, which is not favorable for gaining a deeper insight into these systems. In this paper, a fire-new automatic MCS identification (AMI) method is used to capture four categories of MCSs with different sizes and shapes from numerical satellite infrared data. 47,468 MCSs are identified over Asia and western Pacific region during the warm season (May to October) from 1995 to 2008. Based on this database, MCS characteristics such as shape, size, duration, velocity, geographical distribution, intermonthly variation, and lifecycle are studied. Results indicate that the number of linear MCSs is 2.5 times that of circular MCSs. The former is of a larger size while the latter is of a longer duration. The 500 hPa steering flow plays an important role in the MCS movement. MCSs tend to move faster after they reach the maximum extent. Four categories of MCS have similar characteristics of geographical distribution and intermonthly variation. Basically, MCSs are zonally distributed, with three zones weakening from south to north. The intermonthly variation of MCSs is related to the seasonal adjustment of the large-scale circulation. As to the MCSs over China, they have different lifecycle characteristics over different areas. MCSs over plateaus and hill areas, with only one peak in their lifecycle curves, tend to form in the afternoon, mature at nightfall, and dissipate at night. On the other hand, MCSs over plains, which have several peaks in their lifecycle curves, may form either in the afternoon or at night, whereas MCSs over the oceans tend to form at midnight. Affected by the sea-land breeze circulation, MCSs over coastal areas of Guangdong and Guangxi always come into being at about 1500 or 1600 (local time), while MCSs over the Sichuan Basin, affected by the mountain-valley breeze circulation, generally initiate nocturnally.
基金Supported by the National(Key)Basic Research and Development(973)Program of China(2013CB430103)National Natural Science Foundation of China(40875028)Forecaster Special Project Funded by the Jiangsu Meteorological Bureau(2012-8)
文摘Mesoscale convective systems （MCSs） are severe disaster-producing weather systems. Radar data and infrared satellite image are useful tools in MCS surveillance. The previous method of MCS census is to look through the printed infrared imagery manually. This method is not only subjective and inaccurate, but also inefficient. Different from previous studies, a new automatic MCS identification （AMI） method, which overcomes the above disadvantages, is used in the present study. The AMI method takes three steps： searching potential MCS profiles, tracking the MCS, and assessing the MCS, so as to capture MCSs from infrared satellite images. Finally, 47468 MCSs are identified over Asia and the western Pacific region during the warm seasons （May-October） from 1995 to 2008. From this database, the geographical distribution and diurnal variation of MCSs are analyzed. The results show that different types of MCSs have similar geographical distributions. Latitude is the main control factor for MCS distribution. MCSs are most frequent over the central Tibetan Plateau; meanwhile, this area also has the highest hail frequency according to previous studies. ~rther, it is found that the diurnal variation of MCSs has little to do with MCSs＇ size or shape; MCSs in different areas have their own particular diurnal variation patterns. Based on the diurnal variation characteristics, MCSs are classified into four categories： the whole-day occurring MCSs in low latitude, the whole-day occurring MCSs in high latitude, the nocturnal MCSs, and the postmeridian MCSs. MCSs over most places of China's Mainland are postmeridian; but MCSs over the Sichuan basin and its vicinity are nocturnal. This conclusion is coincidental with the hail climatology of China.
