ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 44,Issue 6,2018 Table of Contents
2018, 44(6):725-736.
DOI: 10.7519/j.issn.1000-0526.2018.06.001
Abstract:
Dust storm is a typical weather disaster which outbreaks in arid and semi-arid areas globally. The dust aerosol generated from dust storm dominates the aerosol loading in the troposphere and has comprehensive impacts on the global environment, weather, climate and ecology. As a kind of absorbing aerosol, dust aerosol has strong absorption on the incoming solar radiation. Dust aerosol can affect the climate through the semi-direct effect, such as heating the atmosphere, changing the atmospheric stability, evaporating the cloud droplet and reducing the cloud amount. Satellite remote sensing has showed special priority on dust monitoring and has become an indispensable way for dust aerosol study. The main satellite-based dust aerosol remote sensing methods are summarized in this paper as the visible-infrared method, thermal infrared method, microwave method, ultraviolet method and active lidar-based method. In addition, typical instruments and products are introduced, and the accuracy of products and the validation by ground-based remote sensing network are discussed. Based on the radiation transfer theory, the visible-infrared and thermal infrared radiance observed by satellite are simulated. Moreover, the effect of surface albedo and the channel selection issue are discussed for the visible remote sensing and thermal infrared hyperspectral remote sensing separately. Finally, some prospects in the future study for the satellite-based dust aerosol remote sensing are presented.
Dust storm is a typical weather disaster which outbreaks in arid and semi-arid areas globally. The dust aerosol generated from dust storm dominates the aerosol loading in the troposphere and has comprehensive impacts on the global environment, weather, climate and ecology. As a kind of absorbing aerosol, dust aerosol has strong absorption on the incoming solar radiation. Dust aerosol can affect the climate through the semi-direct effect, such as heating the atmosphere, changing the atmospheric stability, evaporating the cloud droplet and reducing the cloud amount. Satellite remote sensing has showed special priority on dust monitoring and has become an indispensable way for dust aerosol study. The main satellite-based dust aerosol remote sensing methods are summarized in this paper as the visible-infrared method, thermal infrared method, microwave method, ultraviolet method and active lidar-based method. In addition, typical instruments and products are introduced, and the accuracy of products and the validation by ground-based remote sensing network are discussed. Based on the radiation transfer theory, the visible-infrared and thermal infrared radiance observed by satellite are simulated. Moreover, the effect of surface albedo and the channel selection issue are discussed for the visible remote sensing and thermal infrared hyperspectral remote sensing separately. Finally, some prospects in the future study for the satellite-based dust aerosol remote sensing are presented.
2018, 44(6):737-751.
DOI: 10.7519/j.issn.1000-0526.2018.06.002
Abstract:
Based on the China regional grid precipitation dataset CN05.1 and EAR-Interim reanalysis data, the seasonal modulation of the impact of Madden-Julian Oscillation (MJO) on China’s precipitation anomaly is studied, and a dynamical-statistical downscaling model which focuses on extended-range precipitation forecast is established based on the MJO prediction by numerical model. The results show that the impact of MJO on precipitation anomaly is modulated by seasonal cycle obviously. When the MJO convection is active in tropical Indian Ocean, the above normal precipitation area advance northward along with the changes of seasons. When the MJO convection is active in the maritime continent, precipitation in eastern China and Tibet Plateau is abnormally less in autumn and winter, but this situation is gradually weakened or even reversed in spring and summer. The position and amplitude variation of MJO convection and basic state (especially the subtropical westerly jet) lead to different extra-tropical circulation responses, which are the main causes for these seasonal variations. The model verification suggests that the prediction skill of target pentad RMM index based on BCC_AGCM2.2 can extend to 18 days. In addition, a seasonal rol-ling MJO dynamical-statistical downscaling precipitation prediction model is established based on the forecasted RMM indices by dynamical model. The independent sample tests show that the dynamical-statistical model achieves higher skills in predicting the low-frequency precipitation anomaly than the direct output of BCC_AGCM2.2 in MJO high impact area during long lead time (10-20 d). The improvement is more obvious in the MJO active period. These findings could provide new thoughts for the MJO interpretation.
Based on the China regional grid precipitation dataset CN05.1 and EAR-Interim reanalysis data, the seasonal modulation of the impact of Madden-Julian Oscillation (MJO) on China’s precipitation anomaly is studied, and a dynamical-statistical downscaling model which focuses on extended-range precipitation forecast is established based on the MJO prediction by numerical model. The results show that the impact of MJO on precipitation anomaly is modulated by seasonal cycle obviously. When the MJO convection is active in tropical Indian Ocean, the above normal precipitation area advance northward along with the changes of seasons. When the MJO convection is active in the maritime continent, precipitation in eastern China and Tibet Plateau is abnormally less in autumn and winter, but this situation is gradually weakened or even reversed in spring and summer. The position and amplitude variation of MJO convection and basic state (especially the subtropical westerly jet) lead to different extra-tropical circulation responses, which are the main causes for these seasonal variations. The model verification suggests that the prediction skill of target pentad RMM index based on BCC_AGCM2.2 can extend to 18 days. In addition, a seasonal rol-ling MJO dynamical-statistical downscaling precipitation prediction model is established based on the forecasted RMM indices by dynamical model. The independent sample tests show that the dynamical-statistical model achieves higher skills in predicting the low-frequency precipitation anomaly than the direct output of BCC_AGCM2.2 in MJO high impact area during long lead time (10-20 d). The improvement is more obvious in the MJO active period. These findings could provide new thoughts for the MJO interpretation.
2018, 44(6):752-758.
DOI: 10.7519/j.issn.1000-0526.2018.06.003
Abstract:
Using the radar data of CINRAD/CD in Guiyang, Guizhou Province, in the period from May to August in 2014-2016, the spatial and temporal distribution characteristics of convective precipitation in Guiyang area were analyzed. First, 551 cases of convective precipitation echoes were selected, and then the echoes were statistically analyzed from six aspects of morphological characteristics, occurrence frequency, location, diurnal variation, duration and large-scale background conditions. The results showed that the convective precipitation echoes can be classified into cell type, linear and regional type, of which the linear type is about 50%, being the most common form of convection organization in Guiyang area. Compared to the linear and regional types, the convective duration of cell type is the shortest and has obviously local characteristics. More than 70% of convective precipitation events occur under the southwest vortex or southwest airflow weather condition. Convective precipitation often occurs in the southwest and southeast of Guiyang and rarely in the north. Convective initiation time has two peaks in the afternoon and around midnight, respectively. Finally, three representative convective precipitation events were carefully examined in terms of lifetime, coverage and intensity of precipitation.
Using the radar data of CINRAD/CD in Guiyang, Guizhou Province, in the period from May to August in 2014-2016, the spatial and temporal distribution characteristics of convective precipitation in Guiyang area were analyzed. First, 551 cases of convective precipitation echoes were selected, and then the echoes were statistically analyzed from six aspects of morphological characteristics, occurrence frequency, location, diurnal variation, duration and large-scale background conditions. The results showed that the convective precipitation echoes can be classified into cell type, linear and regional type, of which the linear type is about 50%, being the most common form of convection organization in Guiyang area. Compared to the linear and regional types, the convective duration of cell type is the shortest and has obviously local characteristics. More than 70% of convective precipitation events occur under the southwest vortex or southwest airflow weather condition. Convective precipitation often occurs in the southwest and southeast of Guiyang and rarely in the north. Convective initiation time has two peaks in the afternoon and around midnight, respectively. Finally, three representative convective precipitation events were carefully examined in terms of lifetime, coverage and intensity of precipitation.
2018, 44(6):759-770.
DOI: 10.7519/j.issn.1000-0526.2018.06.004
Abstract:
By using satellite images, weather radar data, combined with the environmental situation and physical characteristics, two mesoscale convective complex (MCC) events in northern Shandong and southern Hebei in 15-16 August 2011 (“0815MCC”), and central and southern regions of Shandong in 30-31 July 2015 (“0730MCC”) are analyzed. Comparisons show that (1) the distribution of heavy rainfall is asymmetric, mainly in the center of TBB and its west and south side. The precipitation is concentrated in the stage from formation to mature stage of MCC. The intensity and moving direction of surface mesoscale convergence system are closely related to the development of new cells. (2) The overlapping area of the high vorticity, divergence and vertical velocity is favorable for the development of MCC, which is the main factor for its movement toward southwest. (3) Radar VWP product shows that the establishment of the ultra-lower-level jet helps the happening of severe precipitation and maintenance of MCC. When the ultra-low-level jet velocity difference increases to a certain extent, the heavy rainfall begins. (4) The low-level convergence and high-level divergence of “0815 MCC” offer dynamic conditions, causing higher development, lower cloud top temperature, larger area of cold cloud than “0730 MCC”; meanwhile, the strong vertical wind shear brings the ice crystals to the thunder head, which may reduce the precipitation efficiency, so the 0815 MCC’s rainstorm range and maximum precipitation intensity are less than those of “0730 MCC”.
By using satellite images, weather radar data, combined with the environmental situation and physical characteristics, two mesoscale convective complex (MCC) events in northern Shandong and southern Hebei in 15-16 August 2011 (“0815MCC”), and central and southern regions of Shandong in 30-31 July 2015 (“0730MCC”) are analyzed. Comparisons show that (1) the distribution of heavy rainfall is asymmetric, mainly in the center of TBB and its west and south side. The precipitation is concentrated in the stage from formation to mature stage of MCC. The intensity and moving direction of surface mesoscale convergence system are closely related to the development of new cells. (2) The overlapping area of the high vorticity, divergence and vertical velocity is favorable for the development of MCC, which is the main factor for its movement toward southwest. (3) Radar VWP product shows that the establishment of the ultra-lower-level jet helps the happening of severe precipitation and maintenance of MCC. When the ultra-low-level jet velocity difference increases to a certain extent, the heavy rainfall begins. (4) The low-level convergence and high-level divergence of “0815 MCC” offer dynamic conditions, causing higher development, lower cloud top temperature, larger area of cold cloud than “0730 MCC”; meanwhile, the strong vertical wind shear brings the ice crystals to the thunder head, which may reduce the precipitation efficiency, so the 0815 MCC’s rainstorm range and maximum precipitation intensity are less than those of “0730 MCC”.
2018, 44(6):771-780.
DOI: 10.7519/j.issn.1000-0526.2018.06.005
Abstract:
The warm-sector rainstorms over the southern of middle and lower reaches of the Yangtze River are defined, and they can be divided into four types based on synoptic situation, including warm shear-line, cold-front, subtropical high and severe southwest jet. By using the conventional and non-conventional observation data such as the hourly precipitation data of automatic weather station (AWS) from May to September during 2010-2016, we statistically analyzed the temporal-spatial distribution of warm-sector rainstorms and the nature of precipitation as well as the causes for their formation. In addition, based on NCEP FNL opearational global analysis data and the technology of mesoscale analysis, the system configurations of four kinds of rainstorms are built. (1) All the four types are decentralized local precipitation, and the precipitation usually occurs near the uneven surface, which is transitional zones between mountains, plains and lakes, etc. The warm shear-line type precipitation mainly happens in the mid-west of this area with wide range, most intensive intensity and most obvious extremes. The precipitation of the cold-front type is concentrated, and it has a higher intensity and a certain degree of extremes, distributing mainly in the middle of the area. The precipitation with the subtropical high often occurs in the mid-east of this area with weak intensity. The severe southwest jet mainly appears in the western part. (2) The warm shear-line and the severe southwest jet are dominated by night precipitation, and the subtropical high precipitation is mainly concentrated in the afternoon. However, the diurnal variation of the cold-front type does not show a distinct difference throughout the day. (3) The warm-sector rainstorms consist of steady and convective precipitation. The heavier the daily rainfall is, the more obvious convection the precipitation has. (4) With high humidity, unstable energy accumulation and other favorable background, the warm shear-line, cold-front and subtropical high are mostly generated by boundary layer (ground) mesoscale convergence lines, coupled with the place of the coupling of upper and low-level jet. The severe southwest jet is generally formed near the mesoscale wind velocity fluctuation and ground mesoscale convergence lines on the low-level jet stream. The stronger the low-level jet stream is, the greater the intensity of the rainfall is. (5) The rainfall region of the warm shear-line and the cold-front are respectively located in the wet zone with the south of warm shear-line in the lower level and the pre-front. The rainfall region of the subtropical high and the severe southwest jet are respectively located in the water vapor and the unstable atmosphere in the subtropical high and the left front of the strong low-level jet streams. Four types usually manifest as long-life moving mesoscale rain clusters. When it goes through mountains, rivers and lakes and other uneven surface, its rainfall intensity usually increases and moving speed slows down, which is the main reason for the formation of the local heavy rainfall of warm-sector rainstorms.
The warm-sector rainstorms over the southern of middle and lower reaches of the Yangtze River are defined, and they can be divided into four types based on synoptic situation, including warm shear-line, cold-front, subtropical high and severe southwest jet. By using the conventional and non-conventional observation data such as the hourly precipitation data of automatic weather station (AWS) from May to September during 2010-2016, we statistically analyzed the temporal-spatial distribution of warm-sector rainstorms and the nature of precipitation as well as the causes for their formation. In addition, based on NCEP FNL opearational global analysis data and the technology of mesoscale analysis, the system configurations of four kinds of rainstorms are built. (1) All the four types are decentralized local precipitation, and the precipitation usually occurs near the uneven surface, which is transitional zones between mountains, plains and lakes, etc. The warm shear-line type precipitation mainly happens in the mid-west of this area with wide range, most intensive intensity and most obvious extremes. The precipitation of the cold-front type is concentrated, and it has a higher intensity and a certain degree of extremes, distributing mainly in the middle of the area. The precipitation with the subtropical high often occurs in the mid-east of this area with weak intensity. The severe southwest jet mainly appears in the western part. (2) The warm shear-line and the severe southwest jet are dominated by night precipitation, and the subtropical high precipitation is mainly concentrated in the afternoon. However, the diurnal variation of the cold-front type does not show a distinct difference throughout the day. (3) The warm-sector rainstorms consist of steady and convective precipitation. The heavier the daily rainfall is, the more obvious convection the precipitation has. (4) With high humidity, unstable energy accumulation and other favorable background, the warm shear-line, cold-front and subtropical high are mostly generated by boundary layer (ground) mesoscale convergence lines, coupled with the place of the coupling of upper and low-level jet. The severe southwest jet is generally formed near the mesoscale wind velocity fluctuation and ground mesoscale convergence lines on the low-level jet stream. The stronger the low-level jet stream is, the greater the intensity of the rainfall is. (5) The rainfall region of the warm shear-line and the cold-front are respectively located in the wet zone with the south of warm shear-line in the lower level and the pre-front. The rainfall region of the subtropical high and the severe southwest jet are respectively located in the water vapor and the unstable atmosphere in the subtropical high and the left front of the strong low-level jet streams. Four types usually manifest as long-life moving mesoscale rain clusters. When it goes through mountains, rivers and lakes and other uneven surface, its rainfall intensity usually increases and moving speed slows down, which is the main reason for the formation of the local heavy rainfall of warm-sector rainstorms.
2018, 44(6):781-789.
DOI: 10.7519/j.issn.1000-0526.2018.06.006
Abstract:
Based on the observational precipitation data from Hangzhou Climate Observatory and the simulated precipitation data of the global climate model CMIP5, the long-term trends of precipitation variation in Hangzhou City are investigated. Moreover, the risks of extreme precipitation in Hangzhou City under future climate scenarios are estimated by using a downscaling method that adopts the cumulative distribution function transform (CDF-T). The results show that there is no significantly increasing or decreasing trend in centennial precipitation series (1907-2015) at Hangzhou Climate Observatory, but the precipitation in spring obviously decreases with a rate of 32.1 mm·（10 a）-1 and the winter precipitation significantly increases with a rate of 35.4 mm·（10 a）-1 during 1980-2015. The extreme precipitation in Hangzhou City has been intensifying, which can be interpreted by that the maximum values of 3 h, 6 h and daily precipitation have been increased and the return periods of extreme precipitation have been shortened. Du-ring the period from 1988 to 2015, the values of the 3 h, 6 h and daily precipitation of each return periods are higher than that of the period from 1961 to 1987. An extreme daily precipitation whose probability is once in 100 years during 1961-1987 has become an event with probability once in 50 years or once in 20 years during 1988-2015. The CDF-T downscaling analysis of simulated precipitation of the CMIP5 models indicates that the occurrence probability of extreme precipitation in Hangzhou City during 2020-2039 might increase under all of the RCPs future climate scenarios. In the period from 2020 to 2039, the occurrence probability of the extreme precipitation over R95p and R99p in Hangzhou City will be 11.08 d·a-1 and 2.24 d·a-1 respectively. Compared with the average values of current climate, the occurrence probability of the over R95p and R99p is increased by 3.52 d·a-1 and 0.69 d·a-1, respectively.
Based on the observational precipitation data from Hangzhou Climate Observatory and the simulated precipitation data of the global climate model CMIP5, the long-term trends of precipitation variation in Hangzhou City are investigated. Moreover, the risks of extreme precipitation in Hangzhou City under future climate scenarios are estimated by using a downscaling method that adopts the cumulative distribution function transform (CDF-T). The results show that there is no significantly increasing or decreasing trend in centennial precipitation series (1907-2015) at Hangzhou Climate Observatory, but the precipitation in spring obviously decreases with a rate of 32.1 mm·（10 a）-1 and the winter precipitation significantly increases with a rate of 35.4 mm·（10 a）-1 during 1980-2015. The extreme precipitation in Hangzhou City has been intensifying, which can be interpreted by that the maximum values of 3 h, 6 h and daily precipitation have been increased and the return periods of extreme precipitation have been shortened. Du-ring the period from 1988 to 2015, the values of the 3 h, 6 h and daily precipitation of each return periods are higher than that of the period from 1961 to 1987. An extreme daily precipitation whose probability is once in 100 years during 1961-1987 has become an event with probability once in 50 years or once in 20 years during 1988-2015. The CDF-T downscaling analysis of simulated precipitation of the CMIP5 models indicates that the occurrence probability of extreme precipitation in Hangzhou City during 2020-2039 might increase under all of the RCPs future climate scenarios. In the period from 2020 to 2039, the occurrence probability of the extreme precipitation over R95p and R99p in Hangzhou City will be 11.08 d·a-1 and 2.24 d·a-1 respectively. Compared with the average values of current climate, the occurrence probability of the over R95p and R99p is increased by 3.52 d·a-1 and 0.69 d·a-1, respectively.
2018, 44(6):790-801.
DOI: 10.7519/j.issn.1000-0526.2018.06.007
Abstract:
The multi-cell storm in northeast of Huabei Region and squall line in Huanghuai Region happened under the same circulation background of northeast cold vortex on 22 August 2015. Based on meteorological observation data, this paper first shows the dynamic and thermodynamic effects of largescale cold vortex on the development of mesoscale convective systems. Then, based on the results of WRF mesoscale numerical model simulation, the differences between shape structure evolution and movement process of the two convective systems are compared. The reasons for structural evolution differences and effect of cold vortex are analyzed as well. The research suggests that: (1) Both of the two convection systems are located behind the cold vortex, but their shape evolutions of the two mesoscale convective systems are different. The northern convection was impacted jointly by surface winds and uplift of terrain, forming a multi-cell storm with a northwest-southeast alignment. It traveled slowly south-southeast by downwind propagation, bringing short-time severe rainstorm. The southern linear convection was formed by combination of several isolated cells which formed in northwest of Shandong and north of Henan. Later, the linear convection developed in Huanghuai Region into a squall line system, which moved rapidly to southeast under the action of advection movement, resulting in thunderstorm and hail. (2) The northern multi-cell storm formed in the interface of cold and warm air masses, located in the southwestern quadrant of cold vortex with sufficient low-level water vapor and energy. After being triggered by the boundary layer, the new convective cell propagated along lower shear line to the high-energy zone. (3) The southern squall line system formed in low pressure belt of surface warm area behind cold trough. Cold pool and outflow of thunderstorm high pressure generated by mesoscale convective system interacted with the environment, causing cell to continue to spread, merge and develop into a squall line system. (4) The intensity of mid-level rear inflow and water vapor condition had significantly different effects on the organization of the two convective systems. The increase of rear inflow of squall line in middle layer mainly came from the increase of westerly component, which was related to enhancement of environmental wind field caused by evolution of cold vortex. The mid-layer wind field where the northern convection was located was weak and the whole layer was wet, which was not conducive to the development of multiple cell storm organizations. The middle troposphere of south squall line was located in westerly steering airflow which was stronger than the northern convection. The inflow was strong and ambient air was dry, favorable for the formation of strong descending airflow, enhancing the development of thunderstorm high pressure and cold pool. Strong downdraft increased wind speed in middle and lower layers and enhanced vertical wind shear, which is conducive to the development of convective cell organization and formation of linear convection.
The multi-cell storm in northeast of Huabei Region and squall line in Huanghuai Region happened under the same circulation background of northeast cold vortex on 22 August 2015. Based on meteorological observation data, this paper first shows the dynamic and thermodynamic effects of largescale cold vortex on the development of mesoscale convective systems. Then, based on the results of WRF mesoscale numerical model simulation, the differences between shape structure evolution and movement process of the two convective systems are compared. The reasons for structural evolution differences and effect of cold vortex are analyzed as well. The research suggests that: (1) Both of the two convection systems are located behind the cold vortex, but their shape evolutions of the two mesoscale convective systems are different. The northern convection was impacted jointly by surface winds and uplift of terrain, forming a multi-cell storm with a northwest-southeast alignment. It traveled slowly south-southeast by downwind propagation, bringing short-time severe rainstorm. The southern linear convection was formed by combination of several isolated cells which formed in northwest of Shandong and north of Henan. Later, the linear convection developed in Huanghuai Region into a squall line system, which moved rapidly to southeast under the action of advection movement, resulting in thunderstorm and hail. (2) The northern multi-cell storm formed in the interface of cold and warm air masses, located in the southwestern quadrant of cold vortex with sufficient low-level water vapor and energy. After being triggered by the boundary layer, the new convective cell propagated along lower shear line to the high-energy zone. (3) The southern squall line system formed in low pressure belt of surface warm area behind cold trough. Cold pool and outflow of thunderstorm high pressure generated by mesoscale convective system interacted with the environment, causing cell to continue to spread, merge and develop into a squall line system. (4) The intensity of mid-level rear inflow and water vapor condition had significantly different effects on the organization of the two convective systems. The increase of rear inflow of squall line in middle layer mainly came from the increase of westerly component, which was related to enhancement of environmental wind field caused by evolution of cold vortex. The mid-layer wind field where the northern convection was located was weak and the whole layer was wet, which was not conducive to the development of multiple cell storm organizations. The middle troposphere of south squall line was located in westerly steering airflow which was stronger than the northern convection. The inflow was strong and ambient air was dry, favorable for the formation of strong descending airflow, enhancing the development of thunderstorm high pressure and cold pool. Strong downdraft increased wind speed in middle and lower layers and enhanced vertical wind shear, which is conducive to the development of convective cell organization and formation of linear convection.
2018, 44(6):802-813.
DOI: 10.7519/j.issn.1000-0526.2018.06.008
Abstract:
Using Beijing CINRADSA Radar reflectivity and radial velocity products about 19 cases of thunderstorm from 2010 to 2014, radar echo characteristics of thunderstorm gales in different life periods in Beijing are analyzed. It is found that 77.8% and 100% thunderstorm gales caused by the beltshaped and bow radar echo can be respectively forcasted and warned early, and 67% of them can be issued early warning in 30 min lead time. No gust front echo was observed in the front of the isolated block echo, the inflow jet was not seen in the radial velocity map, and the radial velocity was not obvious.However, the middle radial convergence, the inflow jet and the gust front observed on the radial velocity map provide important indicative features for the early warning of thunderstorm gale.
Using Beijing CINRADSA Radar reflectivity and radial velocity products about 19 cases of thunderstorm from 2010 to 2014, radar echo characteristics of thunderstorm gales in different life periods in Beijing are analyzed. It is found that 77.8% and 100% thunderstorm gales caused by the beltshaped and bow radar echo can be respectively forcasted and warned early, and 67% of them can be issued early warning in 30 min lead time. No gust front echo was observed in the front of the isolated block echo, the inflow jet was not seen in the radial velocity map, and the radial velocity was not obvious.However, the middle radial convergence, the inflow jet and the gust front observed on the radial velocity map provide important indicative features for the early warning of thunderstorm gale.
2018, 44(6):814-824.
DOI: 10.7519/j.issn.1000-0526.2018.06.009
Abstract:
Satellite observation and radiation transfer analysis have proved that the infrared water vapor of convective cloud cluster and window band brightness temperature difference （BTD）(H2O, IRW) have significant features, which means BTD can be used to identify the convection clouds. The global convection diagnostic (GCD) algorithm based on the BTD characteristics of convective cloud cluster, can detect convective cloud cluster by establishing a single BTD threshold, but it can not further quantify the intensity of convective clouds. Using FY2G VISSR infrared observations and CINRAD CAR radar observation data, we did the comparative study, and the results show that BTD/CAR has a good linear positive correlation, which shows BTD can be used not only to identify the presence of convective clouds, but also to further quantify the intensity of convective cloud cluster. The BTD is a factor for convective cloud recognition superior to the single IRW brightness temperature method. Based on the BTD/CAR relationship, radar echo intensity thresholds can be transferred into the corresponding BTD threshold. These BTD thresholds can be used to identify and differentiate intensity of convective cloud by using of geostationary satellite infrared water vapor and window band observation.
Satellite observation and radiation transfer analysis have proved that the infrared water vapor of convective cloud cluster and window band brightness temperature difference （BTD）(H2O, IRW) have significant features, which means BTD can be used to identify the convection clouds. The global convection diagnostic (GCD) algorithm based on the BTD characteristics of convective cloud cluster, can detect convective cloud cluster by establishing a single BTD threshold, but it can not further quantify the intensity of convective clouds. Using FY2G VISSR infrared observations and CINRAD CAR radar observation data, we did the comparative study, and the results show that BTD/CAR has a good linear positive correlation, which shows BTD can be used not only to identify the presence of convective clouds, but also to further quantify the intensity of convective cloud cluster. The BTD is a factor for convective cloud recognition superior to the single IRW brightness temperature method. Based on the BTD/CAR relationship, radar echo intensity thresholds can be transferred into the corresponding BTD threshold. These BTD thresholds can be used to identify and differentiate intensity of convective cloud by using of geostationary satellite infrared water vapor and window band observation.
2018, 44(6):825-836.
DOI: 10.7519/j.issn.1000-0526.2018.06.010
Abstract:
Using the mesoscale TJ-WRF model, we studied the influence of Tianjin urban heat island effect on the sea breeze (front) circulation triggered local thunderstorms which tend to occur in urban areas by changing the land use type of the underlying surface in the sensitivity numerical simulation tests. The results show that the effect of urban heat island is different due to the different types of urban underlying surfaces. The urban heat island effect is more obvious and the impact scope is expanded when the land type of suburb surface is changed to urban and built-up land; when the urban surface is changed to dry land and pasture, there is no urban heat island effect near Tianjin City. At the same time, we can see that when there is urban heat island effect near urban area of Tianjin, the sea breeze (front) circulation is strengthened and its speed is accelerated. So, the more obvious the urban heat island effect is, the more obvious the strengthening and acceleration of the sea breeze (front) circulation is. The speed of the sea breeze (front) is faster than the speed without urban heat island by 9.3 km·h-1. But when it moves near the city and encounters the urban heat island circulation, the sea breeze (front) circulation is blocked and its speed slows down quickly. And the north-south branch flowing and climbing up of its rear airflow becomes obvious. The convergence and upward motion are also enhanced when the two circulations meet and superimposed. The more obvious the effect of urban heat island is, the more obvious the blocking effect of sea wind (front) circulation is, the slower down the speed of the sea breeze (front) circulation is, and the stronger the convergence and upward motion are when the two circulations meet and superimposed.In addition, when sea breeze (front) circulation moves toward the city, it will result in the decrease in temperature and the increase in moisture content of the lower-level air. However, due to the existence of the urban heat island effect, the thickness of the wet air layer in the airflow after the sea breeze (front) circulation is greatly reduced, and the more obvious the effect of the urban heat island is, the more obvious the thickness of the wet air layer decreases.
Using the mesoscale TJ-WRF model, we studied the influence of Tianjin urban heat island effect on the sea breeze (front) circulation triggered local thunderstorms which tend to occur in urban areas by changing the land use type of the underlying surface in the sensitivity numerical simulation tests. The results show that the effect of urban heat island is different due to the different types of urban underlying surfaces. The urban heat island effect is more obvious and the impact scope is expanded when the land type of suburb surface is changed to urban and built-up land; when the urban surface is changed to dry land and pasture, there is no urban heat island effect near Tianjin City. At the same time, we can see that when there is urban heat island effect near urban area of Tianjin, the sea breeze (front) circulation is strengthened and its speed is accelerated. So, the more obvious the urban heat island effect is, the more obvious the strengthening and acceleration of the sea breeze (front) circulation is. The speed of the sea breeze (front) is faster than the speed without urban heat island by 9.3 km·h-1. But when it moves near the city and encounters the urban heat island circulation, the sea breeze (front) circulation is blocked and its speed slows down quickly. And the north-south branch flowing and climbing up of its rear airflow becomes obvious. The convergence and upward motion are also enhanced when the two circulations meet and superimposed. The more obvious the effect of urban heat island is, the more obvious the blocking effect of sea wind (front) circulation is, the slower down the speed of the sea breeze (front) circulation is, and the stronger the convergence and upward motion are when the two circulations meet and superimposed.In addition, when sea breeze (front) circulation moves toward the city, it will result in the decrease in temperature and the increase in moisture content of the lower-level air. However, due to the existence of the urban heat island effect, the thickness of the wet air layer in the airflow after the sea breeze (front) circulation is greatly reduced, and the more obvious the effect of the urban heat island is, the more obvious the thickness of the wet air layer decreases.
2018, 44(6):837-843.
DOI: 10.7519/j.issn.1000-0526.2018.06.011
Abstract:
The purpose of this paper is to help medical institutions in terms of a reasonable allocation of medical hands, beds and medical drugs, and also to help people in high stroke risk by mean of timely intervention, reducing the risk of stroke occurrence. The data of the cases of stroke in four hospitals from 2013 to 2016 were analyzed, and the number of daily patients in the hospital was divided into six grades. By taking the support vector machine (SVM) and the random forest (RF) methods, and using the corresponding local daily meteorological data collected, we established the prediction model for daily patients and the correlation model related to meteorological factors. The results showed that: (1) the number of daily patients with stroke was not balanced and the accuracy of traditional prediction model was relatively low. (2) By constantly adjusting the initial weight of the SVM prediction model, we found that, after 4 attempts of optimization, the prediction accuracy of the number of daily patients increased from 52.46% to 94.56%. (3) The results of the random forest model showed that the three meteorological factors affecting the incidence of stroke are the maximum temperature, the minimum temperature and the mean temperature. Thus, the research results of the correlation between stroke diseases and meteorological factors based on machine learning model could improve the prediction accuracy of medical meteorological statistical models, and have good application and promotion values.
The purpose of this paper is to help medical institutions in terms of a reasonable allocation of medical hands, beds and medical drugs, and also to help people in high stroke risk by mean of timely intervention, reducing the risk of stroke occurrence. The data of the cases of stroke in four hospitals from 2013 to 2016 were analyzed, and the number of daily patients in the hospital was divided into six grades. By taking the support vector machine (SVM) and the random forest (RF) methods, and using the corresponding local daily meteorological data collected, we established the prediction model for daily patients and the correlation model related to meteorological factors. The results showed that: (1) the number of daily patients with stroke was not balanced and the accuracy of traditional prediction model was relatively low. (2) By constantly adjusting the initial weight of the SVM prediction model, we found that, after 4 attempts of optimization, the prediction accuracy of the number of daily patients increased from 52.46% to 94.56%. (3) The results of the random forest model showed that the three meteorological factors affecting the incidence of stroke are the maximum temperature, the minimum temperature and the mean temperature. Thus, the research results of the correlation between stroke diseases and meteorological factors based on machine learning model could improve the prediction accuracy of medical meteorological statistical models, and have good application and promotion values.
2018, 44(6):844-849.
DOI: 10.7519/j.issn.1000-0526.2018.06.012
Abstract:
The outgoing longwave radiation (OLR) product processing of FY3B/VIRR adopts the same method as that used in NOAA/AVHRR, that is, the regression equation relating flux equivalent brightness temperature with window channel brightness temperature is used to calculate OLR. But the OLR products of the two satellites have a negative bias of 10 W·m-2 when compared with the clouds and earth’s radiant energy system (CERES) observed OLR product, which is considered the best OLR product in quality in the world. The cause for the FY3B OLR bias is the lower accuracy of the software used in infrared radiative transfer model during the process of developing OLR retrieval model. Herein, with American line-by-line radiative transfer model software (LBLRTM) developed in 21st century, the spectral radiances at the top of atmosphere (TOA) for 2521 global atmospheric profiles are simulated, and then the OLR and window channel radiance of FY-3B/VIRR are calculated. By applying the least square method to sum up and regress the simulated data, this paper rebuilds the regression equation and coefficient of OLR, which are calculated by the FY3B/VIRR window channel5 brightness temperature. The FY-3B L1 data are applied to the model and the daily global OLR data in January, March, July, October of 2016 are processed out. Comparing the processed data with the CERES OLR products, the following results are obtained: daily averaged OLR: RMSE=9-15 W·m-2, R=0.9834, Bias=-0.3 W·m-2, monthly averaged OLR: RMSE=4-7 W·m-2, R=0.9915, Bias=-0.3 W·m-2. The validation results indicate that the improved model can work out the OLR data without systematic bias and the accuracy is basically similar with the CERES〖JP〗 observation although the inherent model regression error might exist in the single channel retrieval method.
The outgoing longwave radiation (OLR) product processing of FY3B/VIRR adopts the same method as that used in NOAA/AVHRR, that is, the regression equation relating flux equivalent brightness temperature with window channel brightness temperature is used to calculate OLR. But the OLR products of the two satellites have a negative bias of 10 W·m-2 when compared with the clouds and earth’s radiant energy system (CERES) observed OLR product, which is considered the best OLR product in quality in the world. The cause for the FY3B OLR bias is the lower accuracy of the software used in infrared radiative transfer model during the process of developing OLR retrieval model. Herein, with American line-by-line radiative transfer model software (LBLRTM) developed in 21st century, the spectral radiances at the top of atmosphere (TOA) for 2521 global atmospheric profiles are simulated, and then the OLR and window channel radiance of FY-3B/VIRR are calculated. By applying the least square method to sum up and regress the simulated data, this paper rebuilds the regression equation and coefficient of OLR, which are calculated by the FY3B/VIRR window channel5 brightness temperature. The FY-3B L1 data are applied to the model and the daily global OLR data in January, March, July, October of 2016 are processed out. Comparing the processed data with the CERES OLR products, the following results are obtained: daily averaged OLR: RMSE=9-15 W·m-2, R=0.9834, Bias=-0.3 W·m-2, monthly averaged OLR: RMSE=4-7 W·m-2, R=0.9915, Bias=-0.3 W·m-2. The validation results indicate that the improved model can work out the OLR data without systematic bias and the accuracy is basically similar with the CERES〖JP〗 observation although the inherent model regression error might exist in the single channel retrieval method.
2018, 44(6):850-856.
DOI: 10.7519/j.issn.1000-0526.2018.06.013
Abstract:
The main characteristics of the general atmospheric circulation are as follows. Double polar vortex centers existed in the Northern Hemisphere. The circulation in Eurasian middlehigh latitudes showed a threewave pattern. The strength of Western Pacific subtropical high was a little weaker than normal years, and the intensity of south branch through was almost equal to normal. The monthly mean temperature was 7.0℃, 2.9℃ higher than normal, breaking the record since 1961. The monthly mean precipitation amount was 29.4 mm, which is almost equal to normal. One nationwide medium cold air process occurred in central and eastern China, and one strong cold air process in northern China in this month. Five obvious rainfall processes occurred in southern China, and three dust weather events happened in northern China. Strong winds and hails hit some areas of Jiangxi, Hubei, Hunan, and Guangxi.
The main characteristics of the general atmospheric circulation are as follows. Double polar vortex centers existed in the Northern Hemisphere. The circulation in Eurasian middlehigh latitudes showed a threewave pattern. The strength of Western Pacific subtropical high was a little weaker than normal years, and the intensity of south branch through was almost equal to normal. The monthly mean temperature was 7.0℃, 2.9℃ higher than normal, breaking the record since 1961. The monthly mean precipitation amount was 29.4 mm, which is almost equal to normal. One nationwide medium cold air process occurred in central and eastern China, and one strong cold air process in northern China in this month. Five obvious rainfall processes occurred in southern China, and three dust weather events happened in northern China. Strong winds and hails hit some areas of Jiangxi, Hubei, Hunan, and Guangxi.
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ISSN:1000-0526 CN:11-2282/P