Warm-sector heavy rainfalls along the south China coast from April to June during 2009-2014 can be divided into two main types based on their low-level circulations. Type I is the southerly pattern with meridional con...Warm-sector heavy rainfalls along the south China coast from April to June during 2009-2014 can be divided into two main types based on their low-level circulations. Type I is the southerly pattern with meridional convergence line at the west of the Pearl River estuary, which is formed by the convergence of southeasterly, southerly, and southwesterly flows. Type II is the southwesterly pattern with a latitudinal convergence line at the east of the Pearl River estuary, which is formed by the convergence of westerly and southwesterly flows. Statistics on 6-hourly heavy rainfall events indicates that, during the afore-mentioned 6 years, there were on average 73.2 occurrences of the southerly pattern and 50.3 occurrences of the southwesterly pattern per year. After the onset of summer monsoon in the South China Sea, the occurrence frequencies of both patterns increase remarkably. The synthetic diagnosis of pattern circulation shows that, at 500 h Pa, for the southerly pattern, there is a broad warm high ridge, and a temperature ridge is behind the high ridge, which causes an obvious warm advection at the high ridge area. There is no frontal region. For the southwesterly pattern, the circulation is a weak trough with a temperature trough behind it. The position of the frontal region is near Yangzi River, and the south China coast is in the warm-sector of the frontal region. At the vertical cross-section of each of the two categories of heavy rainfall, there is a strong vertical motion center stretching to 400 hPa, where the convergence layer in the rainfall region is deep and with several vertical convergence centers overlapping one another. Both types of heavy rainfalls are with abundant water vapor, accompanied with deep convective instability energy layers, and with strong release of latent heat caused by condensation of water vapor. The release of latent heat leads to the warming-up and stretching of the air column, thus strengthens deep convergence and vertical velocity upward. There is a stronger latent heat-release in the southwesterly pattern than in the southerly pattern,while in the southerly pattern, the warm advection at middle and upper levels is stronger than the latent head release.To study the thermo-dynamic development mechanisms, weather research and forecasting model(WRF) numerical simulations are made and the results show that, in the two rainstorm regions, latent heat release warms up the air column, hence significantly increase the depth and strength of the vertical velocity. Moreover, the release of latent heat strengthens convergent circulation at lower levels and weakens divergent circulation at middle levels, whose influence can be as strong as 30%-50% of the wind circulation strength of the two types of the warm-sector heavy rainfall over the south China coast, and further enhances deep convection, promoting warm-sector storm development.展开更多
Using the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data at 1°× 1° o resolution, analysis is performed on a persistent heavy rainfall event w...Using the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data at 1°× 1° o resolution, analysis is performed on a persistent heavy rainfall event with two rain bands to the south of the Yangtze River during 17-22 June 2005. The northern rain band was related to the atmospheric mass adjustment of cold front precipitation and the associated ageostrophic feature to the rear right of subtropical westerly jets, while the southern counterpart formed under the joint influence of easterly/westerly jets and the South Asian high (SAH). The ageostrophic wind field to the rear right of the easterly jet center gives rise to an anti-circulation that favors the genesis of the southern belt. The feature ofdu/dt 〈0 around the SAH ridge line and to the rear right of the easterly jet streak results in a strong v - vg〈O field in the vicinity of the rain region as well as to its south. When westerly jets move southward, an intense v Vg〉0 feature appears to the north of the rain region, i.e., behind the center of the westerly jets. The associated mass adjustment leads to vigorous divergence over the rain region, which is responsible for the strong precipitation from the warm sector of the front. Also, a θe front at the middle level of the southern rain band and the cold front favor the release of instable energy to enhance the rainstorm. The southern and northern fronts approach each other and the two rain belts merge into one.展开更多
Based on data collected during the first U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) field campaigns at Shouxian, east- ern China in 2008, the effects of clouds and aerosols on the surf...Based on data collected during the first U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) field campaigns at Shouxian, east- ern China in 2008, the effects of clouds and aerosols on the surface radiation budget during the period Octo- ber-December 2008 were studied. The results revealed that the largest longwave (LW), shortwave (SW), and net Aerosol Radiative Effects (AREs) are 12.7, -37.6, and -24.9 W rn-2, indicating that aerosols have LW warming impact, a strong SW cooling effect, and a net cooling ef- fect on the surface radiation budget at Shouxian during the study period 15 October-15 December 2008. The SW cloud radiative forcing (CRF) is -135.1 W m-2, much cooler than ARE (about 3.6 times), however, the LW CRF is 43.6 W m 2, much warmer than ARE, and resulting in a net CRF of-91.5 W m-2, about 3.7 times of net ARE. These results suggest that the clouds have much stronger LW warming effect and SW cooling effect on the surface radiation budget than AREs. The net surface radiation budget is dominated by SW cooling effect for both ARE and CRE. Furthermore, the precipitatable clouds (PCs) have the largest SW cooling effect and LW warming ef- fect, while optically thin high clouds have the smallest cooling effect and LW warming on the surface radiation budget. Comparing the two selected caseds, CloudSat cloud radar reflectivity agrees very well with the AMF (ARM Mobile Facility) WACR (W-band ARM Cloud Radar) measurements, particularly for cirrus cloud case. These result will provide a ground truth to validate the model simulations in the future.展开更多
Climate change has increased extreme events over globe and the most robust occurrences of concurrent drought and floods have become more common in Africa. This study focuses on the observed and projected analysis of r...Climate change has increased extreme events over globe and the most robust occurrences of concurrent drought and floods have become more common in Africa. This study focuses on the observed and projected analysis of rainfall extremes of consecutive dry day (CDD) and maximum monthly five day precipitation (RX5day) from Expert Team on Climate Change Detection and Indices (ETCCDI) in June-August season over Africa. The daily CORDEX Africa, reanalysis and CRU datasets were analyzed for extreme trends under RCP4.5 and RCP8.5 scenarios for the periods of 1980 to 2100. The spatiotemporal variability, trend, and magnitude of JJA seasonal rainfall performance exhibits a significant decreasing tendency over Eastern Africa compared to West Africa. The observed results of consecutive dry day (CDD) reveal that increasing trend and moreover RX5day shows that promising positive trend. Both rainfall extremes are influenced by the combined effect of large scale indexes and appear to be correlated negatively and positively with ENSO, NAO and AO. The CORDEX ensemble mean projections of JJA seasonal rainfall performance show a widespread significant change and the first mode of EOF depicts that 13.8% and 24.9% under the RCP4.5 and the highest variability is under RCP8.5 scenario. The projected CDD extreme exhibit an increasing trend in the coming periods and the percentage change revealed that increasing from 25.11%, 28.02% over West and 26.49%, 31.66% East Africa under RCP4.5 and RCP8.5 scenarios respectively. This situation will exacerbate increasing of frequent and intensified drought extremes over Africa. Additionally, the future RX5day indicated that mixed trend and revealed that increasing 3.72%, 2.54% over West and decreases -16.12%, -22.47% over East Africa under RCP4.5 and RCP8.5 respectively. Generally, rainfall extremes of CDD are projected to increase and RX5day shows a mixed trend in the coming periods over Africa and calls for further verification by using high resolution datasets.展开更多
In recent years, there has been increasing demand for high-resolution seasonal climate forecasts at sufficient lead times to allow response planning from users in agriculture, hydrology, disaster risk management, and ...In recent years, there has been increasing demand for high-resolution seasonal climate forecasts at sufficient lead times to allow response planning from users in agriculture, hydrology, disaster risk management, and health, among others. This paper examines the forecasting skill of the North American Multi-model Ensemble (NMME) over Ethiopia during the June to September (JJAS) season. The NMME, one of the multi-model seasonal forecasting systems, regularly generates monthly seasonal rainfall forecasts over the globe with 0.5 <span style="font-family:Verdana;">-</span><span style="font-family:;" "=""><span style="font-family:Verdana;"> 11.5 months lead time. The skill and predictability of seasonal rainfall are assessed using 28 years of hindcast data from the NMME models. The forecast skill is quantified using canonical correlation analysis (CCA) and root mean square error. The results show that the NMME models capture the JJAS seasonal rainfall over central, northern, and northeastern parts of Ethiopia while exhibiting weak or limited skill across western and southwestern Ethiopia. The performance of each model in predicting the JJAS seasonal rainfall is variable, showing greater skill in predicting dry conditions. Overall, the performance of the multi-model ensemble was not consistently better than any single ensemble member. The correlation of observed and predicted </span><span style="font-family:Verdana;">seasonal rainfall for the better performing models</span></span><span style="font-family:Verdana;">—GFDL-CM2p5-FLOR-A06,</span><span style="font-family:Verdana;"> CMC2-CanCM4, GFDL-CM2p5-FLOR-B01 and NASA-GMAO-062012</span><span style="font-family:Verdana;">—</span><span style="font-family:Verdana;">is 0.68, 0.58, 0.52, and 0.5, respectively. The COLA-RSMAS-CCSM4, CMC1-</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">CanCM3 and NCEP-CFSv2 models exhibit less skill, with correlations less than 0.4. In general, the NMME offers promising skill to predict seasonal rainfall over Ethiopia during the June-September (JJAS) season, motivating further work to assess its performance at longer lead times.</span>展开更多
Meter Data Collection Building Area Network(MDCBAN) deployed in high rises is playing an increasingly important role in wireless multi-hop smart grid meter data collection. Recently, increasingly numerous application ...Meter Data Collection Building Area Network(MDCBAN) deployed in high rises is playing an increasingly important role in wireless multi-hop smart grid meter data collection. Recently, increasingly numerous application layer data traffic makes MDCBAN be facing serious communication pressure. In addition, large density of meter data collection devices scattered in the limited geographical space of high rises results in obvious communication interference. To solve these problems, a traffic scheduling mechanism based on interference avoidance for meter data collection in MDCBAN is proposed. Firstly, the characteristics of network topology are analyzed and the corresponding traffic distribution model is proposed. Next, a wireless multi-channel selection scheme for different Floor Gateways and a single-channel time unit assignment scheme for data collection devices in the same Floor Network are proposed to avoid interference. At last, a data balanced traffic scheduling algorithm is proposed. Simulation results show that balanced traffic distribution and highly efficient and reliable data transmission can be achieved on the basis of effective interference avoidance between data collection devices.展开更多
基金National Natural Science Foundation of China,“The Dynamic Structures and Maintaining Mechanisms of Oceanic Meso-scale Eddies”(41276033)National Natural Science Foundation of China Youth Science Fund Project “Research on Intelligent Identification,Forecast and Early-warning of Downburst”(41805033)
文摘Warm-sector heavy rainfalls along the south China coast from April to June during 2009-2014 can be divided into two main types based on their low-level circulations. Type I is the southerly pattern with meridional convergence line at the west of the Pearl River estuary, which is formed by the convergence of southeasterly, southerly, and southwesterly flows. Type II is the southwesterly pattern with a latitudinal convergence line at the east of the Pearl River estuary, which is formed by the convergence of westerly and southwesterly flows. Statistics on 6-hourly heavy rainfall events indicates that, during the afore-mentioned 6 years, there were on average 73.2 occurrences of the southerly pattern and 50.3 occurrences of the southwesterly pattern per year. After the onset of summer monsoon in the South China Sea, the occurrence frequencies of both patterns increase remarkably. The synthetic diagnosis of pattern circulation shows that, at 500 h Pa, for the southerly pattern, there is a broad warm high ridge, and a temperature ridge is behind the high ridge, which causes an obvious warm advection at the high ridge area. There is no frontal region. For the southwesterly pattern, the circulation is a weak trough with a temperature trough behind it. The position of the frontal region is near Yangzi River, and the south China coast is in the warm-sector of the frontal region. At the vertical cross-section of each of the two categories of heavy rainfall, there is a strong vertical motion center stretching to 400 hPa, where the convergence layer in the rainfall region is deep and with several vertical convergence centers overlapping one another. Both types of heavy rainfalls are with abundant water vapor, accompanied with deep convective instability energy layers, and with strong release of latent heat caused by condensation of water vapor. The release of latent heat leads to the warming-up and stretching of the air column, thus strengthens deep convergence and vertical velocity upward. There is a stronger latent heat-release in the southwesterly pattern than in the southerly pattern,while in the southerly pattern, the warm advection at middle and upper levels is stronger than the latent head release.To study the thermo-dynamic development mechanisms, weather research and forecasting model(WRF) numerical simulations are made and the results show that, in the two rainstorm regions, latent heat release warms up the air column, hence significantly increase the depth and strength of the vertical velocity. Moreover, the release of latent heat strengthens convergent circulation at lower levels and weakens divergent circulation at middle levels, whose influence can be as strong as 30%-50% of the wind circulation strength of the two types of the warm-sector heavy rainfall over the south China coast, and further enhances deep convection, promoting warm-sector storm development.
基金National Program on Basic Research Project (973 Program) (2009CB421503)Natural Science Foundation of China (40975037)Natural Science Foundation of China (40775033)
文摘Using the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data at 1°× 1° o resolution, analysis is performed on a persistent heavy rainfall event with two rain bands to the south of the Yangtze River during 17-22 June 2005. The northern rain band was related to the atmospheric mass adjustment of cold front precipitation and the associated ageostrophic feature to the rear right of subtropical westerly jets, while the southern counterpart formed under the joint influence of easterly/westerly jets and the South Asian high (SAH). The ageostrophic wind field to the rear right of the easterly jet center gives rise to an anti-circulation that favors the genesis of the southern belt. The feature ofdu/dt 〈0 around the SAH ridge line and to the rear right of the easterly jet streak results in a strong v - vg〈O field in the vicinity of the rain region as well as to its south. When westerly jets move southward, an intense v Vg〉0 feature appears to the north of the rain region, i.e., behind the center of the westerly jets. The associated mass adjustment leads to vigorous divergence over the rain region, which is responsible for the strong precipitation from the warm sector of the front. Also, a θe front at the middle level of the southern rain band and the cold front favor the release of instable energy to enhance the rainstorm. The southern and northern fronts approach each other and the two rain belts merge into one.
基金sponsored by the U.S. DOE Office of Energy Research,Office of Health and Environmental Research,Environmental Sciences Divisionthe support of DOE Atmospheric System Research(ASR) project with award number DE-SC0008468 at University of North Dakota+3 种基金funded by the Key Laboratory of Meteorological Disaster of Ministry of Education (KLME)(KLME1206)the National Natural Science Foundation of China(41275043 and 41175035)a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)the National Basic Research Program of China(973 Program,2013CB955800) at Beijing Normal University
文摘Based on data collected during the first U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) field campaigns at Shouxian, east- ern China in 2008, the effects of clouds and aerosols on the surface radiation budget during the period Octo- ber-December 2008 were studied. The results revealed that the largest longwave (LW), shortwave (SW), and net Aerosol Radiative Effects (AREs) are 12.7, -37.6, and -24.9 W rn-2, indicating that aerosols have LW warming impact, a strong SW cooling effect, and a net cooling ef- fect on the surface radiation budget at Shouxian during the study period 15 October-15 December 2008. The SW cloud radiative forcing (CRF) is -135.1 W m-2, much cooler than ARE (about 3.6 times), however, the LW CRF is 43.6 W m 2, much warmer than ARE, and resulting in a net CRF of-91.5 W m-2, about 3.7 times of net ARE. These results suggest that the clouds have much stronger LW warming effect and SW cooling effect on the surface radiation budget than AREs. The net surface radiation budget is dominated by SW cooling effect for both ARE and CRE. Furthermore, the precipitatable clouds (PCs) have the largest SW cooling effect and LW warming ef- fect, while optically thin high clouds have the smallest cooling effect and LW warming on the surface radiation budget. Comparing the two selected caseds, CloudSat cloud radar reflectivity agrees very well with the AMF (ARM Mobile Facility) WACR (W-band ARM Cloud Radar) measurements, particularly for cirrus cloud case. These result will provide a ground truth to validate the model simulations in the future.
文摘Climate change has increased extreme events over globe and the most robust occurrences of concurrent drought and floods have become more common in Africa. This study focuses on the observed and projected analysis of rainfall extremes of consecutive dry day (CDD) and maximum monthly five day precipitation (RX5day) from Expert Team on Climate Change Detection and Indices (ETCCDI) in June-August season over Africa. The daily CORDEX Africa, reanalysis and CRU datasets were analyzed for extreme trends under RCP4.5 and RCP8.5 scenarios for the periods of 1980 to 2100. The spatiotemporal variability, trend, and magnitude of JJA seasonal rainfall performance exhibits a significant decreasing tendency over Eastern Africa compared to West Africa. The observed results of consecutive dry day (CDD) reveal that increasing trend and moreover RX5day shows that promising positive trend. Both rainfall extremes are influenced by the combined effect of large scale indexes and appear to be correlated negatively and positively with ENSO, NAO and AO. The CORDEX ensemble mean projections of JJA seasonal rainfall performance show a widespread significant change and the first mode of EOF depicts that 13.8% and 24.9% under the RCP4.5 and the highest variability is under RCP8.5 scenario. The projected CDD extreme exhibit an increasing trend in the coming periods and the percentage change revealed that increasing from 25.11%, 28.02% over West and 26.49%, 31.66% East Africa under RCP4.5 and RCP8.5 scenarios respectively. This situation will exacerbate increasing of frequent and intensified drought extremes over Africa. Additionally, the future RX5day indicated that mixed trend and revealed that increasing 3.72%, 2.54% over West and decreases -16.12%, -22.47% over East Africa under RCP4.5 and RCP8.5 respectively. Generally, rainfall extremes of CDD are projected to increase and RX5day shows a mixed trend in the coming periods over Africa and calls for further verification by using high resolution datasets.
文摘In recent years, there has been increasing demand for high-resolution seasonal climate forecasts at sufficient lead times to allow response planning from users in agriculture, hydrology, disaster risk management, and health, among others. This paper examines the forecasting skill of the North American Multi-model Ensemble (NMME) over Ethiopia during the June to September (JJAS) season. The NMME, one of the multi-model seasonal forecasting systems, regularly generates monthly seasonal rainfall forecasts over the globe with 0.5 <span style="font-family:Verdana;">-</span><span style="font-family:;" "=""><span style="font-family:Verdana;"> 11.5 months lead time. The skill and predictability of seasonal rainfall are assessed using 28 years of hindcast data from the NMME models. The forecast skill is quantified using canonical correlation analysis (CCA) and root mean square error. The results show that the NMME models capture the JJAS seasonal rainfall over central, northern, and northeastern parts of Ethiopia while exhibiting weak or limited skill across western and southwestern Ethiopia. The performance of each model in predicting the JJAS seasonal rainfall is variable, showing greater skill in predicting dry conditions. Overall, the performance of the multi-model ensemble was not consistently better than any single ensemble member. The correlation of observed and predicted </span><span style="font-family:Verdana;">seasonal rainfall for the better performing models</span></span><span style="font-family:Verdana;">—GFDL-CM2p5-FLOR-A06,</span><span style="font-family:Verdana;"> CMC2-CanCM4, GFDL-CM2p5-FLOR-B01 and NASA-GMAO-062012</span><span style="font-family:Verdana;">—</span><span style="font-family:Verdana;">is 0.68, 0.58, 0.52, and 0.5, respectively. The COLA-RSMAS-CCSM4, CMC1-</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">CanCM3 and NCEP-CFSv2 models exhibit less skill, with correlations less than 0.4. In general, the NMME offers promising skill to predict seasonal rainfall over Ethiopia during the June-September (JJAS) season, motivating further work to assess its performance at longer lead times.</span>
基金supported by the National Science and Technology Support Program of China (2015BAG10B01)the National Science Foundation of China under Grant No. 61232016, No.U1405254the PAPD fund
文摘Meter Data Collection Building Area Network(MDCBAN) deployed in high rises is playing an increasingly important role in wireless multi-hop smart grid meter data collection. Recently, increasingly numerous application layer data traffic makes MDCBAN be facing serious communication pressure. In addition, large density of meter data collection devices scattered in the limited geographical space of high rises results in obvious communication interference. To solve these problems, a traffic scheduling mechanism based on interference avoidance for meter data collection in MDCBAN is proposed. Firstly, the characteristics of network topology are analyzed and the corresponding traffic distribution model is proposed. Next, a wireless multi-channel selection scheme for different Floor Gateways and a single-channel time unit assignment scheme for data collection devices in the same Floor Network are proposed to avoid interference. At last, a data balanced traffic scheduling algorithm is proposed. Simulation results show that balanced traffic distribution and highly efficient and reliable data transmission can be achieved on the basis of effective interference avoidance between data collection devices.