Capture of a strong elevated ducting event,especially its maintenance and sudden change,is of great value to airborne radar to achieve its beyond-the-line-of-sight detection.However,the knowledge is not easily accessi...Capture of a strong elevated ducting event,especially its maintenance and sudden change,is of great value to airborne radar to achieve its beyond-the-line-of-sight detection.However,the knowledge is not easily accessible over the open ocean and hence very rare.During the Air–Sea Interaction Survey(ASIS)over the western North Pacific(WNP)in May 2016,a strong elevated ducting event with a long-life period and sudden change in its evolution was observed.Measurements from the ASIS,images from the Himawari-8 satellite,reanalysis data from the ECMWF,and Weather Research and Forecasting(WRF)model,were used to analyze the maintenance and sudden change of this strong ducting event,together with the model performance on simulating it.The results showed that the maintenance of strong elevated ducts,with their tops ranging from 750 to 1050 m and average strength of approximately 38 M units,was caused by a strong dry air mass capping over the wet marine atmospheric boundary layer(MABL),together with the subsidence inversion associated with high pressure.The WRF model performs well in simulating them.However,a sudden increase in duct height with a slight decrease of strength was recorded by the subsequent GPS radiosonde,which was finally contributed to the mechanical turbulent inversion and hydrolapse associated with the marine low-level jet(MLLJ).The height of the maximum horizontal wind speed(Umh)of the MLLJ corresponds well with the bottom of the trapping layer.However,these jet-relevant ducts are generally weak and it is difficult to accurately simulate them by using the mesoscale numerical model,since the wind-shear produced eddies are too small to be properly parameterized.展开更多
Both low clouds and elevated ducts are common phenomena in the oceanic atmosphere. Low clouds affect elevated ducts by changing the structure of atmospheric temperature and humidity. However, due to the limitation of ...Both low clouds and elevated ducts are common phenomena in the oceanic atmosphere. Low clouds affect elevated ducts by changing the structure of atmospheric temperature and humidity. However, due to the limitation of met-ocean measurements, research on them is still scattered. This paper presents the distribution of elevated ducts and clouds over the central Western Pacific Ocean(WPO) based on Global Position System(GPS) sounding data and Himawari-8 satellite products from November 2015 to January 2016. Results show that the frequency of elevated ducts detected by ship-based GPS soundings was as high as 77% over the central WPO. The height and frequency of elevated ducts are closely related to the low clouds. If there are no clouds, the occurrence probability and mean base height of the elevated ducts are 14% and 730 m, respectively. By comparison, the occurrence probability and mean base height increase up to 24% and 1471 m, respectively, in the presence of cumulus(Cu) clouds, and 22% and 1511 m, respectively, in the presence of stratocumulus(Sc) clouds. Elevated ducts occur near the cloud top. The analysis of geopotential height and wind fields from the European Centre for Medium-Range Weather Forecasts(ECMWF) reanalysis dataset(ERA-interim) shows that the study area is covered by a strong and stable subtropical high, and slowly sinking dry air masses inside the subtropical high are above the moist boundary-layer air mass. The appearance and evolution of low clouds will adjust the temperature and humidity structure of the lower troposphere. If there are no clouds, the marine boundary layer(MBL) is the classic mixed boundary layer. Humidity gradient and subsidence inversion are formed atop the mixed layer. When low clouds are present, long wave radiation and entrainment atop clouds form a strong temperature inversion and humidity gradient, which strengthen elevated ducts. However, when Sc clouds are decoupled, a weaker temperature inversion and humidity gradient may occur between the surface mixed layer and subc展开更多
The air pollution in Urumqi which is located on the northern slope of the Tianshan Mountains in northwestern China,is very serious in winter.Of particular importance is the influence of terrain-induced shallow foehn,k...The air pollution in Urumqi which is located on the northern slope of the Tianshan Mountains in northwestern China,is very serious in winter.Of particular importance is the influence of terrain-induced shallow foehn,known locally as elevated southeasterly gale(ESEG).It usually modulates atmospheric boundary layer structure and wind field patterns and produces favorable meteorological conditions conducive to hazardous air pollution.During 2013-17,Urumqi had an average of 50 d yr-1 of heavy pollution(daily average PM2.5 concentration>150μg m-3),of which 41 days were in winter.The majority(71.4%)of heavy pollution processes were associated with the shallow foehn.Based on microwave radiometer,wind profiler,and surface observations,the surface meteorological fields and boundary layer evolution during the worst pollution episode in Urumqi during 16-23 February 2013 are investigated.The results illustrate the significant role of shallow foehn in the building,strengthening,and collapsing of temperature inversions.There were four wind field patterns corresponding to four different phases during the whole pollution event.The most serious pollution phase featured shallow foehn activity in the south of Urumqi city and the appearance of an intense inversion layer below 600 m.Intense convergence caused by foehn and mountain-valley winds was sustained during most of the phase,resulting in pollutants sinking downward to the lower boundary layer and accumulating around urban area.The key indicators of such events identified in this study are highly correlated to particulate matter concentrations and could be used to predict heavy pollution episodes in the feature.展开更多
利用常规气象观测资料、6.7μm卫星水汽图像和TBB、闪电定位资料以及NCEP/NCAR 1°×1°再分析资料,对2009年3月3日南方地区一次高架雷暴天气过程进行诊断研究。结果表明,该过程主要影响系统是中低层低槽、低涡切变线、西...利用常规气象观测资料、6.7μm卫星水汽图像和TBB、闪电定位资料以及NCEP/NCAR 1°×1°再分析资料,对2009年3月3日南方地区一次高架雷暴天气过程进行诊断研究。结果表明,该过程主要影响系统是中低层低槽、低涡切变线、西南低空急流、南北支西风急流。低空急流造成暖湿气流输送和高空急流造成冷平流侵入是对流触发机制。近地层为层结稳定的"冷空气垫",位势不稳定出现在低空急流与中高层干冷气流之间,并因急流中的下沉运动得以加强;西南暖湿气流与其北部干冷气流在中低层形成湿斜压锋区,西南气流的下沉支和北方下沉气流汇合在近地层形成的东北风回流与上部西南风生成锋面次级环流圈及中高层上升气流与北支急流中的下沉气流耦合形成次级正环流圈有利于倾斜上升运动的发展;低空急流的强暖平流和水汽通量辐合、北支急流入口区右侧的强辐散和南支急流北侧的辐合均加强了中尺度上升运动。湿层浅薄、上下干层较为深厚、强垂直风切变、低层逆温、-20~0℃过冷水层气流强上升运动等有利于雷暴天气的发生。雷电和冰雹出现在TBB、低空急流风速、θse、水汽通量以及300 h Pa散度等值线密集区附近。展开更多
利用陕西地面气象站观测资料、FY-2G逐小时卫星相当黑体温度(Temperature of Black Body,TBB)资料、闪电定位检测资料、西安CINRAD/CB型多普勒雷达探测资料、美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)...利用陕西地面气象站观测资料、FY-2G逐小时卫星相当黑体温度(Temperature of Black Body,TBB)资料、闪电定位检测资料、西安CINRAD/CB型多普勒雷达探测资料、美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)的1°×1°逐6 h再分析资料及常规气象观测资料,探讨了2016年11月22—23日陕西地区一次罕见的伴随"高架雷暴"暴雪天气过程成因机制。结果表明:500 h Pa高空槽、700 h Pa低空切变线和低空急流为陕西地区此次暴雪天气过程的影响系统,700 h Pa西南急流提供了充足的水汽条件,850 h Pa低空急流和地面倒槽的偏东气流为暴雪与高架雷暴提供深厚的冷垫。此次伴随暴雪出现的高架雷暴,是典型的"冷区雷暴",700 h Pa以下维持较强的逆温层,700 h Pa以上为湿中性层结,上升气流较强,易引发深厚湿对流;锋面次级环流圈有利于倾斜上升运动的发展;强垂直风切变,对流回波强度为30—50 d Bz,回波顶高为10—12 km,对流层顶高度超过-20～0℃的过冷水层高度,易导致雷电发生。雷电和冰雹出现在低空急流入口区左侧、TBB、水汽通量、θse密集区附近。展开更多
研究大气CO_2浓度升高对不同层次土壤有机碳(SOC)稳定性的影响对深入理解高浓度CO_2下SOC转化具有重要意义.以FACE(Free Air Carbon-dioxide Enrichment)平台长期定位试验水稻土为研究对象,通过SOC物理分级及矿化培养试验,研究大气CO_2...研究大气CO_2浓度升高对不同层次土壤有机碳(SOC)稳定性的影响对深入理解高浓度CO_2下SOC转化具有重要意义.以FACE(Free Air Carbon-dioxide Enrichment)平台长期定位试验水稻土为研究对象,通过SOC物理分级及矿化培养试验,研究大气CO_2浓度升高对稻田SOC含量、颗粒有机质(POM)含量、SOC矿化强度和酶活性变化的影响,探讨CO_2浓度升高对不同层次稻田SOC稳定性的影响.结果表明:大气CO_2浓度升高对表层SOC含量无显著影响,但使表层土壤POM-C显著增加了93.7%,同时使表层土壤蔗糖酶和多酚氧化酶活性分别提高了61.1%和83.7%,从而降低了表层SOC稳定性;大气CO_2浓度升高对深层SOC含量及其稳定性均无显著影响.研究结果将有助于评估土壤固定和储备碳的能力,为今后温室效应下农田管理提供科学依据.展开更多
基金Supported by the National Natural Science Foundation of China(41775017 and 41675058)。
文摘Capture of a strong elevated ducting event,especially its maintenance and sudden change,is of great value to airborne radar to achieve its beyond-the-line-of-sight detection.However,the knowledge is not easily accessible over the open ocean and hence very rare.During the Air–Sea Interaction Survey(ASIS)over the western North Pacific(WNP)in May 2016,a strong elevated ducting event with a long-life period and sudden change in its evolution was observed.Measurements from the ASIS,images from the Himawari-8 satellite,reanalysis data from the ECMWF,and Weather Research and Forecasting(WRF)model,were used to analyze the maintenance and sudden change of this strong ducting event,together with the model performance on simulating it.The results showed that the maintenance of strong elevated ducts,with their tops ranging from 750 to 1050 m and average strength of approximately 38 M units,was caused by a strong dry air mass capping over the wet marine atmospheric boundary layer(MABL),together with the subsidence inversion associated with high pressure.The WRF model performs well in simulating them.However,a sudden increase in duct height with a slight decrease of strength was recorded by the subsequent GPS radiosonde,which was finally contributed to the mechanical turbulent inversion and hydrolapse associated with the marine low-level jet(MLLJ).The height of the maximum horizontal wind speed(Umh)of the MLLJ corresponds well with the bottom of the trapping layer.However,these jet-relevant ducts are generally weak and it is difficult to accurately simulate them by using the mesoscale numerical model,since the wind-shear produced eddies are too small to be properly parameterized.
基金supported by the National Natural Science Foundation of China (No. 41975008)。
文摘Both low clouds and elevated ducts are common phenomena in the oceanic atmosphere. Low clouds affect elevated ducts by changing the structure of atmospheric temperature and humidity. However, due to the limitation of met-ocean measurements, research on them is still scattered. This paper presents the distribution of elevated ducts and clouds over the central Western Pacific Ocean(WPO) based on Global Position System(GPS) sounding data and Himawari-8 satellite products from November 2015 to January 2016. Results show that the frequency of elevated ducts detected by ship-based GPS soundings was as high as 77% over the central WPO. The height and frequency of elevated ducts are closely related to the low clouds. If there are no clouds, the occurrence probability and mean base height of the elevated ducts are 14% and 730 m, respectively. By comparison, the occurrence probability and mean base height increase up to 24% and 1471 m, respectively, in the presence of cumulus(Cu) clouds, and 22% and 1511 m, respectively, in the presence of stratocumulus(Sc) clouds. Elevated ducts occur near the cloud top. The analysis of geopotential height and wind fields from the European Centre for Medium-Range Weather Forecasts(ECMWF) reanalysis dataset(ERA-interim) shows that the study area is covered by a strong and stable subtropical high, and slowly sinking dry air masses inside the subtropical high are above the moist boundary-layer air mass. The appearance and evolution of low clouds will adjust the temperature and humidity structure of the lower troposphere. If there are no clouds, the marine boundary layer(MBL) is the classic mixed boundary layer. Humidity gradient and subsidence inversion are formed atop the mixed layer. When low clouds are present, long wave radiation and entrainment atop clouds form a strong temperature inversion and humidity gradient, which strengthen elevated ducts. However, when Sc clouds are decoupled, a weaker temperature inversion and humidity gradient may occur between the surface mixed layer and subc
基金supported by Central Scientific Research and Operational Project (IDM2020001)National Natural Science Foundation of China (Grant No. 41575011)China Desert Funds (Sqj2017013, Sqj2019004)
文摘The air pollution in Urumqi which is located on the northern slope of the Tianshan Mountains in northwestern China,is very serious in winter.Of particular importance is the influence of terrain-induced shallow foehn,known locally as elevated southeasterly gale(ESEG).It usually modulates atmospheric boundary layer structure and wind field patterns and produces favorable meteorological conditions conducive to hazardous air pollution.During 2013-17,Urumqi had an average of 50 d yr-1 of heavy pollution(daily average PM2.5 concentration>150μg m-3),of which 41 days were in winter.The majority(71.4%)of heavy pollution processes were associated with the shallow foehn.Based on microwave radiometer,wind profiler,and surface observations,the surface meteorological fields and boundary layer evolution during the worst pollution episode in Urumqi during 16-23 February 2013 are investigated.The results illustrate the significant role of shallow foehn in the building,strengthening,and collapsing of temperature inversions.There were four wind field patterns corresponding to four different phases during the whole pollution event.The most serious pollution phase featured shallow foehn activity in the south of Urumqi city and the appearance of an intense inversion layer below 600 m.Intense convergence caused by foehn and mountain-valley winds was sustained during most of the phase,resulting in pollutants sinking downward to the lower boundary layer and accumulating around urban area.The key indicators of such events identified in this study are highly correlated to particulate matter concentrations and could be used to predict heavy pollution episodes in the feature.
文摘利用常规气象观测资料、6.7μm卫星水汽图像和TBB、闪电定位资料以及NCEP/NCAR 1°×1°再分析资料,对2009年3月3日南方地区一次高架雷暴天气过程进行诊断研究。结果表明,该过程主要影响系统是中低层低槽、低涡切变线、西南低空急流、南北支西风急流。低空急流造成暖湿气流输送和高空急流造成冷平流侵入是对流触发机制。近地层为层结稳定的"冷空气垫",位势不稳定出现在低空急流与中高层干冷气流之间,并因急流中的下沉运动得以加强;西南暖湿气流与其北部干冷气流在中低层形成湿斜压锋区,西南气流的下沉支和北方下沉气流汇合在近地层形成的东北风回流与上部西南风生成锋面次级环流圈及中高层上升气流与北支急流中的下沉气流耦合形成次级正环流圈有利于倾斜上升运动的发展;低空急流的强暖平流和水汽通量辐合、北支急流入口区右侧的强辐散和南支急流北侧的辐合均加强了中尺度上升运动。湿层浅薄、上下干层较为深厚、强垂直风切变、低层逆温、-20~0℃过冷水层气流强上升运动等有利于雷暴天气的发生。雷电和冰雹出现在TBB、低空急流风速、θse、水汽通量以及300 h Pa散度等值线密集区附近。
文摘利用陕西地面气象站观测资料、FY-2G逐小时卫星相当黑体温度(Temperature of Black Body,TBB)资料、闪电定位检测资料、西安CINRAD/CB型多普勒雷达探测资料、美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)的1°×1°逐6 h再分析资料及常规气象观测资料,探讨了2016年11月22—23日陕西地区一次罕见的伴随"高架雷暴"暴雪天气过程成因机制。结果表明:500 h Pa高空槽、700 h Pa低空切变线和低空急流为陕西地区此次暴雪天气过程的影响系统,700 h Pa西南急流提供了充足的水汽条件,850 h Pa低空急流和地面倒槽的偏东气流为暴雪与高架雷暴提供深厚的冷垫。此次伴随暴雪出现的高架雷暴,是典型的"冷区雷暴",700 h Pa以下维持较强的逆温层,700 h Pa以上为湿中性层结,上升气流较强,易引发深厚湿对流;锋面次级环流圈有利于倾斜上升运动的发展;强垂直风切变,对流回波强度为30—50 d Bz,回波顶高为10—12 km,对流层顶高度超过-20～0℃的过冷水层高度,易导致雷电发生。雷电和冰雹出现在低空急流入口区左侧、TBB、水汽通量、θse密集区附近。
文摘研究大气CO_2浓度升高对不同层次土壤有机碳(SOC)稳定性的影响对深入理解高浓度CO_2下SOC转化具有重要意义.以FACE(Free Air Carbon-dioxide Enrichment)平台长期定位试验水稻土为研究对象,通过SOC物理分级及矿化培养试验,研究大气CO_2浓度升高对稻田SOC含量、颗粒有机质(POM)含量、SOC矿化强度和酶活性变化的影响,探讨CO_2浓度升高对不同层次稻田SOC稳定性的影响.结果表明:大气CO_2浓度升高对表层SOC含量无显著影响,但使表层土壤POM-C显著增加了93.7%,同时使表层土壤蔗糖酶和多酚氧化酶活性分别提高了61.1%和83.7%,从而降低了表层SOC稳定性;大气CO_2浓度升高对深层SOC含量及其稳定性均无显著影响.研究结果将有助于评估土壤固定和储备碳的能力,为今后温室效应下农田管理提供科学依据.
