利用常规气象观测站、地面自动站、温度廓线仪和多普勒天气雷达等资料分析2012年12月13—14日济南地区一次雨—雨夹雪—雪—雨降水过程的降水相态复杂变化的成因。结果表明:济南地区此次降水过程是由江淮气旋的影响发生的,冷空气较弱是...利用常规气象观测站、地面自动站、温度廓线仪和多普勒天气雷达等资料分析2012年12月13—14日济南地区一次雨—雨夹雪—雪—雨降水过程的降水相态复杂变化的成因。结果表明:济南地区此次降水过程是由江淮气旋的影响发生的,冷空气较弱是降水相态发生二次转换的主要原因。弱冷空气入侵导致近地面层气温降低,降水相态由雨转为雪;随着西南涡和江淮气旋北上,近地面层气温略上升,降水相态又由雪转为雨。近地面层先降温后升温,导致雨雪相态的二次转换;这种温度变化与近地面弱冷空气强度的变化有关。对于此次降水过程,1000 h Pa至地面层温度和0℃层亮带的高度均可作为判断降水相态的判据,位势厚度对降水有一定的指示意义,且对雨转雪过程比雪转雨过程的指示意义明显。展开更多
Atmospheric turbulence plays a vital role in the formation and dissipation of fog. However,studies of such turbulence are typically limited to observations with ultrasonic anemometers less than 100 m above ground. Thu...Atmospheric turbulence plays a vital role in the formation and dissipation of fog. However,studies of such turbulence are typically limited to observations with ultrasonic anemometers less than 100 m above ground. Thus,the turbulence characteristics of upper fog layers are poorly known. In this paper,we present 4-layers of data,measured by ultrasonic anemometers on a wind tower about 400 m above the sea surface; we use these data to characterize atmospheric turbulence atop a heavy sea fog. Large differences in turbulence during the sea fog episode were recorded. Results showed that the kinetic energy,momentum flux,and sensible heat flux of turbulence increased rapidly during the onset of fog. After onset,high turbulence was observed within the uppermost fog layer. As long as this turbulence did not exceed a critical threshold,it was crucial to enhancing the cooling rate,and maintaining the fog. Vertical momentum flux and sensible heat flux generated by this turbulence weakened wind speed and decreased air temperature during the fog. Towards the end of the fog episode,the vertical distribution of sensible heat flux reversed,contributing to a downward momentum flux in all upper layers. Spatial and temporal scales of the turbulence eddy were greater before and after the fog,than during the fog episode. Turbulence energy was greatest in upper levels,around 430 m and 450 m above mean sea level(AMSL),than in lower levels of the fog(390 m and 410 m AMSL); turbulence energy peaked along the mean wind direction. Our results show that the status of turbulence was complicated within the fog; turbulence caused fluxes of momentum and sensible heat atop the fog layer,affecting the underlying fog by decreasing or increasing average wind speed,as well as promoting or demoting air temperature stratification.展开更多
文摘利用常规气象观测站、地面自动站、温度廓线仪和多普勒天气雷达等资料分析2012年12月13—14日济南地区一次雨—雨夹雪—雪—雨降水过程的降水相态复杂变化的成因。结果表明:济南地区此次降水过程是由江淮气旋的影响发生的,冷空气较弱是降水相态发生二次转换的主要原因。弱冷空气入侵导致近地面层气温降低,降水相态由雨转为雪;随着西南涡和江淮气旋北上,近地面层气温略上升,降水相态又由雪转为雨。近地面层先降温后升温,导致雨雪相态的二次转换;这种温度变化与近地面弱冷空气强度的变化有关。对于此次降水过程,1000 h Pa至地面层温度和0℃层亮带的高度均可作为判断降水相态的判据,位势厚度对降水有一定的指示意义,且对雨转雪过程比雪转雨过程的指示意义明显。
基金Supported by the Marine Science and Technology Projects of Shanghai Committee of Science and Technology,China(No.10DZ1210802)
文摘Atmospheric turbulence plays a vital role in the formation and dissipation of fog. However,studies of such turbulence are typically limited to observations with ultrasonic anemometers less than 100 m above ground. Thus,the turbulence characteristics of upper fog layers are poorly known. In this paper,we present 4-layers of data,measured by ultrasonic anemometers on a wind tower about 400 m above the sea surface; we use these data to characterize atmospheric turbulence atop a heavy sea fog. Large differences in turbulence during the sea fog episode were recorded. Results showed that the kinetic energy,momentum flux,and sensible heat flux of turbulence increased rapidly during the onset of fog. After onset,high turbulence was observed within the uppermost fog layer. As long as this turbulence did not exceed a critical threshold,it was crucial to enhancing the cooling rate,and maintaining the fog. Vertical momentum flux and sensible heat flux generated by this turbulence weakened wind speed and decreased air temperature during the fog. Towards the end of the fog episode,the vertical distribution of sensible heat flux reversed,contributing to a downward momentum flux in all upper layers. Spatial and temporal scales of the turbulence eddy were greater before and after the fog,than during the fog episode. Turbulence energy was greatest in upper levels,around 430 m and 450 m above mean sea level(AMSL),than in lower levels of the fog(390 m and 410 m AMSL); turbulence energy peaked along the mean wind direction. Our results show that the status of turbulence was complicated within the fog; turbulence caused fluxes of momentum and sensible heat atop the fog layer,affecting the underlying fog by decreasing or increasing average wind speed,as well as promoting or demoting air temperature stratification.
