The relative dispersion of cloud and fog droplets has significant impacts on aerosol indirect effects,radiative transfer,and microphysical processes.However,previous studies have been mostly concerned with clouds,with...The relative dispersion of cloud and fog droplets has significant impacts on aerosol indirect effects,radiative transfer,and microphysical processes.However,previous studies have been mostly concerned with clouds,with limited studies on fog,particularly those that examine the combined influences of all key physical processes and their roles during fog evolution.As such,this study aims to conduct a comprehensive investigation by examining the relationships between relative dispersion and other microphysical variables,as well as the underlying microphysical and dynamic processes,based on field fog campaigns in polluted and clean conditions.In polluted fog,droplet concentrations are higher,leading to smaller droplets and increased dispersion.The correlation between dispersion and droplet volume-mean radius is positive in the polluted fog,but shifts to negative in clean fog.We attribute the difference to various microphysical processes like aerosol activation,condensation,collision-coalescence,and entrainment-mixing.In polluted fog,high aerosol concentrations,low supersaturations,and strong turbulence(entrainment-mixing)provide suitable conditions for the simultaneous occurrence of droplet condensation and aerosol activation,resulting in a positive correlation between dispersion and volume-mean radius,especially during the fog formation stage.In contrast,during the mature stage in clean fog,condensation is dominant with weak aerosol activation leading to a negative correlation between relative dispersion and volume-mean radius.The collision-coalescence process is more active in the mature stage,increasing radii and leading to the negative correlation between dispersion and volume-mean radius.This result sheds new light on understanding the relative dispersion and mechanisms in fog under different aerosol backgrounds.展开更多
沙尘天气对社会经济与生态环境产生不利影响,认识其年代际变化并探索其未来态势具有重要意义。本文使用站点资料与再分析数据,研究了调控1961—2020年3—4月华北地区沙尘日数年代际变化的关键大气环流,并利用CMIP6和CESM-LE两套模式数...沙尘天气对社会经济与生态环境产生不利影响,认识其年代际变化并探索其未来态势具有重要意义。本文使用站点资料与再分析数据,研究了调控1961—2020年3—4月华北地区沙尘日数年代际变化的关键大气环流,并利用CMIP6和CESM-LE两套模式数据预估其近期变化。结果表明,华北地区沙尘日数在20世纪80年代末90年代初发生了显著突变,高发时期(1961—1989年,P1)的沙尘日数大约是低发时期(1992—2020年,P2)的3.5倍。这一变化受到由西欧平原东传至乌拉尔山及蒙古高原的波列系统(西欧低压-乌拉尔山高压-蒙古低压异常,anomaly of geopotential height in Western Europe,Ural Mountains and Mongolia,简称EUM)影响。相较于P2时期,P1时期波列较强,乌拉尔山地区位势高度升高,其东部异常偏北气流有利于冷空气南下。蒙古地区位势高度降低,显著的蒙古气旋异常为华北地区沙尘天气提供了动力条件。同时沙源地上空水汽辐散,不利于降水。EUM指数具有与华北地区沙尘日数较为一致的年代际变化特征,对后者未来变化有一定的指示作用。但不同模式对EUM年代际变化的模拟能力差异较大。通过筛选能够再现EUM年代际减弱特征的最优模式集合,发现在高排放情境下,未来近期(2021—2050年,P3)EUM显著增强,有利于华北地区沙尘天气增加。展开更多
【目的】为分析昭通机场辐射雾变化特征,总结预报指标。【方法】利用昭通机场2013—2022年地面观测资料,对辐射雾过程的气候特征及气象要素特征进行统计,并用ERA5再分析数据对辐射雾过程的天气形势和物理量进行合成分析。【结果】1)昭...【目的】为分析昭通机场辐射雾变化特征,总结预报指标。【方法】利用昭通机场2013—2022年地面观测资料,对辐射雾过程的气候特征及气象要素特征进行统计,并用ERA5再分析数据对辐射雾过程的天气形势和物理量进行合成分析。【结果】1)昭通机场辐射雾逐年减少,10月—次年1月为高发期,多形成于07时,消散于10—11时。2)昭通机场辐射雾基本形成于降温降水天气转晴后,辐射雾形成的夜间地面多为偏南微风,相对湿度在辐射雾生成前5 h达90%以上,夜间最低气温基本低于前1 d 16时的露点温度。3)物理量合成表明,辐射雾过程中湿度垂直配置为下湿中干,春夏季辐射雾形成过程中水汽作用较大,秋冬季辐射雾形成过程中夜间降温冷却的作用更加明显。【结论】昭通机场辐射雾主要出现在秋冬季的07—10时,降水低温天气转晴后的1~3 d内,地面弱气压场、近地面高湿、偏南微风的配置有利于辐射雾的形成。展开更多
基金supported by the Chinese National Natural Science Foundation under Grant Nos.(41975181,42325503,42375197,42575207,42205090)Y.LIU is supported by the U.S.Department of Energy’s Atmospheric System Research(ASR)program.
文摘The relative dispersion of cloud and fog droplets has significant impacts on aerosol indirect effects,radiative transfer,and microphysical processes.However,previous studies have been mostly concerned with clouds,with limited studies on fog,particularly those that examine the combined influences of all key physical processes and their roles during fog evolution.As such,this study aims to conduct a comprehensive investigation by examining the relationships between relative dispersion and other microphysical variables,as well as the underlying microphysical and dynamic processes,based on field fog campaigns in polluted and clean conditions.In polluted fog,droplet concentrations are higher,leading to smaller droplets and increased dispersion.The correlation between dispersion and droplet volume-mean radius is positive in the polluted fog,but shifts to negative in clean fog.We attribute the difference to various microphysical processes like aerosol activation,condensation,collision-coalescence,and entrainment-mixing.In polluted fog,high aerosol concentrations,low supersaturations,and strong turbulence(entrainment-mixing)provide suitable conditions for the simultaneous occurrence of droplet condensation and aerosol activation,resulting in a positive correlation between dispersion and volume-mean radius,especially during the fog formation stage.In contrast,during the mature stage in clean fog,condensation is dominant with weak aerosol activation leading to a negative correlation between relative dispersion and volume-mean radius.The collision-coalescence process is more active in the mature stage,increasing radii and leading to the negative correlation between dispersion and volume-mean radius.This result sheds new light on understanding the relative dispersion and mechanisms in fog under different aerosol backgrounds.
文摘沙尘天气对社会经济与生态环境产生不利影响,认识其年代际变化并探索其未来态势具有重要意义。本文使用站点资料与再分析数据,研究了调控1961—2020年3—4月华北地区沙尘日数年代际变化的关键大气环流,并利用CMIP6和CESM-LE两套模式数据预估其近期变化。结果表明,华北地区沙尘日数在20世纪80年代末90年代初发生了显著突变,高发时期(1961—1989年,P1)的沙尘日数大约是低发时期(1992—2020年,P2)的3.5倍。这一变化受到由西欧平原东传至乌拉尔山及蒙古高原的波列系统(西欧低压-乌拉尔山高压-蒙古低压异常,anomaly of geopotential height in Western Europe,Ural Mountains and Mongolia,简称EUM)影响。相较于P2时期,P1时期波列较强,乌拉尔山地区位势高度升高,其东部异常偏北气流有利于冷空气南下。蒙古地区位势高度降低,显著的蒙古气旋异常为华北地区沙尘天气提供了动力条件。同时沙源地上空水汽辐散,不利于降水。EUM指数具有与华北地区沙尘日数较为一致的年代际变化特征,对后者未来变化有一定的指示作用。但不同模式对EUM年代际变化的模拟能力差异较大。通过筛选能够再现EUM年代际减弱特征的最优模式集合,发现在高排放情境下,未来近期(2021—2050年,P3)EUM显著增强,有利于华北地区沙尘天气增加。
文摘【目的】为分析昭通机场辐射雾变化特征,总结预报指标。【方法】利用昭通机场2013—2022年地面观测资料,对辐射雾过程的气候特征及气象要素特征进行统计,并用ERA5再分析数据对辐射雾过程的天气形势和物理量进行合成分析。【结果】1)昭通机场辐射雾逐年减少,10月—次年1月为高发期,多形成于07时,消散于10—11时。2)昭通机场辐射雾基本形成于降温降水天气转晴后,辐射雾形成的夜间地面多为偏南微风,相对湿度在辐射雾生成前5 h达90%以上,夜间最低气温基本低于前1 d 16时的露点温度。3)物理量合成表明,辐射雾过程中湿度垂直配置为下湿中干,春夏季辐射雾形成过程中水汽作用较大,秋冬季辐射雾形成过程中夜间降温冷却的作用更加明显。【结论】昭通机场辐射雾主要出现在秋冬季的07—10时,降水低温天气转晴后的1~3 d内,地面弱气压场、近地面高湿、偏南微风的配置有利于辐射雾的形成。
