共查询到20条相似文献，搜索用时 31 毫秒
1.
Cloud radiative and microphysical effects on the relation between spatial mean rain rate, rain intensity and fractional rainfall coverage are investigated in this study by conducting and analyzing a series of two-dimensional cloud resolving model sensitivity experiments of pre-summer torrential rainfall in June 2008. The analysis of time-mean data shows that the exclusion of radiative effects of liquid clouds reduces domain mean rain rate by decreasing convective rain rate mainly through the reduced convective-rainfall area associated with the strengthened hydrometeor gain in the presence of radiative effects of ice clouds, whereas it increases domain mean rain rate by enhancing convective rain rate mainly via the intensified convective rain intensity associated with the enhanced net condensation in the absence of radiative effects of ice clouds. The removal of radiative effects of ice clouds decreases domain mean rain rate by reducing stratiform rain rate through the suppressed stratiform rain intensity related to the suppressed net condensation in the presence of radiative effects of liquid clouds, whereas it increases domain mean rain rate by strengthening convective rain rate mainly via the enhanced convective rain intensity in response to the enhanced net condensation in the absence of radiative effects of liquid clouds. The elimination of microphysical effects of ice clouds suppresses domain mean rain rate by reducing stratiform rain rate through the reduced stratiform-rainfall area associated with severely reduced hydrometeor loss. 相似文献
2.
Two experiments were carried out using a two-dimensional cloud-resolving model to study the effects of diurnally varying sea surface temperature (SST) on diurnal variations of tropical convective and stratiform rainfall. Experiment SST29 is imposed by a constant SST of 29°C, whereas experiment SST29D is imposed by a diurnally varying SST with a time-mean of 29°C and a diurnal difference of 1°C. Both experiments are also zonally uniformly imposed by a zero vertical velocity and a constant zonal wind, and are integrated for 40 days to reach quasi-equilibrium states. The model domain mean surface rain rate is larger in SST29D than in SST29 in the late afternoon, when the ocean surface is warmer in SST29D. Convective-stratiform rainfall partitioning analysis reveals that the late-afternoon convective rainfall is larger in SST29D than in SST29, whereas the stratiform rainfalls are similar in both experiments. Further analysis of surface rainfall and cloud microphysical budgets over convective regions shows that, in the late afternoon, the larger amount of water vapor is pumped into the non-raining region through the larger surface evaporation associated with the warmer SST. This water vapor is then transported into convective regions to produce more vapor condensation and greater collection of cloud water by raindrops and larger convective rainfall in SST29D than in SST29. 相似文献
3.
The effects of sea surface temperature (SST), radiation, cloud microphysics, and diurnal variations on the vertical structure of tropical tropospheric temperature are investigated by analyzing 10 two-dimensional equilibrium cloud-resolving model simulation data. The increase of SST, exclusion of diurnal variation of SST, and inclusion of diurnal variation of solar zenith angle, radiative effects of ice clouds, and ice microphysics could lead to tropical tropospheric warming and increase of tropopause height. The increase of SST and the suppression of its diurnal variation enhance the warming in the lower and upper troposphere, respectively, through increasing latent heat and decreasing IR cooling. The inclusion of diurnal variation of solar zenith angle increases the tropospheric warming through increasing solar heating. The inclusion of cloud radiative effects increases tropospheric warming through suppressing IR cooling in the mid and lower troposphere and enhancing solar heating in the upper troposphere. The inclusion of ice microphysics barely increases warming in the mid and lower troposphere because the warming from ice radiative effects is nearly offset by the cooling from ice microphysical effects, whereas it causes the large warming enhancement in the upper troposphere due to the dominance of ice radiative effects. The tropopause height is increased mainly through the large enhancement of IR cooling. 相似文献
4.
Both water vapor and heat processes play key roles in producing surface rainfall.While the water vapor effects of sea surface temperature and cloud radiative and microphysical processes on surface rainfall have been investigated in previous studies,the thermal effects on rainfall are analyzed in this study using a series of two-dimensional equilibrium cloud-resolving model experiments forced by zonally-uniform,constant,large-scale zonal wind and zero large-scale vertical velocity.The analysis of thermally-related surface rainfall budget reveals that the model domain mean surface rain rate is primarily associated with the mean infrared cooling rate.Convective rainfall and transport of hydrometeor concentration from convective regions to raining stratiform regions corresponds to the heat divergence over convective regions,whereas stratiform rainfall corresponds to the transport of hydrometeor concentration from convective regions and heat divergence over raining stratiform regions.The heat divergence over convective regions is mainly balanced by the heat convergence over rainfall-free regions,which is,in turn,offset by the radiative cooling over rainfall-free regions.The sensitivity experiments of rainfall to the effects of sea surface temperature and cloud radiative and microphysical processes show that the sea surface temperature and cloud processes affect convective rainfall through the changes in infrared cooling rate over rainfall-free regions and transport rate of heat from convective regions to rainfall-free regions. 相似文献
5.
Torrential rainfall responses to radiative and microphysical processes of ice clouds during a landfall of severe tropical storm Bilis (2006) 总被引：1，自引：0，他引：1
Ice clouds are an important component in precipitation systems. The radiative processes of ice clouds directly impact radiation in heat budget and the microphysical processes of ice clouds directly affect latent heat and net condensation through deposition processes, which may eventually change surface rainfall. Thus, torrential rainfall responses to radiative and microphysical processes of ice clouds during a landfall of severe tropical storm Bilis (2006) are investigated with the analysis of sensitivity experiments. The two-dimensional cloud-resolving model is integrated for 3 days with imposed zonally uniform vertical velocity, zonal wind, horizontal temperature and vapor advection from NCEP/GDAS data. One sensitivity experiment excludes the radiative effects of ice clouds and the other sensitivity experiment excludes ice microphysics and associated radiative and microphysical processes. Model domain mean surface rain rate is barely changed by the exclusion of radiative effects of ice clouds due to the small decrease in net condensation associated with the small reduction in latent heat as a result of the offset between the increase in radiative cooling and the decrease in heat divergence. The exclusion of microphysical effects of ice clouds decreases the mean rain rate simply through the suppression of latent heat as a result of the removal of deposition processes. The total exclusion of ice microphysics decreases the mean rain rate mainly through the exclusion of microphysical effects of ice clouds. 相似文献
6.
Cloud is essential in the atmosphere, condensing water vapor and generating strong convective or large-scale persistent precipitation. In this work, the relationships between cloud vertical macro- or microphysical properties, radiative heating rate, and precipitation for convective and stratiform clouds in boreal summer over the Tibetan Plateau (TP) are analyzed and compared with its neighboring land and tropical oceans based on CloudSat/CALIPSO satellite measurements and TRMM precipitation data. The precipitation intensity caused by convective clouds is twofold stronger than that by stratiform clouds. The vertical macrophysics of both cloud types show similar features over the TP, with the region weakening the precipitation intensity and compressing the cloud vertical expansion and variation in cloud top height, but having an uplift effect on the average cloud top height. The vertical microphysics of both cloud types under conditions of no rain over the TP are characterized by lower-level ice water, ice particles with a relatively larger range of sizes, and a relatively lower occurrence of denser ice particles. The features are similar to other regions when precipitation enhances, but convective clouds gather denser and larger ice particles than stratiform clouds over the TP. The atmospheric shortwave (longwave) heating (cooling) rate strengthens with increased precipitation for both cloud types. The longwave cooling layer is thicker when the rainfall rate is less than 100 mm d?1, but the net heating layer is typically compressed for the profiles of both cloud types over the TP. This study provides insights into the associations between clouds and precipitation, and an observational basis for improving the simulation of convective and stratiform clouds over the TP in climate models. 相似文献
7.
Atmospheric Intercomparison Project simulations of the summertime diurnal cycle of precipitation and low-level winds over subtropical China by Intergovernmental Panel on Climate Change Fifth Assessment Report models were evaluated. By analyzing the diurnal variation of convective and stratiform components, results confirmed that major biases in rainfall diurnal cycles over subtropical China are due to convection parameterization and further pointed to the diurnal variation of convective rainfall being closely related to the closure of the convective scheme. All models captured the early-morning peak of total rainfall over the East China Sea, but most models had problems in simulating diurnal rainfall variations over land areas of subtropical China. When total rainfall was divided into stratiform and convective rainfall, all models successfully simulated the diurnal variation of stratiform rainfall with a maximum in the early morning. The models, overestimating noon-time （nocturnal） total rainfall over land, generally simulated too much convective rainfall, which peaked close to noon （midnight）, sharing some similarities in the closures of their deep convection schemes. The better performance of the Meteorological Research Institute atmospherer. ocean coupled global climate model version 3 （MRI-CGCM3） is attributed to the well captured ratio of the two kinds of rainfall, but not diurnal variations of the two components. Therefore, a proper ratio of convective and stratiform rainfall to total rainfall is also important to improve simulated diurnal rainfall variation. 相似文献
8.
The effects of ice microphysics on tropical atmospheric and oceanic variability are investigated with a two-dimensional coupled ocean-cloud resolving atmosphere model forced by the large-scale vertical velocity and zonal wind derived from Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE). The experiment without ice microphysics is compared to a control experiment with ice microphysics. Compared to the control experiment, the experiment without ice microphysics generates a more humid and colder atmosphere by suppressing stratiform clouds and rainfall and associated latent heating; the experiment without ice microphysics produces a saltier mixed layer by a larger saline forcing associated with a weaker stratiform rainfall. Ocean mixed-layer temperature is insensitive to the atmospheric variability associated with ice microphysics. 相似文献
9.
Cloud microphysical processes associated with the diurnal variations of tropical convection: A 2D cloud resolving modeling study 总被引：7，自引：0，他引：7
Summary Cloud microphysical processes associated with the diurnal variations of tropical convection are investigated based on hourly
data from a 2D coupled ocean-cloud resolving atmosphere simulation. The model is forced by the large-scale vertical velocity
and zonal wind derived from TOGA COARE for a 50-day period. The diurnal composites are carried out in weak diurnal SST variations
(case W) and strong diurnal SST signals (case S). The ice water path is larger than the liquid water path in case W than it
is in case S. The difference is enhanced in the morning in case W and in the early afternoon in case S when the surface rain
rates reach their peaks. Further comparison of cloud microphysics budgets, associated with rainfall peaks, between cases S
and W shows that solar heating in case S warms air to reduce the contribution of vapor deposition to cloud growth, which decreases
ice water path compared to those in case W. While the collection of cloud water by rain is a major contributor to the surface
precipitation in both cases, the melting of precipitation ice (sum of snow and graupel) contributes less to the rainfall in
case S than in case W. 相似文献
10.
Numerical simulation of meso-β-scale convective cloud systems associated with a PRE-STORM MCC case has been carried out using a 2-D version of the CSU Regional Atmospheric Modeling System (RAMS) nonhydrostatic model with parameterized microphysics. It is found that the predicted meso-γ-scale convective phenomena are basically unsteady under the situation of strong shear at low-levels, white the meso-β-scale convective system is maintained up to 3 hours or more. The meso-β-scale cloud system exhibits characteristics of a multi-celled convective storm in which the meso-γ-scale convective cells have lifetime of about 30 min. Pressure perturbation depicts a meso-low after a half hour in the low levels. As the cloud system evolves, the meso-low inten-sifies and extends to the upshear side and covers the entire domain in the mid-lower levels with the peak values of 5-8 hPa. Temperature perturbation depicts a warm region in the middle levels through the entire simulation period. The meso-γ-scale warm cores with peak values of 4-8oC are associated with strong convective cells. The cloud top evapo-ration causes a stronger cold layer around the cloud top levels.Simulation of microphysics exhibits that graupel is primarily concentrated in the strong convective cells forming the main source of convective rainfall after one hour of simulation time. Aggregates are mainly located in the stratiform region and decaying convective cells which produce the stratiform rainfall. Riming of the ice crystals is the predominant precipitation formation mechanism in the convection region, whereas aggregation of ice crystals is the predominant one in the stratiform region, which is consistent with observations. Sensitivity experiments of ice-phase microphysical processes show that the microphysical structures of the convective cloud system can be simulated better with the diagnosed aggregation collection efficiencies. 相似文献
11.
Regional dependence of microphysical and radiative effects of ice clouds on vertical structure of tropical tropospheric temperature is examined by analyzing thermodynamic budgets over clear sky, raining stratiform, convective, and non-raining stratiform regions with three two-dimensional sensitivity equilibrium cloud-resolving model simulation data. The decrease in the mean tropospheric cooling caused by radiative effects of ice clouds results from the decreases in local atmospheric cooling over clear sky regions around 12?C16?km through the decrease in heat divergence and below 7.5?km through the decrease in radiative cooling and over non-raining stratiform regions around 6?C13?km through the increase in latent heat. The increase in the mean tropospheric cooling caused by microphysical effects of ice clouds results from the increases in local atmospheric cooling over clear sky regions through the decrease in heat convergence below 4?km the increase in radiative cooling around 4?C8?km and over non-raining stratiform regions through the increase in radiative cooling around 7?C10?km. The raining regions do not show any significant thermal changes due to the cancellation between heat convergence and latent heat. 相似文献
12.
The diurnal cycles of precipitation over north China during summer in four strong rainfall years are examined using two-dimensional cloud-resolving modeling data. The diurnal signals are analyzed in terms of precipitation budget, fractional rainfall coverage and rain intensity over convective and stratiform rainfall area. The analysis of precipitation budget shows that the diurnal cycles of convective and stratiform precipitation mainly correspond respectively to those of water vapor convergence and transport of hydrometeor from convective rainfall area to stratiform rainfall area in 1964, 1994 and 1995, whereas they mainly correspond to those of water vapor convergence in 2013. The diurnal cycles of convective and stratiform precipitation are mainly associated with those of rain intensity in 1964, 1994 and 1995. In 2013, the diurnal cycle of stratiform precipitation is mainly related to that of fractional rainfall coverage over stratiform rainfall area. The multiple peaks of convective precipitation mainly correspond to the rain intensity maxima associated with strong water vapor convergence. 相似文献
13.
Diurnal variation in the initiation of rainfall over the Indian subcontinent during two different monsoon seasons of 2008 and 2009 总被引：1，自引：1，他引：0
In the present study, the diurnal variations in the time of initiation of rainfall, during two contrasting monsoon seasons of 2008 (below normal) and 2009 (normal) over the Indian subcontinent and surrounding oceanic areas has been analyzed. Harmonic analysis was used to detect the spatial variation of the diurnal cycle of the time of initiation of rainfall, as obtained at half-hourly intervals from the Kalpana 1 satellite. In general, the diurnal cycle in the time of initiation is strongest in regions where convective clouds are predominant, while it is weaker in regions where the clouds are predominantly stratiform with long-lived medium to high cloud cover. In the interior of the subcontinent, the time of maximum mainly occurred in the afternoon to evening hours, with a distinct southeast to northwest gradation. Substantial spatial variations were detected in the diurnal patterns between a normal and below normal monsoon years. Spatially, rainfall is initiated later in 2009 compared to 2008 over most of the interior of the Indian subcontinent. The most distinct difference was observed over the core monsoon region in central India, where the diurnal patterns were stronger in 2009 compared to 2008. On the other hand, over the oceans surrounding the Indian subcontinent, the initiation times are generally earlier in 2009. 相似文献
14.
The effects of vertical wind shear, radiation and ice microphysics on precipitation efficiency （PE） were investigated through analysis of modeling data of a torrential rainfall event over Jinan, China during July 2007. Vertical wind shear affected PE by changing the kinetic energy conversion between the mean and perturbation circulations. Clou~radiation interaction impacted upon PE, but the relationship related to cloud radiative effects on PE was not statistically significant. The reduction in deposition processes as- sociated with the removal of ice microphysics suppressed efficiency. The relationships related to effects of vertical wind shear, radiation and ice clouds on PEs defined in cloud and surface rainfall budgets were more statistically significant than that defined in the rain microphysical budget. 相似文献
15.
This paper summarizes the recent progress in studies of the diurnal variation of precipitation over con- tiguous China. The main results are as follows. （1） The rainfall diurnal variation over contiguous China presents distinct regional features. In summer, precipitation peaks in the late afternoon over the south- ern inland China and northeastern China, while it peaks around midnight over southwestern China. In the upper and middle reaches of Yangtze River valley, precipitation occurs mostly in the early morning. Summer precipitation over the central eastern China （most regions of the Tibetan Plateau） has two diurnal peaks, i.e., one in the early morning （midnight） and the other in the late afternoon. （2） The rainfall diurnal variation experiences obvious seasonal and sub-seasonal evolutions. In cold seasons, the regional contrast of rainfall diurnal peaks decreases, with an early morning maximum over most of the southern China. Over the central eastern China, diurnal monsoon rainfall shows sub-seasonal variations with the movement of summer monsoon systems. The rainfall peak mainly occurs in the early morning （late afternoon） during the active （break） monsoon period. （3） Cloud properties and occurrence time of rainfall diurnal peaks are different for long- and short-duration rainfall events. Long-duration rainfall events are dominated by strat- iform precipitation, with the maximum surface rain rate and the highest profile occurring in the late night to early morning, while short-duration rainfall events are more related to convective precipitation, with the maximum surface rain rate and the highest profile occurring between the late afternoon and early night. （4） The rainfall diurnal variation is influenced by multi-scale mountain-valley and land-sea breezes as well as large-scale atmospheric circulation, and involves complicated formation and evolution of cloud and rainfall systems. The diurnal cycle of winds in the lower troposphere also contributes to the regional differences 相似文献
16.
混合相态层状云与对流云的微物理特征有很大的差异性,但现阶段数值模式中并没有充分考虑两者的区别,这是导致云降水的模拟有较大不确定性的原因之一。为了加深对层状云与对流云的微物理特征差异的理解,并为模式的验证和参数化开发提供支撑,本文基于在中落基山地区进行的Ice in Clouds Experiment—Layer Clouds（ICE-L）项目和High Plain Cumulus（HiCu）项目的飞机观测资料,定量对比分析了该地区大陆性混合相态冬季较浅薄的层状云与较弱及中等强度的夏季对流云的微物理特征。其中,粒子图像和粒子谱通过2D-Cloud和2D-Precipitation探头得到,液态水含量通过热线式King探头测量得到,冰水含量基于粒子谱计算得到。主要结论有:（1）在?30°C～0°C的温度层范围内,夏季对流云内的液态水含量比冬季层状云高一个数量级,冰水含量高一到两个数量级,并且在对流云云顶附近观测到更多的过冷水。此外,夏季对流云中液态水含量在?20°C～0°C上随温度降低而升高,而冬季层状云则相反。夏季对流云中更活跃的冰晶生成和生长过程使得云内液态水质量分数小于层状云。（2）冬季层状云与夏季对流云内相态空间分布极不均匀。随着温度从0°C降低到?30°C,在冬季层状云中冰晶发生贝吉龙过程,云中的过冷水为主的区域向混合相态和冰相转化。而夏季对流云中相态结构更为复杂,体现了对流云中复杂的冰水相互作用。（3）在?30°C～0°C的温度范围内,夏季对流云的粒子谱宽度大于冬季层状云。随着温度的降低,冬季层状云与夏季对流云均存在粒子谱增宽的现象。（4）冬季层状云中,温度低于?20°C时冰晶主要为无规则状,在?20°C～?10°C观测到了辐枝状和无规则状冰晶,在?10°C以上观测到了柱状和无规则状冰晶,说明冰晶的生长主要为凝华增长和碰并增长。而夏季对流云以冻滴、霰粒子与不规则冰晶为主,说明主要为液滴冻结、淞附增长和碰并增长为主。（5）在夏季对流云较强的上升气流中存在较高的液态水含量,但垂直速度与云内冰水含量没有明显的相关性。 相似文献
17.
Diurnal phase of late-night against late-afternoon of stratiform and convective precipitation in summer southern contiguous China 总被引：7，自引：0，他引：7
Using the tropical rainfall measuring mission (TRMM) Precipitation Radar (PR) observations combined with the surface rain
gauge data during 1998–2006, the robust diurnal features of summer stratiform and convective precipitation over the southern
contiguous China are revealed by exploring the diurnal variations of rain rate and precipitation profile. The precipitation
over the southern contiguous China exhibits two distinguishing diurnal phases: late-night (2200–0600 LST) and late-afternoon
(1400–2200 LST), dependent on the location, precipitation type and duration time. Generally, the maximum rain rate and the
highest profile of stratiform precipitation occur in the late-afternoon (late-night) over the southeastern (southwestern)
China, while most of the stratiform short-duration rain rate tends to present late-afternoon peaks over the southern China.
For convective precipitation, the maximum rain rate and the highest profile occur in the late-afternoon over most of the southern
contiguous China, while the convective long-duration rain rate exhibits late-night peaks over the southwestern China. Without
regional dependence, the convective precipitation exhibits much larger amplitude of diurnal variations in both near surface
rain rate and vertical extension compared with stratiform precipitation and the convective rain top rises most rapidly between
noon and afternoon. However, there are two distinctive sub-regions. The diurnal phases of precipitation there are very weakly
dependent on precipitation type and duration time. Over the eastern periphery of the Tibetan Plateau, the maximum rain rate
and the highest profile of either convective or stratiform precipitation occur in the late-night. Over the southeastern coastal
regions, both the near surface rain rate and rain top of convective and stratiform precipitation peak in the late-afternoon. 相似文献
18.
中国大陆降水日变化研究进展 总被引：32，自引：4，他引：28
文章概述了中国大陆降水日变化的最新研究成果,给出了中国大陆降水日变化的整体图像,指出目前数值模式模拟降水日变化的局限性,为及时了解和掌握降水日变化研究进展、开展相关科学研究和进行降水预报服务提供了有价值的科学依据和参考。现有研究表明：（1）中国大陆夏季降水日变化的区域特征明显。在夏季,东南和东北地区的降水日峰值主要集中在下午;西南地区多在午夜达到降水峰值;长江中上游地区的降水多出现在清晨;中东部地区清晨、午后双峰并存;青藏高原大部分地区是下午和午夜峰值并存。（2）降水日变化存在季节差异和季节内演变。冷季降水日峰值时刻的区域差异较暖季明显减小,在冷季南方大部分地区都表现为清晨峰值;中东部地区暖季降水日变化随季风雨带的南北进退表现出清晰的季节内演变,季风活跃（间断）期的日降水峰值多发生在清晨（下午）。（3）持续性降水和局地短时降水的云结构特性以及降水日峰值出现时间存在显著差异。持续性降水以层状云特性为主,地表降水和降水廓线的峰值大多位于午夜后至清晨;短时降水以对流降水为主,峰值时间则多出现在下午至午夜前。（4）降水日变化涉及不同尺度的山-谷风、海-陆风和大气环流的综合影响,涉及复杂的云雨形成和演变过程,对流层低层环流日变化对降水日变化的区域差异亦有重要影响。（5）目前数值模式对中国降水日变化的模拟能力有限,且模拟结果具有很强的模式依赖性,仅仅提高模式水平分辨率并不能总是达到改善模拟结果的目的,关键是要减少存在于降水相关的物理过程参数化方案中的不确定性问题。 相似文献
19.
1960年以来东亚季风区云-降水微物理的直接观测研究 总被引：1，自引：0，他引：1
云-降水的直接观测结果是云微物理参数化的重要依据。自1960年以来,处于东亚季风影响下的中国实施了大量对云-降水微物理参数的观测和研究,旨在加深对云-降水微物理过程的认识,从而改进数值模式中云微物理参数化方案和指导人工影响天气作业。云-降水微物理参数包括气溶胶、冰核、云滴、雨滴、冰晶、雪晶、冰雹等粒子浓度和谱分布,以及云滴、雨滴含水量等。中国已有云-降水微物理参数的成果可归纳为:(1)通常云-降水微物理粒子浓度变化较大,但总体变化有一定的范围;(2)采用Γ函数拟合云滴谱更接近实际谱,但不同拟合谱参数差异较大;(3)可用指数函数和Γ函数来拟合层状云降水雨滴谱,Γ函数拟合积云和层积混合云降水雨滴谱精度更高;(4)中国冰核浓度较高,冰核浓度随温度的降低近似成指数变化;(5)冰晶谱、雪晶谱、冰雹谱通常采用指数函数来描述;(6)通常使用荣格(Junge)和Γ函数来分段描述气溶胶粒子谱拟合误差更小。由于云-降水过程及其反馈作用描述不准确是数值模式预报结果不确定性的最大因素,中国正在不断地推进云降水的微物理观测研究,以期进一步加深对东亚季风区云-降水微物理特征的认识,从而为模式中微物理参数化方案的改进提供观测依据和科学指导。基于数值预报模式中云微物理过程参数化发展的需要,总结了中国1960年以来云-降水微物理直接观测的研究成果,可为东亚地区云-降水微物理研究及其模式参数化方案的改进提供观测依据。此外,针对云微物理参化发展的需求,结合过去已有的大量观测提出了几点建议,为今后云-降水物理综合性观测方案的设计提供参考。 相似文献
20.
It is well known that the sum of the turbulent sensible and latent heat fluxes as measured by the eddy-covariance method is systematically lower than the available energy (i.e., the net radiation minus the ground heat flux). We examine the separate and joint effects of diurnal and spatial variations of surface temperature on this flux imbalance in a dry convective boundary layer using the Weather Research and Forecasting model. Results show that, over homogeneous surfaces, the flux due to turbulent-organized structures is responsible for the imbalance, whereas over heterogeneous surfaces, the flux due to mesoscale or secondary circulations is the main contributor to the imbalance. Over homogeneous surfaces, the flux imbalance in free convective conditions exhibits a clear diurnal cycle, showing that the flux-imbalance magnitude slowly decreases during the morning period and rapidly increases during the afternoon period. However, in shear convective conditions, the flux-imbalance magnitude is much smaller, but slightly increases with time. The flux imbalance over heterogeneous surfaces exhibits a diurnal cycle under both free and shear convective conditions, which is similar to that over homogeneous surfaces in free convective conditions, and is also consistent with the general trend in the global observations. The rapid increase in the flux-imbalance magnitude during the afternoon period is mainly caused by the afternoon decay of the turbulent kinetic energy (TKE). Interestingly, over heterogeneous surfaces, the flux imbalance is linearly related to the TKE and the difference between the potential temperature and surface temperature, ΔT; the larger the TKE and ΔT values, the smaller the flux-imbalance magnitude. 相似文献