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1.
The short-term tropical surface rainfall processes in rainfall regions (raining stratiform and convective regions) and rainfall-free regions (non-raining stratiform and clear-sky regions) are investigated based on the hourly data from a two-dimensional cloud-resolving model simulation. The model is integrated over a 21-day period with imposed zonally uniform vertical velocity, zonal wind, horizontal temperature and vapor advection, and sea surface temperature from the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE). The analysis of the model domain-mean surface rainfall budget reveals that surface rainfall is mainly associated with water vapor convergence and local atmospheric drying. The mean surface rainfall lags the mean water vapor convergence by 3?h. The convective?Cstratiform rainfall separation analysis shows that convective rainfall is associated with water vapor convergence, whereas stratiform rainfall is related to the local atmospheric drying and hydrometeor loss/convergence. The transport of water vapor from rainfall-free regions to rainfall regions creates the main water vapor source for rainfall while it balances local atmospheric drying in rainfall-free regions. Surface evaporation plays a minor role in short-term surface rainfall processes.  相似文献   

2.
In this study,two convective-stratiform rainfall partitioning schemes are evaluated using precipitation and cloud statistics for different rainfall types categorized by applying surface rainfall equation on grid-scale data from a two-dimensional cloud-resolving model simulation.One scheme is based on surface rainfall intensity whereas the other is based on cloud content information.The model is largely forced by the large-scale vertical velocity derived from the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment(TOGA COARE).The results reveal that over 40% of convective rainfall is associated with water vapor divergence,which primarily comes from the rainfall type with local atmospheric drying and water hydrometeor loss/convergence,caused by precipitation and evaporation of rain.More than 40% of stratiform rainfall is related to water vapor convergence,which largely comes from the rainfall type with local atmospheric moistening and hydrometeor loss/convergence attributable to water clouds through precipitation and the evaporation of rain and ice clouds through the conversion from ice hydrometeor to water hydrometeor.This implies that the separation methods based on surface rainfall and cloud content may not clearly separate convective and stratiform rainfall.  相似文献   

3.
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   

4.
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   

5.
Cloud microphysical and rainfall responses to radiative processes are examined through analysis of cloud-resolving model sensitivity experiments of Typhoon Fitow(2013) during landfall.The budget analysis shows that the increase in the mean rainfall caused by the exclusion of radiative effects of water clouds corresponds to the decrease in accretion of raindrops by cloud ice in the presence of radiative effects of ice clouds,but the rainfall is insensitive to radiative effects of water clouds in the absence of radiative effects of ice clouds.The increases in the mean rainfall resulting from the removal of radiative effects of ice clouds correspond to the enhanced net condensation.The increases(decreases) in maximum rainfall caused by the exclusion of radiative effects of water clouds in the presence(absence) of radiative effects of ice clouds,or the removal of radiative effects of ice clouds in the presence(absence) of radiative effects of water clouds,correspond mainly to the enhancements(reductions) in net condensation.The mean rain rate is a product of rain intensity and fractional rainfall coverage.The radiation-induced difference in the mean rain rate is related to the difference in rain intensity.The radiation-induced difference in the maximum rain rate is associated with the difference in the fractional coverage of maximum rainfall.  相似文献   

6.
The third algorithm intercomparison project （AIP-3） involved rain estimates from more than 50 satellite rainfall algorithms and ground radar measurements within the Intensive Flux Array （IFA） over the equatorial western Pacific warm pool region during the Tropical Ocean Global Atmosphere coupled Ocean-Atmosphere Response Experiment （TOGA COARE）. Early results indicated that there was a sys- tematic bias between rainrates from satellite passive microwave and ground radar measurements. The mean rainrate from radar measurements is about 50% underestimated compared to that from passive microwave-based retrieval algorithms. This paper is designed to analyze rain patterns from the Florida State University rain retrieval algorithm and radar measurements to understand physically the rain discrep- ancies. Results show that there is a clear range-dependent bias associated with the radar measurements. However, this range-dependent systematical bias is almost eliminated with the corrected radar rainrates. Results suggest that the effects from radar attenuation correction, calibration and beam filling are the major sources of rain discrepancies. This study demonstrates that rain retrievals based on satellite mea- surements from passive microwave radiometers such as the Special Sensor of Microwave Imager （SSM/I） are reliable, while rain estimates from ground radar measurements are correctable.  相似文献   

7.
The radiative and microphysical effects of ice clouds on a torrential rainfall event over Hunan,China in June 2004 are investigated by analyzing the sensitivity of cloud-resolving model simulations.The model is initialized by zonally-uniform vertical velocity,zonal wind,horizontal temperature and vapor advection from National Centers for Environmental Prediction(NCEP) /National Center for Atmospheric Research(NCAR) reanalysis data.The exclusion of radiative effects of ice clouds increases model domain mean surface rain rates through the increase in the mean net condensation associated with the increase in the mean radiative cooling during the onset phase and the increases in the mean net condensation and the mean hydrometeor loss during the mature phase.The decrease in the mean rain rate corresponds to the decreased mean net condensation and associated mean latent heat release as the enhanced mean radiative cooling by the removal of radiative effects of ice clouds cools the mean local atmosphere during the decay phase.The removal of microphysical effects of ice clouds decreases the mean rain rates through the decrease in the mean net condensation during the onset phase,while the evolution of mean net condensation and the mean hydrometeor changes from decrease to increase during the mature phase.The reduction in the mean rain rate is primarily associated with the mean hydrometeor change in the absence of microphysical effects of ice clouds during the decay phase.  相似文献   

8.
COOL AND FRESHWATER SKIN OF THE OCEAN DURING RAINFALL   总被引：2，自引：0，他引：2  
Rainfall over the sea modifies the molecular boundary layers of the upper ocean through a variety of different effects. These cover the freshwater flux stabilizing the near-surface layer, additional heat flux established due to rain versus surface temperature differences, modification of physical parameters by temperature and salinity changes, enhancement of the surface roughness, damping of short gravity waves, surface mixing by rain, and transfer of additional momentum from air to sea. They are separately described and included in our surface renewal model to investigate the rain's influence on the cool skin of the ocean and the creation of a haline molecular diffusion layer. Simulations with the upgraded model show that the most important effect on the conductive layer is that of reduced renewal periods followed by additional surface cooling due to rain on the order of 0.1 K. At rain rates below 50 mm h-1 rainfall is not able to completely destroy the mean temperature difference across the cool skin. A freshwater skin is created that exhibits a salinity difference exceeding 4 under strong rainfall. Comparisons with field data of the cool skin taken during the Coupled Ocean Atmosphere Response Experiment confirm the upgraded renewal model. Surface salinity measurements taken during the same field campaign are consistent with the calculated salinity differences across the freshwater skin. The enhancement of surface roughness by natural rain is less pronounced than described in earlier laboratory studies of rain with large drop sizes only.  相似文献   

9.
A new scheme that separates convective-stratiform rainfall is developed using threshold values of liquid water path (LWP) and ice water path (IWP). These cloud contents can be predicted with radiances at the Advanced Microwave Sounding Unit (AMSU) channels (23.8, 31.4, 89, and 150 GHz) through linear regression models. The scheme is demonstrated by an analysis of a two-dimensional cloud resolving model simulation that is imposed by a forcing derived from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The rainfall is considered convective if associated LWP is larger than 1.91 mm or IWP is larger than 1.70 mm. Otherwise, the rainfall is stratiform. The analysis of surface rainfall budget demonstrates that this new scheme is physically meaningful.  相似文献   

10.
Effects of time-dependent large-scale forcing (LSF), solar zenith angle (SZA), and sea surface temperature (SST) on time-mean rainfall processes during Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) are examined by conducting a control experiment and a series of sensitivity experiments with a two-dimensional cloud-resolving model. The model is forced by time-dependent LSF, SZA, and SST in the control experiment. The sensitivity experiments are forced only by either time-dependent LSF, or SZA, or SST while others are replaced with their time averages. When the model is imposed by time-dependent LSF, time dependence of SZA and SST has no discernable effect on surface rainfall, but it affects rainfall processes. The rainfall is reduced by 15% when the time-dependent LSF is replaced by its time mean. The reduction of rainfall is associated with the suppression of water vapor convergence as a result of low correlation between upward motion and water vapor variation.  相似文献   

11.
Effects of time-dependent large-scale forcing, solar zenith angle, and sea surface temperature on time-mean rainfall during the Tropical Ocean Global Atmosphere Coupled Ocean?CAtmosphere Response Experiment (TOGA COARE) are examined through a partitioning analysis of a series of sensitivity cloud-resolving model experiment data based on surface rainfall budget. The model is forced by time-dependent large-scale forcing (LSF), solar zenith angle (SZA), and sea surface temperature (SST) in the control experiment and is forced only by either time-dependent LSF, SZA, or SST while others are replaced with their time averages in the sensitivity experiments. The rainfall associated with water vapor divergence and local atmospheric drying and hydrometeor loss/convergence has the largest contribution to total rainfall among eight rainfall types. The largest rainfall contribution is increased in the simulations where either time-dependent LSF, SZA, or SST is replaced with its average, whereas it is decreased in the simulation where COARE-derived large-scale vertical velocity is replaced with zero vertical velocity. The contribution of the rainfall associated with water vapor convergence to total rainfall is decreased in the simulations with time-mean LSF, SZA, and SST, whereas it is increased in the simulation without large-scale vertical velocity.  相似文献   

12.
The surface rainfall processes and diurnal variations associated with tropical oceanic convection are examined by analyzing a surface rainfall equation and thermal budget based on hourly zonal-mean data from a series of two-dimensional cloud-resolving simulations. The model is integrated for 21 days with imposed large-scale vertical velocity, zonal wind, and horizontal advection obtained from the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) in the control experiment. Diurnal analysis shows that the infrared radiative cooling after sunset, as well as the advective cooling associated with imposed large-scale ascending motion, destabilize the atmosphere and release convective available potential energy to energize nocturnal convective development. Substantial local atmospheric drying is associated with the nocturnal rainfall peak in early morning, which is a result of the large condensation and deposition rates in the vapor budget. Sensitivity experiments show that diurnal variations of radiation and large-scale forcing can produce a nocturnal rainfall peak through infrared and advective cooling, respectively.  相似文献   

13.
The diurnal variation of tropical rainfall is examined through the analysis of an equilibrium cloud-resolving model experiment. Model domain mean rain rate is defined as a product of rain intensity and fractional rainfall coverage. The diurnal variation of the mean rain rate is associated with that of fractional rainfall coverage because the diurnal variation of rain intensity is significantly weakened through the decrease in rainfall in early morning hours. The decrease in rainfall corresponds to the reduction in secondary circulations through the barotropic conversion from the perturbation kinetic energy to the mean kinetic energy under the imposed negative vertical gradient of westerly winds. The fractional rainfall coverage shows the diurnal signal with the maximum in the early morning hours primarily due to nocturnal infrared radiative cooling.  相似文献   

14.
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   

15.
This study evaluates the spectral scaling of a heavy rainfall event and assesses the performance of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) model in terms of the multiscale variability of rainfall in the temporal spectral domain. The event occurred over southern Malay Peninsula on 18 December 2006 and was simulated at high resolutions. 10, 5 and 1?min aggregate rainfall data from rain gauge stations in Singapore and simulated rainfall sampled at different evaluation points on 0.9, 0.3 and 0.1?km grids were utilized. The simulated and observed rain rates were compared via Fourier and wavelet analyses. A scaling regime was noted in the observed rainfall spectra in the timescales between 60?min and 2?min. The scaling exponent obtained from the observed spectra has a value of about 2, which may be indicative of the physics of turbulence and raindrop coalescence and might suggest the predominance of a characteristic raindrop size. At 0.9?km resolution, the model rainfall spectra showed similar scaling to the observed down to about 10?min, below which a fall-off in variance was noted as compared to observations. Higher spatial resolution of up to 0.1?km was crucial to improve the ability of the model to resolve the shorter timescale variability. We suggest that the evaluation of dynamical models in the spectral domain is a crucial step in the validation of quantitative precipitation forecasts and assessing the minimal grid resolution necessary to capture rainfall variability for certain short timescales may be important for hydrological predictions.  相似文献   

16.
Summary Cloud microphysical properties in tropical convective and stratiform regions are examined based on hourly zonal-mean data from a two-dimensional cloud-resolving simulation. The model is integrated for 21 days with the imposed large-scale vertical velocity, zonal wind and horizontal advections obtained from Tropical Ocean Global Atmosphere Coupled Ocean-atmosphere Response Experiment (TOGA COARE). Time-mean cloud microphysical budgets are analyzed in raining stratiform regions, convective regions, and non-raining stratiform regions, respectively. In raining stratiform regions, ice water path (IWP) and liquid water path (LWP) have similar magnitudes. The collection process contributes slightly more to the growth of raindrops than the melting processes do, and surface rain rate is higher than the raindrop-related microphysical rate, indicating that the hydrometeor convergence from the convective regions plays a role in surface rainfall processes. In convective regions, IWP is much smaller than LWP, the collection process is dominant in producing raindrops, and surface rain rate is lower than the raindrop-related microphysical rate. In non-raining stratiform regions, IWP is much larger than LWP, and the melting processes are important in maintaining the raindrop budget. The statistical analysis of hourly data suggests that the slopes of linear regression equations between IWP and LWP in three regions are different. Rain producing processes in convective regions are associated with the water cloud processes regardless of convection intensity.  相似文献   

17.
The authors examine the Indian Ocean sea surface temperature(SST) biases simulated by a Flexible Regional Ocean Atmosphere Land System(FROALS) model.The regional coupled model exhibits pronounced cold SST biases in a large portion of the Indian Ocean warm pool.Negative biases in the net surface heat fluxes are evident in the model,leading to the cold biases of the SST.Further analysis indicates that the negative biases in the net surface heat fluxes are mainly contributed by the biases of sensible heat and latent heat flux.Near-surface meteorological variables that could contribute to the SST biases are also examined.It is found that the biases of sensible heat and latent heat flux are caused by the colder and dryer near-surface air in the model.  相似文献   

18.
利用CAM5.1大气环流模式研究中国东部大规模城市化对东亚夏季大气环流及降水分布的影响。通过在模式中修改中国东部地区(22～42°N,110～125°E)城市比重的方法,探讨东亚地区夏季大气环流与降水等气象要素在一般城市化及极端城市化两种情景下的响应。结果表明:(1)CAM5.1模式能够很好地模拟出东亚地区夏季大气环流形势及降水分布。(2)城市比重增大后,晴空时地面吸收的净辐射增多,近地层气温升高,低层增温中心上空的大气由于受热产生上升运动,35°N以南的气流向增温区辐合,东亚夏季风出现增强的趋势,大量暖湿水汽往北输送,导致降水在中国北方地区增多而南方减少。(3)城市化的发展程度越高,它所产生的气候效应对各气象要素的影响就表现得越明显。  相似文献   

19.
Summary The NOAA Aeronomy Laboratory has developed a 915 MHz lower tropospheric wind profiler designed primarily for measuring wind in the planetary boundary layer of the tropics. In recent years the profiler has been used in many field programs worldwide. The profiler is being deployed by the Aeronomy Laboratory at several locations in the tropics to provide long-term measurements for the Tropical Ocean Global Atmosphere (TOGA) program and the Global Ocean Atmosphere Land Surface (GOALS) program. In the absence of precipitating cloud systems the profiler observes winds routinely up to altitudes of 3 to 6 km in the tropics depending primarily on humidity. In the presence of precipitating cloud systems, however, the profiler height coverage is substantially increased due to the presence of hydrometeors to which the profiler is sensitive at its wavelength of 33 cm. In this paper we examine the application of the 915 MHz profiler to the diagnosis and classification of precipitating cloud systems in the tropics. Preliminary results from Christmas Island confirm that at least half of tropical rainfall is stratiform in nature being associated with mesoscale convective systems. The 915 MHz profiler provides a means for the development of a climatology of tropical precipitating cloud systems. Such a climatology is needed to specify diabatic heating rates in large-scale numerical weather prediction and climate models. It should also help develop improved rain retrieval algorithms from satellite observations.With 10 Figures  相似文献   

20.
In this study,the application of artificial intelligence to monthly and seasonal rainfall forecasting in Queensland,Australia,was assessed by inputting recognized climate indices,monthly historical rainfall data,and atmospheric temperatures into a prototype stand-alone,dynamic,recurrent,time-delay,artificial neural network.Outputs,as monthly rainfall forecasts 3 months in advance for the period 1993 to 2009,were compared with observed rainfall data using time-series plots,root mean squared error(RMSE),and Pearson correlation coefficients.A comparison of RMSE values with forecasts generated by the Australian Bureau of Meteorology’s Predictive Ocean Atmosphere Model for Australia(POAMA)-1.5 general circulation model(GCM) indicated that the prototype achieved a lower RMSE for 16 of the 17 sites compared.The application of artificial neural networks to rainfall forecasting was reviewed.The prototype design is considered preliminary,with potential for significant improvement such as inclusion of output from GCMs and experimentation with other input attributes.  相似文献   

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