A Modified Kain–Fritsch Scheme and Its Application for the Simulation of an Extreme Precipitation Event in Vietnam

2009 ◽  
Vol 137 (2) ◽  
pp. 766-789 ◽  
Author(s):  
Nguyen Minh Truong ◽  
Tran Tan Tien ◽  
Roger A. Pielke ◽  
Christopher L. Castro ◽  
Giovanni Leoncini

Abstract From 24 to 26 November 2004, an extreme heavy rainfall event occurred in the mountainous provinces of central Vietnam, resulting in severe flooding along local rivers. The Regional Atmospheric Modeling System, version 4.4, is used to simulate this event. In the present study, the convective parameterization scheme includes the original Kain–Fritsch scheme and a modified one in which a new diagnostic equation to compute updraft velocity, closure assumption, and trigger function are developed. These modifications take the vertical gradient of the Exner function perturbation into account, with an on–off coefficient to account for the role of the advective terms. According to the event simulations, the simulated precipitation shows that the modified scheme with the new trigger function gives much better results than the original one. Moreover, the interaction between convection and the larger-scale environment is much stronger near the midtroposphere where the return flow associated with lower-level winter monsoon originates. As a result, the modified scheme produces larger and deeper stratiform clouds and leads to a significant amount of resolvable precipitation. On the contrary, the resolvable precipitation is small when the original scheme is used. The improvement in the simulated precipitation is caused by a more explicit physical mechanism of the new trigger function and suggests that the trigger function needs to be developed along with other components of the scheme, such as closure assumption and cloud model, as a whole. The formalistic inclusion of the advective terms in the new equation gives almost no additional improvement of the simulated precipitation.

2014 ◽  
Vol 2014 ◽  
pp. 1-17 ◽  
Author(s):  
Nathan Hosannah ◽  
Jorge E. Gonzalez

Urban environments influence precipitation formation via response to dynamic effects, while aerosols are intrinsically necessary for rainfall formation; however, the partial contributions of each on urban coastal precipitation are not yet known. Here, the authors use aerosol particle size distributions derived from the NASA aerosol robotic network (AERONET) to estimate submicron cloud condensation nuclei (CCN) and supermicron CCN (GCCN) for ingestion in the regional atmospheric modeling system (RAMS). High resolution land data from the National Land Cover Database (NLCD) were assimilated into RAMS to provide modern land cover and land use (LCLU). The first two of eight total simulations were month long runs for July 2007, one with constant PSD values and the second with AERONET PSDs updated at times consistent with observations. The third and fourth runs mirrored the first two simulations for “No City” LCLU. Four more runs addressed a one-day precipitation event under City and No City LCLU, and two different PSD conditions. Results suggest that LCLU provides the dominant forcing for urban precipitation, affecting precipitation rates, rainfall amounts, and spatial precipitation patterns. PSD then acts to modify cloud physics. Also, precipitation forecasting was significantly improved under observed PSD and current LCLU conditions.


2014 ◽  
Vol 18 (9) ◽  
pp. 3711-3732 ◽  
Author(s):  
A. T. Woldemichael ◽  
F. Hossain ◽  
R. Pielke Sr.

Abstract. This study adopted a differential land-use/land-cover (LULC) analysis to evaluate dam-triggered land–atmosphere interactions for a number of LULC scenarios. Two specific questions were addressed: (1) can dam-triggered LULC heterogeneities modify surface and energy budget, which, in turn, change regional convergence and precipitation patterns? (2) How extensive is the modification in surface moisture and energy budget altered by dam-triggered LULC changes occurring in different climate and terrain features? The Regional Atmospheric Modeling System (RAMS, version 6.0) was set up for two climatologically and topographically contrasting regions: the American River watershed (ARW), located in California, and the Owyhee River watershed (ORW), located in eastern Oregon. For the selected atmospheric river precipitation event of 29 December 1996 to 3 January 1997, simulations of three pre-defined LULC scenarios are performed. The definition of the scenarios are (1) the "control" scenario, representing the contemporary land use, (2) the "pre-dam" scenario, representing the natural landscape before the construction of the dams and (3) the "non-irrigation" scenario, representing the condition where previously irrigated landscape in the control is transformed to the nearby land-use type. Results indicated that the ARW energy and moisture fluxes were more extensively affected by dam-induced changes in LULC than the ORW. Both regions, however, displayed commonalities in the modification of land–atmosphere processes due to LULC changes, with the control–non-irrigation scenario creating more change than the control–pre-dam scenarios. These commonalities were: (1) the combination of a decrease in temperature (up to 0.15 °C) and an increase at dew point (up to 0.25 °C) was observed; (2) there was a larger fraction of energy partitioned to latent heat flux (up to 10 W m−2) that increased the amount of water vapor in the atmosphere and resulted in a larger convective available potential energy (CAPE); (3) low-level wind-flow variation was found to be responsible for pressure gradients that affected localized circulations, moisture advection and convergence. At some locations, an increase in wind speed up to 1.6 m s−1 maximum was observed; (4) there were also areas of well-developed vertical motions responsible for moisture transport from the surface to higher altitudes that enhanced precipitation patterns in the study regions.


2017 ◽  
Vol 56 (8) ◽  
pp. 2141-2153 ◽  
Author(s):  
Paul E. Schmid ◽  
Dev Niyogi

AbstractThis study introduces a methodology to simulate how spatially heterogeneous urban aerosols modify a precipitating thunderstorm in a numerical weather model. An air quality model (simple photochemical model) was coupled with a high-resolution mesoscale weather model (the Regional Atmospheric Modeling System) and generated variable urban cloud condensation nuclei values consistent with those measured in previous field studies. The coupled emission model was used to simulate the passage of a synoptic low pressure system with embedded thunderstorms over an idealized city using the real-atmosphere idealized land surface (RAIL) method. Experiments were conducted to calibrate the surface formation of cloud-nucleating aerosols in an urban environment and then to assess the specific response of different aerosol loads on simulated precipitation. The model response to aerosol heterogeneity reduced the total precipitation but significantly increased simulated rain rates. High-aerosol-loading scenarios produced a peak city-edge precipitation rate of over 100 mm h−1 greater than a control containing only a city land surface with no emissions. In comparing the control with a scenario with no city, it was seen that the land surface effect produced a rain rate increase of up to 20 mm h−1. Results indicate, within the limits of the model framework, that the urban rainfall modification is a combination of land heterogeneity causing the dynamical lifting of the air mass and aerosols, with rainfall enhancement being maintained and synergistically increased because of the aerosol indirect effects on cloud properties.


2020 ◽  
Author(s):  
Pei-Hsin Liu ◽  
Jen-Ping Chen ◽  
Xiquan Dong ◽  
Yi-Chiu Lin

<p>Arctic stratiform clouds (ASC) often exhibit phase inversion structure (i.e., liquid top and mixed- or ice-phase below) and can persist for a very long time. According to past studies, the phase inversion structure is the result of persistent liquid cloud generation aloft and gravitational ice precipitation; however, observation reveals that the largest cloud reflectivity appears in the middle of the cloud, implying that the gravitational ice precipitation cannot fully explain the mechanism of phase inversion structure. Also, the role of ice nucleation in ASC is not fully addressed before. Ice nucleation processes are affected by temperature, ice nuclei (IN) species and number concentration. As the result, strong inversion or strong vertical gradient of IN number concentration may favor ice nucleation to occur in the lower levels and result in phase inversion.</p><p>This study aims to find out the mechanism of phase inversion and the dominant ice nucleation processes in ASC. Weather Research and Forecasting (WRF) model with detailed ice nucleation mechanisms is applied. The ice nucleation scheme used in the model takes different ice nucleation processes and IN species into account. Dust and soot, taken from MERRA-2, are the two main IN considered in this study and are fitted into lognormal distributions for providing the initial and boundary conditions. The 2008 Mar 04-05 case, chosen from the Atmospheric Radiation Measurement (ARM) program, is simulated. From observation, ASC and the phase inversion structure persisted for half a day. Temperature decreases with height in cloud, indicating that temperature inversion is not the mechanism of phase inversion in this case. More dust in the lower levels is seen from the model simulation results. In this case, strong vertical gradient of IN number concentration serves as the main mechanism of phase inversion, suggesting that ice nucleation process plays an important role in ASC. The role of soot particles will also be addressed.</p>


2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
B. H. Vaid

The Numerical Simulations of the June 16, 2010, Heavy Rainfall Event over Singapore are highlighted by an unprecedented precipitation which produced widespread, massive flooding in and around Singapore. The objective of this study is to check the ability of Weather Research Forecasting version 3 (WRFV3) model to predict the heavy rain event over Singapore. Results suggest that simulated precipitation amounts are sensitive to the choice of cumulus parameterization. Various model configurations with initial and boundary conditions from the NCEP Final Global Analysis (FNL), convective and microphysical process parameterizations, and nested-grid interactions have been tested with 48-hour (June 15–17, 2010) integrations of the WRFV3. The spatial distributions of large-scale circulation and dynamical and thermodynamical fields have been simulated reasonably well in the model. The model produced maximum precipitation of ~5 cm over Changi airport which is very near to observation (6.4 cm recorded at Changi airport). The model simulated dynamic and thermodynamic features at 00UTC of June 16, 2010, lead to understand the structure of the mesoscale convective system (MCS) that caused the extreme precipitation over Singapore. It is observed that Singapore heavy rain was the result of an interaction of synoptic-scale weather systems with the mesoscale features.


2014 ◽  
Vol 71 (9) ◽  
pp. 3223-3249 ◽  
Author(s):  
Michael D. Toy ◽  
Richard H. Johnson

Abstract A long-lived heavy precipitation area was observed along the southwest coast of Taiwan from 13 to 18 June 2008 during the Terrain-Influenced Monsoon Rainfall Experiment (TiMREX). Rainfall amounts exceeded 500 mm along portions of the coast, and the coastal plains experienced severe flooding. The precipitation systems were influenced by blocking effects, as the southerly moist monsoon flow impinged on the island. A relatively strong gradient in the sea surface temperature (SST) off the southwest coast of Taiwan existed during the rainfall event. Mesoscale SST fronts are known to influence the planetary boundary layer (PBL) such that low-level convergence and precipitation are enhanced under certain circumstances. In this study, the authors investigate the role of the SST front in enhancing the 13–18 June 2008 precipitation event over Taiwan using the Weather Research and Forecasting (WRF) Model. In control simulations with the observed SST, there is a transition from a well-mixed to a stable PBL across the front, causing the low-level flow to decelerate, resulting in an enhancement of horizontal convergence. Such a transition in the PBL and the associated convergence is greatly reduced in smoothed SST gradient model simulations, which produce over 20% less precipitation over southwest Taiwan. Sensitivity tests show that, qualitatively, the results are independent of the existence of the island of Taiwan. These findings indicate that the SST gradient over the northern South China Sea during the early summer monsoon can have a significant impact on the intensity of rainfall over Taiwan.


2016 ◽  
Vol 9 (2) ◽  
pp. 368
Author(s):  
Ricardo Antonio Mollmann Junior ◽  
Rita De Cassia Marques Alves ◽  
Gabriel Bonow Muchow ◽  
Bruno Dias Rodrigues ◽  
Rosiberto Salustiano da Silva Junior ◽  
...  

O objetivo do presente do estudo foi observar a sensibilidade das parametrizações do modelo WRF ao quantificar as variáveis em superfície: pressão atmosférica, temperatura do ar, umidade relativa e precipitação durante o Inverno de 2014 no Estado do Rio Grande do Sul (RS). Os resultados foram demonstrados a partir de análise dos índices estatísticos, bias e Raiz do Erro Quadrático Médio (REQM), quando calculados para comparações entre os dados extraídos de 6 experimentos de simulações do modelo WRF com dados de estações de monitoramento do Instituto Nacional de Meteorologia (INMET) no RS. Os experimentos foram configurados com diferentes parametrização físicas, para assim poder verificar qual combinação apresenta melhor desempenho na representação das condições de Inverno do RS. A partir do reconhecimento das diferentes interpretações físicas que cada conjunto de parametrização pode representar, foi apresentado um estudo de caso afim de diagnosticar as precipitações ocorridas no Estado, principalmente no município de Irai-RS. As análises partiu de um acompanhamento de evento de chuvas ocorrido entre os dias 25 e 30 de junho de 2014, utilizando-se de cartas dos campos meteorológicos de Linhas de Corrente em 850hPa e Precipitação. Percebeu-se que tanto temperatura quanto pressão, o bias e o REQM obtiveram diferenças não significativas entre os experimentos. A UR, no cálculo do bias mostrou uma grande diferença entre os experimentos, devido a forma de seu cálculo considerar apenas o erros sistemáticos, podendo haver cancelamento de erros entre subestimativas e superestimativas. A REQM para a mesma variável, mostrou que os experimentos não se diferenciaram em valores significativos, obtendo apenas nos experimentos 3 e 5, menor valor de erro em comparação aos outros experimentos (~2%). Ao tecer considerações sobre a precipitação, o bias diagnosticou subestimativas nos experimentos para as chuvas durante o inverno de 2014, entretanto no cálculo da REQM os experimentos não tiveram assentimento entre si, exceto o 4 e o 6, onde os valores dos erros totais ficaram inferiores à 2mm. Para o estudo de caso, onde foi acompanhado as chuvas ocorridas durante a passagem de um fenômeno Ciclone Extratropical, em todos os experimentos mostrou a caracterização do evento de precipitação. Com isso, ao diagnosticar a quantidade de precipitação durante o evento ocorrido sobre a estação meteorológica de Irai-RS com os dados do modelo, somado as análises estatísticas, o experimento 6 dentre as combinações de parametrizações apresentadas neste estudo, obteve o melhor desempenho para caracterizar o estado atmosférico durante o período de inverno no RS.   ABSTRACT The objective of this study is to observe the sensitivity of parameterizations of the WRF model to quantify the variables in surface: atmospheric pressure, air temperature, relative humidity and precipitation during the winter of 2014 in the State of Rio Grande do Sul (RS).  The results were demonstrated from analysis of statistical indices, bias and Mean Squared Error root (RMSE) calculated for comparisons between the data extracted from 6 experiments of the WRF model simulations with data from the National Institute of Meteorology monitoring stations (INMET) in RS. The experiments were configuring with different physical parameterization, so that it may examine what combination performs better in the representation of the RS winter conditions. From the recognition of different physical interpretations that each set of parameterization can represent, a case study was made in order to diagnose the precipitations that occurred in the State, mainly in the municipality of Irai. The analysis came from a monitoring rain event occurred between 25 and 30 June 2014, using meteorological fields of 850hPa stream lines and rainfall. However, realizes that both temperature as pressure, the bias and the RMSE obtained no significant differences between experiments. UR, in the calculation of bias showed a big difference between the experiments, because of the manner of calculation only considers the systematic errors, which may cause cancellation of errors between underestimation and overestimation. The RMSE for the same variable showed no differences in significant amounts in the experiments, only in experiments 3 and 5, smallest error value when compared to the other experiments (~ 2%). To develop some considerations on the precipitation, the bias diagnosed underestimates the experiments for the rains during the winter of 2014; however, in the calculation of RMSE the experiments had not consent to each other, except 4 and 6, where the values of total errors were lower to 2mm. For the case study, which was accompanied rainfall occurred during the passage of an extratropical cyclone, in all experiments showed the characterization of the precipitation event. Thus, to diagnose the amount of precipitation during the event occurring on the Irai weather station with model data, combined with statistical analysis, the experiment 6 from the parameterization of combinations shown in this study had the best performance to characterize the atmospheric state during the winter period in the RS. Keywords: Weather numerical forecast, WRF, physical parameterization, atmospheric modeling.   


2014 ◽  
Vol 11 (5) ◽  
pp. 5037-5075 ◽  
Author(s):  
A. T. Woldemichael ◽  
F. Hossain ◽  
R. Pielke

Abstract. This study adopted a differential land-use/land-cover (LULC) analysis to evaluate dam-triggered land–atmosphere interactions for a number of LULC scenarios. Two specific questions were addressed: (1) can dam-triggered LULC heterogeneities modify surface and energy budget which, in turn, change regional convergence and precipitation patterns? and (2) how extensive is the modification in surface moisture and energy budget altered by dam-triggered LULC changes occurring in different climate and terrain features? The Regional Atmospheric Modeling System (RAMS, version 6.0) was set up for two climatologically and topographically contrasting regions: the American River Watershed (ARW) located in California and the Owyhee River Watershed (ORW) located in eastern Oregon. For the selected atmospheric river precipitation event of 29 December 1996 to 3 January 1997, simulations of three pre-defined LULC scenarios are performed. The definition of the scenarios are: (1) the control scenario representing the contemporary land-use, (2) the pre-dam scenario representing the natural landscape before the construction of the dams and (3) the non-irrigation scenario representing the condition where previously irrigated landscape in the control is transformed to the nearby land-use type. Results indicated that the ARW energy and moisture fluxes were more extensively affected by dam-induced changes in LULC than the ORW. Both regions, however, displayed commonalities in the modification of land–atmosphere processes due to LULC changes, with the control–non-irrigation scenario creating more change than the control–pre-dam scenarios. These commonalities were: (1) the combination of a decrease in temperature (up to 0.15 °C) and an increase in dewpoint (up to 0.25 °C) was observed, (2) there was a larger fraction of energy partitioned to latent heat flux (up to 10 W m−2) that increased the amount of water vapor to the atmosphere and resulted in a larger convective available potential energy (CAPE), (3) low level wind flow variation was found to be responsible for pressure gradients that affected localized circulations, moisture advection and convergence. At some locations, an increase in wind speed up to 1.6 m s−1 maximum was observed, (4) there were also areas of well developed vertical motions responsible for moisture transport from the surface to higher altitudes that enhanced precipitation patterns in the study regions.


2009 ◽  
Vol 66 (6) ◽  
pp. 1489-1506 ◽  
Author(s):  
Roel A. J. Neggers

Abstract This paper presents the extension of the eddy diffusivity mass flux (EDMF) framework for turbulent transport into the statistical modeling of boundary layer clouds. The advection–diffusion decomposition that defines EDMF is projected onto the turbulent distribution as used in the statistical cloud model. Each EDMF component is thus assigned its own independent probability density function (PDF), resulting in an updraft PDF and a diffusive PDF. This double PDF system is configured and integrated in conserved variable space, with the position and orientation of each PDF determined by its unique nature. The parameterization of the associated updraft/diffusion decomposition of variance introduces close ties to the transport scheme; whereas the grid box mean variance is reconstructed using a prognostic variance budget, the variance of the updraft component is parameterized as a function of the spread among various resolved model updrafts. Individual model components and the scheme as a whole are evaluated in detail against large-eddy simulations of a number of prototype subtropical trade wind cases. The results show that various structures in cloud fraction, condensate, and variance are reproduced. The diffusive PDF acts to represent stratiform clouds; the advective PDF represents cumuliform clouds in conditionally unstable layers. This allows representation of complex scenarios in which both cloud forms occur, such as the transitional trade wind regime featuring cumulus rising into stratocumulus.


2008 ◽  
Vol 25 (8) ◽  
pp. 1469-1476 ◽  
Author(s):  
Edwin F. Campos ◽  
Wayne Hocking ◽  
Frédéric Fabry

Abstract Using radar observations to quantify precipitation intensity requires the intervention of the radar equation, which converts the precipitation signal into reflectivity units. This equation generally assumes that the reflectivity is uniform within each sampling gate and that the sidelobes of the antenna pattern are negligible. The purpose here is to provide a more realistic approach that eliminates these assumptions when computing profiles of precipitation intensity (by using a height-variable reflectivity and antenna pattern of significant sidelobes to compute profiles of a radar reflectivity factor). To achieve this, simultaneous observations of collocated vertically pointing radars operating in the VHF and X bands were obtained. Raindrop measurements were used to correct for attenuation in the precipitation signal at the X band. Then the precipitation signal in the VHF radar was simulated by combining this X-band signal and the VHF antenna pattern into a general version of the radar equation. The simulated precipitation signal at VHF compares well with actual measurements of the rain signal (range gates centered at 2.5, 3.0, and 3.5 km) by the VHF radar, and this validates the analysis methods. In conclusion, the analysis indicates that VHF reflectivity at gates above the melting layer is artificially enhanced by the precipitation signal collected in the sidelobe direction. Similar enhancement will be expected wherever there is a strong vertical gradient of reflectivity (i.e., on the order of 10 dB km−1 or larger).


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