Implementation of the Unified Representation of Deep Moist Convection in the CWBGFS

2021 ◽  
Vol 149 (10) ◽  
pp. 3525-3539
Author(s):  
Chun-Yian Su ◽  
Chien-Ming Wu ◽  
Wei-Ting Chen ◽  
Jen-Her Chen
Keyword(s):  
Multiple Scales ◽  
Horizontal Resolution ◽  
Cumulus Parameterization ◽  
Moist Convection ◽  
Short Term ◽  
Local Circulation ◽  
Convective Systems ◽  
Simulated Precipitation ◽  
Deep Moist Convection ◽  
Central Weather Bureau

AbstractThis study implements the unified parameterization (UP) in the Central Weather Bureau Global Forecast System (CWBGFS) based on the relaxed Arakawa–Schubert scheme (RAS) at a horizontal resolution of 15 km. The new cumulus parameterization that incorporates the UP framework is called URAS. The UP generalizes the representation of moist convection between the parameterized and the explicitly resolved processes according to the process-dependent convective updraft fraction (σ). Short-term hindcasts are performed to investigate the impacts of the UP on the simulated precipitation variability and organized convective systems over the Maritime Continent when multiple scales of convection occurred. The result shows that σ is generally larger when convective systems develop, which adaptively reduces the parameterized convection and increases the spatial variation of moisture. In the URAS experiment, the moisture hotspots within organized convective systems contribute to the enhanced local circulation and the more significant variability of precipitation. Consequently, the URAS has a more realistic precipitation spectrum, an improved relationship between the maximum precipitation and the horizontal scale of the convective systems, and an improved column water vapor–precipitation relationship.

A Unified Representation of Deep Moist Convection in Numerical Modeling of the Atmosphere. Part I

2013 ◽  
Vol 70 (7) ◽  
pp. 1977-1992 ◽  
Author(s):  
Akio Arakawa ◽  
Chien-Ming Wu
Keyword(s):  
General Circulation ◽  
Thermal Structure ◽  
Quadratic Function ◽  
Grid Cell ◽  
Horizontal Resolution ◽  
Smooth Transition ◽  
Cumulus Parameterization ◽  
Moist Convection ◽  
Eddy Transport ◽  
Deep Moist Convection

Abstract A generalized framework for cumulus parameterization applicable to any horizontal resolution between those typically used in general circulation and cloud-resolving models is presented. It is pointed out that the key parameter in the generalization is σ, which is the fractional area covered by convective updrafts in the grid cell. Practically all conventional cumulus parameterizations assume σ ≪ 1, at least implicitly, using the gridpoint values of the thermodynamic variables to define the thermal structure of the cloud environment. The proposed framework, called “unified parameterization,” eliminates this assumption from the beginning, allowing a smooth transition to an explicit simulation of cloud-scale processes as the resolution increases. If clouds and the environment are horizontally homogeneous with a top-hat profile, as is widely assumed in the conventional parameterizations, it is shown that the σ dependence of the eddy transport is through a simple quadratic function. Together with a properly chosen closure, the unified parameterization determines σ for each realization of grid-scale processes. The parameterization can also provide a framework for including stochastic parameterization. The remaining issues include parameterization of the in-cloud eddy transport because of the inhomogeneous structure of clouds.

Mesoscale Convective Vortices in Multiscale, Idealized Simulations: Dependence on Background State, Interdependency with Moist Baroclinic Cyclones, and Comparison with BAMEX Observations

2010 ◽  
Vol 138 (4) ◽  
pp. 1119-1139 ◽  
Author(s):  
Robert J. Conzemius ◽  
Michael T. Montgomery
Keyword(s):  
Tangential Velocity ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Pressure Amplitude ◽  
Moist Convection ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Common Center ◽  
Deep Moist Convection ◽  
Convective Vortices

Abstract A set of multiscale, nested, idealized numerical simulations of mesoscale convective systems (MCSs) and mesoscale convective vortices (MCVs) was conducted. The purpose of these simulations was to investigate the dependence of MCV development and evolution on background conditions and to explore the relationship between MCVs and larger, moist baroclinic cyclones. In all experiments, no mesoscale convective system (MCS) developed until a larger-scale, moist baroclinic system with surface pressure amplitude of at least 2 hPa was present. The convective system then enhanced the development of the moist baroclinic system by its diabatic production of eddy available potential energy (APE), which led to the enhanced baroclinic conversion of basic-state APE to eddy APE. The most rapid potential vorticity (PV) development occurred in and just behind the leading convective line. The entire system grew upscale with time as the newly created PV rotated cyclonically around a common center as the leading convective line continued to expand outward. Ten hours after the initiation of deep moist convection, the simulated MCV radii, heights of maximum winds, tangential velocity, and shear corresponded reasonably well to their counterparts in BAMEX. The increasing strength of the simulated MCVs with respect to larger values of background CAPE and shear supports the hypothesis that as long as convection is present, CAPE and shear both add to the strength of the MCV.

scholarly journals Simulation of the Summer Monsoon Rainfall over East Asia Using the NCEP GFS Cumulus Parameterization at Different Horizontal Resolutions

2014 ◽  
Vol 29 (5) ◽  
pp. 1143-1154 ◽  
Author(s):  
Kyo-Sun Sunny Lim ◽  
Song-You Hong ◽  
Jin-Ho Yoon ◽  
Jongil Han
Keyword(s):  
Summer Monsoon ◽  
Monsoon Rainfall ◽  
Asian Summer Monsoon ◽  
Monsoon Season ◽  
Wrf Model ◽  
Horizontal Resolution ◽  
Cumulus Parameterization ◽  
Grid Spacing ◽  
Simulated Precipitation ◽  
Horizontal Grid

Abstract The most recent version of the simplified Arakawa–Schubert (SAS) cumulus scheme in the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) (GFS SAS) is implemented in the Weather Research and Forecasting (WRF) Model with a modification of the triggering condition and the convective mass flux in order to make it dependent on the model’s horizontal grid spacing. The East Asian summer monsoon season of 2006 is selected in order to evaluate the performance of the modified GFS SAS scheme. In comparison to the original GFS SAS scheme, the modified GFS SAS scheme shows overall better agreement with the observations in terms of the simulated monsoon rainfall. The simulated precipitation from the original GFS SAS scheme is insensitive to the model’s horizontal grid spacing, which is counterintuitive because the portion of the resolved clouds in a grid box should increase as the model grid spacing decreases. This behavior of the original GFS SAS scheme is alleviated by the modified GFS SAS scheme. In addition, three different cumulus schemes (Grell and Freitas, Kain and Fritsch, and Betts–Miller–Janjić) are chosen to investigate the role of a horizontal resolution on the simulated monsoon rainfall. Although the forecast skill of the surface rainfall does not always improve as the spatial resolution increases, the improvement of the probability density function of the rain rate with the smaller grid spacing is robust regardless of the cumulus parameterization scheme.

scholarly journals Atmospheric CO2 budget over the Amazon basin: the role of convective systems

2011 ◽  
Vol 26 (4) ◽  
pp. 529-540
Author(s):  
Valdir Herrmann ◽  
Saulo Ribeiro de Freitas
Keyword(s):  
Amazon Basin ◽  
Transport Model ◽  
Conservation Equation ◽  
Atmospheric Modeling ◽  
Convective Transport ◽  
Atmospheric Co2 ◽  
Moist Convection ◽  
Convective Systems ◽  
Deep Moist Convection

This work studies the atmospheric CO2 budget in the Amazon basin, focusing on the role of shallow and deep convective systems. The vertical redistribution of CO2 is numerically simulated using an Eulerian transport model coupled to the Brazilian developments on the Regional Atmospheric Modeling System (BRAMS). The transport model includes grid-scale advection, diffusion in the PBL (Planetary Boundary Layer) and convective transport by sub-grid shallow and deep moist convection. In the simulation, the mass conservation equation is solved for six tracers, including or not the shallow and deep moist convection terms. The rectifier effect is also showed through simulation of the transport to the free troposphere of PBL air masses with low CO2 concentrations due to assimilation by vegetation during the afternoon, when both CO2 fixation and convection are at their peak. The model is applied to simulate July 2001 with a 30 km grid resolution covering the northwest part of South America. We compare the model results with airborne CO2 observations collected in the Amazon basin during the 2001 CLAIRE field campaign.

A High-Resolution Modeling Study of the 24 May 2002 Dryline Case during IHOP. Part I: Numerical Simulation and General Evolution of the Dryline and Convection

2006 ◽  
Vol 134 (1) ◽  
pp. 149-171 ◽  
Author(s):  
Ming Xue ◽  
William J. Martin
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
High Resolution ◽  
Companion Paper ◽  
Horizontal Resolution ◽  
Initial Condition ◽  
Moist Convection ◽  
Convective Initiation ◽  
Deep Moist Convection ◽  
Localized Forcing

Abstract Results from a high-resolution numerical simulation of the 24 May 2002 dryline convective initiation (CI) case are presented. The simulation uses a 400 km × 700 km domain with a 1-km horizontal resolution grid nested inside a 3-km domain and starts from an assimilated initial condition at 1800 UTC. Routine as well as special upper-air and surface observations collected during the International H2O Project (IHOP_2002) are assimilated into the initial condition. The initiation of convective storms at around 2015 UTC along a section of the dryline south of the Texas panhandle is correctly predicted, as is the noninitiation of convection at a cold-front–dryline intersection (triple point) located farther north. The timing and location of predicted CI are accurate to within 20 min and 25 km, respectively. The general evolution of the predicted convective line up to 6 h of model time also verifies well. Mesoscale convergence associated with the confluent flow around the dryline is shown to produce an upward moisture bulge, while surface heating and boundary layer mixing are responsible for the general deepening of the boundary layer. These processes produce favorable conditions for convection but the actual triggering of deep moist convection at specific locations along the dryline depends on localized forcing. Interaction of the primary dryline convergence boundary with horizontal convective rolls on its west side provides such localized forcing, while convective eddies on the immediate east side are suppressed by a downward mesoscale dryline circulation. A companion paper analyzes in detail the exact processes of convective initiation along this dryline.

scholarly journals Environment Associated with Deep Moist Convection under SALLJ Conditions: A Case Study

2010 ◽  
Vol 25 (3) ◽  
pp. 970-984 ◽  
Author(s):  
Paloma Borque ◽  
Paola Salio ◽  
Matilde Nicolini ◽  
Yanina García Skabar
Keyword(s):  
Frontal Zone ◽  
Mesoscale Convective Systems ◽  
South American ◽  
Moist Convection ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Low Level Jet ◽  
Deep Moist Convection

Abstract The present work focuses on the study of the environmental conditions preceding the development of a group of subtropical mesoscale convective systems over central and northern Argentina on 6–7 February 2003 during the South American Low Level Jet Experiment. This period was characterized by an extreme northerly low-level flow along the eastern Andes foothills [South American low-level jet (SALLJ)]. The entire studied episode was dominated by the presence of a very unstable air mass over northern Argentina and a frontal zone near 40°S. The SALLJ generated an important destabilization of the atmosphere due to the strong humidity and differential temperature advection. Orography provided an extra lifting motion to the configuration of the regional wind field, which was efficient in forcing the initiation of convection. Once convection developed, it moved and regenerated in regions where the convective instability was horizontally homogeneous and stronger.

The Use of Moisture Flux Convergence in Forecasting Convective Initiation: Historical and Operational Perspectives

2005 ◽  
Vol 20 (3) ◽  
pp. 351-366 ◽  
Author(s):  
Peter C. Banacos ◽  
David M. Schultz
Keyword(s):  
Numerical Models ◽  
Convective Available Potential Energy ◽  
Moisture Flux ◽  
Cumulus Parameterization ◽  
Moist Convection ◽  
Convective Initiation ◽  
Moisture Flux Convergence ◽  
Case Examples ◽  
Surface Data ◽  
Deep Moist Convection

Abstract Moisture flux convergence (MFC) is a term in the conservation of water vapor equation and was first calculated in the 1950s and 1960s as a vertically integrated quantity to predict rainfall associated with synoptic-scale systems. Vertically integrated MFC was also incorporated into the Kuo cumulus parameterization scheme for the Tropics. MFC was eventually suggested for use in forecasting convective initiation in the midlatitudes in 1970, but practical MFC usage quickly evolved to include only surface data, owing to the higher spatial and temporal resolution of surface observations. Since then, surface MFC has been widely applied as a short-term (0–3 h) prognostic quantity for forecasting convective initiation, with an emphasis on determining the favorable spatial location(s) for such development. A scale analysis shows that surface MFC is directly proportional to the horizontal mass convergence field, allowing MFC to be highly effective in highlighting mesoscale boundaries between different air masses near the earth’s surface that can be resolved by surface data and appropriate grid spacing in gridded analyses and numerical models. However, the effectiveness of boundaries in generating deep moist convection is influenced by many factors, including the depth of the vertical circulation along the boundary and the presence of convective available potential energy (CAPE) and convective inhibition (CIN) near the boundary. Moreover, lower- and upper-tropospheric jets, frontogenesis, and other forcing mechanisms may produce horizontal mass convergence above the surface, providing the necessary lift to bring elevated parcels to their level of free convection without connection to the boundary layer. Case examples elucidate these points as a context for applying horizontal mass convergence for convective initiation. Because horizontal mass convergence is a more appropriate diagnostic in an ingredients-based methodology for forecasting convective initiation, its use is recommended over MFC.

Evaluation of scale-aware convection schemes at the kilometer-scale resolution

2020 ◽  
Author(s):  
Xu Zhang ◽  
Jian-Wen Bao ◽  
Baode Chen
Keyword(s):  
Deep Convection ◽  
Wrf Model ◽  
Horizontal Resolution ◽  
Theory And Practice ◽  
Coarse Grained ◽  
Great Effort ◽  
Moist Convection ◽  
Direct Evaluation ◽  
Deep Moist Convection ◽  
Convection Schemes

<p>Numerical weather predictions (NWP) models are increasingly run using kilometer-scale horizontal grid spacing at which convection is partially resolved and the use of a subgrid convection parameterization scheme is still required. Traditionally, subgrid deep convection has been represented by mass flux-based convection parameterizations based on the ensemble-mean closure concept. Recently, a great effort has been made to develop scale-aware subgrid convection schemes that can be used in kilometer-scale NWP models. However, direct evaluation of these schemes is rarely done using coarse-grained large-eddy simulation (LES).</p><p>In this study, an idealized LES of deep moist convection is performed to assess the performance of three widely-used scale-aware subgrid convection schemes in the Weather Research and Forecast (WRF) model that is run at 3-km horizontal resolution. It is found that the simulations using the three schemes not only differ from each other but also do not converge to the coarse-grained LES, indicating that further investigation is required as to what “scale-awareness” means in theory and practice.</p>

Improving Operational Numerical Prediction of Afternoon Thunderstorms over Taiwan through Surface Data Assimilation

2020 ◽  
Author(s):  
I-Han Chen ◽  
Jing-Shan Hong ◽  
Ya-Ting Tsai ◽  
Chin-Tzu Fong
Keyword(s):  
Data Assimilation ◽  
Radar Data ◽  
Precipitation Forecast ◽  
Cold Pool ◽  
Moist Convection ◽  
Convective Systems ◽  
Forecast Lead Time ◽  
Deep Moist Convection ◽  
Outflow Boundary ◽  
Surface Observations

<p>Taiwan, a subtropical island with steep mountains, is influenced by diverse weather systems, including typhoons, monsoons, frontal, and convective systems. Of these, the prediction of deep, moist convection here is particularly challenging due to complex topography and apparent landsea contrast. This study explored the benefits of assimilating surface observations on prediction of afternoon thunderstorms using a 2-km resolution WRF and WRFDA model system with rapid update cycles. Consecutive afternoon thunderstorm events during 30 June to 08 July 2017 are selected. Five experiments, consisting of 240 continuous cycles are designed to evaluate the data assimilation strategy and observation impact. Statistical results show that assimilating surface observations systematically improves the accuracy of wind and temperature prediction near the surface. Also, assimilating surface observations alone in one-hour intervals improves model quantitative precipitation forecast (QPF) skill, extending the forecast lead time in the morning. Furthermore, radar data assimilation can benefit by the additional assimilation of surface observations, particularly for improving the model QPF skill for large rainfall thresholds. An afternoon thunderstorm event that occurred on 06 July 2017 is further examined. By assimilating surface and radar observations, the model is able to capture the timing and location of the convection. Consequently, the accuracy of the predicted cold pool and outflow boundary is improved, when compared to the surface observations.</p>

scholarly journals Mesoscale Convective Systems and Their Synoptic-Scale Environment in Finland

2015 ◽  
Vol 30 (1) ◽  
pp. 182-196 ◽  
Author(s):  
Ari-Juhani Punkka ◽  
Marja Bister
Keyword(s):  
Potential Temperature ◽  
Mesoscale Convective Systems ◽  
Lapse Rate ◽  
Moist Convection ◽  
Mixing Ratio ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Wind Events ◽  
Deep Moist Convection

Abstract The environments within which high-latitude intense and nonintense mesoscale convective systems (iMCSs and niMCSs) and smaller thunderstorm clusters (sub-MCSs) develop were studied using proximity soundings. MCS statistics covering 8 years were created by analyzing composite radar imagery. One-third of all systems were intense in Finland and the frequency of MCSs was highest in July. On average, MCSs had a duration of 10.8 h and traveled toward the northeast. Many of the linear MCSs had a southwest–northeast line orientation. Interestingly, a few MCSs were observed to travel toward the west, which is a geographically specific feature of the MCS characteristics. The midlevel lapse rate failed to distinguish the environments of the different event types from each other. However, in MCSs, CAPE and the low-level mixing ratio were higher, the deep-layer-mean wind was stronger, and the lifting condensation level (LCL) was lower than in sub-MCSs. CAPE, low-level mixing ratio, and LCL height were the best discriminators between iMCSs and niMCSs. The mean wind over deep layers distinguished the severe wind–producing events from the nonsevere events better than did the vertical equivalent potential temperature difference or the wind shear in shallow layers. No evidence was found to support the hypothesis that dry air at low- and midlevels would increase the likelihood of severe convective winds. Instead, abundant low- and midlevel moisture was present during both iMCS cases and significant wind events. These results emphasize the pronounced role of low- and midlevel moisture on the longevity and intensity of deep moist convection in low-CAPE environments.

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