Prediction of Graupel Density in a Bulk Microphysics Scheme

2013 ◽  
Vol 70 (2) ◽  
pp. 410-429 ◽  
Author(s):  
Jason A. Milbrandt ◽  
Hugh Morrison
Keyword(s):  
A Priori ◽  
Kinematic Model ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Atmospheric Conditions ◽  
Microphysics Scheme ◽  
Surface Precipitation ◽  
Convective Region ◽  
Wide Range ◽  
Mesoscale Convective

Abstract A method to predict the bulk density of graupel ρg has been added to the two-moment Milbrandt–Yau bulk microphysics scheme. The simulation of graupel using the modified scheme is illustrated through idealized simulations of a mesoscale convective system using a 2D kinematic model with a prescribed flow field and different peak updraft speeds. To examine the relative impact of the various approaches to represent rimed ice, simulations were run for various graupel-only and graupel-plus-hail configurations. Because of the direct feedback of ρg to terminal fall speeds, the modified scheme produces a much different spatial distribution of graupel, with more mass concentrated in the convective region resulting in changes to the surface precipitation at all locations. With a strong updraft, the model can now produce solid precipitation at the surface in the convective region without a separate hail category. It is shown that a single rimed-ice category is capable of representing a realistically wide range of graupel characteristics in various atmospheric conditions without the need for a priori parameter settings. Sensitivity tests were conducted to examine various aspects of the scheme that affect the simulated ρg. Specific parameterizations pertaining to other hydrometeor categories now have a direct impact on the simulation of graupel, including the assumed aerosol distribution for droplet nucleation, which affects the drop sizes of both cloud and rain, and the mass–size relation for snow, which affects its density and hence the embryo density of graupel converted from snow due to riming.

The Analysis and Prediction of Microphysical States and Polarimetric Radar Variables in a Mesoscale Convective System Using Double-Moment Microphysics, Multinetwork Radar Data, and the Ensemble Kalman Filter

2014 ◽  
Vol 142 (1) ◽  
pp. 141-162 ◽  
Author(s):  
Bryan J. Putnam ◽  
Ming Xue ◽  
Youngsun Jung ◽  
Nathan Snook ◽  
Guifu Zhang
Keyword(s):  
Kalman Filter ◽  
Ensemble Kalman Filter ◽  
Mesoscale Convective System ◽  
Radar Data ◽  
Cold Pool ◽  
Convective System ◽  
Polarimetric Radar ◽  
Microphysics Scheme ◽  
Mesoscale Convective ◽  
Double Moment

Abstract Doppler radar data are assimilated with an ensemble Kalman Filter (EnKF) in combination with a double-moment (DM) microphysics scheme in order to improve the analysis and forecast of microphysical states and precipitation structures within a mesoscale convective system (MCS) that passed over western Oklahoma on 8–9 May 2007. Reflectivity and radial velocity data from five operational Weather Surveillance Radar-1988 Doppler (WSR-88D) S-band radars as well as four experimental Collaborative and Adaptive Sensing of the Atmosphere (CASA) X-band radars are assimilated over a 1-h period using either single-moment (SM) or DM microphysics schemes within the forecast ensemble. Three-hour deterministic forecasts are initialized from the final ensemble mean analyses using a SM or DM scheme, respectively. Polarimetric radar variables are simulated from the analyses and compared with polarimetric WSR-88D observations for verification. EnKF assimilation of radar data using a multimoment microphysics scheme for an MCS case has not previously been documented in the literature. The use of DM microphysics during data assimilation improves simulated polarimetric variables through differentiation of particle size distributions (PSDs) within the stratiform and convective regions. The DM forecast initiated from the DM analysis shows significant qualitative improvement over the assimilation and forecast using SM microphysics in terms of the location and structure of the MCS precipitation. Quantitative precipitation forecasting skills are also improved in the DM forecast. Better handling of the PSDs by the DM scheme is believed to be responsible for the improved prediction of the surface cold pool, a stronger leading convective line, and improved areal extent of stratiform precipitation.

scholarly journals Reducing the Biases in Simulated Radar Reflectivities from a Bulk Microphysics Scheme: Tropical Convective Systems

2011 ◽  
Vol 68 (10) ◽  
pp. 2306-2320 ◽  
Author(s):  
Stephen E. Lang ◽  
Wei-Kuo Tao ◽  
Xiping Zeng ◽  
Yaping Li
Keyword(s):  
Mesoscale Convective System ◽  
Convective System ◽  
Microphysics Scheme ◽  
Upper Troposphere ◽  
Convective Systems ◽  
Mixing Ratios ◽  
Ice Nuclei ◽  
Mesoscale Convective ◽  
Immersion Freezing ◽  
Cloud Ice

Abstract A well-known bias common to many bulk microphysics schemes currently being used in cloud-resolving models is the tendency to produce excessively large reflectivity values (e.g., 40 dBZ) in the middle and upper troposphere in simulated convective systems. The Rutledge and Hobbs–based bulk microphysics scheme in the Goddard Cumulus Ensemble model is modified to reduce this bias and improve realistic aspects. Modifications include lowering the efficiencies for snow/graupel riming and snow accreting cloud ice; converting less rimed snow to graupel; allowing snow/graupel sublimation; adding rime splintering, immersion freezing, and contact nucleation; replacing the Fletcher formulation for activated ice nuclei with that of Meyers et al.; allowing for ice supersaturation in the saturation adjustment; accounting for ambient RH in the growth of cloud ice to snow; and adding/accounting for cloud ice fall speeds. In addition, size-mapping schemes for snow/graupel were added as functions of temperature and mixing ratio, lowering particle sizes at colder temperatures but allowing larger particles near the melting level and at higher mixing ratios. The modifications were applied to a weakly organized continental case and an oceanic mesoscale convective system (MCS). Strong echoes in the middle and upper troposphere were reduced in both cases. Peak reflectivities agreed well with radar for the weaker land case but, despite improvement, remained too high for the MCS. Reflectivity distributions versus height were much improved versus radar for the less organized land case but not for the MCS despite fewer excessively strong echoes aloft due to a bias toward weaker echoes at storm top.

The Role of Cloud Microphysics Parameterization in the Simulation of Mesoscale Convective System Clouds and Precipitation in the Tropical Western Pacific

2013 ◽  
Vol 70 (4) ◽  
pp. 1104-1128 ◽  
Author(s):  
K. Van Weverberg ◽  
A. M. Vogelmann ◽  
W. Lin ◽  
E. P. Luke ◽  
A. Cialella ◽  
...  
Keyword(s):  
Mesoscale Convective System ◽  
Cloud Microphysics ◽  
Western Pacific ◽  
Convective System ◽  
Fall Velocity ◽  
Surface Precipitation ◽  
Cloud Systems ◽  
Tropical Western Pacific ◽  
Mesoscale Convective

Abstract This paper presents a detailed analysis of convection-permitting cloud simulations, aimed at increasing the understanding of the role of parameterized cloud microphysics in the simulation of mesoscale convective systems (MCSs) in the tropical western Pacific (TWP). Simulations with three commonly used bulk microphysics parameterizations with varying complexity have been compared against satellite-retrieved cloud properties. An MCS identification and tracking algorithm was applied to the observations and the simulations to evaluate the number, spatial extent, and microphysical properties of individual cloud systems. Different from many previous studies, these individual cloud systems could be tracked over larger distances because of the large TWP domain studied. The analysis demonstrates that the simulation of MCSs is very sensitive to the parameterization of microphysical processes. The most crucial element was found to be the fall velocity of frozen condensate. Differences in this fall velocity between the experiments were more related to differences in particle number concentrations than to fall speed parameterization. Microphysics schemes that exhibit slow sedimentation rates for ice aloft experience a larger buildup of condensate in the upper troposphere. This leads to more numerous and/or larger MCSs with larger anvils. Mean surface precipitation was found to be overestimated and insensitive to the microphysical schemes employed in this study. In terms of the investigated properties, the performances of complex two-moment schemes were not superior to the simpler one-moment schemes, since explicit prediction of number concentration does not necessarily improve processes such as ice nucleation, the aggregation of ice crystals into snowflakes, and their sedimentation characteristics.

scholarly journals Assimilation of Chinese Doppler Radar and Lightning Data Using WRF-GSI: A Case Study of Mesoscale Convective System

2015 ◽  
Vol 2015 ◽  
pp. 1-17 ◽  
Author(s):  
Yi Yang ◽  
Ying Wang ◽  
Kefeng Zhu
Keyword(s):  
Doppler Radar ◽  
Mesoscale Convective System ◽  
Cumulus Parameterization ◽  
Convective System ◽  
Microphysics Scheme ◽  
Precipitation Prediction ◽  
Mesoscale Convective ◽  
Cloud To Ground Lightning ◽  
Grid Points ◽  
Temperature Tendency

The radar-enhanced GSI (version 3.1) system and the WRF-ARW (version 3.4.1) model were modified to assimilate radar/lightning-proxy reflectivity. First, cloud-to-ground lightning data were converted to reflectivity using a simple assumed relationship between flash density and reflectivity. Next, the reflectivity was used in the cloud analysis of GSI to adjust the cloud/hydrometeors and moisture. Additionally, the radar/lightning-proxy reflectivity was simultaneously converted to a 3D temperature tendency. Finally, the model-calculated temperature tendencies from the explicit microphysics scheme, as well as cumulus parameterization at 3D grid points at which the radar temperature tendency is available, were updated in a forward full-physics step of diabatic digital filter initialization in the WRF-ARW. The WRF-GSI system was tested using a mesoscale convective system that occurred on June 5, 2009, and by assimilating Doppler radar and lightning data, respectively. The forecasted reflectivity with assimilation corresponded more closely to the observed reflectivity than that of the parallel experiment without assimilation, particularly during the first 6 h. After assimilation, the short-range precipitation prediction improved, although the precipitation intensity was stronger than the observed one. In addition, the improvements obtained by assimilating lightning data were worse than those from assimilating radar reflectivity over the first 3 h but improved thereafter.

scholarly journals Simulation of a Serial Upstream-Propagating Mesoscale Convective System Event over Southeastern South America Using Composite Initial Conditions

2009 ◽  
Vol 137 (7) ◽  
pp. 2144-2163 ◽  
Author(s):  
Vagner Anabor ◽  
David J. Stensrud ◽  
Osvaldo L. L. de Moraes
Keyword(s):  
South America ◽  
Gravity Waves ◽  
Initial Conditions ◽  
Mesoscale Convective System ◽  
The United States ◽  
Internal Gravity Waves ◽  
Cold Pool ◽  
Convective System ◽  
Convective Region ◽  
Mesoscale Convective

Serial upstream-propagating mesoscale convective system (MCS) events over southeastern South America are important contributors to the local hydrologic cycle as they can provide roughly half of the total monthly summer precipitation. However, the mechanisms of upstream propagation for these events have not been explored. To remedy this situation, a numerical simulation of the composite environmental conditions from 10 observed serial MCS events is conducted. Results indicate that the 3-day simulation from the composite yields a reasonable evolution of the large-scale environment and produces a large region of organized convection in the warm sector over an extended period as seen in observations. Upstream propagation of the convective region is produced and is tied initially to the development and evolution of untrapped internal gravity waves. However, as convective downdrafts develop and begin to merge and form a surface cold pool in the simulation, the cold pool and its interaction with the environmental low-level flow also begins to play a role in convective evolution. While the internal gravity waves and cold pool interact over a several hour period to control the convective development, the cold pool eventually dominates and determines the propagation of the convective region by the end of the simulation. This upstream propagation of a South American convective region resembles the southward burst convective events described over the United States and highlights the complex interactions and feedbacks that challenge accurate forecasts of convective system evolution.

Investigation of cloud-to-ground flashes in the Non-Precipitating Stratiform Region of a Mesoscale Convective System on 20 August 2019 and Implications for Decision Support Services

2021 ◽  
Author(s):  
CHRISTOPHER J. SCHULTZ ◽  
ROGER E. ALLEN ◽  
KELLEY M. MURPHY ◽  
BENJAMIN S. HERZOG ◽  
STEPHANIE A. WEISS ◽  
...  
Keyword(s):  
Decision Support ◽  
Support Services ◽  
Risk Model ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Surface Precipitation ◽  
Stratiform Region ◽  
Mesoscale Convective ◽  
Average Size ◽  
Differential Reflectivity

AbstractInfrequent lightning flashes occurring outside of surface precipitation pose challenges to Impact-based Decision Support Services (IDSS) for outdoor activities. This paper examines the remote sensing observations from an event on 20 August 2019 where multiple cloud-to-ground flashes occurred over 10 km outside surface precipitation (lowest radar tilt reflectivity <10 dBZ and no evidence of surface precipitation) in a trailing stratiform region of a mesoscale convective system. The goal is to demonstrate the fusion of radar with multiple lightning observations and a lightning risk model to demonstrate how reflectivity and differential reflectivity combined provided the best indicator for the potential of lightning where all of the other lightning safety methods failed.Thirteen lightning flashes were observed by the Geostationary Lightning Mapper (GLM) within the trailing stratiform region between 2100 and 2300 UTC. The average size of the thirteen lightning flashes was 3184 km2, with an average total optical energy of 7734 fJ. Seventy-five NLDN flash locations were coincident with the thirteen GLM flashes, resulting in an average of 5.8 NLDN flashes (in-cloud (IC) and cloud-to-ground (CG)) per 37 GLM flash. Five of the GLM flashes contained at least one positive cloud-to-ground flash (+CG) flash identified by the NLDN, with peak amplitudes ranging between 66 and 136 kA. All eight CG flashes identified by the NLDN were located more than 10 km outside surface precipitation. The only indication of the potential of these infrequently large flashes was the presence of depolarization streaks in differential reflectivity (ZDR) and enhanced reflectivity near the melting layer.

scholarly journals Controls on phase composition and ice water content in a convection-permitting model simulation of a tropical mesoscale convective system

2016 ◽  
Vol 16 (14) ◽  
pp. 8767-8789 ◽  
Author(s):  
Charmaine N. Franklin ◽  
Alain Protat ◽  
Delphine Leroy ◽  
Emmanuel Fontaine
Keyword(s):  
Phase Composition ◽  
Water Content ◽  
Deep Convection ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Microphysics Scheme ◽  
Mesoscale Convective ◽  
Single Moment ◽  
Ice Water Content ◽  
Ice Water

Abstract. Simulations of tropical convection from an operational numerical weather prediction model are evaluated with the focus on the model's ability to simulate the observed high ice water contents associated with the outflow of deep convection and to investigate the modelled processes that control the phase composition of tropical convective clouds. The 1 km horizontal grid length model that uses a single-moment microphysics scheme simulates the intensification and decay of convective strength across the mesoscale convective system. However, deep convection is produced too early, the OLR (outgoing longwave radiation) is underestimated and the areas with reflectivities > 30 dBZ are overestimated due to too much rain above the freezing level, stronger updraughts and larger particle sizes in the model. The inclusion of a heterogeneous rain-freezing parameterisation and the use of different ice size distributions show better agreement with the observed reflectivity distributions; however, this simulation still produces a broader profile with many high-reflectivity outliers demonstrating the greater occurrence of convective cells in the simulations. Examining the phase composition shows that the amount of liquid and ice in the modelled convective updraughts is controlled by the following: the size of the ice particles, with larger particles growing more efficiently through riming and producing larger IWC (ice water content); the efficiency of the warm rain process, with greater cloud water contents being available to support larger ice growth rates; and exclusion or limitation of graupel growth, with more mass contained in slower falling snow particles resulting in an increase of in-cloud residence times and more efficient removal of LWC (liquid water content). In this simulated case using a 1 km grid length model, horizontal mass divergence in the mixed-phase regions of convective updraughts is most sensitive to the turbulence formulation. Greater mixing of environmental air into cloudy updraughts in the region of −30 to 0 °C produces more mass divergence indicative of greater entrainment, which generates a larger stratiform rain area. Above these levels in the purely ice region of the simulated updraughts, the convective updraught buoyancy is controlled by the ice particle sizes, demonstrating the importance of the microphysical processes on the convective dynamics in this simulated case study using a single-moment microphysics scheme. The single-moment microphysics scheme in the model is unable to simulate the observed reduction of mean mass-weighted ice diameter as the ice water content increases. The inability of the model to represent the observed variability of the ice size distribution would be improved with the use of a double-moment microphysics scheme.

scholarly journals Study of Mesoscale Convective Complex (MCC) and its impact over the Makassar Strait (case study: 9 December 2014)

2021 ◽  
Vol 893 (1) ◽  
pp. 012021
Author(s):  
A Ni’amillah ◽  
P Ismail ◽  
E L Siadari ◽  
I J A Saragih
Keyword(s):  
Mesoscale Convective System ◽  
Thermal Conditions ◽  
Cloud Formation ◽  
Convective System ◽  
Atmospheric Conditions ◽  
Weather Forecasts ◽  
South Sulawesi ◽  
Mesoscale Convective ◽  
Convective Cells ◽  
The Impact

Abstract A mesoscale Convective System (MCS) is a system consisting of groups of convective cells in the mesoscale. One of the largest types of MCS subclass is Mesoscale Convective Complex (MCC) occurred in the eastern part of the Makassar Strait near the Madjene and Polewali Mandar regions on 9 December 2014, morning to evening (09.00-15.00 LT). Using MTSAT-2 Satellite Imagery data, reanalysis of the European Centre for Medium-Range Weather Forecasts (ECMWF) interim era, the Global Satellite Mapping of Precipitation (GsMap) rainfall, sea surface temperature, surface air observation, and upper air observation, the author will examine the existence of MCC in the Makassar Strait in terms of atmospheric conditions when MCC enters the initial until extinct and the accompanying effects of precipitation. In general, it is known that the MCC formed in the waters of the Makassar Strait in the morning, and then it moved westward. The mechanism of its formation was through a process of convergence of the lower layers in the waters of the Makassar Strait and its surroundings to trigger the process of cloud formation. Warm thermal conditions also gave a big influence on the lower layers to the top and activate convective in the study area. Meanwhile, the MCC occurrence region also has high relative humidity, negative divergence values, and maximum vorticity values. The impact of the emergence of MCC on that date resulted in areas with very large humidity and cloud formation and produced rain in the surrounding area, in this case using rainfall data from Hasanuddin Meteorological Station, Makassar, South Sulawesi. With a duration of up to seven hours extinct, MCC in the Makassar Strait produces heavy rainfall in the Makassar Strait waters.

Ensemble Probabilistic Prediction of a Mesoscale Convective System and Associated Polarimetric Radar Variables Using Single-Moment and Double-Moment Microphysics Schemes and EnKF Radar Data Assimilation

2017 ◽  
Vol 145 (6) ◽  
pp. 2257-2279 ◽  
Author(s):  
Bryan J. Putnam ◽  
Ming Xue ◽  
Youngsun Jung ◽  
Nathan A. Snook ◽  
Guifu Zhang
Keyword(s):  
Mesoscale Convective System ◽  
Radar Data ◽  
Convective Precipitation ◽  
Convective System ◽  
Ensemble Forecasts ◽  
Verification Methods ◽  
Probabilistic Forecasts ◽  
Mesoscale Convective ◽  
Single Moment ◽  
Double Moment

Abstract Ensemble-based probabilistic forecasts are performed for a mesoscale convective system (MCS) that occurred over Oklahoma on 8–9 May 2007, initialized from ensemble Kalman filter analyses using multinetwork radar data and different microphysics schemes. Two experiments are conducted, using either a single-moment or double-moment microphysics scheme during the 1-h-long assimilation period and in subsequent 3-h ensemble forecasts. Qualitative and quantitative verifications are performed on the ensemble forecasts, including probabilistic skill scores. The predicted dual-polarization (dual-pol) radar variables and their probabilistic forecasts are also evaluated against available dual-pol radar observations, and discussed in relation to predicted microphysical states and structures. Evaluation of predicted reflectivity (Z) fields shows that the double-moment ensemble predicts the precipitation coverage of the leading convective line and stratiform precipitation regions of the MCS with higher probabilities throughout the forecast period compared to the single-moment ensemble. In terms of the simulated differential reflectivity (ZDR) and specific differential phase (KDP) fields, the double-moment ensemble compares more realistically to the observations and better distinguishes the stratiform and convective precipitation regions. The ZDR from individual ensemble members indicates better raindrop size sorting along the leading convective line in the double-moment ensemble. Various commonly used ensemble forecast verification methods are examined for the prediction of dual-pol variables. The results demonstrate the challenges associated with verifying predicted dual-pol fields that can vary significantly in value over small distances. Several microphysics biases are noted with the help of simulated dual-pol variables, such as substantial overprediction of KDP values in the single-moment ensemble.

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