scholarly journals Genesis of Hurricane Julia (2010) within an African Easterly Wave: Developing and Nondeveloping Members from WRF–LETKF Ensemble Forecasts

2014 ◽  
Vol 71 (7) ◽  
pp. 2763-2781 ◽  
Author(s):  
Stefan F. Cecelski ◽  
Da-Lin Zhang ◽  
Takemasa Miyoshi
Keyword(s):  
Surface Pressure ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Ensemble Forecasts ◽  
Upper Troposphere ◽  
African Easterly Wave ◽  
Easterly Wave ◽  
Mesoscale Convective ◽  
Rossby Radius Of Deformation ◽  
Faster Development

Abstract In this study, the predictability of and parametric differences in the genesis of Hurricane Julia (2010) are investigated using 20 mesoscale ensemble forecasts with the finest resolution of 1 km. Results show that the genesis of Julia is highly predictable, with all but two members undergoing genesis. Despite the high predictability, substantial parametric differences exist between the stronger and weaker members. Notably, the strongest-developing member exhibits large upper-tropospheric warming within a storm-scale outflow during genesis. In contrast, the nondeveloping member has weak and more localized warming due to inhibited convective development and a lack of a storm-scale outflow. A reduction in the Rossby radius of deformation in the strongest member aids in the accumulation of the warmth, while little contraction takes place in the nondeveloping member. The warming in the upper troposphere is responsible for the development of meso-α-scale surface pressure falls and a meso-β surface low in the strongest-developing member. Such features fail to form in the nondeveloping member as weak upper-tropospheric warming is unable to induce meaningful surface pressure falls. Cloud ice content is nearly doubled in the strongest member as compared to its nondeveloping counterparts, suggesting the importance of depositional heating of the upper troposphere. It is found that the stronger member undergoes genesis faster due to the lack of convective inhibition near the African easterly wave (AEW) pouch center prior to genesis. This allows for the faster development of a mesoscale convective system and storm-scale outflow, given the already favorable larger-scale conditions.

Origin of the pre-tropical storm Debby (2006) African easterly wave-mesoscale convective system

2013 ◽  
Vol 120 (3-4) ◽  
pp. 123-144 ◽  
Author(s):  
Yuh-Lang Lin ◽  
Liping Liu ◽  
Guoqing Tang ◽  
James Spinks ◽  
Wilson Jones
Keyword(s):  
Mesoscale Convective System ◽  
Tropical Storm ◽  
Convective System ◽  
African Easterly Wave ◽  
Easterly Wave ◽  
Mesoscale Convective

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.

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.

scholarly journals Numerical study of tracers transport by a mesoscale convective system over West Africa

2011 ◽  
Vol 29 (5) ◽  
pp. 731-747 ◽  
Author(s):  
C. Barthe ◽  
C. Mari ◽  
J.-P. Chaboureau ◽  
P. Tulet ◽  
F. Roux ◽  
...  
Keyword(s):  
Numerical Study ◽  
Three Dimensional ◽  
Mesoscale Convective System ◽  
Dimensional Structure ◽  
Convective System ◽  
Upper Troposphere ◽  
Mesoscale Convective ◽  
Cloud Resolving Model ◽  
Passive Tracers ◽  
Two Peaks

Abstract. A three-dimensional cloud-resolving model is used to investigate the vertical transport from the lower to the upper troposphere in a mesoscale convective system (MCS) that occurred over Niger on 15 August 2004. The redistribution of five passive tracers initially confined in horizontally homogeneous layers is analyzed. The monsoon layer tracer (0–1.5 km) is the most efficiently transported in the upper troposphere with concentrations 3 to 4 times higher than the other tracers in the anvil. On the contrary the African Easterly Jet tracer (~3 km) has the lowest contribution above 5 km. The vertical profiles of the mid-troposphere tracers (4.5–10 km) in the MCS exhibit two peaks: one in their initial layers, and the second one at 13–14 km altitude, underlying the importance of mid-tropospheric air in feeding the upper troposphere. Mid-tropospheric tracers also experience efficient transport by convective downdrafts with a consequent increase of their concentrations at the surface. The concentration of the upper troposphere–lower stratosphere tracer exhibits strong gradients at the edge of the cloud, meaning almost no entrainment of this tracer into the cloud. No downward transport from the upper troposphere is simulated below 5 km. A proxy for lightning produced NOx is transported preferentially in the forward anvil in the upper troposphere. Additionally, lateral inflows significantly contribute to the updraft and downdraft airflows emphasizing the three-dimensional structure of the West African MCSs.

scholarly journals Mesoscale convective system surface pressure anomalies responsible for meteotsunamis along the U.S. East Coast on June 13th, 2013

2014 ◽  
Vol 4 (1) ◽  
Author(s):  
Christina A. Wertman ◽  
Richard M. Yablonsky ◽  
Yang Shen ◽  
John Merrill ◽  
Christopher R. Kincaid ◽  
...  
Keyword(s):  
Surface Pressure ◽  
East Coast ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Mesoscale Convective ◽  
The U.S

scholarly journals A Case Study of the Interaction of a Mesoscale Gravity Wave with a Mesoscale Convective System

2014 ◽  
Vol 142 (4) ◽  
pp. 1403-1429 ◽  
Author(s):  
James H. Ruppert ◽  
Lance F. Bosart
Keyword(s):  
Solitary Wave ◽  
Gravity Wave ◽  
Surface Pressure ◽  
Cold Front ◽  
Mesoscale Convective System ◽  
High Amplitude ◽  
Squall Line ◽  
Convective System ◽  
Density Currents ◽  
Mesoscale Convective

Abstract This study documents the high-amplitude mesoscale gravity wave (MGW) event of 7 March 2008 in which two MGWs strongly impacted the sensible weather over a large portion of the Southeast United States. These MGWs exhibited starkly contrasting character despite propagating within similar environments. The primary (i.e., long lived) MGW was manifest by a solitary wave of depression associated with rapid sinking motion and adiabatic warming, while the secondary (short lived) MGW was manifest by a solitary wave of elevation (“MGWEL”), dominated by rising motion and moist adiabatic cooling. Genesis of the primary MGW occurred as a strong cold front arrived at the foot of Mexico’s high terrain and perturbed the appreciable overriding flow. The resulting gravity wave became ducted in the presence of a low-level frontal stable layer, and caused surface pressure falls up to ~4 hPa. The MGW later amplified as it became coupled with a stratiform precipitation system, which led to its evolution into an intense mesohigh–wake low couplet. This couplet propagated as a ducted MGW attached to a stratiform system for ~12 h thereafter, and induced rapid surface pressure falls of ≥10 hPa (including a fall of 6.7 hPa in 10 min), rapid wind vector changes (e.g., 17 m s−1 in 25 min), and high wind gusts (e.g., 20 m s−1) across several states. MGWEL appeared within the remnants of a squall line, and was manifest by a sharp pressure ridge of ~6 hPa with a narrow embedded rainband following the motion of a surface cold front. MGWEL bore resemblance to previously documented gravity waves formed by density currents propagating through stable environments.

scholarly journals Genesis of an East Pacific Easterly Wave from a Panama Bight MCS: A Case Study Analysis from June 2012

2020 ◽  
Vol 77 (10) ◽  
pp. 3567-3584
Author(s):  
Justin W. Whitaker ◽  
Eric D. Maloney
Keyword(s):  
Vertical Structure ◽  
Model Simulation ◽  
Vertical Motion ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Easterly Wave ◽  
Budget Analysis ◽  
East Pacific ◽  
Vorticity Budget ◽  
Mesoscale Convective

AbstractThis study investigates the transition of a Panama Bight mesoscale convective system (MCS) into the easterly wave (EW) that became Hurricane Carlotta (2012). Reanalysis, observations, and a convective-permitting Weather Research and Forecasting (WRF) Model simulation are used to analyze the processes contributing to EW genesis. A vorticity budget analysis shows that convective coupling and vortex stretching are very important to the transition in this case, while horizontal advection is mostly responsible for the propagation of the system. In the model, the disturbance is dominated by stratiform vertical motion profiles and a midlevel vortex, while the system is less top-heavy and is characterized by more prominent low-level vorticity later in the transition in reanalysis. The developing disturbance starts its evolution as a mesoscale convective system in the Bight of Panama. Leading up to MCS formation the Chocó jet intensifies, and during the MCS-to-EW transition the Papagayo jet strengthens. Differences in the vertical structure of the system between reanalysis and the model suggest that the relatively more bottom-heavy disturbance in reanalysis may have stronger interactions with the Papagayo jet. Field observations like those collected during the Organization of Tropical East Pacific Convection (OTREC) campaign are needed to further our understanding of this east Pacific EW genesis pathway and the factors that influence it, including the important role for the vertical structure of the developing disturbances in the context of the vorticity budget.

scholarly journals Simulation of Polarimetric Radar Variables from 2013 CAPS Spring Experiment Storm-Scale Ensemble Forecasts and Evaluation of Microphysics Schemes

2016 ◽  
Vol 145 (1) ◽  
pp. 49-73 ◽  
Author(s):  
Bryan J. Putnam ◽  
Ming Xue ◽  
Youngsun Jung ◽  
Guifu Zhang ◽  
Fanyou Kong
Keyword(s):  
Mesoscale Convective System ◽  
Liquid Water Content ◽  
Convective System ◽  
Polarimetric Radar ◽  
Ensemble Forecasts ◽  
Direct Evaluation ◽  
Mesoscale Convective ◽  
Double Moment ◽  
Size Sorting ◽  
Radar Simulator

Abstract Polarimetric radar variables are simulated from members of the 2013 Center for Analysis and Prediction of Storms (CAPS) Storm-Scale Ensemble Forecasts (SSEF) with varying microphysics (MP) schemes and compared with observations. The polarimetric variables provide information on hydrometeor types and particle size distributions (PSDs), neither of which can be obtained through reflectivity (Z) alone. The polarimetric radar simulator pays close attention to how each MP scheme [including single- (SM) and double-moment (DM) schemes] treats hydrometeor types and PSDs. The recent dual-polarization upgrade to the entire WSR-88D network provides nationwide polarimetric observations, allowing for direct evaluation of the simulated polarimetric variables. Simulations for a mesoscale convective system (MCS) and supercell cases are examined. Five different MP schemes—Thompson, DM Milbrandt and Yau (MY), DM Morrison, WRF DM 6-category (WDM6), and WRF SM 6-category (WSM6)—are used in the ensemble forecasts. Forecasts using the partially DM Thompson and fully DM MY and Morrison schemes better replicate the MCS structure and stratiform precipitation coverage, as well as supercell structure compared to WDM6 and WSM6. Forecasts using the MY and Morrison schemes better replicate observed polarimetric signatures associated with size sorting than those using the Thompson, WDM6, and WSM6 schemes, in which such signatures are either absent or occur at abnormal locations. Several biases are suggested in these schemes, including too much wet graupel in MY, Morrison, and WDM6; a small raindrop bias in WDM6 and WSM6; and the underforecast of liquid water content in regions of pure rain for all schemes.

scholarly journals Bias Correction, Anonymization, and Analysis of Smartphone Pressure Observations Using Machine Learning and Multi-Resolution Kriging

2021 ◽  
Author(s):  
Callie McNicholas ◽  
Clifford F. Mass
Keyword(s):  
Machine Learning ◽  
Surface Pressure ◽  
Bias Correction ◽  
Pressure Sensors ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Weather Events ◽  
Mesoscale Convective ◽  
Technical Issues ◽  
High Impact Weather

AbstractWith over a billion smartphones capable of measuring atmospheric pressure, a global mesoscale surface pressure network based on smartphone pressure sensors may be possible if key technical issues are solved, including collection technology, privacy and bias correction. To overcome these challenges, a novel framework was developed for the anonymization and bias correction of smartphone pressure observations (SPOs) and was applied to billions of SPOs from The Weather Company (IBM). Bias correction using machine learning reduced the errors of anonymous (ANON) SPOs and uniquely identifiable (UID) SPOs by 43% and 57%, respectively. Applying multi-resolution kriging, gridded analyses of bias-corrected smartphone pressure observations were made for an entire year (2018), using both anonymized (ANON) and non-anonymized (UID) observations. Pressure analyses were also generated using conventional (MADIS) surface pressure networks. Relative to MADIS analyses, ANON and UID smartphone analyses reduced domain-average pressure errors by 21% and 31%. The performance of smartphone and MADIS pressure analyses was evaluated for two high-impact weather events: the landfall of Hurricane Michael and a long-lived mesoscale convective system. For these two events, both anonymized and non-anonymized smartphone pressure analyses better captured the spatial structure and temporal evolution of mesoscale pressure features than the MADIS analyses.

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