Evaluación de esquemas de microfísica WRF en la simulación de una línea de turbonada sobre IRAN utilizando datos de radar y de reanálisis

Se registró una línea de turbonada en el puerto de Dayyer, al suroeste de Irán, el 19 de marzo de 2017. En el presente documento, hemos simulado los rasgos característicos asociados con la línea de turbonada mediante el modelo de investigación y pronóstico meteorológico (WRF) utilizando cinco microfísicas diferentes (MP) esquemas. Para validar las características simuladas de la línea de turbonada, la reflectividad de la sección transversal de latitud-altura y longitud-altura y el valor de precipitación derivado de la reflectividad observada recopilada por el radar meteorológico Doppler en Bushehr, datos de la estación meteorológica sinóptica en el puerto de Dayyer junto con NCEP-NCAR y ERA -Se utilizaron datos de reanálisisINTERIM. Para verificar la precipitación simulada, se calculó la curva Fractions Skill Score (FSS). El examen de los resultados de la simulación de la presión geopotencial y al nivel del mar muestra que las simulaciones del modelo que utilizan diferentes esquemas de MP concuerdan bien con los reanálisis de verificación. Además, la distribución espacial de las precipitaciones de las simulaciones y las observaciones de verificación no mostraron grandes diferencias. Sin embargo, existen diferencias significativas en los detalles de las simulaciones, como la reflectividad máxima de las celdas convectivas, la extensión vertical de las celdas de tormenta, la velocidad y dirección del viento, los valores de precipitación y las curvas FSS. Sin embargo, todas las simulaciones han mostrado celdas convectivas sobre el puerto de Dayyer en el momento de la aparición de la línea de turbonada, pero solo la simulación del modelo que usa el esquema Lin MP es consistente con la reflectividad del radar y la extensión vertical correspondientes. El gráfico FSS mostró que la habilidad cambia con la escala espacial. Los resultados utilizando el esquema de microfísica Lin cruzaron la línea FSSuniform a escalas más bajas en comparación con otros esquemas de M

Ensemble prediction of a severe weather event: a study of the 2009 Southern Ontario storm

The tornadic storm of August 20, 2009 of Southern Ontario is studied using a numerical prediction model. It is found that a 3km resolution simulation works as well as a 1km resolution model to model the storms underlying physical processes relevant to supercell mesocyclone formation and storm propagation, although both models showed a significant phase bias in the storm system's squall line position. A 3m resolution ensemble of 20 members is used to model the storm system further, and it is found that the ensemble mean shows the same bias that the 1km and 3km resolution models exhibited. Investigation of ensemble perturbation growth rates from ensemble mean values reveals differing growth rates for baroclinic and convective modes. Ensemble-based sensitivity analyses reveal that there are strong correlations of squall line position with model variables up to 12 hours previously

Retrieval of moisture from GPS slant-path water vapor observations using 3DVAR and its impact on the prediction of convection initiation and precipitation.

The anisotropic explicit filter is computationally expensive in both CPU time and memory usage. Therefore the implicit recursive filter which is computationally much more efficient is implemented in our 3DVAR system, even though its implementation is significantly more complicated. A similar set of water vapor analysis experiments using the recursive filters is performed. The analyses thus obtained are generally comparable to or better than those obtained using the corresponding explicit filters. In addition, the sensitivity of the analyses to the spatial de-correlation scales of the background error is systematically examined.A set of high-resolution numerical experiments is conducted using the Advanced Regional Prediction System (ARPS) for a case that occurred on 12 June, 2002 and involved multiple initiations of convection. The results are verified against the radar composite reflectivity in detail. It is shown that the model performs reasonably well on predicting the initiation timing and location and the subsequent storm evolution for up to 7 hours. Using the most realistic simulation of this case as the 'truth', simulated SWV data and surface moisture observations are generated to perform a set of Observing System Simulation Experiments (OSSEs) using our 3DVAR system with recursive filters. The preliminary results illustrate that convection initiation (CI) without strong low-level mesoscale forcing is highly sensitive to the moisture initial condition and the use of SWV and surface data improves the moisture analysis and thus the prediction of CI and precipitation. The enhanced moisture analysis obtained from the use of anisotropic background error further improves the precipitation forecast though it does not lead to positive impact on the prediction of exact timing and location of the CI due to its high sensitivity to very small-scale moisture structures.The 3DVAR system developed in this study is based on a terrain-following coordinate. A non-negative water vapor weak constraint is included in the cost function. The background term and its associated background error covariance are considered in the system and the latter is modeled using explicit or implicit recursive spatial filters. Most importantly, a direct way to estimate a flow-dependent background error covariance based on the idea of Riishojgaard is proposed for the moisture analysis. The explicit spatial filter first is implemented with both isotropic and anisotropic options. It is demonstrated that this system is robust on deriving mesoscale moisture structures from the GPS SWV and surface observations and the analysis is improved when the anisotropic background error covariance is used. Sensitivity experiments show that surface moisture data are important for the analysis near ground and a vertical filter is essential to obtain an accurate analysis near the surface. The positive impact of flow-dependent background error is enhanced when the density of GPS receiver network is lower.The accurate prediction of convection initiation and the subsequent precipitation in a cloud-resolving numerical model is highly dependent on the precise estimate of the three-dimensional moisture in the initial condition because water vapor is directly involved in the formation of clouds and precipitation. However, the water vapor is currently poorly characterized due to its high variability in space and time. A three-dimensional variational analysis system (3DVAR) is developed in this dissertation to retrieve the moisture field from simulated ground-based GPS slant-path integrated water vapor (SWV) data that are potentially available at high temporal and spatial resolutions

The 2015 Plains Elevated Convection at Night Field Project

The central Great Plains region in North America has a nocturnal maximum in warm-season precipitation. Much of this precipitation comes from organized mesoscale convective systems (MCSs). This nocturnal maximum is counterintuitive in the sense that convective activity over the Great Plains is out of phase with the local generation of CAPE by solar heating of the surface. The lower troposphere in this nocturnal environment is typically characterized by a low-level jet (LLJ) just above a stable boundary layer (SBL), and convective available potential energy (CAPE) values that peak above the SBL, resulting in convection that may be elevated, with source air decoupled from the surface. Nocturnal MCS-induced cold pools often trigger undular bores and solitary waves within the SBL. A full understanding of the nocturnal precipitation maximum remains elusive, although it appears that bore-induced lifting and the LLJ may be instrumental to convection initiation and the maintenance of MCSs at night. To gain insight into nocturnal MCSs, their essential ingredients, and paths toward improving the relatively poor predictive skill of nocturnal convection in weather and climate models, a large, multiagency field campaign called Plains Elevated Convection At Night (PECAN) was conducted in 2015. PECAN employed three research aircraft, an unprecedented coordinated array of nine mobile scanning radars, a fixed S-band radar, a unique mesoscale network of lower-tropospheric profiling systems called the PECAN Integrated Sounding Array (PISA), and numerous mobile-mesonet surface weather stations. The rich PECAN dataset is expected to improve our understanding and prediction of continental nocturnal warm-season precipitation. This article provides a summary of the PECAN field experiment and preliminary findings

Vertical motion structure in tropical mesoscale convective systems

December, 1995.Bibliography: pages 178-187.Sponsored by National Oceanic and Atmospheric Administration NA37J0202

Ground-based detection of sprites and their parent lightning flashes over Africa during the 2006 AMMA campaign

Sprites have been detected in video camera observations from Niger over mesoscale convective systems in Nigeria during the 2006 AMMA (African Monsoon Multidisciplinary Analysis) campaign. The parent lightning flashes have been detected by multiple Extremely Low Frequency (ELF) receiving stations worldwide. The recorded charge moments of the parent lightning flashes are often in excellent agreement between different receiving sites, and are furthermore consistent with conventional dielectric breakdown in the mesosphere as the origin of the sprites. Analysis of the polarization of the horizontal magnetic field at the distant receivers provides evidence that the departure from linear magnetic polarization at ELF is caused primarily by the day–night asymmetry of the Earth–ionosphere cavity. Copyright © 2009 Royal Meteorological SocietyPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69175/1/489_ftp.pd

Airflow and precipitation structure of two leading stratiform mesoscale convective systems

Fall 2001.Also issued as author's thesis (M.S.) -- Colorado State University, 2001.Includes bibliographical references.An analysis of the airflow and precipitation structure of two leading stratiform (LS) mesoscale convective systems is presented. LS systems are defined as linear MCSs that consist of a convective line with leading stratiform rain. Case studies of LS systems on 30 April 2000 and 7 May 1997 were conducted using the available operational datasets. Several of the features observed, though not all, appear as a mirror image of those seen in trailing stratiform (TS) mesoscale convective systems. Their horizontal reflectivity structure has similar aspects, with convective cells which are sometimes elongated and canted with respect to the convective line, a transition zone of lower reflectivity, and an area of enhanced stratiform rain. Cold pools are situated beneath the convective line. The 30 April case shows a leading mesolow that resembles a TS wake low, but its propagation characteristics (and presumably dynamics) differ. A descending leading inflow jet, the counterpart of a rear inflow jet in a TS system, can be detected in both cases underneath a layer of strong ascending rear-to-front flow aloft. A few features of these LS systems are distinctive from TSs. Cells in the convective line appear to be more discontinuous and are elongated more than those of a TS. Rear­ feeding from an elevated Be maximum behind the system is an exclusive feature of these LSs, since TSs are typically fed from the boundary layer. Unlike the rear inflow jet in TS systems, neither case shows a reversal in the leading inflow jet as it descends to low levels near the convective line. Both cases exhibit front-to-rear surface flow throughout the LS systems. Finally, a schematic diagram is presented that illustrates the structure observed in the two cases, based heavily on a Doppler radar analysis of 7 May 1997.Sponsored by NSF under grant ATM-0071371, and a graduate fellowship from the American Meteorological Society

Master of Science

thesisThis work examines in detail the lifecycles of the convection on 20, 23, and 24 May 2011 during the Midlatitude Continental Convective Clouds Experiment (MC3E) field experiment in Oklahoma. Furthermore, specific attention is given to the environmental mechanisms that affect the propagation, maintenance, strength, and morphology of organized convection for the duration of the three cases. This study was conducted using the MC3E field campaign observational database, with particular emphasis on ground and airborne radar, radiosonde, and Oklahoma Mesonet data. This work was motivated by the goals of the MC3E field campaign, including improved understanding of convective evolution, organized convection, microphysics, ultimately leading to improvement of parameterization of convection and mesoscale processes in weather and climate models, and improvement of retrievals of precipitation by remote sensing. The three cases examined exhibited leading line/trailing stratiform mesoscale convective system, supercell, and back-building convective structures, each with a complex evolution. From the data analyzed for these cases, we suggest that given certain initial conditions, the vertical wind shear profile is the dominant factor in the determination of storm morphology. If the source of the buoyant updraft is renewed throughout a system's lifetime, then a convective system's propagation and longevity is tied strongly to the strength of the cold pool produced by convective downdrafts, and formation of new convection along the boundaries of the pool

Doctor of Philosophy

dissertationThis dissertation examines Weather Research and Forecasting (WRF) simulations of Great Salt Lake Effect (GSLE) precipitation. An evaluation of banded and nonbanded GSLE-event simulations shows that WRF has low skill predicting GSLE precipitation. An object-based verification method is used in this evaluation to quantify a precipitation bias that contributes to WRF models' low skill. We also analyze WRF simulations of the 27 October 2010 banded GSLE event to evaluate the sensitivity of precipitation prediction to the choice of microphysics parameterization (MP). WRF simulations of 11 banded and eight nonbanded GSLE events are evaluated with subjective, traditional, and object-based verification. Subjectively, a majority of simulations of banded GSLE events produce realistic precipitation features, whereas a majority of simulations of nonbanded GSLE events do not. Simulations of both banded and nonbanded GSLE events record low equitable threat scores, but simulations of banded GSLE events outperform simulations of nonbanded events. Verification using the Method for Object-based Diagnostic Evaluation (MODE) developed by Davis et al. shows that simulations of banded and nonbanded GSLE events exhibit a southward (rightward and downstream relative to the flow) bias in event total precipitation location that limits forecast skill. WRF simulations of the 27 October 2010 GSLE event are sensitive to the choice of MP. Precipitation simulated using the Thompson MP scheme (THOM) verifies best against radar-estimated precipitation and gauge observations. The Goddard, Morrison, and WRF double-moment 6-class (WDM6) schemes produce more precipitation than THOM, with WDM6 producing the most. Analyses of hydrometeor mass tendencies show that WDM6 creates more graupel and total precipitation than the other schemes and indicate that the rate of graupel and snow production can strongly influence the precipitation efficiency in simulations of lake-effect storms. These results show that significant improvements in deterministic model skill and/or the use of an ensemble approach are necessary to improve the reliability of GSLE simulations. Improved deterministic model skill will likely require observations of GSLE hydrometeor characteristics to improve MP, while rectifying the southward (rightward and downstream relative to the flow) precipitation location bias is crucial for deterministic and ensemble forecasting success