Analysis and modeling of summertime convective cloud and precipitation structure over the Southeastern United States

Data analysis and numerical modeling efforts that are related to the 1986 Satellite Precipitation and Cloud Experiment (SPACE) are discussed. Progress during this period includes the following: further testing and development of the RAMS numerical modeling system on the Alabama CRAY X-MP/24; a continuation of the observational analysis of the 13 July 1986 mesoscale convective system (MCS); and an initial investigation of a small MCS that formed over the COHMEX region on 15 July 1986. Details for each of these individual tasks are given

Precipitating convective cloud downdraft structure: a synthesis of observations and modeling

1985 Spring.Includes bibliographical references (pages 249-264).Original is missing pages 241, 261, and 277.This study represents a comprehensive investigation in which observations are integrated with three-dimensional cloud model results to examine the kinematic, dynamic and thermodynamic structure of downdrafts associated with precipitating convection. One particular downdraft type, the low-level precipitation-associated downdraft, is investigated in considerable detail. It is shown that this downdraft exhibits significant structural, dynamic and thermodynamic properties which differ appreciably from other independent downdrafts within precipitating convective clouds. General airflow and trajectory patterns within low-level downdrafts are typically convergent from ~0.8 km upwards to downdraft top, typically less than 5 km AGL. Observed mass flux profiles often increase rapidly with decreasing height as a result of strong buoyancy forcing below the melting level. Such patterns indicate that strong cooling by melting and evaporation within statically unstable low levels generates low perturbation pressure by virtue of buoyantly-induced pressure perturbations. Cloud model results verify this process and indicate that pressure perturbations are strongest during downdraft developing stages. Maximum modeled pressure reductions up to 2 mb are located within downdrafts and precipitation about 0.6 km below the 273 K level approximately 10 min after heavy precipitation (˃ 2 g kg¯¹) enters low levels. The magnitude of this buoyantly-produced pressure reduction is influenced by temperature, static stability, relative humidity and precipitation characteristics. Model results and related calculations indicate that cooling provides the impetus for downdraft formation. Melting, in particular is generally found to make significant contribution to total cooling in cases having relatively shallow (˂ 2 km) PBL. Cooling by evaporation becomes increasingly important as PBL depth increases. Inflow to the low-level downdraft, although vertically continuous, can be separated into two branches. The up-down branch originating within the PBL initially rises up to 4 km and then descends within the main precipitation downdraft. The midlevel branch, most pronounced during early downdraft stages, originates from above the PBL and transports low-valued ϴₑ to low levels. Pressure forces important along both branches act to lift stable air along the up-down branch, and provide downward forcing of positively-buoyant air in the upper regions of both branches. Two primary conclusions are drawn from the results of this study: (1) Downdrafts are driven at low levels within regions of strong static instability by strong cooling provided by melting and evaporation. Cloud level entrainment effects make secondary contributions. (2) Precipitation size and phase (e.g. melting) are probably the most important controlling parameters for downdraft strength.Sponsored by National Science Foundation - ATM-7908297 - ATM-8113082 - ATM-8312077.Sponsored by the National Aeronautics and Space Administration - NSF-5341.Sponsored by Air Force Geophysics Laboratory - F19628-84-C-0005

Analysis and modeling of summertime convective cloud and precipitation structure over the southeastern United States

Described is work performed under NASA Grant NAG8-654 for the period 15 March to 15 September 1988. This work entails primarily data analysis and numerical modeling efforts related to the 1986 Satellite Precipitation and Cloud Experiment (SPACE). In the following, the SPACE acronym is used along with the acronym COHMEX, which represents the encompassing Cooperative Huntsville Meteorological Experiment. Progress made during the second half of the first year of the study included: (1) installation and testing of the RAMS numerical Modeling system on the Alabama CRAY X-MP/24; (2) a start on the analysis of the mesoscale convection system (MCS) of 13 July 1986 COHMEX case; and (3) a cursory examination of a small MCS that formed over the COHMEX region on 15 July 1986. Details of each of these individual tasks are given

Analysis and modeling of summertime convective cloud and precipitation structure over the Southeastern United States

A summary of an investigation of deep convective cloud systems that typify the summertime subtropical environment of northern Alabama is presented. The major portion of the research effort included analysis of data acquired during the 1986 Cooperative Huntsville Meteorological Experiment (COHMEX), which consisted of the joint programs Satellite Precipitation and Cloud Experiment (SPACE) under NASA direction, the Microburst and Service Thunderstorm (MIST) Program under NSF sponsorship, and the FAA-Lincoln Laboratory Weather Study (FLOWS). This work relates closely to the SPACE component of COHMEX, one of the general goals of which was to further the understanding of kinematic and precipitation structure of convective cloud systems. The special observational plateforms that were available under the SPACE/COHMEX Program are shown. The original objectives included studies of both isolated deep convection and of (small) mesoscale convection systems that are observed in the Southeast environment. In addition, it was proposed to include both observational and comparative numerical modeling studies of these characteristic cloud systems. Changes in scope were made during the course of this investigation to better accommodate both the manpower available and the data that was acquired. A greater emphasis was placed on determination of the internal structure of small mesoscale convective systems, and the relationship of internal dynamical and microphysical processes to the observed cloud top behavior as inferred from GOES IR (30 min) data. The major accomplishments of this investigation are presented

The 2008 Super Tuesday Tornado Outbreak: Synthetic Dual Doppler Analysis of Contrasting Tornadic Storm Types

During the Super Tuesday Tornado Outbreak on 5-6 February, a significant number of storms passed within about 40 km of WSR-88D radars. This distance, combined with the significant motion vector (from the southwest at 20-25 m per second) of relatively steady storms, is amenable to a synthetic dual Doppler analysis during the times when the storms passed the WSR-88D locations. Nine storms will be analyzed using the SDD technique. The following table provides their general characteristics and nearest approach to the 88D radars. For this data set, storm structure ranges from isolated supercell to QLCS. Each storm will be analyzed for a 40-60 min period during passage by the WSR-88D radar to determine general storm properties. Analysis of high-resolution single Doppler data around the time of passage (plus or minus 30 min), combined with 1-2 SDD analyses, will be used to examine the kinematic structure of low-level circulations (e.g., mesocyclone, downdraft) and the relation to the parent storm. This analysis may provide insights on the fundamental differences between cyclonic circulations in supercell storms and those within QCLS's

Dual-Polarimetric Radar-Based Tornado Debris Paths Associated with EF-4 and EF-5 Tornadoes over Northern Alabama During the Historic Outbreak of 27 April 2011

An historic tornado and severe weather outbreak devastated much of the southeastern United States between 25 and 28 April 2011. On 27 April 2011, northern Alabama was particularly hard hit by a large number of tornadoes, including several that reached EF-4 and EF-5 on the Enhanced Fujita damage scale. In northern Alabama alone, there were approximately 100 fatalities and hundreds of more people who were injured or lost their homes during the havoc caused by these violent tornadic storms. Two long-track and violent (EF-4 and EF-5) tornadoes occurred within range of the University of Alabama in Huntsville (UAHuntsville) Advanced Radar for Meteorological and Operational Research (ARMOR, C-band dual-polarimetric). A unique capability of dual-polarimetric radar is the near-real time identification of lofted debris associated with ongoing tornadoes on the ground. The focus of this paper is to analyze the dual-polarimetric radar-inferred tornado debris signatures and identify the associated debris paths of the long-track EF-4 and EF-5 tornadoes near ARMOR. The relative locations of the debris and damage paths for each tornado will be ascertained by careful comparison of the ARMOR analysis with NASA MODIS (Moderate Resolution Imaging Spectroradiometer) and ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite imagery of the tornado damage scenes and the National Weather Service tornado damage surveys. With the ongoing upgrade of the WSR-88D (Weather Surveillance Radar - 1988 Doppler) operational network to dual-polarimetry and a similar process having already taken place or ongoing for many private sector radars, dual-polarimetric radar signatures of tornado debris promise the potential to assist in the situational awareness of government and private sector forecasters and emergency managers during tornadic events. As such, a companion abstract (Schultz et al.) also submitted to this conference explores "The use of dual-polarimetric tornadic debris signatures in an operational setting.

Stratosphere-to-Troposphere Transport Revealed by Ground-based Lidar and Ozonesonde at a Midlatitude Site

This paper presents ozone structures measured by a ground-based ozone lidar and ozonesonde at Huntsville, Alabama, on 27-29 April 2010 originating from a stratosphere-to-troposphere transport event associated with a cutoff cyclone and tropopause fold. In this case, the tropopause reached 6 km and the stratospheric intrusion resulted in a 2-km thick elevated ozone layer with values between 70 and 85 ppbv descending from the 306-K to 298-K isentropic surface at a rate of 5 km day1. The potential temperature was provided by a collocated microwave profiling radiometer. We examine the corresponding meteorological fields and potential vorticity (PV) structures derived from the analysis data from the North American Mesoscale model. The 2-PVU (PV unit) surface, defined as the dynamic tropopause, is able to capture the variations of the ozone tropopause estimated from the ozonesonde and lidar measurements. The estimated ozone/PV ratio, from the measured ozone and model derived PV, for the mixing layer between the troposphere and stratosphere is approximately 41 ppbv/PVU with an uncertainty of approximately 33%. Within two days, the estimated mass of ozone irreversibly transported from the stratospheric into the troposphere is between 0.07 Tg (0.9 10(exp33) molecules) and 0.11 Tg (1.3 10(exp33) molecules) with an estimated uncertainty of 59%. Tropospheric ozone exhibited enormous variability due to the complicated mixing processes. Low ozone and large variability were observed in the mid-troposphere after the stratospheric intrusion due to the westerly advection including the transition from a cyclonic system to an anticyclonic system. This study using high temporal and vertical-resolution measurements suggests that, in this case, stratospheric air quickly lost its stratospheric characteristics once it is irreversibly mixed down into the troposphere

Multisensor Estimation of Mixing Heights over a Coastal City

© Copyright 2008 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act September 2010 Page 2 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (https://www.ametsoc.org/) or from the AMS at 617-227-2425 or [email protected] airborne microwave temperature profiler (MTP) was deployed during the Texas 2000 Air Quality Study (TexAQS-2000) to make measurements of boundary layer thermal structure. An objective technique was developed and tested for estimating the mixed layer (ML) height from the MTP vertical temperature profiles. The technique identifies the ML height as a threshold increase of potential temperature from its minimum value within the boundary layer. To calibrate the technique and evaluate the usefulness of this approach, coincident estimates from radiosondes, radar wind profilers, an aerosol backscatter lidar, and in situ aircraft measurements were compared with each other and with the MTP. Relative biases among all instruments were generally less than 50 m, and the agreement between MTP ML height estimates and other estimates was at least as good as the agreement among the other estimates. The ML height estimates from the MTP and other instruments are utilized to determine the spatial and temporal evolution of ML height in the Houston, Texas, area on 1 September 2000. An elevated temperature inversion was present, so ML growth was inhibited until early afternoon. In the afternoon, large spatial variations in ML height developed across the Houston area. The highest ML heights, well over 2 km, were observed to the north of Houston, while downwind of Galveston Bay and within the late afternoon sea breeze ML heights were much lower. The spatial variations that were found away from the immediate influence of coastal circulations were unexpected, and multiple independent ML height estimates were essential for documenting this feature.Texas Air Research Center National Aeronautics and Space Administration National Oceanic and Atmospheric Administration Texas Commission on Environmental Qualit

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