Engineering topics

Knupp, Kevin R.

Publications and source records attributed to Knupp, Kevin R..

18 records

NASA NTRS2018

Observed Response of the Raindrop Size Distribution to Changes in the Melting Layer

Vertical variability in the raindrop size distribution (RSD) can disrupt the basic assumption of a constant rain profile that is customarily parameterized in radar-based quantitative precipitation estimation (QPE) techniques. This study investigates the utility of melting layer (ML) characteristics to help prescribe the RSD, in particular the mass-weighted mean diameter (Dm), of stratiform rainfall. We utilize ground-based polarimetric radar to map the ML and compare it with Dm observations from the ground upwards to the bottom of the ML. The results show definitive proof that a thickening, and to a lesser extent a lowering, of the ML causes an increase in raindrop diameter below the ML that extends to the surface. The connection between rainfall at the ground and the overlying microphysics in the column provide a means for improving radar QPE at far distances from a ground-based radar or close to the ground where satellite-based radar rainfall retrievals can be ill-defined.

Weather↗

NASA NTRS2012

Dual-Polarimetric Radar-Based Tornado Debris Signatures and Paths Associated with Tornadoes Over Northern Alabama During the Historic Outbreak of 27 April 2011

A 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 40 tornadoes, including 6 that reached EF-4 to EF-5 on the Enhanced Fujita damage scale. In northern Alabama alone, there were approximately 100 fatalities and hundreds of people who were injured or lost their homes during the havoc caused by these violent tornadic storms. Many of these 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. The focus of this paper is to analyze the dual-polarimetric radar-inferred tornado debris signatures in 6 tornadoes in North Alabama on April 27, 2011. Several of these debris signatures were disseminated in real-time to the NWS Huntsville and local media to confirm storm spotter reports, confidence to enhance wording within warnings, and accurately pinpoint the locations of tornadoes for residents downstream of the storm. Also, the debris signature locations were used in post-event storm surveys to help locate areas of damage in regions where damage went unreported, or to help separate tornado tracks that were in close proximity to each other. Furthermore, the relative locations of the debris and damage paths for long track EF-4 and EF-5 tornadoes 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.

Carey, Lawrence D.↗

NASA NTRS2012

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.

Carey, Lawrence D.↗

NASA NTRS2011

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."

Carey, Lawrence D.↗

NASA NTRS2008

The 2008 Super Tuesday Tornado Outbreak: Overview of the Tornadoes and their Parent Storms

The cold-season Tornado outbreak that occurred over the Southeast on 5-6 February 2008 was significant for the following reasons: about 84 tornadoes were documented over a 15 h period between late afternoon on 5 February and early morning on 6 February 2008; a wide variety of parent storms were associated with the tornadoes; a total of five EF-4 tornadoes occurred, with two forming over Alabama during the early morning hours prior to sunrise; there was a significant lull period between the initial convective and the early morning activity over Alabama 10 hours later; and, a wide spectrum of storm types, ranging from isolated supercell storms to QLCS bow echoes, accompanied the tornadoes. The goal of this paper is to provide a general description of the outbreak including the distribution of tornadoes and supercell storms over the region, a detailed map of the tornado tracks, time series of tornadoes and parent storms, and general characteristics of all parent tornado storms. The total number of major storms (duration greater than 3 h, at least three tornadoes produced) was seven. Several noteworthy storms are described: a long track (198 km long) tornado and its parent storm over Arkansas; a prolific supercell storm persisted for 7-8 hours and produced 16 tornadoes from north-central Mississippi to southern KY; and, bow echo storms (QLCS's) were simultaneous over KY and produced 16 tornadoes.

Knupp, Kevin R.↗

NASA NTRS2008

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.

Knupp, Kevin R.↗

NASA NTRS2004

Strong Updraft Feature Associated with Hurricane Earl During Landfall

On 2-3 September 1998 hurricane Earl made landfall along the Gulf of Mexico coast, east of Panama City, FL. The University of Alabama in Huntsville Mobile Integrated Profiling System (MIPS) was located at the airport in Tallahassee, FL and made measurements of Earl with a 915 MHz Doppler wind profiler as the system moved across the Florida panhandle. As the center of Earl approached MIPS, a particularly strong updraft feature, having a magnitude of approx. 15 m/s within the lowest 3.0 km above ground level was associated with a rain band. An analysis of the changes hurricane Earl underwent as it made landfall are presented. Measurements used include surface thermodynamic and pressure observations, lightning data, National Weather Service Doppler Weather Surveillance Radar (WSR-88D) data, and Geostationary Earth Orbiting Satellite (GOES) data. Then an analysis focusing on the boundary layer properties and the updraft feature's depth, intensity and duration as measured by the MIPS 915 MHz Doppler wind profiler are presented.

Roberts, Barry C.↗

NASA NTRS2004

Correlation of Lightning Flash Rates with a Microburst Event

In 1986 the MIST (Microburst and Severe - Thunderstorm) field study took place over northern Alabama. It was noted that the time of day when a peak in microburst activity was observed usually took place around 2000 UTC. It was further confirmed through the examination of the various PAM (Portable Automated Mesonet) stations that this was also the time of day where temperatures would reach their peak. On the afternoon of 18 August 2002, as the temperature approached a daily high temperature of 32 C, the first radar indication of the HSV microburst-producing storm initiated at 2020 UTC.

Altino, Karen M.↗

NASA NTRS1998

A Low Precipitation Supercell over the Southeast US: A Case Study

On 28 March 1997 a low precipitation supercell storm was observed 125 km east of Memphis, TN. The storm exhibited a visual appearance similar to that of Great Plains low precipitation (LP) supercells while it was being video typed for 35 min. beginning at 2335 UTC. While the storm produced hailstones up to 4.5 cm in diameter, and had a 4 hour lifetime, tornadoes were absent. However, over 20 tornadoes were produced in Kentucky and Tennessee (TN) by other thunderstorms during that afternoon and evening. The purpose of this paper is to document this LP supercell that occurred in the Southeastern US. To the authors' knowledge an LP storm has not yet been documented in the Southeastern US. This paper presents a detailed overview of the LP supercell, including synoptic conditions, radar observations, lightning data and visual observations of the storm.

Robert, Barry C.↗

NASA NTRS1991

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.

Knupp, Kevin R.↗

NASA NTRS1991

Kinematic and precipitation structure of a small, long-lived mesoscale convective system

A comprehensive analysis using conventional single Doppler radar analyses, analysis of multiparameter (CP-2) data, network sounding and surface data, and GOES satellite data is presented to characterize the internal kinematic and precipitation structure of a small, long-lived mesoscale convective system. The data pertain to the Cooperative Huntsville Meteorological experiment conducted over northern Alabama and central Tennessee during June and July of 1986. The mesoscale convective system pulsations visible in the IR patterns were associated with the development of closely interacting aggregates of convective elements. The aggregates were about 20 km in diameter, attained echo tops of about 13 km, and were dominated by a single relatively intense convective element. The measured difference in radial velocity across the upper portion of these elements was about 20 m/s over a distance of about 10 km.

Knupp, Kevin R.↗

NASA NTRS1990

Radar observations of precipitation growth and evolution within the anvil region of a MCS

Doppler radar observations of the growth and evolution of precipitation (reflectivity factor) and associated mesoscale motions within the anvil region of an evolving mesoscale convective system (MCS) are presented. This MCS was observed during the Cooperative Huntsville Meteorological Experiment conducted over northern Alabama and central Tennessee during June and July, 1986. During the latter stages of the approximate eight-hour lifetime of this MCS, an extensive region of stratiform precipitation was observed. Attention is given to the initial appearance and subsequent evolution of precipitation within the stratiform region of the MCS, and the relation to the mesoscale flows that are seen within the system.

Knupp, Kevin R.↗

NASA NTRS1990

Tornadogenesis via squall line and supercell interaction revisited - The 15 November 1989 Huntsville tornado

A case study analyzing the environmental setting and storm system morphology that provides observational evidence of a mechanism involving the interaction of a gust front with a preexisting mesocyclone is presented. This case serves to reemphasize the existence of a high conditional probability of tornado occurrence, given the merger of a gust front (or storm outflow) with a moderate to strong thunderstorm ahead of it. The resultant data serve to illustrate some important unresolved issues relevant to the severe weather warning system that involve the present and planned local warning and network radars, and future algorithms that might intelligently integrate other data sources and models with the radar data.

Goodman, Steven J.↗

NASA NTRS1989

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.

Knupp, Kevin R.↗

NASA NTRS1989

Observed structural variability of deep moist convection within a mesoscale convective system

Some radar observations of the convective cloud structure within and around a developing mesoscale convective system (MCS), which attained an eventual horizontal dimension of approximately 100 by 200 km, are reported. Similarities in cloud structure within and outside the MCS include a downshear tilt of the cloud precipitation core and generation of new cells toward the direction of cloud motion and parallel to the major axis of the cloud line. The systematic difference in the longevity and intensity of the clouds is examined.

Knupp, Kevin R.↗

NASA NTRS1988

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.

Knupp, Kevin R.↗

NASA NTRS1987

Downdrafts within High Plains cumulonimbi. I - General kinematic structure

Results from a comprehensive investigation in which observations from several case studies are integrated with three-dimensional cloud model results to examine the general kinematic structure of downdrafts associated with High Plains precipitating convection are presented. One particular downdraft type, the low-level precipitation-associated downdraft, is the focus of this paper. General airflow and trajectory patterns within low-level downdrafts are convergent from 0.8 km upwards to downdraft top, typically less than 5 km AGL. Observed mass flux profiles often increase rapidly with height as a result of strong buoyancy forcing below the melting level. Inflow to the low-level downdraft, although vertically continuous can be separated into two branches. The up-down branch originating within the planetary boundary layer initially rises up to 4 km and then descends within the main precipitation-associated downdraft. The midlevel branch, usually more pronounced during early downdraft stages, originates from above the PBL and transports low-valued theta sub e air to low levels. The depth of the low-level downdraft can be approximated by the environmental sounding transition level, defined as the vertical height interval separating conditionally unstable to neutral air below from roughly stable air above. The low-level downdraft is most frequently located along the upshear storm flank relative to the updraft, although a downshear downdraft may become common under higher environmental wind shear.

Knupp, Kevin R.↗

NASA NTRS1987

Multiscale analysis of a sustained precipitation event

Mesoscale data collected during both the satellite precipitation and cloud experiment and the microburst and severe thunderstorm program are analyzed in order to describe features associated with two distinct mesoscale precipitation events that occurred about 10 hours apart over the region of northern Alabama to central Tennessee in June 1986. Data sets used include mesobeta-scale rawinsonde data, surface mesonet data, RADAP data, and GOES images. The present mesoscale environment involved the merger of Hurricane Bonnie remnants with a preexisting midlatitude short-wave trough.

Knupp, Kevin R.↗