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At least 127 records · Page 7

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NASA NTRS1986

Thunderstorm cloud top dynamics as inferred from satellite observations and a cloud top parcel model

Thunderstorm top temperature-height structure and temperature-height conversion relations in the convective overshooting top region are examined using data from GOES IR, AVHRR, and aircraft overflights, and GOES stereoscopic observations. Using a Lagrangian one-dimensional cloud parcel model applied in the overshooting region, three classes of storm tops are described and the causes of their unique temperature-height structures are explored. Although the parcel model used does not fully reproduce the three-dimensional structure and dynamics of an evolving thunderstorm top, it is shown to crudely reproduce the parcel dynamics of updraft core parcels. The locations of cold points, high points, warm points, and the magnitude of cold-high offsets compare favorably between the model and the satellite observations.

Adler, Robert F.↗

NASA NTRS1988

Lightning threat extent of a small thunderstorm

The concern for safety of the personnel at the Kennedy Space Center (KSC) has caused NASA to promulgate strict safety procedures requiring either termination or substantial curtailment when ground lightning threat is believed to exist within 9.3 km of a covered operation. In cases where the threat is overestimated, in either space or time, an opportunity cost is accrued. This paper describes a small thunderstorm initiated over the KSC by terrain effects, that serves to exemplify the impact such an event may have on ground operations at the Center. Data from the Air Force Lightning Location and Protection System, the AF/NASA Launch Pad Lightning Warning System field mill network, radar, and satellite imagery are used to describe the thunderstorm and to discuss its impact.

Nicholson, James R.↗

NASA NTRS1988

Progress of research to identify rotating thunderstorms using satellite imagery

The possibility of detecting potentially tornadic thunderstorm cells from geosynchronous satelite imagery is determined. During the life of the contract, we examined eight tornado outbreak cases which had a total of 124 individual thunderstorm cells, 37 of which were tornadic.These 37 cells produced a total of 119 tornadoes. The outflow characteristics of all the cells were measured. Through the use of a 2-D flow field model, we were able to simulate the downstream developmemt of an anvil cloud plume which was emitted by the storm updraft at or near the tropopause. We used two parameters to characterize the anvil plume behavior: its speed of downstream propagation (U max) and the clockwise deviation of the centerline of the anvil plume from the storm relative ambient wind at the anvil plume outflow level (MDA). U max was the maximum U-component of the anvil wind parameter required to successfully maintain an envelope of translating particles at the tip of the expanding anvil cloud. MDA was the measured deviation angle acquired from McIDAS, between the storm relative ambient wind direction and the storm relative anvil plume outflow direction; tha latter being manipulated by controlling a tangential wind component to force the envelope of particles to maintain their position of surrounding the expanding outflow cloud.

Anderson, Charles E.↗

NASA NTRS1989

Electrical structure in two thunderstorm anvil clouds

Electrical structures in two thunderstorm anvil clouds (or 'anvils'), one in New Mexico, the other in Oklahoma, were investigated, using measurements of electric field by balloon-carried instruments and a one-dimensional model to calculate the time and spatial variations of electrical parameters in the clear air below the anvil. The electric field soundings through the two thunderstorm anvils showed similar charge structures; namely, negatively charged screening layers on the top and the bottom surfaces, a layer of positive charge in the interior, and one or two layers of zero charge. It is suggested that the positive charge originated in the main positive charge region normally found at high altitudes in the core of thunderclouds, and the negatively charged layers probably formed as screening layers, resulting from the discontinuity in the electrical conductivity at the cloud boundaries.

Marshall, Thomas C.↗

NASA NTRS1989

Electric field measurements within a severe thunderstorm anvil

This paper presents the results of electric field measurements made within a severe thunderstorm in central Oklahoma on June 13, 1983. The observations show the electrical structure of a severe storm anvil to be more complex than the simple structure of a positive interior and thin, negative screening layers. Evidence is found of extensive regions of both positive and negative charge in the interior of the anvil, and the thicknesses of screening layers are found to be about an order of magnitude greater than calculated in previous models. A conceptual model for the development of the electrical structure of thunderstorm anvils is proposed in which anvil dynamics plays an important role.

Byrne, G. J.↗

NASA NTRS1989

Short-term forecasting of thunderstorms at Kennedy Space Center, based on the surface wind field

Techniques incorporating wind convergence that can be used for the short-term prediction of thunderstorm development are described. With these techniques, the convergence signal is sensed by the wind network array 15 to 90 min before actual storm development. Particular attention is given to the convergence cell technique (which has been applied at the Kennedy Space Center) where each convective region is analyzed independently. It is noted that, while the monitoring of areal and cellular convergence can be used to help locate the seeds of developing thunderstorms and pinpoint the lightning threat areas, this forecasting aid cannot be used in isolation.

Watson, Andrew I.↗

NASA NTRS1990

Predicting thunderstorm evolution using ground-based lightning detection networks

Lightning measurements acquired principally by a ground-based network of magnetic direction finders are used to diagnose and predict the existence, temporal evolution, and decay of thunderstorms over a wide range of space and time scales extending over four orders of magnitude. The non-linear growth and decay of thunderstorms and their accompanying cloud-to-ground lightning activity is described by the three parameter logistic growth model. The growth rate is shown to be a function of the storm size and duration, and the limiting value of the total lightning activity is related to the available energy in the environment. A new technique is described for removing systematic bearing errors from direction finder data where radar echoes are used to constrain site error correction and optimization (best point estimate) algorithms. A nearest neighbor pattern recognition algorithm is employed to cluster the discrete lightning discharges into storm cells and the advantages and limitations of different clustering strategies for storm identification and tracking are examined.

Goodman, Steven J.↗

NASA NTRS1991

Thunderstorm detection and warning system atmospheric potential monitor

An new type of electric field instrumentation was developed for lighting prediction at KSC. Currently, it is being installed at several government laboratories and is being made available to the public. It has important advantages over the previous method for measuring electric fields with motor driven field mills: (1) it has no moving parts and requires little maintenance compared to rotating machinery; (2) it is unaffected by rain, snow, sand, or insects, all of which can influence field mills; and (3) the lightweight sensor can be mounted easily on a tall mast. By mounting the instrumentation on a tall mast the instrumentation is placed above much of the blanket of point discharge ions that are emitted from objects on the ground during thunderstorms. This space charge limits the ability of any ground based electric field sensor to accurately measure cloud electric fields which produce lightning. The elevated mounting was demonstrated to significantly improve monitoring of thunderstorm electric fields. This instrumentation measures the atmospheric potential relative to earth at a corona needle sensor on top of a mast which normally is mounted on a tower or roof. The needle is kept in corona at all times by a low power high voltage power supply. This produces a small cloud of ions around the needle allowing a current to flow. Measurement of the current provides the atmospheric potential. The potential divided by the height of the needle above the ground is proportional to the average electric field between the needle and earth. The potential on top of a tall pole or above a rooftop is more representative of the intensity of cloud electrification than electric field measurements made at ground level. Photographs that depict the computer terminal, video display of a two sensor system, and the individual components installed on a tower are presented.

Source record↗

NASA NTRS1990

Remote measurements of the structure of midwest thunderstorm tops and anvils from high altitude aircraft

Results are presented from observations by a visible and IR scanning radiometer, a scanning passive microwave radiometer, and a nadir-viewing cloud lidar system (CLS), carried out from ER-2 overflights for two midwest severe weather events both of which presented following phenomena: (1) a group of severe thunderstorms which later transformed into a linear mesoscale convective system, and (2) a severe thunderstorm which produced large hail. Most of the aircraft in situ and remote measurements pointed to a deep subsidence region and gravity waves downstream of the overshooting cloud tops. The observations do not support a radiative explanation for the warm areas in the anvil.

Heymsfield, Gerald M.↗

NASA NTRS1993

ER-2 investigations of lightning and thunderstorms

The primary objective of the ER-2 lightning program is to investigate relationships between lightning and storm electrification and a number of underlying and interrelated phenomena including the structure, dynamics, and evolution of thunderstorms and thunderstorm systems, precipitation distribution and amounts, atmospheric chemistry processes, and the global electric circuit. This research is motivated by the desire to develop an understanding needed for the effective utilization and interpretation of data from the Lighting Imaging Sensor (LIS), the Lightning Mapper Sensor (LMS), and other satellite-based lightning detectors planned for the late 1900's and early 2000's. These satellite lightning detection systems will be characterized by high detection efficiencies (i.e., 90 percent) and the capability to detect both intracloud and cloud-to-ground discharges during day and night. The Lightning Imaging Sensor (LIS) is being developed by NASA for the Tropical Rainfall Measuring Mission (TRMM) satellite. In the ER-2 and related investigations, the emphasis is on establishing quantitative relationships and developing practical algorithms that employ lightning data, such as could be derived from satellite observations of optical lightning emissions, as the independent variable. Significant accomplishments made during the past year are presented.

Blakeslee, Richard↗

NASA NTRS1992

Techniques used to identify tornado producing thunderstorms using geosynchronous satellite data

Satellite imagery in the outbreak region in the time prior to and during tornado occurrence was examined in detail to obtain descriptive characteristics of the anvil plume. These characteristics include outflow strength (UMAX), departure of anvil centerline from the storm relative ambient wind (MDA), storm relative ambient wind (SRAW), and maximum surface vorticity (SFCVOR). It is shown that by using satellite derived parameters which characterize the flow field in the anvil region, the occurrence and intensity of tornadoes, which the parent thunderstorm produces, can be identified. Analysis of the censored regression models revealed that the five explanatory variables (UMAX, MDA, SRAW, UMAX-2, and SFCVOR) were all significant predictors in the identification of tornadic intensity of a particular thunderstorm.

Schrab, Kevin J.↗

NASA NTRS1992

Final results of an experiment in operational forecasting of sea breeze thunderstorms using a mesoscale numerical model

Sea breeze thunderstorms during quiescent synoptic conductions account for 40 percent of Florida rainfall, and are the dominant feature of April-October weather at the Kennedy Space Center (KSC). An effort is presently made to assess the feasibility of a mesoscale numerical model in improving the point-specific thunderstorm forecasting accuracy at the KSC, in the 2-12 hour time frame. Attention is given to the Applied Regional Atmospheric Modeling System.

Lyons, Walter A.↗

NASA NTRS1993

Comment on 'The effect of liquid water on thunderstorm charging' by C.P.R. Saunders et al

This paper is a comment on the claims made in the paper by Saunders et al. (1991), which reports on a laboratory simulation of ice particle charging in thunderstorms, concerning the microphysical condition of riming ice particles and the conditions for sublimation and negative charging in thunderclouds. It is argued that the interpretation of Saunders is contrary to the findings of Williams et al. (1991), which support the hypothesis that sublimating graupel charge negatively (in collision with smaller ice particles) and graupel in deposition charge positively. Based on microphysical calculations as well as observations in thunderclouds, it is concluded that, while sublimation of the rimer surface and negative charging do not appear to account for the laboratory observations reported by Saunders et al., these authors do not have sufficient evidence for rejecting the sublimation hypothesis presented by Williams et al. (1991) for thunderstorms.

Williams, Earle↗

NASA NTRS1993

The application of VAS satellite imagery to thunderstorm forecasting at Cape Canaveral

The Final Report on the application of VAS satellite imagery to thunderstorm forecasting at Cape Canaveral is presented. The objective of this research was to investigate whether satellite-derived imagery and derived products could be used advantageously in forecasting thunderstorms in the Cape Canaveral area. Specifically, data from the VISSR Atmospheric Sounder that is housed on the current series of GOES geostationary meteorological satellites was used. These satellite data were used extensively in the middle latitudes, but their utility over central Florida where the climate is more tropical had not been examined.

Fuelberg, Henry E.↗

NASA NTRS1994

Low-light video observations of frequent luminous structures in the stratosphere above thunderstorms

A new series of video measurements were made of the phenomenon provisionally termed the cloud-to-stratosphere (CS) event, an electrical discharge extending to great heights above thunderstorm tops. This new series of measurements were accomplished by properly positioning a sensor, the Xybion model ISS 225 low-light monochrome imaging system with a C-mount fl.8 manual zoom lens, and training it on the appropriate portion of the sky above a distant thunderstorm complex mean Fort Collins, Colorado. The resulting images are currently undergoing intensive analysis. Some tentative conclusions are given. Cloud-to-stratosphere events occur far more frequently than previously suspected and are perhaps a ubiquitous aspect of many larger convective systems. Cloud-to-stratosphere events are also of substantial horizontal extent, on the order of tens of kilometers in some cases.

Lyons, Walter A.↗

NASA NTRS1999

Determination of Thunderstorm Anvil Ice Contents and Other Cloud Properties from Satellite Observations of Lightning

The lightning frequency model developed by Baker, Christian and Latham (1995) has been refined and extended, in an effort to provide a more realistic framework from which to examine computationally the relationships that might exist between lightning frequency f (which is now being routinely measured from satellites, using NASA/MSFC devices) and a variety of cloud physical parameters, including precipitation rate, updraught speed and non-precipitating ice content. The charging mechanism incorporated into the model is the non-inductive ice-ice mechanism - involving rebounding collisions between ice crystals and growing graupel pellets - which has achieved significant field, laboratory and modelling support in recent years. Model results indicate the existence of a simple relationship between lightning frequency f and the upward flux of ice crystals into the thunderstorm anvil. It follows that, for a particular situation, one can assign a specific mass of non-precipitating ice to an individual lightning stroke. Therefore it is possible - using satellite measurements of global lightning - to estimate the atmospheric loading of ice crystals in thunderstorm anvils: a parameter of climatological importance. One can also estimate the ice crystal loading associated with more localized storm systems. Early results from this work will be presented, together with further work on the relationships between f and other thundercloud parameters.

Blyth, Alan M.↗

NASA NTRS1999

Evidence for the Absence of Conductivity Variations above Thunderstorms

In recent years, atmospheric conductivity and electric field measurements over thunderstorms have been made at 20 km with a high altitude aircraft. After compensating for the effects of aircraft charging induced by external electric fields no significant variations in ambient conductivity above thunderstorms have been found. These Gerdien results contrast strongly with the large (and frequent) conductivity variations reported in studies using relaxation probe techniques.

Bailey, Jeff C.↗

NASA NTRS1999

Studies of Florida Thunderstorms Using LDAR, LLP, and Single Doppler Radar Data

The paper summarizes results from research conducted on thunderstorms in the vicinity of the Kennedy Space Center (KSC) Florida, between 1993 and 1998. The focus of the research was to identify procedures that would assist weather forecasters at the Cape Canaveral Air Station (CCAS) in real-time detection and forecasting of the lightning threat to launches and daily ground operations at KSC/CCAS sites. The research was divided into three topics: (1) studies aimed at improving the forecasting of the initial cloud-ground (CG) lightning threat, (2) studies aimed at improving the forecasting of the end-of-storm termination of the CG lightning threat, and (3) studies of the location of CG strikes relative to the thunderstorm radar echo and to lightning discharges aloft. Only the first two topics are covered in this preprint.

Forbes, Gregory S.↗