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NASA NTRS1989

Low level remote sensing: The Doppler Radar wind profiler

Mesoscale phenomena such as thunderstorm and sea breeze frontal circulations are being investigated using a 50 MHz Doppler wind profiler at the Kennedy Space Center. The profiler installation will begin October 1, 1988 and will be completed by February 17, 1989. The focus of current research and plans for next year include: examination of vertical velocities associated with local thunderstorm activity and sea breeze frontal circulations and compare the vertical velocities to conceptual mesoscale models; implementation of space-time conversion analysis techniques to blend profiler data with National Meteorological Center's model output and other wind data such as jimsphere, windsonde and rawinsonde for mesoscale analysis; development of suggestions for use of wind profiler data in mesoscale analysis and forecasting at Kennedy Space Center; and problems detection in the quality of the profiler data during this research project. Researchers will work closely with MSFC to identify and solve the data quality problems.

Forbes, Gregory S.↗

NASA NTRS1989

Effects of lightning on operations of aerospace vehicles

Traditionally, aircraft lightning strikes were a major aviation safety issue. However, the increasing use of composite materials and the use of digital avionics for flight critical systems will require that more specific lightning protection measures be incorporated in the design of such aircraft in order to maintain the excellent lightning safety record presently enjoyed by transport aircraft. In addition, several recent lightning mishaps, most notably the loss of the Atlas/Centaur-67 vehicle at Cape Canaveral Air Force Station, Florida in March 1987, have shown the susceptibility of aircraft and launch vehicles to the phenomenon of vehicle-triggered lightning. The recent findings of the NASA Storm Hazards Program were reviewed as they pertain to the atmospheric conditions conducive to aircraft lightning strikes. These data are then compared to recent summaries of lightning strikes to operational aircraft fleets. Finally, the new launch commit criteria for triggered lightning being used by NASA and the U.S. Defense Department are summarized. The NASA Research data show that the greatest probability of a direct strike in a thunderstorm occurs at ambient temperatures of about -40 C. Relative precipitation and turbulence levels were characterized as negligible to light for these conditions. However, operational fleet data have shown that most aircraft lightning strikes in routine operations occur at temperatures near the freezing level in non-cumulonimbus clouds. The non-thunderstorm environment was not the subject of dedicated airborne lightning research.

Fisher, Bruce D.↗

NASA NTRS1988

Final results of the NASA storm hazards program

Lightning swept-flash attachment patterns and the associated flight conditions were recorded from 1980-1986 during 1496 thunderstorm penetrations and 714 direct strikes with a NASA F-1068 research airplane. These data were studied with an emphasis on lightning avoidance by aircraft and on aircraft protection design. The individual lightning attachment spots, along with crew comments and on-board photographic data were used to identify lightning swept-flash attachment patterns and the orientations of the lightning channels with respect to the airplane. The full-scale in-flight data were compared to results from scale-model arc-attachment tests. The airborne and scale-model data showed that any exterior surface of this airplane may be susceptible to direct lightning attachment. In addition, the altitudes, ambient temperatures, and the relative turbulence and precipitation levels at which the strikes occurred in thunderstorms are summarized and discussed. It was found that the peak strike rate occurred at pressure altitudes betwen 38,000 ft and 40,000 ft, corresponding to ambient temperatures colder than -40 C.

Fisher, Bruce D.↗

NASA NTRS1991

Estimating Atmospheric Turbulence From Flight Records

Method for estimation of atmospheric turbulence encountered by airplanes utilizes wealth of data captured by multichannel digital flight-data recorders and air-traffic-control radar. Developed as part of continuing effort to understand how airplanes respond to such potentially hazardous phenomena as: clear-air turbulence generated by destabilized wind-shear layers above mountains and thunderstorms, and microbursts (intense downdrafts striking ground), associated with thunderstorms. Reconstructed wind fields used to predict and avoid future hazards.

Wingrove, R. C.↗

NASA NTRS1991

Effectivity of atmospheric electricity on launch availability

Thunderstorm days at KSC; percentage of frequency of thunderstorms (1957-1989); effect of lightning advisory on ground operations; Shuttle launch history; Shuttle launch weather history; applied meteorology unit; and goals/operational benefits. This presentation is represented by viewgraphs.

Ernst, John A.↗

NASA NTRS1990

Echo size and asymmetry - Impact on NEXRAD storm identification

The effects of echo shape and radar viewing angle on detecting small thunderstorms with the NEXRAD storm identification algorithms are examined. The amorphous low-level echo shapes are modeled as ellipses with major axes ranging from 5-15 km and minor axes varying between 2-5 km. The model echoes are then used to create a 'probability of detection' chart that demonstrates the impact of storm asymmetry on cell identification. The algorithm performance on small thunderstorms observed near Huntsville, Alabama and Kennedy Space Center, Florida is examined. A new algorithm based on the analysis of 15 storms observed in Florida, Alabama, and New Mexico is proposed that would identify storms as having lightning if 40 dBZ reflectivity is present at the -10 C level and the echo top exceeds 9 km. This algorithm would have a 100 percent probability of detecting lightning producing storms 4-33 min before the first flash, a 7 percent false alarm rate and a critical success index of 93 percent.

Buechler, Dennis E.↗

NASA NTRS1991

Microphysical and radiative characteristics of convective clouds during COHMEX

This paper has two purposes: first, to document the structure and evolution of two strong thunderstorms in Alabama using radar multiparameter data; and second, to relate the inferred microphysics to the resulting upwelling microwave radiance observed concurrently by high altitude aircraft. These measurements were collected during the COHMEX field program in the summer of 1986. The radar analysis includes a description of the parameters reflectivity Z, differential reflectivity Z(DR), linear depolarization ratio LDR, and hail signal HS for two thunderstorm cases on July 11, 1986. The simultaneous aircraft data include passive microwave brightness temperature, T(B), measurements at four frequencies ranging from 18 to 183 GHz, as well as visible and infrared data. The remote radar observations reveal the existence of large ice particles within the storms, which is likely to have caused the observed low microwave brightness temperatures. By relating the evolution of the radar measureables to the microwave T(B)s it has been found that knowledge of the storm microphysics and its evolution is important to adequately understand the microwave T(B)s.

Fulton, Richard↗

NASA NTRS1991

Computerized reduction of airborne foil impactor data

A new technique for reducing data obtained from a foil impactor carried on the T-28 thunderstorm penetration aircraft is described. The technique employs a video-image processing system that was originally developed for satellite imagery and a computer-reduction program that was originally developed for determining cloud-size distributions to count and size particle impressions on the foil. This eliminates the tedious manual processing that has limited the usefulness of such devices, while at the same time improving objectivity. The technique has been applied to foil data acquired in thunderstorms in the southeastern United States during the Cooperative Huntsville Meteorological Experiment, where most of the particles were at least roughly spherical. Its usefulness for storms in which highly irregular or fragile ice particles predominate has yet to be established.

Peterson, Bret A.↗

NASA NTRS1992

Severe turbulence and maneuvering from airline flight records

Digital flight records from reported clear-air turbulence incidents are used to determine winds, to determine maneuver G loads, and to analyze control problems. Severe turbulence is found downwind of mountains and thunderstorms associated with vortices in atmospheric waves. It is also found in strong updrafts above thunderstorm buildups that are not detected by onboard weather radar. An important finding is that there are large maneuvering loads in over half of the reported clear-air turbulence incidents. Maneuvering loads are determined through an analysis of the short-term variations in elevator deflection and aircraft pitch angle. For altitude control in mountain waves the results indicate that small pitch angle changes with proper timing are sufficient to counter the vertical winds. For airspeed control in strong mountain waves, however, there is neither the available thrust nor the quickness in engine response necessary to counter the large and rapid variations in horizontal wind.

Wingrove, R. C.↗

NASA NTRS1992

On the microwave measurement of precipitation in tropics

The difference between the brightness temperature structure over a typical tropical rain system and that of the midlatitude thunderstorms is examined. It is also determined how the brightness temperature and the rain rate relationship at the microwave frequencies deviates from that in the thunderstorms. It is shown, in particular, that the theoretical brightness temperature and rain rate relationship at 19.35 GHz provides good estimates of the surface rain rates for either convective or stratiform precipitation, but the relationship at 37 and 85.5 GHz may result in a significant overestimation of surface rain rate, especially for stratiform precipitation.

Weng, Fuzhong↗

NASA NTRS1993

Global surface temperatures and the atmospheric electrical circuit

To monitor future global temperature trends, it would be extremely useful if parameters nonlinearly related to surface temperature could be found, thereby amplifying any warming signal that may exist. Evidence that global thunderstorm activity is nonlinearly related to diurnal, seasonal and interannual temperature variations is presented. Since global thunderstorm activity is also well correlated with the earth's ionospheric potential, it appears that variations of ionospheric potential, that can be measured at a single location, may be able to supply valuable information regarding global surface temperature fluctuations. The observations presented enable a prediction that a 1 percent increase in global surface temperatures may result in a 20 percent increase in ionospheric potential.

Price, Colin↗

NASA NTRS1994

The gradient of meteorological and chemical variables across the tropopause

The downward transport of air through the tropopause can bring substantial amounts of ozone and reactive nitrogen into the upper troposphere. In this cold region of the atmosphere, O3 is particularly effective as a greenhouse gas. As part of the North Dakota Thunderstorm Project in June 1989, the NCAR Sabreliner made five flights through the tropopause. We measured ozone, nitric oxide (NO), total reactive nitrogen (NO(y)), carbon monoxide (CO), and water vapor (H2)), and took grab samples for hydrocarbon (HC) analysis. Hydrocarbons, CO, and H2O, species with sources primarily at the earth's surface, showed a strong concentration decrease with increasing altitude, while O3 and NO(y), species with a source in the stratosphere, showed a strong concentration increase with increasing altitude. Stratospheric concentrations of NO(x), NO(y), and H2O were all high relative to winter observations made during NASA's AASE. We suggest that midlatitude thunderstorms may inject wet, NO-rich air into the lower stratosphere. Calculation based on measured ratios of NO(x) and NO(y) to O3 yield a total flux of reactive nitrogen from the Northern Hemisphere stratosphere into the troposphere of 1 to 2 Tg(N) yr(exp -1) with about 8 percent in the form of NO(x). This value is higher than reported estimates of total stratospheric nitrogen fixation.

Dickerson, Russell R.↗

NASA NTRS1994

Experiments with the Mesoscale Atmospheric Simulation System (MASS) using the synthetic relative humidity

This study is intended to examine the impact of the synthetic relative humidity on the model simulation of mesoscale convective storm environment. The synthetic relative humidity is derived from the National Weather Services surface observations, and non-conventional sources including aircraft, radar, and satellite observations. The latter sources provide the mesoscale data of very high spatial and temporal resolution. The synthetic humidity data is used to complement the National Weather Services rawinsonde observations. It is believed that a realistic representation of initial moisture field in a mesoscale model is critical for the model simulation of thunderstorm development, and the formation of non-convective clouds as well as their effects on the surface energy budget. The impact will be investigated based on a real-data case study using the mesoscale atmospheric simulation system developed by Mesoscale Environmental Simulations Operations, Inc. The mesoscale atmospheric simulation system consists of objective analysis and initialization codes, and the coarse-mesh and fine-mesh dynamic prediction models. Both models are a three dimensional, primitive equation model containing the essential moist physics for simulating and forecasting mesoscale convective processes in the atmosphere. The modeling system is currently implemented at the Applied Meteorology Unit, Kennedy Space Center. Two procedures involving the synthetic relative humidity to define the model initial moisture fields are considered. It is proposed to perform several short-range (approximately 6 hours) comparative coarse-mesh simulation experiments with and without the synthetic data. They are aimed at revealing the model sensitivities should allow us both to refine the specification of the observational requirements, and to develop more accurate and efficient objective analysis schemes. The goal is to advance the MASS (Mesoscal Atmospheric Simulation System) modeling expertise so that the model output can provide reliable guidance for thunderstorm forecasting.

Chang, Chia-Bo↗

NASA NTRS1994

Coupling of ELF/ULF energy from lightning and MeV particles to the middle atmosphere, inosphere, and global circuit

In an attempt to explain numerous atmospheric electrical phenomena, the elements of the global electrical circuit are reexamined. In addition to being a 'quasi-static 'DC' generator' and source of radiated energy at VLF and higher, the thunderstorm is found to be a pulse generator, with most of the external energy contained in ELF and ULF pulse currents to the ionosphere (and Earth). The pulse energy is found to deposit largely in the middle atmosphere above the thunderstorm. The VLF and above components are well understood, as are the ULF components due to the conductivity gradient. However, a previously poorly understood ELF component on the millsecond timescale, or 'slow tail,' contains a large fraction of the electrical energy. This component couples strongly to the ionosphere and also launches a unipolar transverse electromagnetic (TEM) wavelet in the radial Earth-ionosphere transmission line. The increase in charge with distance associated with such wavelets, and their ensemble sum at a point, may explain some large mesospheric 'DC' fields but there are still difficulties explaining other than rare occurrences, except for antipodal reconvergence. These millisecond duration unipolar wavelets also coupled to the ionosphere and may trigger other lightning at a distance. A schema is elucidated by which the charge of MeV particles deposited in the middle atmosphere persists for much longer than the local relaxation time. This also gives rise to unipolar waves of global extent which may explain lower-latitude field perturbations associated with solar/geomagnetic events.

Hale, Leslie C.↗

NASA NTRS1995

Observations of lightning in the stratosphere

An examination and analysis of video images of lightning, captured by the payload bay TV cameras of the space shuttle, provided a variety of examples of lightning in the stratosphere above thunderstorms. These images were obtained on several recent shuttle flights while conducting the Mesoscale Lightning Experiment (MLE). The images of stratospheric lightning illustrate the variety of filamentary and broad vertical discharges in the stratosphere that may accompany a lightning flash. A typical event is imaged as a single or multiple filament extending 30 to 40 km above a thunderstorm that is illuminated by a series of lightning strokes. Examples are found in temperate and tropical areas, over the oceans, and over the land.

Boeck, William L.↗

NASA NTRS1995

Preliminary results from the Sprites94 aircraft campaign: 2. Blue jets

Initial observations of a newly documented type of optical emission above thunderstorms are reported. 'Blue jets', or narrowly collimated beams of blue light that appear to propagate upwards from the tops of thunderstorms, were recorded on B/W and color video cameras for the first time during the Sprites94 aircraft campaign, June-July, 1994. The jets appear to propagate upward at speeds of about 100 km/s and reach terminal altitudes of 40-50 m. Fifty six examples were recorded during a 22 minute interval during a storm over Arkansas. We examine some possible mechanisms, but have no satisfactory theory of this phenomenon.

Wescott, E. M.↗

NASA NTRS1995

Instrument Records Magnetic Fields Generated By Lightning

Portable, self-contained, compact instrument measures and records transient magnetic fields particularly those generated by nearby lightning strikes. Designed to be placed near sensitive electronic equipment in anticipation of thunderstorms. Data recorded during thunderstorms analyzed afterward to determine whether magnetic effects of lightning strong enough to have damaged and/or affected operation of sensitive equipment. Provides data helping engineers decide whether sensitive equipment should be tested for damage and/or other effects caused by lightning. Typical installations in which instrument beneficial include outdoor sensing equipment, computer rooms, broadcasting stations, and powerplant control rooms.

Medelius, Pedro J.↗

NASA NTRS1995

Optical imaging of cloud-to-stratosphere/mesosphere lightning over the Amazon Basin (CS/LAB)

The purpose of the CS/LAB project was to obtain images of cloud to stratosphere lightning discharges from aboard NASA's DC-8 Airborne Laboratory while flying in the vicinity of thunderstorms over the Amazon Basin. We devised a low light level imaging package as an add-on experiment to an airborne Laboratory deployment to South America during May-June, 1993. We were not successful in obtaining the desired images during the South American deployment. However, in a follow up flight over the American Midwest during the night of July 8-9, 1993 we recorded nineteen examples of the events over intense thunderstorms. From the observations were estimated absolute brightness, terminal altitudes, flash duration, horizontal extents, emission volumes, and frequencies relative to negative and positive ground strokes.

Sentman, Davis D.↗