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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Satellite infrared imagery, rawinsonde data, and gravity wave remote sensing of severe convective storms

GOES digital infrared data during the time period between two hours before the touchdown of tornado and the tornado touchdown time were used in this study. Comparison between tornado-associated clouds and non-tornado-associated clouds indicates that the difference between overshooting cloud top temperature and the tropopause temperature, or how much the cloud has penetrated above the tropopause, rather than either the absolute temperature of penetrative cloud top or the height of the top of overshooting turret is significant for the possible formation of severe storms. The penetrative overshooting cloud top collapses about 15 to 30 minutes before the touchdown of tornado. Gravity waves were detected from the severe convective storms.

Hung, R. J.↗
NASA NTRS1985

Convective storm downdraft outflows detected by NASA/MSFC's Airborne 10.6 micron pulsed Doppler Lidar System

The capability of a unique Airborne Doppler Lidar System to measure the horizontal winds in the vicinity of severe storm activity is demonstrated. The Airborne Doppler Lidar System (ADLS), developed at NASA/MSFC, was flown on a CV990 research aircraft during the CCOPE (Cooperative Convective Precipitation Experiments, Montana, Summer 1981). Flown between 400 and 600 m AGL, the lidar probed the subcloud regions of several deep convection storms. ADLS data collected near storms on 21 and 23 July 1981 are presented along with satellite imagery, radar echo maps and surface station measurements. These case studies are evidence of the successful performance of an airborne remote wind sensing system and the advantages of two dimension flow visualization of storm outflow structures and interactions.

Emmitt, G. D.↗
NASA NTRS1980

Evaluation and development of satellite inferences of convective storm intensity using combined case study analysis and thunderstorm model simulations

Major research accomplishments which were achieved during the first year of the grant are summarized. The research concentrated in the following areas: (1) an examination of observational requirements for predicting convective storm development and intensity as suggested by recent numerical experiments; (2) interpretation of recent 3D numerical experiments with regard to the relationship between overshooting tops and surface wind gusts; (3) the development of software for emulating satellite-inferred cloud properties using 3D cloud model predicted data; and (4) the development of a conceptual/semi-quantitative model of eastward propagating, mesoscale convective complexes forming to the lee of the Rocky Mountains.

Cotton, W. R.↗
NASA NTRS1988

Use of VAS data to diagnose the mesoscale environment of convective storms

The utility of VISSR Atmospheric Sounder (VAS) retrieval datasets for mesoscale analysis is explored. A detailed mesoscale air mass analysis method is presented in which VAS soundings, satellite imagery, and conventional surface data are used to diagnose mesoscale differences in air mass character. Comparisons are made with radiosonde observations of the same air mass differences. A mesoscale air mass analysis is presented with a discussion of the role that the various air masses play in subsequent convective development. In a second technique, several VAS-derived thermodynamic parameters, such as positive and negative buoyant energy, are shown to be well suited to operational forecasting of convective storm development and evolution. The derivation of these parameters and their applications in forecasting are illustrated.

Zehr, Raymond M.↗
NASA NTRS1981

Mesoscale aspects of convective storms

The structure, evolution and mechanisms of mesoscale convective disturbances are reviewed and observation techniques for "nowcasting" their nature are discussed. A generalized mesometeorological scale is given, classifying both low and high pressure systems. Mesoscale storms are shown often to induce strong winds, but their wind speeds are significantly less than those accompanied by submesoscale disturbances, such as tornadoes, downbursts, and microbursts. Mesoscale convective complexes, severe storm wakes, and flash floods are considered. The understanding of the evolution of supercells is essential for improving nowcasting capabilities and a very accurate combination of radar and satellite measurements is required.

Fujita, T. T.↗
NASA NTRS1994

The evolution of convective storms from their footprints on the sea as viewed by synthetic aperture radar from space

SEASAT synthetic aperture radar (SAR) echoes from the sea have previously been shown to be the result of rain and winds produced by convective stroms; rain damps the surface waves and causes ech-free holes, while the diverging winds associated with downdraft generate waves and associated echoes surrounding the holes. Gust fronts are also evident. Such a snapshot from 8 July 1978 has been examined in conjunction with ground-based radar. This leads to the conclusion that the SAR storm footprints resulted from storm processes that occurred up to an hour or more prior to the snapshot. A sequence of events is discerned from the SAR imagery in which new cell growth is triggered in between the converging outflows of two preexisting cells. In turn, the new cell generates a mini-squall line along its expanding gust front. While such phenomena are well known over land, the spaceborne SAR now allows important inferences to be made about the nature and frequency of convective storms over the oceans. The storm effects on the sea have significant implications for spaceborne wind scatterometry and rainfall measurements. Some of the findings herein remain speculative because of the great distance to the Miami weather radar-the only source of corroborative data.

Atlas, David↗
NASA NTRS1983

A case study of gravity waves-convective storms interaction 9 May 1979

An analysis is presented of a series of severe storms which occurred in the north central United States on 9 May 1979 and whose spatial distribution and movement correlate well with observed gravity waves. Two gravity wave trains of 2.1-3 mb amplitude, 2.5-3.3 h period and 240-265 km horizontal wavelength were isolated through power spectra analysis and cross-correlation techniques applied to National Weather Service barograph traces. The wave trains propagated in the 200 deg direction, which coincided with the jet axis, with a phase velocity of 20-30 m/s and within a 300 km wide band. The storms were identified on enhanced infrared GOES satellite pictures with the help of radar summaries. These convective systems initially developed in Nebraska and propagated north-northeast at 25 m/s, revealing wave-like characteristics with a separation of 300-400 km. The convective systems were closely linked to the observed wave trains with cell intensity, height and associated rainfall maximized at the wave ridge. One of the two wave trains developed in regions of weak or no convection and appeared to initiate more intense convective clusters downstream from the point of origin. It is shown that the characteristics of the wave trains are consistent with those of gravity waves generated in a region of strong vertical shear associated with the jet. It is suggested that the wave trains continue to extract energy from the basic state all along their track through critical level interaction.

Stobie, J. G.↗
NASA NTRS1991

Radar and microphysical characteristics of convective storms simulated from a numerical model using a new microphysical parameterization

The basic features of a new and improved bulk-microphysical parameterization capable of simulating the hydrometeor structure of convective systems in all types of large-scale environments (with minimal adjustment of coefficients) are studied. Reflectivities simulated from the model are compared with radar observations of an intense midlatitude convective system. Simulated reflectivities using the novel four-class ice scheme with a microphysical parameterization rain distribution at 105 min are illustrated. Preliminary results indicate that this new ice scheme works efficiently in simulating midlatitude continental storms.

Ferrier, Brad S.↗
NASA NTRS1985

Remote sensing of severe convective storms

The Tibet Plateau significantly affects the initiation and development of heavy rainfall and severe storms in China, just as the Rocky Mountains influence local severe storms in the United States. The study shows that the heavy rainfall in the Plateau area is usually preceded by a high growth rate of the convective clouds, followed by a rapid collapse of the cloud top. The study also shows that the tops of the convective clouds associated with heavy rainfall over the Plateau usually lie between the altitude of the two tropopauses which exist over the Plateau. There is good agreement between the collapsing of the cloud as observed from the satellite imagery, and the beginning of the rainfall observed by the ground stations and also between the dissipation of the cloud observed from the satellite infrared imagery, and the ending of the rainfall, observed by the ground stations. Comparison of the volumetric dissipation of clouds per unit area over the location of the ground station with the rainfall recorded at that station shows a linear relationship for rainfall mounts exceeding 8 mm. The ratio of observed rainfall at the ground station over the satellite observed cloud volume dissipation per unit area was also computed. The result shows that the ratio is almost constant with the value of 9.55 mm/(pixel . km/pixel) for rainfall amounts exceeding 15 mm; and the variation is less then 10 percent for rainfall mounts between 8 and 15 mm. Needless to say, further investigation is required to verify this ratio.

Hung, R. J.↗
NASA NTRS1989

Planned ER-2 Doppler radar (EDOP) for studying convective storms and mesoscale phenomena

A radar development is presently funded by the NASA Mesoscale Atmospheric Research Program to build an X-band Doppler radar (EDOP) for the ER-2 aircraft for measuring the structure of updrafts and downdrafts in deep convective systems. In this paper, the radar's scientific objectives and characteristics are briefly reviewed. These objectives include documentation of deep isolated thunderstorms, examination of cloud top and anvil structure, structure of microscale convective systems, cloud microphysics, and testing of satellite precipitation estimation algorithms. System specifications for the radar are given.

Heymsfield, Gerald M.↗
NASA NTRS1976

High resolution radiometric measurements of convective storms during the GATE experiment

Using passive microwave data from the NASA CV-990 aircraft and radar data collected during the Global Atmospheric Research Program Atlantic Tropical Experiment (GATE), an empirical model was developed relating brightness temperatures sensed at 19.35 GHz to surface rainfall rates. This model agreed well with theoretical computations of the relationship between microwave radiation and precipitation in the tropics. The GATE aircraft microwave data was then used to determine the detailed structure of convective systems. The high spatial resolution of the data permitted identification of individual cells which retained unique identities throughout their lifetimes in larger cloud masses and allowed analysis of the effects of cloud merger.

Fowler, G.↗
NASA NTRS2026

Ice in Convective Storm Environments: Assessing Impacts of Microphysics on Simulated Reflectivities

Satellite radar retrievals of clouds and precipitation rely on assumptions about the microphysical properties of hydrometeors such as particle size distributions (PSDs) and massdimensional relationships, which have been shown to vary in distinct environments. A deeper understanding of linkages between mass-dimensional relationships, ice crystal shape, and radar reflectivities across cloud and precipitation regimes is necessary for developing new retrievals for upcoming satellite radar missions, including the INvestigation of Convective UpdraftS (INCUS), as well as future missions that will feature space-borne radars observing clouds, convection, and precipitation. This study investigates ice microphysical characteristics through aircraft in-situ and remote sensing observations from two convective events during the Mid-latitude Continental Convective Clouds Experiment (MC3E) in the Southern Great Plains, and tests implications for ice particle habit in forward modeled radar observations. During MC3E, the Ka/Ku- band High Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP) was onboard the NASA ER-2 aircraft, while in-situ measurements were taken onboard the University of North Dakota Citation. In-situ PSDs and particle shape information from optical array probe data are used to forward model radar reflectivities from particle scattering databases and are compared against HIWRAP reflectivities. Various particle combinations can be used to find agreement with HIWRAP observations, and the forward modeled reflectivities were sensitive to particle type. Varying the riming on the aggregate and graupel particles resulted in larger than 10 dB differences in reflectivities. The in-situ and radar observations imply the occurrence of aggregation, size sorting and lofting particles.

Julia A. Shates↗
NASA NTRS1983

Laboratory and field observations related to ice particle and aircraft charging in convective storms

Graupel particle charging in simulated cloud conditions which show the need for the presence of ice crystals and cloud water simultaneously except under conditions where secondary ice crystal production occurs when charging initially occurs in the absence of ice crystals was examined. The magnitude of the charging increases with size of ice crystals, and impact velocity; it is also sensitive to impurities. The magnitude of the charge is also sensitive to temperature and the sign changes between -10 and -20 C, depending on cloud liquid water content. Aircraft studies were carried out in Montana convective clouds to test the validity of the extrapolation of the laboratory data to the atmosphere from the viewpoint of generation of charge, electric field, and aircraft charging during cloud penetration.

Christian, H.↗
NASA NTRS1981

Mesoscale aspects of jet streak coupling and implications for the short term forecasting of severe convective storms

An analysis of a tornado outbreak in Wichita Falls, Texas was analyzed. The coupling of upper and lower tropospheric jet streaks, leading to severe storm outbreaks is illustrated. The high resolution SESAME data sets indicate that mass and momentum adjustments which couple upper and lower tropospheric jets occur within a 3 to 6 hr time frame over a 100 to 500 km domain, and establish the role of isallobaric forcing in the storm development. It is suggested that the output rate of data from the existing 12 hr network be increased to provide better temporal resolution of wind, mass and moisture data.

Uccellini, L. W.↗
NASA NTRS1984

Severe convective storm detection based on satellite infrared imagery analysis

Several cases of GOES digital infrared data and Doppler Sounder array data during the three-hour time period immediately preceding the touchdown of the tornado were analyzed. Tornado-associated clouds are compared with non-tornado-associated clouds using satellite infrared data, ray tracing of gravity waves detected by the Doppler Sounder array and rawinsonde data. The satellite observations are at 15-minute intervals. Our study shows that tornado-associated clouds are always accompanied by overshooting turrets penetrating above the tropopause. The growth rate of the overshooting turret above the tropopause for severe storm-associated clouds is much greater than that for non-severe storm-associated clouds.

Hung, R. J.↗
NASA NTRS1990

Observations on thermospheric and mesospheric density disturbances caused by typhoons and convective storms

Atmospheric parameter observations have been conducted during the passage of typhoons and tropical storms, from the troposphere to the middle atmosphere, and thence to the thermosphere, using the VHF radar and HF Doppler sounder at an observation site in Taiwan. The density perturbations caused by the propagation of gravity waves due to the typhoons and tropical storms were calculated on the basis of these observations. The short-term middle atmospheric and thermospheric density changes are significant factors in spacecraft launches. The successful remote measurement of three-dimensional winds, gravity waves, and density perturbations is demonstrated for this subtropical site.

Hung, R. J.↗