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Fenn, D. D.

Publications and source records attributed to Fenn, D. D..

11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Detection of severe Midwest thunderstorms using geosynchronous satellite data

In the present exploration of the effectiveness of severe thunderstorm detection in the Midwestern region of the U.S. by means of approximately 5-min interval geosynchronous satellite data, thunderstorms are defined in IR data as points of relative minimum in brightness temperature T(B) having good time continuity and exhibiting a period of rapid growth. The four parameters of rate of T(B) decrease in the upper troposphere and stratosphere, isotherm expansion, and storm lifetime minimum T(B), are shown to be statistically related to the occurrence of severe weather on four case study days and are combined into a Thunderstorm Index which varies among values from 1 to 9. Storms rating higher than 6 have a much higher probability of severe weather reports, yielding a warning time lead of 15 min for hail and 30 min for the first tornado report.

Adler, R. F.↗
NASA NTRS1983

Thunderstorm top structure observed by aircraft overflights with an infrared radiometer

Thunderstorm top structure is examined with high spatial resolution radiometric data (visible and infrared) from aircraft overflights together with other storm views, including geosynchronous satellite observations. Results show that overshooting cumuliform towers appear as distinct cold areas in the high resolution, 11-micron IR aircraft images, but that the geosynchronous satellite observations significantly overestimate the thunderstorm-top IR brightness temperature, T(B), due to field of view effects. Profiles of cloud top height and T(B) across overshooting features indicate an adiabatic cloud surface lapse rate. However, one-dimensional cloud model results indicate that when comparing thunderstorm top temperature and height at different times or different storms, a temperature-to-height conversion of about 7 K/km is appropriate. Examination of mature storm evolution indicates that, during periods when the updraft is relatively intense, the satellite IR 'cold point' is aligned with the low-level radar reflectivity maximum, but during periods of updraft weakening and lowering cloud top heights, the satellite T(B) minimum occurs downwind with cirrus anvil debris. The growth period of a relatively weak cumulonimbus cluster is also examined with aircraft and satellite data.

Adler, R. F.↗
NASA NTRS1981

Satellite-observed cloud-top height changes in tornadic thunderstorms

Eleven tornadic storms are evaluated with respect to cloud top temperature changes relative to tornado touchdown. Digital IR data from the SMS/GOES geosynchronous satellites were employed for 10 F2 and one F1 tornadoes. A rapid ascent of the cloud tops 30-45 min before tornado touchdown, a temperature decrease of 0.4 K/min, and an ascent rate of about 3 m/sec were observed. The presence of an operating Doppler radar for three of the sample storms allowed detection of a mesocyclone coincident with the rapid cloud top ascent. The intensification and descent of the vortex to form a tornado is concluded to be due to a weakening of the updraft, the formation of a downdraft, and a shift of the vortex to the updraft-downdraft boundary, leading to dominance of the tilting term in the generation of vorticity.

Adler, R. F.↗
NASA NTRS1981

Spiral feature observed at top of rotating thunderstorm

A dark spiral feature is noted in the geosynchronous satellite visible image of the top of a thunderstorm which also has a Doppler radar-observed mesocyclone. Although the evidence is not conclusive, the feature may represent cyclonic rotation at cloud top associated with the pre-tornado mesocyclone.

Adler, R. F.↗
NASA NTRS1981

Detection of severe thunderstorms using short interval geosynchronous satellite data

The potential and limitations of using short interval (3-7 minutes) geosynchronous, infrared data to ascertain thunderstorm intensity, and therefore indirectly detect severe thunderstorms are discussed. Thunderstorms on four case study days were analyzed over selected areas and time periods using SMS/GOES data, and derived satellite based intensity parameters were compared to severe weather reports. Young, growing thunderstorms are intensity rated using the rate of decrease of the satellite observed cloud top minimum equivalent blackbody temperature. Since most storms cannot be observed until they penetrate through the cirrus overcast produced by previous convection, minimum cloud temperature and rate of blackbody temperature isotherm expansion are then used as intensity indicators. Results are presented and problems and limitations of the techniques and the data are examined. In addition, an analysis of cloud top height variations (as viewed by the satellite) in relation to tornado touchdown times and, in a few cases, to mesocyclone formation times is also presented.

Adler, R. F.↗
NASA NTRS1979

Thunderstorm vertical velocities estimated from satellite data

Infrared geosynchronous satellite data with an interval of 5 min between images are used to estimate thunderstorm top ascent rates on two case study days. A mean vertical velocity of 3.4 m/sec for 23 clouds is calculated at a height of 8.7 km. This upward motion is representative of an area of approximately 10 km on a side. Thunderstorm mass flux of approximately 2 times 10 to the 8th power kg/sec is calculated, which compares favorably with previous estimates. There is a significant difference in the mean calculated vertical velocity between elements associated with severe weather reports (omega = 4.9 m/sec) and those with no such reports (2.4 m/sec). Calculations were made using a velocity profile for an axially symmetric jet to estimate the peak updraft velocity. For the largest observed omega value of 7.8 m/sec the calculation indicates a peak updraft of approximately 50 m/sec.

Adler, R. F.↗
NASA NTRS1979

Thunderstorm intensity as determined from satellite data

Digital infrared data from SMS 2 obtained on May 6, 1975 are used to study thunderstorm vertical growth rates and cloud top structure in relation to the occurrence of severe weather (tornadoes, hail, and high wind) on the ground. All thunderstorms from South Dakota to Texas along a N-S oriented cold front were monitored for a 4 h period with 5 min interval data. Thunderstorm growth rate, as determined by the rate of blackbody temperature isotherm expansion and minimum cloud top temperature, are shown to be correlated with reports of severe weather on the ground.

Adler, R. F.↗
NASA NTRS1979

Thunderstorm vertical velocities and mass flux estimated from satellite data

Infrared geosynchronous satellite data with an interval of five minutes between images are used to estimate thunderstorm top ascent rates on two case study days. A mean vertical velocity of 3.5/ms for 19 clouds is calculated at a height of 8.7 km. This upward motion is representative of an area of approximately 10km on a side. Thunderstorm mass flux of approximately 2x10 to the 11th power/gs is calculated, which compares favorably with previous estimates. There is a significant difference in the mean calculated vertical velocity between elements associated with severe weather reports (w bar=4.6/ms) and those with no such reports (2.5/ms). Calculations were made using a velocity profile for an axially symmetric jet to estimate the peak updraft velocity. For the largest observed w value of 7.8/ms the calculation indicates a peak updraft of approximately 50/ms.

Adler, R. F.↗
NASA NTRS1977

Thunderstorm monitoring from a geosynchronous satellite

It has been shown that SMS digital IR data can be used to calculate parameters which appear to be related to cloud or thunderstorm growth rates and variations in cloud top structure. The data appear to be useful in examining both clearly defined single clouds and cold areas within mature cirrus anvils. The data used for this study were blackbody temperatures derived from digital IR data from SMS-2 for a series of storms over the midwest United States on May 6, 1975.

Adler, R. F.↗
NASA NTRS1977

Satellite-based thunderstorm intensity parameters

Thunderstorm growth rates are investigated through use of infrared data furnished by the Synchronous Meteorological Satellite. Blackbody temperature isotherms provide an accurate method of delineating the areal expansion of cold areas; the blackbody temperature isotherms are valuable analytical tools even in cases when there is very little decrease with time of the minimum cloud top temperature. In an application of the severe storm monitoring technique, the origin of tornadoes is found to be closely linked to a rapid expansion of cold areas in seven out of eight cases.

Adler, R. F.↗