Engineering topics

Pearl, E. W.

Publications and source records attributed to Pearl, E. W..

4 records

NASA NTRS1975

Satellite-tracked cumulus velocities

Basic problems in the interpretation of satellite-tracked low-cloud velocities are reviewed. The METRACOM system of cloud velocity computation is outlined, and caution is urged in converting cloud velocities into wind velocities. The motion of various cumulus cells over Springfield, Mo., Barbados, and Tampa, Fla., is analyzed. It is shown that multiturret cells do not always move with the wind, that addition and deletion of turrets belonging to a specific cell may cause erratic motion in a tracer cell, and that cumulus turrets between 0.3 and 2 miles in size are the best targets for inferring the mean wind velocity within the subcloud layers. It is concluded that the accuracy of wind velocity estimates will be no better than 2 meters/sec unless the physical and dynamic characteristics of cumulus motion are further investigated.

Fujita, T. T.↗

NASA NTRS1975

Cloud-top parameters - A hail indicator

Airborne photographic observations of four hail-producing storms are discussed. With the exception of one storm producing a tornadic event, the overshooting tops were nearly steady-state. The tops were consistently high and wide, reaching maximum heights within about 5 minutes of the initiation of hail. Measured updraft velocities in the turrets composing the overshooting top were 25 m/sec. The dimensions of the overshooting tops were sufficiently large to permit satellite observation.

Pearl, E. W.↗

NASA NTRS1973

Satellite-tracked cumulus velocities

The research indicates that extreme caution must be exercised in converting cloud velocities into winds. The motion of fair-weather cumuli obtained by tracking their shadows over Springfield, Missouri revealed that the standard deviation in the individual cloud motion is several times the tracking error. The motion of over-ocean cumuli near Barbados clearly indicated the complicated nature of cumulus velocities. Analysis of whole-sky images obtained near Tampa, Florida failed to show significant continuity and stability of cumulus plumes, less than 0.3 mile in diameter. Cumulus turrets with 0.3 to 2 mile in size appear to be the best target to infer the mean wind within the subcloud layers. Cumulus or stratocumulus cells consisting of x number of turrets do not always move with wind. The addition and deletion of turrets belonging to a specific cell appear to be the cause of the erratic motion of a tracer cell. It may by concluded that the accuracy of wind estimates is unlikely to be better than 2m/sec unless the physical and dynamical characteristics of cumulus motion is futher investigated.

Fujita, T. T.↗

NASA NTRS1973

Characteristics of anvil-top associated with the Poplar Bluff tornado of 7 May 1973

Investigation of potential tornado-producing thunderstorms was performed during part of the 1972 and 1973 tornado seasons. On May 7, 1973 twenty-one tornadoes were confirmed over southern Missouri, northern Arkansas, and southwestern Illinois. The region was surveyed by high altitude photography performed on a Learjet over the region of reported tornadoes. Two storms were chosen from aircraft observation with the guidance of ground and radar reports, and a series of photographs were taken of a tornado producing cloud. An analysis of the activity before and during the tornado is made, and most noteworthy were changes detected in the growth and collapse of overshooting domes above the anvil. Suggestions are included for a comprehensive study.

Pearl, E. W.↗