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Title:
The First Hook Echo Ever Recorded - April 09, 1953
Description:
On Thursday, 9 April 1953, the first recorded radar observations of a tornadic thunderstorm were made by Mr. Donald Staggs using a research radar system operated by the Illinois State Water Survey (ISWS) at Champaign. Mr. Staggs, an electrical engineer, was testing the radar in preparation for an upcoming field project. He recognized the intriguing nature of the echo patterns that were being detected late that afternoon and voluntarily continued the radar operations into the evening hours. Some of the resultant data were included in several 16mm motion picture films that were produced at the Water Survey in the 1950's. The images collected on this web page have been extracted from digitized versions of the original ISWS movies. The radar used for these observations was an APS-15A that had originally been designed as an airborne surveillance system installed aboard US Naval aircraft during World War II. To support rainfall estimation studies, engineers at the Water Survey modified the APS-15 so that the receiver gain could be stepped through a series of pre-set sensitivity levels. The antenna made continuous sweeps at a single fixed elevation angle of ~0 degrees. A 35 mm camera automatically recorded the Plan Position Indicator (PPI) display during each complete 360 degree antenna revolution. Some performance characteristics of the Water Survey radar are summarized below: APS-15A Radar Characteristics Wavelength: 3 cm Antenna diameter: 36 inches Antenna beamwidth: 3 degrees Peak transmit power: 35 kW Pulse duration: 2 microseconds Minimum detectable signal: Approximately -97 dBm Recorded data: Black and white photographs of the PPI scope displaying the analog returned power level (without range normalization) At the time of the hook echo observations, the APS-15 was mounted on an approximately 50 foot high tower next to the ISWS quonset hut at the University of Illinois - Willard Airport (CMI). The thunderstorm of interest on 4/9/53 moved generally from west to east along a path that passed a short distance north of the radar. As the storm emerged from the ground clutter pattern north of the radar, an appendage on the right rear flank of the parent echo became visible. (Range rings are at 10 nm / 18.5 km intervals). Within a few minutes, this echo appendage began to curl into a hook shape. As the cyclonic curl-up process continued, a weak echo "eye" could be seen at some receiver gain settings. The width of the hook echo increased as the storm moved away towards the northeast. An attenuation "notch" became more evident due to the heavy rain and hail that was falling within the parent echo. The tornado produced by this thunderstorm caused two fatalities. During the two months following this event, destructive tornadoes also took place at Waco, Texas (5/11/53; 119 fatalities), Flint Michigan (6/8/53; 115 fatalities), and Worcester, Massachusetts (6/9/53; 94 fatalities). Thus, the ISWS 4/9/53 data were of considerable research interest for studying the relationships between radar echo features and tornadoes.
Author:
Legend813a
Tags:
Radar, Hook, Echo, Tornado, 1953, Legend813,
The First Hook Echo Ever Recorded - April 09, 1953
Description:
On Thursday, 9 April 1953, the first recorded radar observations of a tornadic thunderstorm were made by Mr. Donald Staggs using a research radar system operated by the Illinois State Water Survey (ISWS) at Champaign. Mr. Staggs, an electrical engineer, was testing the radar in preparation for an upcoming field project. He recognized the intriguing nature of the echo patterns that were being detected late that afternoon and voluntarily continued the radar operations into the evening hours. Some of the resultant data were included in several 16mm motion picture films that were produced at the Water Survey in the 1950's. The images collected on this web page have been extracted from digitized versions of the original ISWS movies. The radar used for these observations was an APS-15A that had originally been designed as an airborne surveillance system installed aboard US Naval aircraft during World War II. To support rainfall estimation studies, engineers at the Water Survey modified the APS-15 so that the receiver gain could be stepped through a series of pre-set sensitivity levels. The antenna made continuous sweeps at a single fixed elevation angle of ~0 degrees. A 35 mm camera automatically recorded the Plan Position Indicator (PPI) display during each complete 360 degree antenna revolution. Some performance characteristics of the Water Survey radar are summarized below: APS-15A Radar Characteristics Wavelength: 3 cm Antenna diameter: 36 inches Antenna beamwidth: 3 degrees Peak transmit power: 35 kW Pulse duration: 2 microseconds Minimum detectable signal: Approximately -97 dBm Recorded data: Black and white photographs of the PPI scope displaying the analog returned power level (without range normalization) At the time of the hook echo observations, the APS-15 was mounted on an approximately 50 foot high tower next to the ISWS quonset hut at the University of Illinois - Willard Airport (CMI). The thunderstorm of interest on 4/9/53 moved generally from west to east along a path that passed a short distance north of the radar. As the storm emerged from the ground clutter pattern north of the radar, an appendage on the right rear flank of the parent echo became visible. (Range rings are at 10 nm / 18.5 km intervals). Within a few minutes, this echo appendage began to curl into a hook shape. As the cyclonic curl-up process continued, a weak echo "eye" could be seen at some receiver gain settings. The width of the hook echo increased as the storm moved away towards the northeast. An attenuation "notch" became more evident due to the heavy rain and hail that was falling within the parent echo. The tornado produced by this thunderstorm caused two fatalities. During the two months following this event, destructive tornadoes also took place at Waco, Texas (5/11/53; 119 fatalities), Flint Michigan (6/8/53; 115 fatalities), and Worcester, Massachusetts (6/9/53; 94 fatalities). Thus, the ISWS 4/9/53 data were of considerable research interest for studying the relationships between radar echo features and tornadoes.
Author:
Legend813a
Tags:
Radar, Hook, Echo, Tornado, 1953, Legend813,
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