Project NIMROD

The project was set up by Ted Fujita and Ramesh Srivastava from University of Chicago with research assistants Roger Wakimoto and Gregory S. Forbes, as well as researcher Jim Wilson from NCAR.[1] The NIMROD network included 3 Doppler weather radars disposed in a triangular baseline at approximately 60 km from one to the other and 27 mobile automatic weather station from NCAR forming a mesonet in and around the area.[2][3] Two of the radars were operating in C-band (CP-3 and CP-4), the other was the CHILL Doppler S band radar with multi-elevation PPI and operating continuously. About 200 rawinsondes were released at 30 to 60-min intervals from the coordination position as needed on experiment days.[2][3]

O’Hare International Airport was chosen because one of the major objectives was also to determine the low-level winds in and around major airports. It was in corn fields area and late spring timeframe was chosen as damage to the corn could be used as indicators of high velocity wind at the surface.[2] Nominal height of wind sensors was 4 m although some of the stations were located in the suburbs while others were in open fields. The mesonet data was obtained at 1-min resolution.[2] Network operations were directed from the NCAR CP-3 radar site while US National Weather Service local bureau notified the team of significant downburst and/or tornadic events, and even assisted in damage surveys.[2]

Bow echoes are associated with different types of severe winds.

Studies on downdrafts from thunderstorms have been few and the extension of their effects were not well known. Dr Fujita suspected that localized downdraft, later called microbursts, were responsible for damage on the ground and a weather hazard involved in some airplane crashes like the one on 24 June 1975 Eastern Airlines Flight 66 during landing at New York's John F. Kennedy International Airport, killing 113 and injuring 11.[4]

Fujita had hypothesized during the inquiry that the cause was such phenomena from his previous study of the effects of the damage caused by the atomic bomb dropped on Nagasaki in August 1945, and some unexplained damages during the 1974 Super Outbreak of tornadoes.[5] However, there was strong resistance from the meteorological community.[6] He convinced the National Science Foundation and NCAR to fund projects to study thunderstorms downdrafts.[6] NIMROD was the first large scale experiment to study this phenomena and it was the first time that Fujita had used Doppler radar data, having no previous experience in the interpretation of their data, but was rapidly confortable with them.[6]

Shortly after the start of the field program, the first recorded microburst on Doppler radar was viewed on the CP-3 radar at Yorkville, Illinois, on 29 May 1978. On the first scan of a thunderstorm, the Doppler velocity display showed a doublet of inbound-outbound velocities which was followed by observation of a gust front. Data obtained during the whole project permitted to describe the 3 dimensions motion of the air in thunderstorms and their structure as single cells, multi-cells, bow echoes or other types.[6][7]

This first experiment have been followed by numerous ones since 1978. One can name (JAWS Joint Airport and Weather Studies) in 1982 and MIST (Microburst and Severe Thunderstorm Experiment) in 1986 led by Fujita[6] and the VORTEX projects. All of them leading to better understanding of summer severe weather for airport and public safety.[6][8]

• Fujita, T. T. (1978). Manual of downburst identification for project Nimrod (PDF). Satellite and Mesometeorology Research Paper. 156. Dept. of Geophysical Sciences, University of Chicago. Lay summary..
• Fujita, T. T. (1978). Objective, operation, and results of Project NIMROD. 11th Conf. on Severe Local Storms. Kansas City, MO: Amer. Meteor. Soc. pp. 259–266..