A Report on the Upper-Level Wind Conditions Preceding and During the Shuttle Challenger (STS 51L) Explosion

The synoptic-scale weather conditions preceding and following the ill-fated Space Shuttle Challenger launch are documented, with particular emphasis on the upper-level winds for central and northern Florida. Operational radiosonde data collected by the National Weather Service, visible and infrared imagery from the Geostationary Operational Environmental Satellite, and water-vapor imagery from the VISSR (Visible Infrared Spin Scan Radiometer) Atmospheric Sounder, ozone data collected by the Total Ozone Mapping Spectrometer aboard the Nimbus-7, and soundings collected at Cape Canaveral (XMR) are described. Analyses derived from these data sets point to the juxtaposition of two distinct jet-stream systems (a polar-front jet [PFJ] and a subtropical jet [STJ]) over north-central Florida on the morning of the launch. Both jets were characterized by regions of significant vertical wind shear, which was especially strong above and below the core of the STJ. Data from a radiosonde released at Cape Canaveral 10 min after the shuttle accident combined with radiosonde and jimsphere wind measurements before the shuttle launch reveal that, over XMR, the magnitude of the maximum wind in the PFJ was increasing with time while the magnitude of the STJ was decreasing. Even with the decreasing magnitude of wind speeds in the core of the STJ over XMR, large vertical wind shears and low Richardson numbers were still diagnosed near the PFJ and beneath the core of the STJ at the time of launch (1639 GMT). The low Richardson numbers associated with the presence of vertical wind shear indicate that conditions were favorable for shear-induced turbulence at the time of the shuttle explosion. The results from the analyses of the synoptic radiosonde data are inconclusive due to the poor temporal and horizontal spatial resolution of the observational data base and the large number of missing data reports at numerous stations in the southeastern United States (including XMR). In an attempt to overcome this deficiency, numerical simulations of the atmospheric conditions were conducted using a mesoscale numerical model. The simulations initialized at 1200 GMT 28 January confirm the juxtaposition of two distinct jet systems over north-central Florida at the time of the shuttle launch and the presence of large vertical wind shears and low Richardson numbers associated with these jets. Given the rapid temporal evolution of atmospheric flow regimes which involve strong wind shears, we recomm