SCATCAT (Severe Clear Air Turbulence Colliding with Aircraft Traffic) 2001 was an experiment to examine clear-air turbulence associated with jet streams and upper fronts. NOAA's Gulfstream-IV aircraft was the principal observing platform, encompassing high resolution dropsonde releases and in-situ measurements. One particular flight, centered around 0Z 18 February 2001, observed an intense jet stream and upper-level frontal structure. While passing over this jet, the aircraft encountered moderate clear-air turbulence.

To examine the dynamics of the 18 February 2001 case in more detail, a multi-faceted numerical modeling approach is used. First, the COAMPS model is configured surrounding the region of observations using two computational domains with 54 km and 18 km horizontal grid spacings respectively. COAMPS is initialized using NOGAPS analyses at 12Z 17 February, and continues for 18 hours until 6Z 18 February. Considering the paucity of observations in the region, COAMPS produces a reasonably good representation of the observed flow, with a qualitatively similar jet and frontal structure. To examine the dynamics at higher resolution, the 18 km domain from COAMPS is used to initialize and force a cloud-scale model (the Clark model). Using the Clark model's two-way nesting capabilities, the jet and frontal structures are better resolved in both the horizontal and vertical.

Similar to the observations, vertically-propagating gravity waves that extend above the jet into the lower-stratosphere are produced in the numerical simulations. The location of these waves corresponds to regions of turbulence encountered by the aircraft. While the propagating gravity waves have too large a horizontal scale to produce a turbulent response in an aircraft, they do play a role in the turbulence generation through an interaction with the jet stream. The mechanisms underlying this interaction will be presented, along with a discussion of the robustness of the results.