Monday, 3 August 2015
Back Bay Ballroom (Sheraton Boston )
In this study we discuss results from high-resolution numerical simulations of an observed case of widespread clear-air turbulence influenced by organized convection occurring in the vicinity of a strong jet stream. The case of interest featured turbulence at cruising altitudes (31-39 kft) over the North Atlantic south of maritime Canada, where cirrus banding was widespread over scales of approximately 1000 km to the south of antecedent deep convection associated with a surface front and strong upper-level jet stream. Over a broad horizontal region near the simulated cirrus bands, criteria for both moist static instability and inertial instability were locally satisfied indicating the possibility these disparate mechanisms could be acting cooperatively to produce the observed turbulence. Though the turbulence occurred several hundred km south of ongoing deep convection, a dry simulation suggests the important role of remote deep convection in the turbulence generation as neither of the above instability criteria were satisfied and model TKE values were substantially smaller than in the full-physics run that allowed for convection. Cases such as the current one, which may be mistaken for the more "classic" clear-air turbulence (CAT) in the vicinity of jet streams, are more common than previously anticipated and pose a particular challenge to commercial aviation since the turbulence can occur through deep layers and affect large horizontal areas.
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