Turbulence In MCS Anvils: Observations and Analyses From Bamex

Abstract

The occurrence of large mesoscale convective systems (MCSs) during the warm season over much of the central United States presents a hazard to aviation that has not been thoroughly assessed. In addition to lightning and hail, the extensive mid- to upper-level anvil clouds that form in these systems can cause severe turbulence. Although avoidance of the most intense convection in these areas by passenger aircraft and general aviation is usually possible, it is advantageous to know the risk of turbulence in regions within and close to the anvil clouds. If the risk can be determined, aircraft travel through these large anvils could become acceptable. Furthermore, if an algorithmic estimate of this risk could be developed, it could contribute to turbulence forecasting and warning. Unfortunately, avoidance also means that observations within MCSs are few. During the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX; Davis et al., 2002) held in the central United States in summer 2003, however, several midtroposphere (2 to 4 km) research flights observed state and aircraft flight variables within and near the edges of large mesoscale anvils. A dropsonde aircraft (Learjet) flying at high levels was coordinated with two P-3 research aircraft below. During at least two of these flights (10 June and 23 June), the mission scientist and the lead cloud physics scientist on board the NOAA P-3 described in their logs several periods of moderate to heavy turbulence. These two and perhaps ten other BAMEX missions offer the opportunity to diagnose turbulence episodes having dropsonde launches and in-situ aircraft measurements at mid-levels in anvil regions where the intensity and frequency of turbulence is relatively unknown. We examine in detail the composite structure of the MCS that occurred on 10 June 2003 using observations from three project aircraft, Rapid Update Cycle (RUC) model data, and operational observation platforms. These observational and exploratory results lay the foundation for analyses of fields in regions where the possibility of air traffic exists and where there is high likelihood of turbulence as indicated by quantitative algorithms. Our analyses focus on near-anvil regions and on physical mechanisms (primarily mid-level rear inflow jets) that pose a turbulence threat. Based on these analyses, we discuss possible developments of more automated and quantitative assessment of the turbulence threat to general aviation and passenger airlines in the vicinity of anvil regions during mature and late stages of MCSs. Finally, we present observations from eight other BAMEX cases that are incorporated into a generalized composite profile of turbulence-sensitive parameters in the rear inflow region of MCSs.