Hazard Avoidance Products for Convectively-Induced Turbulence in Support of High-Altitude Global Hawk Aircraft Missions
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A combination of satellite-based and ground-based information is used to identify regions of intense convection that may act as a hazard to high-altitude aircraft. Motivated by concerns that Global Hawk pilotless aircraft, flying near 60,000 feet, might encounter significant convectively-induced turbulence during research overflights of tropical cyclones, strict rules were put in place to avoid such hazards. However, these rules put constraints on science missions focused on sampling convection with onboard sensors. To address these concerns, three hazard avoidance tools to aid in real-time mission decision support are used to more precisely identify areas of potential turbulence: Satellite-derived Cloud-top height and tropical overshooting tops, and ground-based global network lightning flashes. These tools are used to compare an ER-2 aircraft overflight of tropical cyclone Emily in 2005, which experienced severe turbulence, to Global Hawk overflights of tropical cyclones Karl and Matthew in 2010 that experienced no turbulence. It is found that the ER-2 overflew the lowest cloud tops and had the largest vertical separation from them compared to the Global Hawk flights. Therefore, cold cloud tops alone cannot predict turbulence. Unlike the overflights of Matthew and Karl, Emily exhibited multiple lightning flashes and a distinct overshooting top coincident with the observed turbulence. Therefore, these tools in tandem can better assist in identifying likely regions/periods of intense active convection. The primary outcome of this study is an altering of the Global Hawk overflight rules to be more flexible based on the analyzed conditions.
KeywordsAircraft hazard avoidance high-altitude observations satellite observations
The authors wish to acknowledge the encouragement of several individuals to the advancement of this work: Ed Zipser, Scott Braun, Dan Cecil, Gerald Heymsfield, Jason Dunion, Gary Wick, Peter Black, Kris Bedka, Andy Heidinger, Wayne Feltz, Amber Emory. Support for this research was provided by the following programs: NASA HS3, NOAA GOES-R Risk Reduction, and NOAA SHOUT.
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