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Weather Avoidance Guidelines for NASA Global Hawk High-Altitude Unmanned Aircraft Systems (UAS)The current Global Hawk flight rules would probably not have been effective in the single event of greatest concern (the Emily encounter). The cloud top had not reached 50,000 ft until minutes before the encounter. The TOT and lightning data would not have been available until near the overflight time since this was a rapidly growing cell. This case would have required a last‐minute diversion when lightning became frequent. Avoiding such a cell probably requires continual monitoring of the forward camera and storm scope, whether or not cloud tops have been exceeding specific limits. However, the current overflight rules as strictly interpreted would have prohibited significant fractions of the successful Global Hawk overpasses of Karl and Matthew that proved not to be hazardous. Many other high altitude aircraft (ER‐2 and Global Hawk) flights in NASA tropical cyclone field programs have successfully overflown deep convective clouds without incident.The convective cell that caused serious concern about the safety of the ER‐2 in Emily was especially strong for a tropical cyclone environment, probably as strong or stronger than any that was overflown by the ER‐2 in 20 previous flights over tropical cyclones. Specifically, what made that cell a safety concern was the magnitude of the vertical velocity of the updraft, at least 20 m/s (4000 ft/minute) at the time the ER‐2 overflew it. Such a strong updraft can generate strong gravity waves at and above the tropopause, posing a potential danger to aircraft far above the maximum altitude of the updraft itself or its associated cloud top. Indeed, the ER‐2 was probably at least 9000 ft above that cloud top. Cloud‐top height, by itself, is not an especially good indicator of the intensity of convection and the likelihood of turbulence. Nor is overflying high cloud tops (i.e. > 50,000 ft) of particular concern unless there is other evidence of very strong convective updrafts beneath those tops in the path of the aircraft. center dot Lightning, especially lightning with a high flash rate, is well correlated with convective intensity. Lightning with a minimal flash rate (say 1‐3 flashes per minute) is indicative of updraft speeds of about 10 m/s in the mixed phase region where charge is being separated, generally at altitudes about 20‐25 kft in a hurricane. That is still stronger than typical updrafts (more like 5 m/s). An unresolved issue is whether there is a high and instantaneous correlation between vertical velocity in the middle troposphere (necessary for lightning generation) and near cloud top (more direct concern for overflights).
Document ID
20140008781
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Cecil, Daniel J.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Zipser, Edward J.
(Utah Univ. Salt Lake City, UT, United States)
Velden, Chris S.
(Wisconsin Univ. Madison, WI, United States)
Monette, Sarah A.
(Wisconsin Univ. Madison, WI, United States)
Heymsfield, Gerald M.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Braun, Scott A.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Newman, Paul A.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Black, Peter G.
(Science Applications International Corp. Monterey, CA, United States)
Black, Michael L.
(National Oceanic and Atmospheric Administration Miami, FL, United States)
Dunion, Jason P.
(Miami Univ. Miami, FL, United States)
Date Acquired
July 8, 2014
Publication Date
February 2, 2014
Subject Category
Air Transportation And Safety
Meteorology And Climatology
Report/Patent Number
M14-3294
Meeting Information
Meeting: American Meteorological Society (AMS) Annual Meeting
Location: Atlanta, GA
Country: United States
Start Date: February 2, 2014
End Date: February 6, 2014
Sponsors: American Meteorological Society
Distribution Limits
Public
Copyright
Public Use Permitted.
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