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Evidence for the Absence of Conductivity Variations above ThunderstormsOver the last decade, atmospheric conductivity measurements over thunderstorms have been made at 20 km with high altitude aircraft. These measurements show no significant variations in conductivity above thunderstorms once the effects of aircraft charge are removed. The polar conductivities (alpha(sub +) and alpha(sub -)) were simultaneously acquired using a pair of Gerdien probes. In addition, the vertical electric field and the aircraft self charge were measured using two field mills installed nearly symmetrically on the top and bottom of the aircraft. The measurements were collected during the COHMEX (1986), CaPE (1991), STORM-FEST (1992), TOGA COARE (1993) and CAMEX-1, 2 (1993 1995) field campaigns. This extensive data set includes more than 330 overflights of electrified storms (> 170 over storms producing lightning) and represents a broad sample of storm types, seasonal regimes, and geographical distribution. Most of the observed variations in conductivity are caused by charge induced on the aircraft (and hence on the exterior case of the conductivity probes). Theory (Swann, 1914) indicates that some ions with the same sign as the induced charge will be deflected from the air stream reducing the measured conductivity of that polarity. For the opposite polarity, the additional ions that are attracted by the induced charge are collected on the exterior case rather than the inner electrode, leaving the ambient measurement unaltered. The aircraft observations, in agreement with theory, show reductions proportional to the magnitude of the aircraft self charge for conductivity of the same polarity as the self charge and no change for conductivity of opposite polarity. After compensating for the effects of aircraft charge no significant variations in conductivity above thunderstorms have been found. These Gerdien results contrast strongly with the large (and frequent) conductivity variations reported in studies using relaxation probe techniques.
Document ID
19990064337
Acquisition Source
Marshall Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Bailey, Jeff C.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Blakeslee, Richard J.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Driscoll, Kevin T.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Date Acquired
August 19, 2013
Publication Date
January 1, 1999
Subject Category
Meteorology And Climatology
Meeting Information
Meeting: Atmospheric Electricity
Location: Gutersville, AL
Country: United States
Start Date: June 7, 1999
End Date: June 11, 1999
Distribution Limits
Public
Copyright
Other

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