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Durham e-Theses
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Point discharge in atmospheric electricity

Kirkman, J. R. (1956) Point discharge in atmospheric electricity. Doctoral thesis, Durham University.



Investigations of the current from an earth-connected point 0.002 cm in diameter, supported by masts at heights of 20m, 27m end 34m are described. Simultaneous measurements of the potential gradient at the ground to windward of the point, and wind speed at the point, indicate that the current can be represented by the equation I = K(W + C) (F - M) where I is the point discharge current in mioroamps W the wind speed in metres per second F the potential gradient in volts per metre M the onset value of the potential gradient (200 v/m at 20m, 135 v/m at 27m, l00 v/m at 34m) C and K are constants (C = 4 m/s and K = 2.56 x 10(^-4)µa per v/m per m/s at 27m) The general equation still holds when the potential gradient is measured 7m below the 34m mast but at 2m below the 20m point the equation is I = A(W + D) (F - M)(^n) where A and D are constants is dependent on wind speed. Measurements of point discharge currents down the trunk of a tree indicate that these are somewhat lower than those through a single point of corresponding height in similar conditions. The results are compared with those of previous workers and discrepancies are attributed to wind speed and wind direction effects, whilst good agreement is found between the present findings and the theoretical work of Chalmers and Mapleson (1955) and Chapman (1956). A reassessment of the Alti-Electrograph results of Simpson and scrase (1937) is made and suggests that the potential gradients measured by this means immediately below thunderclouds are of the earns order of magnitude as those measured by observers in aircraft (Gunnl953).

Item Type:Thesis (Doctoral)
Award:Doctor of Philosophy
Thesis Date:1956
Copyright:Copyright of this thesis is held by the author
Deposited On:13 Nov 2013 16:14

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