An examination of the convective charging hypothesis: Cloud charge structure and Maxwell currents.

 

Helsdon, J.H., Jr., S. Gattaleeradapan, R.D. Farley, and C.C. Waits, 2002

(JGR-Atmospheres, in press.)

Abstract
            An examination of the convective charging hypothesis is undertaken using our three-dimensional Storm Electrification Model.  In an attempt to cover the range of storm conditions over which the convective mechanism might be expected to operate, two storms are simulated: a small, weak storm and a larger, severe storm.  Elements of the model relevant to the convective hypothesis are the full treatment of small ions, including attachment to hydrometeors; the inclusion of field-dependent surface point discharge; and the components of the Maxwell current.  For comparison purposes, each storm is also simulated using a noninductive mechanism.  Results from both the small and large storm simulations using convective-only charging indicate disorganized, weak electrical structures during the mature and dissipating stages.  Conversely, the use of noninductive charging produces strong electrification in both storms.  Maxwell current analysis shows that, for the most part, currents within the storm are dissipative and that the cloud acts as a barrier to the external conduction current when convective-only charging is considered.  For the noninductive simulations the Maxwell current is that of a generator.  The treatment of small ions and their attachment to hydrometeors accounts for the formation of screening layers, thus this aspect of the convective charging mechanism still plays an important role in the modeling of thunderstorm charge structures.  However, since the convective charging hypothesis, by itself, is unable to produce significant charging or strong electric fields in either simulated cloud, we conclude that it is not a viable mechanism for thunderstorm electrification.

Please click on the thumbnail to see full-page versions of the figures.

          

Figure 1                  Figure 2a               Figure 2b               Figure 2c            Figure 2D

 

       

Figure 3                Figure 4a                Figure 4b            Figure 5                    Figure 6a

 

       

Figure 6b                Figure 7                Figure 8                Figure 9a            Figure 9b

 

       

Figure 10a               Figure 10b            Figure 11            Figure 12            Figure 13

 

 

Figure 14                Figure A1