HR: 1340h
AN: AE23A-0841    [Abstracts]
TI: Thermodynamic Conditions Favorable to Thunderclouds with Inverted Electrical Polarity
AU: Mushtak, V
EM: vadimcm@direcway.com
AF: Parsons Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139
AU: * Williams, E
EM: earlew@ll.mit.edu
AF: Parsons Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139
AU: Rosenfeld, D
EM: daniel@vms.huji.ac.il
AF: Atmospheric Sciences, Hebrew University, Jerusalem, 02139 Israel
AU: Goodman, S
EM: steven.j.goodman@msfc.nasa.gov
AF: Global Hydrology and Climate Research Center, NASA MSFC, Huntsville, AL 35805
AU: Boccippio, D
EM: dennis.boccippio@msfc.nasa.gov
AF: Global Hydrology and Climate Research Center, NASA MSFC, Huntsville, AL 35805
AB: Cloud base height has recently been suggested as a key parameter in accounting for the order-of-magnitude contrast in land-ocean lightning activity (Williams and Stanfill, 2002), and the factor of 2-3 contrast in lightning activity over the Amazon and Congo River basins (Williams and Satori, 2004). The present study examines the influence of cloud base height in reversing the polarity of the main cloud dipole, for which there is increasing evidence (e.g., Krehbiel et al, 2000; Rust and MacGorman, 2002; Lang et al, 2004). Numerous laboratory studies indicate that the positive charging of large ice particles is associated with large cloud water contents (Takahashi, 1978; Saunders et al, 1991; Pereyra et al, 2000). The latter circumstance is encouraged by broad, undiluted updrafts, or by a suppression of warm rain coalescence. Both situations are favored by high cloud base heights. These qualitative ideas are supported by thermodynamic climatologies of cloud base height (dew point depression) and wet bulb potential temperature (a proxy for instability) over the CONUS, showing maximum cloud base height coincident with maximum Šw in the immediate lee of the Rocky Mountains, where both clustered positive ground flash activity and inverted polarity storms have been most prevalent. Clustered +CG activity is relatively scarce in thunderstorm-rich Florida and Alabama, where cloud base heights are half as high, but CAPE values are comparable to those in the Great Plains.
DE: 3324 Lightning
DE: 3354 Precipitation (1854)
DE: 3304 Atmospheric electricity
DE: 3314 Convective processes
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting