Lightning mapping observations of volcanic lightning from the 2009 eruption of Redoubt Volcano, Alaska, USA, have been used to calculate lightning flash energy spectra. The formulation of the flash energy spectrum was determined from dimensional arguments recently developed by Bruning and MacGorman , who postulated that the kinematic and electrical components of thunderstorms are coupled via advection of charged precipitation. The Redoubt eruption consisted of a series of distinct explosive eruptions that differed in duration and eruption column height allowing for comparison of flash energy spectra between eruptive events with varying energy input. The duration of infrasound produced by the expulsion and jetting of volcanic ejecta is used as a proxy for kinematic energy input into the eruption column. The transition from high turbulent forcing by the eruptive jet to less-turbulent motions can be examined because each infrasound event ends relatively abruptly. The data show an evolution in the spectral shape of flash energy that correlates with different phases of eruption column evolution. For example, during the period of initial eruption column ascent the peak in flash energy typically occurred at small flash sizes. Following termination of energy input into the eruption column the peak shifted to larger flashes sizes, which would be expected to occur as turbulence subsides. These results show that changes in lightning length scales reflect changes in the kinematic structure of volcanic eruption columns, supporting the hypothesis that kinematic and electrical energy are linked.
|State||Published - 2014|
|Event||15th International Conference on Atmospheric Electricity, ICAE 2014 - Norman, United States|
Duration: Jun 15 2014 → Jun 20 2014
|Conference||15th International Conference on Atmospheric Electricity, ICAE 2014|
|Period||06/15/14 → 06/20/14|