HR: 09:45h
AN: AE41A-08 [WITHDRAWN]    [Abstracts]
TI: Early VLF perturbations observed in Crete, Greece in relation with TLEs over southwest Europe
AU: * Haldoupis, C
EM: chald@physics.uoc.gr
AF: Physics Department, University of Crete, Heraklion, Crete, 71003, Greece
AU: Mika, A
EM: agnes@physics.uoc.gr
AF: Physics Department, University of Crete, Heraklion, Crete, 71003, Greece
AU: Inan, U
EM: inan@stanford.edu
AF: STAR Laboratory, Stanford University, Packard Buildings, 350 Serra Mall, Stanford, CA 94305-9, United States
AU: Neubert, T
EM: neubert@space.dtu.dk
AF: Danish National Space Center, Juliane Maries Vej 30, Copenhagen, FIN-2100, Denmark
AB: In support of the summer EuroSprite campaigns in southwest Europe, and in the framework of an EU-RTN (European Union research training network) project (e.g., http://www.dsri.dk/cal/), a Stanford narrow band VLF receiver was installed in Crete, Greece (35.31 deg. N; 25.08 deg. E) and started operation in the summer of 2003. The Crete VLF station was capable of monitoring several transmitters, some of them chosen in order to provide VLF links that traverse subionospheric regions in the proximity of the areas viewed for transient luminous event detection (sprites and elves) by the EuroSprite cameras. In this presentation we summarize several observational findings regarding the so called "early" VLF events of ionospheric perturbations which are found to occur in relation with sprites and elves. In particular, we focus on a new category of early type perturbations, which, contrary to the so called "early/fast" events whose onset duration is less than ~20 ms, are characterized by a gradual growth and thus a "slow" onset duration ranging from about 0.5 to 2.5 s. These long growths are indicative of a new physical process at work which, following a sprite-causative cloud-to-ground discharge, leads to a gradual ionization build up in the lower ionosphere which can be responsible for the long onset duration of the observed perturbations. We postulate that such long onset durations are due to secondary ionization build-up in the upper D region below the nighttime VLF reflection heights, caused mainly by the impact on sprite-produced electrons of sequential electromagnetic pulses radiated upwards from in-cloud discharges. Also, the measured early event recoveries are modeled to obtain estimates of sprite-related electron density in the upper D region.
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: 2007 Fall Meeting