Midlatitude nighttime D region ionosphere variability on hourly to monthly time scales
Abstract
Significant temporal variability of the nighttime D region is well known, but its
inaccessibility means that the time scales, magnitudes, and sources for that variability
are not well understood. We probed the ionospheric D region by measuring the high-power
broadband very low frequency (VLF) signals launched by lightning and propagating in
the Earth-ionosphere waveguide. We analyzed broadband sferic data of July and August
2005 recorded by our sensors located near Duke University by comparing measured sferic
spectra to model results and extracted the height of an assumed exponential electron
density profile for each measurement. The measured nighttime D region electron density
profile heights showed large temporal variations of several kilometers on some nights
and relatively stable behaviors on others. The measured hourly average heights in
260 h ranged between 82.0 and 87.2 km, with a mean value of 84.9 km and a standard
deviation of 1.1 km. The maximum variation in the 5 h period was around just above
4.0 km and the maximum variation in the 1 h period was around 1.3 km, with sharper
gradients observed over shorter time periods. We also observed spatial variability
as large as 2.0 km over 5° latitudes on some nights and no spatial variability on
others. On some nights, the temporal variability exhibited a close correlation with
the occurrence rate of lightning discharges under the probed region. This suggests
that the direct energy coupling between lightning discharges and lower ionosphere
can be a significant source of the D region variability. However, on other nights,
the measured height temporal variability showed weak to no correlation with local
lightning, displaced lightning (as would be expected for lightning-induced electron
precipitation), or geomagnetic activities. These measurements suggest that nighttime
D region variability may be driven by many sources. Copyright 2010 by the American
Geophysical Union.
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https://hdl.handle.net/10161/4169Published Version (Please cite this version)
10.1029/2010JA015437Publication Info
Han, F; & Cummer, SA (2010). Midlatitude nighttime D region ionosphere variability on hourly to monthly time scales.
Journal of Geophysical Research: Space Physics, 115(9). pp. A09323. 10.1029/2010JA015437. Retrieved from https://hdl.handle.net/10161/4169.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Steven A. Cummer
William H. Younger Distinguished Professor of Engineering
Dr. Steven Cummer received his Ph.D. in Electrical Engineering from Stanford University
in 1997 and prior to joining Duke University in 1999 he spent two years at NASA Goddard
Space Flight Center as an NRC postdoctoral research associate. Awards he has received
include a National Science Foundation CAREER award and a Presidential Early Career
Award for Scientists and Engineers (PECASE) in 2001. His current work is in a variety
of theoretical and experimental electromagnetic problems related to g

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