scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Solar flare effects on ionospheric electron densities as measured by the Arecibo
incoherent scatter radar
Haldoupis Christos 1 , Bourdillon Alain 2 , Zhou Qihou 3 , Meek Chris 4
1 Physics Department, University of Crete, Heraklion, Greece, 2 IETR/CNRS, Université de Rennes 1,
Rennes, France, 3 Department of Electrical and Computer Engineering, Miami University, Ohio,
USA, 4 Institute of Space and Atmospheric Studies, University of Saskatchewan, Canada
The explosive emission of electromagnetic radiation from solar flares is confined mostly in
the X-ray and EUV bands of the solar spectrum. This energetic radiation is capable of causing
pronounced changes on ionospheric electron densities, which then become responsible for a
range of well-known phenomena classified as “sudden ionospheric disturbances” or SID.
Although the study of SID, that uses mostly radio wave propagation and absorption
techniques, can arrive at some indirect inferences on the modified electron densities in the
lower ionosphere, direct measurements of flare-induced ionospheric electron density profiles
for most of the ionosphere are rather limited. Surprisingly, there are only very few direct
electron density measurements during solar flare events reported in the open literature that
have been made with incoherent scatter radars (ISR), particularly the powerful ISR at
Arecibo. Here, we take advantage of an existing data base to report on solar flare-related
electron density measurements made with the Arecibo radar which monitored the ionosphere
from 60 to 430 km altitude with a height resolution of ~600 m and a time resolution of ~ 1.8
min. The results to be discussed refer to several solar flares in the range from about C50 to
X50, that is, the X-ray fluxes in the 1.0 – 8.0 Å band range from 5 μW/m 2 to 5 mW/m 2 , as
measured and classified by the GOES satellite space environment X-ray monitor. The
emphasis is placed on the structure of the modified electron density profiles and the temporal
altitudinal variations of electron densities relative to the radiation changes measured by GOES
in the long (XL) and short (XS) X-ray bands of 0.5 to 4.0 Å and 1.0 to 8.0 Å, respectively.
These results can be useful in the validation of existing D region photochemical models as
well as VLF (very low frequency) and HF (high frequency) radio wave propagation models.
In addition, they can provide a judgement on the significance of ionospheric TEC (total
electron content) changes anticipated during solar flare events of different magnitude.