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

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Solar cycle dependence of ionospheric irregularities, as deduced from CHAMP and
GRACE
Lühr Hermann , Park Jaeheung , Xiong Chou
Deutsches GeoForschungsZentrum, GFZ
The low-latitude ionosphere in the post-sunset time sector is known to be susceptible to
instabilities. The resulting electron density irregularities cause severe degradations of
communication and navigation signals. Systematic surveys of irregularities over the past
decade by the satellites CHAMP and GRACE provide unprecedented insights into the
distribution of these phenomena. We show the seasonal/longitudinal distribution of the
occurrence rates and how it varies during the declining solar cycle 23. As we have
measurements at two different altitudes, the upward propagation manifests itself in the
difference in local time distributions at the two spacecraft. Also the very few observations of
plasma bubbles by GRACE during the late years suggest that the irregularities do not reach
490km altitude at low solar flux levels.
Our observations further confirm the existence of neutral density depletions accompanying
plasma bubble. These, although small, undulations in neutral mass density play an important
role in the pressure balance between the magnetic, plasma and neutral particle pressure.
Besides the plasma depletions there are also enhancements called plasma blobs. Both, plasma
bubbles and blobs are generally accompanied by field-aligned currents which manifest the
electrodynamic nature of these phenomena.