Chart of the VHF Riometer at HAARP from UTC 2007-01-28_12:00 until 2007-01-30_00:00. It shown an event which causes an increased ionospheric absorption.
HAARP
CC BY 3.0
<a rel="nofollow" class="external free" href="http://www.haarp.alaska.edu/haarp/Rio.html">http://www.haarp.alaska.edu/haarp/Rio.html</a> (archive: <a rel="nofollow" class="external free" href="https://web.archive.org/web/20130404234726/http://www.haarp.alaska.edu/haarp/Rio.html">https://web.archive.org/web/20130404234726/http://www.haarp.alaska.edu/haarp/Rio.html</a> )