Abstract
Gravity waves (GWs) play an important role in the dynamics and
energetics of the mesosphere. Geomagnetic activity is a known source of
GWs in the upper atmosphere. However, how deep the effects of
geomagnetic activity induced GWs penetrate into the mesosphere remains
an open question. We use temperature measurements from the SABER/TIMED
instrument between 2002 - 2018 to study the variations of mesospheric GW
activity following intense geomagnetic disturbances identified by AE and
Dst indices. By considering several case studies, we show for the first
time that the GWs forced by geomagnetic activity can propagate down to
about 80 km in the high latitude mesosphere. Only regions above 55°
latitudes show a clear response. The fraction of cases in which there is
an unambiguous enhancement in GW activity following the onset of
geomagnetic disturbance is smaller during summer than other seasons.
Only about half of the events show an unambiguous increase in GW
activity during non-summer periods and about one quarter of the events
in summer show an enhancement in GWs. In addition, we also find that the
high latitude mesopause is seen to descend in altitude following onset
of geomagnetic activity in the non-summer high latitude region.