Ground GNSS Ionosphere Sounding - GNSS Remote Sensing: Theory, Methods and Applications - page 78

Average amplitude(TECU) Initial phase on day 76 in 2002 (degree)

0 o 0 o

180 o W 180 o W

4.5 5 5.5 0 1 2 3 4 5

Fig. 4.6 GPS TEC average annual amplitudes and initial phases over Antarctica

These storms also can disturb Earth's ionosphere from several hours to several days.
Nowadays, GNSS will be a new and powerful tool for solar flare and its effects
monitoring. For example, Fig. 4.7 b shows the VTEC time series at the grid points
of different latitudes, ( 15 ı S, 145 ı E), ( 30 ı S, 145 ı E) and ( 45 ı S, 145 ı E) in
Australia during the geomagnetic storm from 19 to 21 Nov 2003 with the time series
of the Dst index, and geomagnetic activity index Kp (Fig. 4.7 a). The Dst profile is
the solid line and Kp indexes are the dash line. The Dst index is used to define
the occurrence, duration and magnitude of a storm, whose unit is nT, nanotesla.
And the Kp index is a disturbed level of geomagnetic field. The Kp indexes reach
a value of 9(close to its maximum, from 20:00 on 20 Nov and 4:00 UT on 21
Nov 2003, indicating a severely disturbed geomagnetic condition during these time.
The Dst index also reaches the summit at 20:00 on 20 Nov, indicating a stronger
geomagnetic activity. The TECs normally vary from day to night on 19 Nov 2003.
But it suddenly reduces from 8:00 to 16:00 20 Nov 2003, and rarely varies from day
to night on 21 Nov 2003. It is obvious to see that the TEC has a severe effect due to
suffering a great geomagnetic storm.

4.3.2.3 TEC Disturbances Following Earthquakes

Robust seismic signals around the globe could estimate the gross nature of
earthquakes, but the details are usually unclear due to the lack of near-field obser-
vations. Although ground measurements, e.g., GNSS/InSAR and strong motion
measurements, provide unique insights on the kinematic rupture and nature of
the earthquake, but the temporal-spatial resolutions are still limited. It may help