Ground GNSS Ionosphere Sounding - GNSS Remote Sensing: Theory, Methods and Applications - page 91

Fig. 4.16 Comparison of
F2-layer peak heights (hmF2)
from the monthly median,
ionosonde and GPS
observations on 20 November
2003

550

Monthly median
Ionosonde
GPS by this study

500

450

400

350

300

250

0 5 10 15 20 25

Time (UT: hour)

Anyang station. The GPS-derived F2-layer peak density (NmF2) has an anomalous
change at 9:00 UT and increases from 10:00 UT until 19:00 UT. The F2-layer
peak height (hmF2) suddenly rises from 8:00 UT when the shock of this storm just
started, and reaches the maximum height at about 16:00 UT with a maximum Kp
value of 9, and then gradually descends until 21:00 UT (Fig. 4.16 ). The significant
increases of F2-layer peak height and density last for about 10 h and is classified
as a long-duration ionospheric positive storm (Huang et al. 2005 ). The electron
density profile comparison also shows the same enhancements of the F2-region
from 10:00 UT to 19:00 UT. For example, Fig. 4.17 is a comparison of electron
density profiles between the GPS, ionosonde data and monthly median at 13:00 UT.
It can be clearly seen that the electron density profiles are significantly increased
above the F region on 20 November 2003, especially the NmF2 which increased by
about 45 % accompanied by a significant uplift in the height of the F2 layer peak
(the hmF2), while on the quiet day (23 November) the electron density profiles are
almost close to the monthly median value. In addition, the responses of the NmF2
and hmF2 to this storm at different latitudes (i.e. different grid sites) were analyzed,
and almost similar results were obtained, which is mainly due to the small area of
South Korea. As the TEC is the integrated electron density along a path through the
ionosphere, the TEC variations over South Korea during this storm are similar to
the NmF2 behaviour.
The uplift of the F2 layer is mainly associated with a strong eastward electric
field. The increase of electron density in the F2-layer peak depends mainly on
the molecular nitrogen concentration [N 2 ] with some contribution from molecular
oxygen concentration [O 2 ], while the production rate depends on the atomic oxygen
concentration [O]. However, the O/N 2 ratio from the GUVI instrument on board
the TIMED satellite shows no significant change during this geomagnetic storm. It
suggests that the increase in NmF2 is not caused by changes in neutral composition,