Global Positioning System Reference
In-Depth Information
550
Monthly median
Ionosonde
GPS by this study
500
450
400
350
300
250
0
5
10
15
20
25
Time (UT: hour)
Fig. 13. The hmF2 variations from monthly median, ionosonde and GPS observations on 20
November 2003
Normally the increase/loss rate of F region electron density depends mainly on the
molecular nitrogen concentration [N2] and atomic oxygen concentration [O] [8]. However,
the O/N2 ratio obtained by the GUVI instrument on board the TIMED satellite doesn't
show significant changes in South Korea where the increased NmF2 was observed,
indicating that the increased NmF2 in South Korea is not caused by changes in neutral
composition, and other possible non-chemical effects, such as dynamical changes of vertical
ion motions induced by winds and E×B drifts, tides and waves in the mesosphere/lower
thermosphere (MLT) region, which can be dynamically coupled upward to generate
ionospheric perturbations and oscillations.
4. Conclusion
The GPS signals are delayed due to the effects of dry gas and water vapor when
propagating through the neutral atmosphere. The hydrostatic delay is proportional to the
surface pressure and the wet delay is a key parameter in atmospheric radiation,
hydrological cycle, energy transfer and the formation of clouds via latent heat. Thereby, the
total tropospheric delay (ZTD) is an important parameter of the atmosphere, which directly
or indirectly reflects the weather and climate processes, variations, and atmospheric vertical
motions, etc. Comparing the time series of the zenith tropospheric delay (ZTD), zenith
hydrostatic delay (ZHD), zenith wet delay (ZWD), surface temperature, pressure and
relative humidity, it has been noted that the ZHD is highly proportional to the atmospheric
pressure at the site and relatively stable and the ZWD is positively correlated with the
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