Simulation of long-term variations of the F2-layercritical frequency f0F2 at the northern tropical crest of ionization at Phu Thuy, Hanoi, Vietnam using the thermosphere-ionosphere-electrodynamicsgeneral circulation model (TIE-GCM)

Abstract

In this work, the long-term variations of the simulated f0F2 by the NCAR thermosphere ionosphere-electrodynamics general
circulation model (TIE-GCM) at the northern tropical crest of ionization at Phu Thuy, Hanoi, Vietnam (geographic latitudes
21.030N and longitude: 105.950E) during the period from 1962 to 2002 are examined to evaluate the ability of this model to
reproduce the major features of the f0F2 as observed. The TIE-GCM simulates the influences of migrating and non-migrating diurnal
and semidiurnal tides at the lower thermosphere, and changes of geomagnetic activity on the long-term variations of the f0F2. It
reproduces well the diurnal and seasonal variations. We analyze the diurnal and seasonal variations of the observed f0F2 at Phu Thuy
in approximately the same solar activity condition as in 1964, 1996 for the March and September equinoxes and June and December
solstices. The local time and seasonal structures of these simulated results correspond well to those that are observed in 1964. On the
contrary, the TIE-GCM does not reproduce the amplitude observed at Phu Thuy in 1996. The TIE-GCM with the chosen inputs does
not yet allow us to explain well the long-term variations observed at Phu Thuy. We also try the different numerical simulations to
understand how the long-term variations of the f0F2 is formed, how it relates to the current global system and its relationship with
the thermosphere wind. The simulations show that the calculated NmF2 values are lower than the observed values. We find that the
modeled contributions of the migrating and non-migrating diurnal and semidiurnal tides may cause them to play a major role in
reducing the amplitude of the NmF2. The contributions of the integrated hemispheric power of auroral electrons and the cross polar
cap potential seem to play an important role in increasing the amplitude of the NmF2.

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