Kornyanat Hozumi

Regional map of the F2-layer critical frequency over Southeast Asia

This paper presents the development of a regional ionospheric F2 layer critical frequency (foF2) map over Southeast Asia using parabolic curve fitting. To produce the map, the foF2 values measured by the ionosonde measurement at Chiang Mai, Chumphon and Kototabang are used as the input of the ionospheric map. To examine the performance of the foF2 mapping, our local maps and the global maps (IRI-Plas 2015 online under IONOLAB website) are compared at five stations over Southeast Asia, including Chiang Mai, Chumphon, Kototabang, Bac Lieu, and Phu Thuy. The results on equinox day (20th March) in 2009 and 2015 are analyzed. The results show that our map produces foF2 values close to the observed data while the global map underestimates the measured data in 2009 and it overestimates in 2015. The results of this paper are important for managing and designating the maximum usable frequency (MUF) of HF communication systems over Southeast Asia region.

Statistical analysis of high frequency radio parameters on St. Patrick's day in Thailand

The ionospheric irregularities on St. Patricks day (17 March 2015) at Chiang Mai and Chumphon stations are affected by the strongest of the 24th solar storm cycle. The ionogram data in this research is obtained from the frequency modulated/carrier waves (FM/CW) ionosonde at Chiang Mai station and near the magnetic equator, namely, Chumphon station. The parameters in this research include the critical frequency of F2 layer, the virtual height of F layer, and the maximum height of F2 layer. Overall, we found that the ionosphere layer at Chiang Mai and Chumphon stations are disturbed by the geomagnetic storm. The result indicate that the radio frequency transmission is affected by geomagnetic storm at both stations and the observation differ from the median value is specified in part of the percentage of coefficient deviation.

A new expression for computing topside scale height for satellite-based communications

It is well-known that the NeQuick 2 model provides analytical expressions showing a relationship between topside and bottomside ionospheres. Its bottomside thickness parameter (B2bot) is a key parameter for studying topside electron density profile (EDP) and topside parameters, and its topside scale height (Hsc) is also used to identify the topside electron density profile. The B2bot computed using ionogram-derived ionospheric parameters can be used to calculate the Hsc. Unfortunately, the Hsc computed by the original B2bot expression (Hsc_old) are significantly higher than the scale heights obtained from digisondes (Hm) and the diurnal variations of the Hsc_old are quite different from those of the Hm. Hence, a new expression of B2bot for computing the Hsc is suggested in this work relying on the available expressions of the NeQuick 2 model. Our results show that (1) the Hsc computed by the new expression of B2bot (Hsc_new) are comparable to the Hm and the diurnal variations in Hsc_new are the same trends as those in Hm; (2) all of the scale heights show diurnal variations with higher values during daytime than during nighttime and the secondary peaks can be found different local times relying on the locations; and (3) the peaks of scale height cause higher absolute differences between Hsc_new and Hm (D_SH).