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Author: search.filters.author.Komolmis, Tharadol

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    The disturbance effects on single frequency GPS positioning at low geomagnetic latitude stations in Thailand
    (2020-07-01)
    Tongkasem, Napat
    ;
    Myint, Lin M.M.
    ;
    Supnithi, Pornchai
    ;
    Komolmis, Tharadol
    ;
    Hozumi, Kornyanat
    The ASEAN IVO project currently supports the research related to GNSS and ionospheric data products for disaster prevention and aviation in low-latitude regions. In the positioning system, the atmosphere is the main medium along the propagation path that includes some ions, water vapor, and noise. These are the causes of the propagation delay time especially the ions in the ionosphere. At the present, there are many Global Positioning System (GPS) stations worldwide. Therefore, we can check the performances of the positioning system by using the positioning error calculation. In this work, the positioning errors are calculated from the 16 GPS stations at the low geomagnetic latitude region (Thailand) with the single frequency algorithm on a disturbance day. Then, we compute the 95-percentile and the maximum of the positioning errors. The results show approximately the difference of 95-percentile value 1.799 meters on the horizontal axis and 2.289 meters on the vertical axis and maximum positioning error can be up to 11.413 meters on the disturbed time on the disturbance day.
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    Ionospheric peak height at the magnetic equator: Comparison between ionosonde measurements and IRI
    (2017-07-15)
    Maruyama, Takashi
    ;
    Ma, Guanyi
    ;
    Tsugawa, Takuya
    ;
    Supnithi, Pornchai
    ;
    Komolmis, Tharadol
    The ionospheric peak height in the F layer (hmF2) varies with not only thermospheric conditions but also dynamic processes in the upper atmosphere. At mid-latitudes, the field-aligned diffusion and recombination loss determine the hmF2 in the absence of applied vertical drift. Vertical drifts displace the hmF2 to a new equilibrium position in conjunction with the field-aligned redistribution of the plasma. In the vicinity of the magnetic equator, however, the equilibrium state would be different from low and mid-latitudes because the direct vertical coupling of plasma through the diffusion process is not allowed. Thus the behavior of hmF2 cannot be simply an extrapolation of that at low latitudes. In this paper, ionosonde measurements of the hmF2 near the magnetic equator and off-equatorial latitudes are compared with the IRI output.
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    Detection of ruptures of Andaman fault segments in the 2004 great Sumatra earthquake with coseismic ionospheric disturbances
    (2006-09-04)
    Heki, Kosuke
    ;
    Otsuka, Yuichi
    ;
    Choosakul, Nithiwatthn
    ;
    Hemmakorn, Narong
    ;
    Komolmis, Tharadol
    We Near-field coseismic perturbations of ionospheric total electron content (TEC), caused by direct acoustic waves from focal regions, can be observed with Global Positioning System (GPS). They appear 10-15 min after the earthquake with typical periods of ∼4-5 min and propagate as fast as ∼1 km/s toward directions allowed by ambient geomagnetic fields. Ionospheric disturbance, associated with the 2004 December 26 great Sumatra-Andaman earthquake, was recorded with nine continuous GPS receiving stations in Indonesia and Thailand. Here we explore the possibility to constrain the rupture process of the earthquake with the observed ionospheric disturbances. We assumed linearly distributed point sources along the zone of coseismic uplift extending ∼1300 km from Sumatra to the Andaman Islands that excited acoustic waves sequentially as the rupture propagate northward by 2.5 km/s. TEC variations for several satellite-receiver pairs were synthesized by simulating the propagation of acoustic waves from the ground to the ionosphere and by integrating the TEC perturbations at intersections of line of sights and the ray paths. The TEC perturbations from individual point sources were combined using realistic ratios, and the total disturbances were compared with the observed signals. Prescribed ratios based on geodeticatly inferred coseismic uplifts reproduced the observed signals fairly well. Similar calculation using a rupture propagation speed of 1.7 km/s degraded the fit. Suppression of acoustic waves from the segments north of the Nicobar Islands also resulted in a poor fit, which suggests that ruptures in the northern half of the fault were slow enough to be overlooked in short-period seismograms but fast enough to excite atmospheric acoustic waves. Coseismic ionospheric disturbance could serve as a new indicator of faulting sensitive to ruptures with timescale up to 4-5 min. Copyright 2006 by the American Geophysical Union.