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Author: search.filters.author.Supnithi, P.Subject: search.filters.subject.Solar activity

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    Comparison of ionosphere characteristic parameters obtained by ionosonde with IRI-2007 model over Southeast Asia
    (2013-11-15)
    Wichaipanich, N.
    ;
    Supnithi, P.
    ;
    Tsugawa, T.
    ;
    Maruyama, T.
    ;
    Nagatsuma, T.
    In this work, the foF2 and hmF2 parameters at the conjugate points near the magnetic equator of Southeast Asia are studied and compared with the International Reference Ionosphere (IRI) model. Three ionosondes are installed nearly along the magnetic meridian of 100 E; one at the magnetic equator, namely Chumphon (10.72 N, 99.37 E, dip angle 3.0 N), and the other two at the magnetic conjugate points, namely Chiang Mai (18.76 N, 98.93 E, dip angle 12.7 N) and Kototabang (0.2 S, 100.30 E, dip angle 10.1 S). The monthly hourly medians of the foF2 and hmF2 parameters are calculated and compared with the predictions obtained from the IRI-2007 model from January 2004 to February 2007. Our results show that: the variations of foF2 and hmF2 predicted by the IRI-2007 model generally show the similar feature to the observed data. Both parameters generally show better agreement with the IRI predictions during daytime than during nighttime. For foF2, most of the results show that the IRI model overestimates the observed foF2 at the magnetic equator (Chumphon), underestimates at the northern crest (Chiang Mai) and is close to the measured ones at the southern crest of the EIA (Kototabang). For hmF2, the predicted hmF2 values are close to the hmF2(M3000F2 <inf>OBS</inf> ) during daytime. During nighttime, the IRI model gives the underestimation at the magnetic equator and the overestimation at both EIA crests. The results are important for the future improvements of the IRI model for foF2 and hmF2 over Southeast Asia region. © 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.
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    Item type:Publication,
    Thailand low and equatorial F2-layer peak electron density and comparison with IRI-2007 model
    (2012-01-01)
    Wichaipanich, N.
    ;
    Supnithi, P.
    ;
    Tsugawa, T.
    ;
    Maruyama, T.
    Ionosonde measurements obtained at two Thailand ionospheric stations, namely Chumphon (10.72°N, 99.37°E, dip 3.0°N) and Chiang Mai (18.76°N, 98.93°E, dip 12.7°N) are used to examine the variation of the F<inf>2</inf>-layer peak electron density (N<inf>m</inf>F<inf>2</inf>) which is derived from the F<inf>2</inf>-layer critical frequency, f<inf>0</inf>F <inf>2</inf>. Measured data from September 2004 to August 2005 (a period of low solar activity) are analyzed based on the diurnal and seasonal variation and then compared with IRI-2007 model predictions. Our results show that, in general, the diurnal and seasonal variations of the N<inf>m</inf>F<inf>2</inf> predicted by the IRI (URSI and CCIR options) model show a feature generally similar to the observed N<inf>m</inf>F<inf>2</inf>. Underestimation mostly occurs in all seasons except during the September equinox and the December solstice at Chumphon, and the September equinox and the March equinox at Chiang Mai, when they overestimate those measured. The best agreement between observation and prediction occurs during the pre-sunrise to post-sunrise hours. The best agreement of the %PD values of both the options occurs during the March equinox, while the agreement is the worst during the September equinox. The N<inf>m</inf>F<inf>2</inf> values predicted by the CCIR option show a smaller range of deviation than the N<inf>m</inf>F<inf>2</inf> values predicted by the URSI option. During post-sunset to morning hours (around 21:00-09:00 LT), the observed N<inf>m</inf>F<inf>2</inf> at both stations are almost identical for the periods of low solar activity. However, during daytime, the observed N <inf>m</inf>F<inf>2</inf> at Chumphon is lower than that at Chiang Mai. The difference between these two stations can be explained by the equatorial ionospheric anomaly (EIA). These results are important for future improvements of the IRI model for N<inf>m</inf>F<inf>2</inf> over Southeast Asia, especially for the areas covered by Chumphon and Chiang Mai stations. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).