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Author: search.filters.author.Supnithi, PornchaiSubject: search.filters.subject.Equatorial latitude

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    Study of ionospheric topside variations based on NeQuick topside formulation and comparisons with the IRI-2012 model at equatorial latitude station, Chumphon, Thailand
    (2017-07-15)
    Jamjareegulgarn, Punyawi
    ;
    Supnithi, Pornchai
    ;
    Hozumi, Kornyanat
    ;
    Tsugawa, Takuya
    It is well-known that the equatorial anomaly at equatorial and low latitudes is caused by the fountain effect, therefore, the modeling of topside electron density profiles (EDPs) and the knowledge of electron density distribution in the region are particular challenging. Chumphon station, Thailand, is located within this region. However, at this station, since only an FMCW ionosonde system is installed, the topside EDP cannot be automatically obtained. Therefore, in this work, the topside EDPs are derived using the NeQuick topside formulation of the NeQuick 2 model (namely, NeQuick-derived topside EDPs) and then compared with those of three options of the IRI-2012 model including NeQuick, IRI01-corr, and IRI2001 options. The results show that, at Chumphon station, the NeQuick-derived topside EDPs are generally closer to the topside EDPs of IRI01-corr option in winter season and the topside EDPs of NeQuick option in equinox and summer seasons. When analyzing the topside TEC values obtained from each profile and the IGS TEC, it is found that the topside TEC values integrated from NeQuick-derived topside EDPs and predicted by both IRI01-corr and IRI-2001 options of the IRI-2012 model are sometimes higher than the IGS TEC values observed at Chumphon. In addition, we study the diurnal variations of the scale height computed from NeQuick topside formulation (H <inf>sc</inf> ), hmF2 and foF2 parameters. The correlation of H <inf>sc</inf> with the parameters hmF2 and the bottomside thickness parameter of NeQuick model (B2 <inf>bot</inf> ). The computed H <inf>sc</inf> values during daytime are lower than those during nighttime and they show non-linear correlations with hmF2 and B2 <inf>bot</inf> . The main cause of these discrepancies are possibly due to the B2 <inf>bot</inf> expressions used to compute the H <inf>sc</inf> .
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    A new expression for computing the bottomside thickness parameter and comparisons with the NeQuick and IRI-2012 models during declining phase of solar cycle 23 at equatorial latitude station, Chumphon, Thailand
    (2017-07-15)
    Jamjareegulgarn, Punyawi
    ;
    Supnithi, Pornchai
    ;
    Watthanasangmechai, Kornyanat
    ;
    Yokoyama, Tatsuhiro
    ;
    Tsugawa, Takuya
    This paper proposes a new expression for computing the bottomside thickness parameter at equatorial latitude station, Chumphon (10.72°N, 99.37°E), Thailand. Its diurnal variations from 2004 to 2006 at this location are then studied. The proposed expression is derived based on two experimental data sources: FMCW ionosonde and dual-frequency GPS system, and some expressions of the NeQuick 2 model. Hence, after both the bottomside thickness parameter computed by the proposed equation, B2bot_Pro, and the bottomside shape parameter (namely, B1_Pro in this work) are computed, the bottomside electron density and the height where the bottomside electron density drops down to be 24% of the NmF2 (namely, h0.24) can be computed and shown in this work using the analytical functions of the IRI model. Moreover, the diurnal variations of the B2bot_Pro are compared with those computed from the NeQuick model, B2bot_NeQ, and the predicted B0 of the IRI-2012 model with ABT-2009 and Bil-2000 options (namely, “B0_ABT” and “B0_Bil”, respectively). The averaged, minimum, and maximum values of percentage deviations among these bottomside thickness parameters are also computed and shown in this work. Our results show that the diurnal variations of B2bot_Pro at Chumphon station have the following patterns: they start to increase during nighttime to the first peaks during pre-sunrise hours, and then decrease abruptly to their minimum values during sunrise hours. Afterward, they increase again to reach the second peaks around local noontime and fall gradually to their starting times during 20–04 LT. The diurnal variations of B2bot_Pro follow generally the same trends as those of the B2bot_NeQ and the B0_ABT, except pre-sunrise hours. The pre-sunrise peaks and sunrise collapses in both the B2bot_NeQ and the B0_ABT can be found occasionally. On the other hand, the diurnal variations in B2bot_Pro differ from those in B0_Bil due to the flattened variation in B0_Bil and the pre-sunrise peaks as well as sunrise collapses in B0_Bil disappear. The pre-sunrise peaks of the B2bot_Pro at the Chumphon station are higher than those of the B2bot_NeQ, the B0_ABT, and the observed B0 at other regions. Furthermore, the percentage deviations between the B2bot_Pro and the B0_ABT (PD_B2B0ABT) are mostly lower than 30% for all seasons of the studied years, opposite to the other percentage deviations studied in this work. The proposed B2bot_Pro parameters in this work follow a similar trend to the B2bot_NeQ and the B0_ABT, but it is not conclusive that the proposed values are equivalent to them.
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    Ionospheric variation at Thailand equatorial latitude station: Comparison between observations and IRI-2001 model predictions
    (2010-01-15)
    Wichaipanich, Noraset
    ;
    Supnithi, Pornchai
    ;
    Ishii, Mamoru
    ;
    Maruyama, Takashi
    In this paper, the F2-layer critical frequency (foF2) and peak height (hmF2) measured by the FM/CW ionosonde at Thailand equatorial latitude station, namely Chumphon (10.72°N, 99.37°E, dip 3.22) are presented. The measurement data during low solar activity from January 2004 to December 2006 are analyzed based on the diurnal, seasonal variation. The results are then compared with IRI-2001 model predictions. Our study shows that: (1) In general, both the URSI and CCIR options of the IRI model give foF2 close to the measured ones, but the CCIR option produces a smaller range of deviation than the URSI option. The agreement during daytime is generally better than during nighttime. Overestimation mostly occurs in 2004 and 2006, while underestimation is during pre-sunrise hours in June solstice in 2005. The peak foF2 around sunset is higher during March equinox and September equinox than the other seasons, with longer duration of maximum levels in March equinox than September equinox. Large coefficients of variability foF2 occur during pre-sunrise hours. Meanwhile, the best agreement between the observed foF2 and the IRI model is obtained in June solstice. (2) In general, The IRI (CCIR) model predicts the observed hmF2 well during daytime in June solstice from 2004-2006, but it overestimates during March equinox, September equinox and December solstice. For nighttime, the model overestimates hmF2 values for all seasons especially during March equinox and September equinox. However, the model underestimates hmF2 values during September equinox and for some cases during June solstice and December solstice at pre-sunrise. The agreement between the IRI model and the hmF2(M3000 <inf>OBS</inf> ) is worst around noontime, post-sunset and pre-sunrise hours. All comparative studies give feedback for new improvements of CCIR and URSI IRI models. © 2009.