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Sporadic E critical frequency detection using three EIA region ionosonde stations over Southeast Asia
(2025-03-01)
Wichaipanich, Noraset
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Nishioka, Michi
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Min Myint, Lin Min
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Supnithi, Pornchai
This paper presents the occurrence of the sporadic E layer critical frequency (foEs) measured from three ionosonde stations in the Southeast Asia equatorial ionization anomaly (EIA) regions. These three ionosonde stations include two in Thailand: Chiang Mai (18.76°N, 98.93°E, Dip 12.7°) and Chumphon (10.72°N, 99.37°E, Dip 3.0°), and one in Indonesia: Kototabang (0.2°S, 100.32°E, Dip −10.1°). The daily hourly foEs values observed during 2010 and 2015 were statistically analyzed for foEs occurrence during low and high solar activity periods. Additionally, the number of foEs occurrences was analyzed in terms of the percentage of occurrence (%foEs). The results show that the occurrences of foEs from all three stations were similar, with the monthly hourly occurrence of foEs peaking in the June solstice season (May, June, July, August). Meanwhile, foEs appeared relatively low during the September equinox (September, October) and the December solstice (November, December, January, February) seasons. Furthermore, the frequency of foEs occurrence peaks around 16–20 LT, except in 2015 at Chiang Mai and Chumphon, where peaks were observed at 10 LT and 15 LT, respectively. Additionally, comparing the three stations reveals that in 2010, the maximum number of foEs occurrences was at Chiang Mai (≈21 %), followed by Kototabang (≈19 %) and Chumphon (≈16 %). In 2015, the highest number was observed at Kototabang (≈17 %), followed by Chumphon (≈14 %) and Chiang Mai (≈8%). Furthermore, the maximum frequency of foEs was highest at Chiang Mai (20–25 MHz), followed by Chumphon (15–20 MHz) and Kototabang (10–15 MHz). Additionally, foEs occurrences during low solar activity (2010) were higher than those during high solar activity (2015). It was assumed that the occurrence of foEs in the Southeast Asian sector was anti-correlated with the solar cycle and asymmetric characteristics. We hope that this analytical information will be useful for future HF and VHF communications design in the Southeast Asia region.
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Improving the modeling of bottomside thickness parameters over midlatitudes and high latitudes
(2020-02-01)
Jamjareegulgarn, Punyawi
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Supnithi, Pornchai
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Kenpankho, Prasert
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Wichaipanich, Noraset
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Nayak, Chinmaya
This paper investigates bottomside thickness parameters at Digisonde stations over midlatitude and high latitude regions, and compares the diurnal, seasonal, and solar activity variations in 2014 and 2009. The geographic latitudes of high latitude considered in this work are located beyond ±60° and those of midlatitude are located between ±40° and ±60°. The IRI-modeled B0 with ABT-2009 option (B0_IRI) are also examined and compared with four kinds of the B0 values, i.e., the observed B0 (B0_obs) from GIRO, the computed B0 following to Jamjareegulgarn et al. (2017a) (B0_old), the calculated B0 with a correction factor regarding to Jamjareegulgarn et al. (2017b) (B0_new), and the B0 with an average correction factor (B0_new_c_av). The average correction factors are proposed additionally in this work so as to assist occasionally the experimental B0 nonexistence of Digisonde which are equal to 0.2658 and 0.2058 for midlatitudes and high latitudes, respectively. Results show that the diurnal variations of B0_new and B0_new_c_av are in a good agreement with those of B0_obs evidently compared with those of B0_IRI and B0_old at every station during the three seasons over high and middle latitudes. During the three seasons, the diurnal variations of B0_new_c_av show similar trends and are close to one another with the B0_obs and the B0_new with small deviations. The differences between the B0obs and the B0_new_c_av also show similar trends and are close to one another with those between the B0obs and the B0_new. In contrast, the B0_IRI with ABT-2009 option seems to predict the B0 values poorly during the three seasons at high latitudes and some seasons at midlatitudes. The proposed B0_new is useful for computing approximately the observed B0 and the ionogram-based total electron content (ITEC) of Digisonde, and the plasma scale height over midlatitudes and high latitudes.
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Sub-30 ppm/oC high-frequency temperature-compensated CMOS relaxation oscillator
(2018-07-02)
Sakphrom, Siraporn
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Limpiti, Thunyawat
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Wichaipanich, Noraset
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Thanachayanont, Apinunt
This paper describes the design and realization of a high-frequency temperature-compensated CMOS relaxation oscillator in a 0.35-µm CMOS technology. The proposed oscillator employs the current-controlled topology with a resistive source-degeneration transconductor and a current comparator in order to achieve high oscillation frequency and low power dissipation. Temperature compensation of the oscillation frequency is achieved by simulation results show that, at a nominal oscillation frequency of 32.48 MHz, the proposed oscillator exhibited a temperature coefficient of less than 28.41 ppm/oC over a temperature range of -40oC to +120oC, while consuming 241.5 µW from a 2.5-V single power supply voltage.
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A comparison of neural network-based predictions of foF2 with the IRI-2012 model at conjugate points in Southeast Asia
(2017-06-15)
Wichaipanich, Noraset
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Hozumi, Kornyanat
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Supnithi, Pornchai
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Tsugawa, Takuya
This paper presents the development of Neural Network (NN) model for the prediction of the F2 layer critical frequency (foF2) at three ionosonde stations near the magnetic equator of Southeast Asia. Two of these stations including Chiang Mai (18.76°N, 98.93°E, dip angle 12.7°N) and Kototabang (0.2°S, 100.3°E, dip angle 10.1°S) are at the conjugate points while Chumphon (10.72°N, 99.37°E, dip angle 3.0°N) station is near the equator. To produce the model, the feed forward network with backpropagation algorithm is applied. The NN is trained with the daily hourly values of foF2 during 2004–2012, except 2009, and the selected input parameters, which affect the foF2 variability, include day number (DN), hour number (HR), solar zenith angle (C), geographic latitude (θ), magnetic inclination (I), magnetic declination (D) and angle of meridian (M) relative to the sub-solar point, the 7-day mean of F10.7 (F10.7_7), the 81-day mean of SSN (SSN_81) and the 2-day mean of Ap (Ap_2). The foF2 data of 2009 and 2013 are then used for testing the NN model during the foF2 interpolation and extrapolation, respectively. To examine the performance of the proposed NN, the root mean square error (RMSE) of the observed foF2, the proposed NN model and the IRI-2012 (CCIR and URSI options) model are compared. In general, the results show the same trends in foF2 variation between the models (NN and IRI-2012) and the observations in that they are higher during the day and lower at night. Besides, the results demonstrate that the proposed NN model can predict the foF2 values more closely during daytime than during nighttime as supported by the lower RMSE values during daytime (0.5 ≤ RMSE ≤ 1.0 for Chumphon and Kototabang, 0.7 ≤ RMSE ≤ 1.2 at Chiang Mai) and with the highest levels during nighttime (0.8 ≤ RMSE ≤ 1.5 for Chumphon and Kototabang, 1.2 ≤ RMSE ≤ 2.0 at Chiang Mai). Furthermore, the NN model predicts the foF2 values more accurately than the IRI model at the three sites on average, as clearly seen on the yearly RMSE averages. The RMSE values of NN model are lower than those of both CCIR and URSI options, and in terms of the yearly percentage improvements, the NN model gives improvement of around 10–15% in 2009 and 10% in 2013 for Chiang Mai, 20–25% in 2009 and 5–10% in 2013 for Chumphon, and around 18–25% in 2009 and 20–30% in 2013 at Kototabang. Although the NN model predicts the foF2 values closely to the observed data and produces more accurate prediction than the IRI models, in some cases, the IRI model performs better than the NN model. Hence, there is still room for further improvement of the proposed NN model.
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A comparative study of ionospheric profile parameters B0 and B1 over Chumphon with IRI-2012
(2015-08-17)
Jamjareegulgarn, Punyawi
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Supnithi, Pornchai
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Wichaipanich, Noraset
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Ishii, Mamoru
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Maruyama, Takashi
Average diurnal variations of ionospheric profile parameters B0 and B1 in 2009 are studied over Chumphon province, Thailand, and compared those variations with IRI-2012 model. The thickness parameter (B0) and the shape parameter (B1) are two main parameters to compute and depict the F2-layer electron density profile. IRI-2012, the latest version of IRI model, offers three options to provide B0 and B1, i.e., Bil-2000, Gul-1987, ABT-2009. Those options have never been taken for studying and comparing with the ionospheric observation data from a FM/CW ionosonde, Chumphon. Moreover, the observed B0 and B1 from Thailand have never been analyzed nor used while establishing the new table of (B0, B1) values of the IRI model. Hence, B0 and B1 observation is necessary as a part of the global validation study of the IRI-2012 model. Our studies show that: (1) In general, the average diurnal variations of B0 for the observation and the IRI-2012 model show the same trends, except B0 of Gul-1987 during 20:00 - 02:00 LT. The observed B0 averages are equal to 166.13 km and 99.18 km in the daytime and nighttime, respectively. (2) The average diurnal variations of B1 for the observation and the IRI-2012 model show the same trends, except B1 of ABT-2009. Average diurnal variations of the observed B1 look like a sine wave where the peak and lowest values can be found around the midnight and the noontime, respectively. For the IRI-2012 model, B1 of Gul-1987 is the same value as B1 of Bil-2000. The observed B1 averages are equal to 1.98 and 2.51 in the daytime and nighttime, respectively. Our observed B0 and B1 results are similar to other studies in equatorial latitude and low latitude stations. Our comparative studies provide some details for improving B0 and B1 parameters of CCIR-based IRI model in the equatorial latitude region.
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Prediction of foF2 using Neural Network at Thailand equatorial latitude station, Chumphon
(2014-01-01)
Wichaipanich, Noraset
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Supnithi, Pornchai
This paper proposes the development of a Neural Network (NN) model for the prediction of the F2 layer critical frequency (foF2) at the magnetic equator over Chumphon (10.72°N, 99.37°E, dip angle 3.3°N), Thailand and then compared with the IRI model and the experimental ones. The feed forward network with backpropagation algorithm has been developed for predicting the foF2 values. The NN is trained with the daily hourly values of foF2 during the period from 2004 to 2008 and the input parameters affecting the foF2 variability including the hour number, day number, F10.7 index and sunspot number (SSN). To examine the performance of the proposed NN, the root mean square error (RMSE) of the observed foF2, the proposed NN model and the IRI (both CCIR and URSI options) model are compared in 2009. The results show that the NN model predicts the foF2 values close to the observed data, particularly during daytime. Moreover, the NN model can predicts more accurate than the IRI model that is supported by the lower RMSE. However, the NN model provides slightly deviation of prediction during pre-sunrise hours since the observed foF2 data for NN training in this periods are fewer than those during daytime. © 2014 IEEE.
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Ionospheric variation at Thailand equatorial latitude station: Comparison between observations and IRI-2001 model predictions
(2010-01-15)
Wichaipanich, Noraset
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Supnithi, Pornchai
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Ishii, Mamoru
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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.
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Thailand equatorial F2-layer peak height and comparison with the IRI-2001 model
(2009-12-01)
Wichaipanich, Noraset
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Supnithi, Pornchai
In this paper, the F2-layer peak height (hmF2) are calculated from the observed M(3000)F2 and then compared with IRI-2001 model. The data used for this study are obtained from bottomside ionogram recorded by the FM/CW ionosonde at Chumphon campus of King Mongkut's institute of Technology Ladkrabang (latitude 10.72°N and longitude 99.37°E), Thailand, located near the magnetic equator. The measurement data including March, June, September and December in 2004, 2005 and 2006 for the period of low solar activity, are analyzed and then compared with IRI-2001 model predictions. Our study shows that the agreement between the data and the model at Southeast Asia will be better if the Shimazaki's formula is used. The results are important for the future improvements of the IRI model for the hmF2 at Thailand equatorial latitude. ©2009 IEEE.

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