Low latitude ionosphere-thermosphere dynamics studies with inosonde chain in Southeast Asia

Maruyama, Takashi; Kawamura, M.; Saito, Susumu; Nozaki, Kengo; Kato, Hisao; Hemmakorn, Narong; Boonchuk, T.; Komolmis, Tharadol; Duyen, C. Ha

doi:10.5194/angeo-25-1569-2007

Cited by 80 publications

(61 citation statements)

References 37 publications

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“…The details of the ionosonde observation are provided elsewhere (e.g., Maruyama et al, 2007). In this study, ESF days are defined only when ESF is detected before 21:00 THA.…”

Section: Data Set and Analysis Methodsmentioning

confidence: 99%

“…Considering the retardation effect on the echo trace, h F scaled at the lower frequency is more adequate to evaluate the E × B drift of PRE, on the contrary, scaling h F at the lower frequency is more likely to be interfered by the sporadic E-layer. In this context, h F at the frequency of 2.5 MHz is manually scaled to derive the PRE strength as performed by earlier studies (e.g., Saito and Maruyama, 2006;Maruyama et al, 2007). On the basis of the findings by Bittencourt and Abdu (1981), a peak of h F during the period from 18:00 to 21:00 THA reflects a timecumulative E × B drift of PRE.…”

Section: Data Set and Analysis Methodsmentioning

confidence: 99%

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Relationships between pre-sunset electrojet strength, pre-reversal enhancement and equatorial spread-F onset

et al. 2010

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Abstract. The virtual height of the bottom side F-region (h F ) and equatorial spread-F (ESF) onsets at Chumphon (10.7 • N, 99.4 • E; 3.3 • N magnetic latitude) were compared with the behaviour of equatorial electrojet (EEJ) ground strength at Phuket (8.1 • N, 98.3 • E; 0.1 • N magnetic latitude) during the period from November 2007 to October 2008. Increase in the F-layer height and ESF onsets during the evening hours were well connected with the EEJ ground strength before sunset, namely, both the height increase and ESF onsets were suppressed when the integrated EEJ ground strength for the period from 1 to 2 h prior to sunset was negative. The finding suggests observationally that the pre-sunset E-region dynamo current and/or electric field are related to the F-region dynamics and ESF onsets around sunset.

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“…The details of the ionosonde observation are provided elsewhere (e.g., Maruyama et al, 2007). In this study, ESF days are defined only when ESF is detected before 21:00 THA.…”

Section: Data Set and Analysis Methodsmentioning

confidence: 99%

Section: Data Set and Analysis Methodsmentioning

confidence: 99%

Relationships between pre-sunset electrojet strength, pre-reversal enhancement and equatorial spread-F onset

et al. 2010

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“…The data used in this study are collected by two FM/CW ionosonde (Maruyama et al, 2007) stations at Chumphon campus of King Mongkut's Institute of Technology Ladkrabang, Chumphon province (10.72…”

Section: Methodsmentioning

confidence: 99%

Thailand low and equatorial F 2-layer peak electron density and comparison with IRI-2007 model

et al. 2012

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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 2 -layer peak electron density (N m F 2 ) which is derived from the F 2 -layer critical frequency, f o F 2 . 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 m F 2 predicted by the IRI (URSI and CCIR options) model show a feature generally similar to the observed N m F 2 . 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 m F 2 values predicted by the CCIR option show a smaller range of deviation than the N m F 2 values predicted by the URSI option. During post-sunset to morning hours (around 21:00-09:00 LT), the observed N m F 2 at both stations are almost identical for the periods of low solar activity. However, during daytime, the observed N m F 2 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 m F 2 over Southeast Asia, especially for the areas covered by Chumphon and Chiang Mai stations.

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“…Multipoint ionosonde observation was conducted along the 100 • E meridian in the Southeast Asia low-latitude ionospheric network (SEALION) (Maruyama et al, 2007 At low latitudes, equatorward winds push up the ionosphere to higher altitudes, and poleward winds depress it to lower altitudes. Therefore, the height difference between the two conjugate stations is related to the transequatorial meridional wind.…”

Section: Observationsmentioning

confidence: 99%

Equinoctial asymmetry of a low-latitude ionosphere-thermosphere system and equatorial irregularities: evidence for meridional wind control

et al. 2009

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Abstract. Nocturnal ionospheric height variations were analyzed along the meridian of 100 • E by using ionosonde data. Two ionosondes were installed near the magnetic conjugate points at low latitudes, and the third station was situated near the magnetic equator. Ionospheric virtual heights were scaled every 15 min and vertical E×B drift velocities were inferred from the equatorial station. By incorporating the inferred equatorial vertical drift velocity, ionospheric bottom heights with the absence of wind were modeled for the two low-latitude conjugate stations, and the deviation in heights from the model outputs was used to infer the transequatorial meridional thermospheric winds. The results obtained for the September and March equinoxes of years 2004 and 2005, respectively, were compared, and a significant difference in the meridional wind was found. An oscillation with a period of approximately 7 h of the meridional wind existed in both the equinoxes, but its amplitude was larger in September as compared to that in March. When the equatorial height reached the maximum level due to the evening enhancement of the zonal electric field, the transequatorial meridional wind velocity reached approximately 10 and 40 m/s for the March and September equinoxes, respectively. This asymmetry of the ionosphere-thermosphere system was found to be associated with the previously reported equinoctial asymmetry of equatorial ionospheric irregularities; the probability for equatorial irregularities to occur is higher in March as compared to that in September at the Indian to Western Pacific Correspondence to: T. Maruyama (tmaru@nict.go.jp) longitudes. Numerical simulations of plasma bubble developments were conducted by incorporating the transequatorial neutral wind effect, and the results showed that the growth time (e-folding time) of the bubble was halved when the wind velocity changed from 10 to 40 m/s.

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Low latitude ionosphere-thermosphere dynamics studies with inosonde chain in Southeast Asia

Cited by 80 publications

References 37 publications

Relationships between pre-sunset electrojet strength, pre-reversal enhancement and equatorial spread-F onset

Relationships between pre-sunset electrojet strength, pre-reversal enhancement and equatorial spread-F onset

Thailand low and equatorial F 2-layer peak electron density and comparison with IRI-2007 model

Equinoctial asymmetry of a low-latitude ionosphere-thermosphere system and equatorial irregularities: evidence for meridional wind control

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