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Variations of ionospheric slab thickness over the magnetic equator of Southeast Asia
(2016-09-06)
Jamjareegulgarn, P.
;
Supnithi, P.
;
Watthanasangmechai, K.
;
Yokoyama, T.
;
Tsugawa, T.
In this paper, the diurnal and seasonal variations of the ionospheric slab thickness in an ionosonde chain over magnetic equator of Southeast Asia are studied. Three ionosonde stations of SEALION project located along the magnetic meridian of 100°E are selected to investigate, including two stations in Thailand, namely Chumphon and Chiang Mai, and one station in Indonesia, namely Kototabang. The monthly hourly medians of the foF2 from three ionosonde stations in 2010 are used to compute the observed NmF2. Refer to the TEC data; it can be obtained directly from GPS receiver at Chumphon station since the TEC data in 2010 were observed completely. In contrast, the TEC data at Chiang Mai station lost extremely and those at Kototabang station were unavailable. Hence, the TEC data used for these two stations are obtained from the International GNSS service (IGS). Our results show that 1) for all seasons, the NmF2 values during daytime have the successive decreasing values from Chiang Mai, Kototabang, and Chumphon. While the NmF2 values at three stations are almost identical during nighttime; 2) for all seasons at these three stations, the TEC values in the daytime are larger than those in the nighttime and their maximum values in the equinox and winter are higher than those in the summer; 3) the slab thickness values in all seasons during nighttime are generally larger than those during daytime for all three stations. Meanwhile, during daytime for all seasons, the slab thickness at Chumphon station is the highest among these three stations due to the fountain effect over magnetic equator.
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Low-latitude ionospheric height variation as observed by meridional ionosonde chain: Formation of ionospheric ceiling over the magnetic equator
(2014-01-01)
Maruyama, Takashi
;
Uemoto, Jyunpei
;
Ishii, Mamoru
;
Tsugawa, Takuya
;
Supnithi, Pornchai
A multipoint ionosonde observation campaign was conducted along the magnetic meridional plane in Southeast Asia to study ionosphere-thermosphere coupling. One station was near the magnetic equator and two of the other stations were at off-equatorial latitudes (∼10° magnetic latitude). The daytime ionospheric peak height (h<inf>m</inf>F<inf>2</inf>) was analyzed for each season during the solar minimum years, 2006-2007 and 2009. The peak height increased for ∼3 h after sunrise at the magnetic equator and off-equatorial latitudes, as expected from the daytime upward E × B drift. The apparent upward drift at the magnetic equator ceased before noon, while the drift at the off-equatorial latitudes continued upward and the layer height exceeded the equatorial height around noon. The noontime limited layer peak height at the magnetic equator, which was termed the ionospheric ceiling, did not depend on the season, while the maximum peak height at the off-equatorial latitudes largely varied with each season. Numerical modeling using the SAMI2 code was conducted and the features of the ionospheric ceiling were reproduced quite well. The dynamical parameters provided by the SAMI2 modeling runs showed that the ionospheric ceiling is formed by the field-aligned plasma diffusion, which is a part of the fountain effect. Key Points Multipoint ionosonde observation along the magnetic meridian in Southeast Asia Noontime restricted F layer peak height at the magnetic equator Revisiting the equatorial anomaly from the viewpoint of height variations

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