Annual and seasonal variations in the low-latitude topside ionosphere

Su, Yi; Bailey, G. J.; Oyama, K. I.

doi:10.1007/s00585-998-0974-0

Cited by 53 publications

(79 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The winter anomaly can not be simply attributed to the ratio of [O / N 2 ]. Another possible mechanism of the direction change of neutral wind that results from the coupling of the neutral gas and plasma (Su et al, 1998) may have a significant contribution.…”

Section: Discussionmentioning

confidence: 99%

Climatology of the ionospheric slab thickness along the longitude of 120° E in China and its adjacent region during the solar minimum years of 2007–2009

Huang

Yuan

2015

Ann. Geophys.

View full text Add to dashboard Cite

Abstract. The ionospheric slab thickness is defined as the ratio of the total electron content (TEC) to the ionospheric F2 layer peak electron density (NmF2). In this study, the slab thickness is determined by measuring the ionospheric TEC from dual-frequency Global Positioning System (GPS) data and the NmF2 from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC). A statistical analysis of the diurnal, seasonal and spatial variation in the ionospheric slab thickness is presented along the longitude of 120 • E in China and its adjacent region during the recent solar minimum phase (2007)(2008)(2009). The diurnal ratio, defined as the maximum slab thickness to the minimum slab thickness, and the night-to-day ratio, defined as the slab thickness during daytime to the slab thickness during night-time, are both analysed. The results show that the TEC of the northern crest is greater in winter than in summer, whereas NmF2 is greater in summer than in winter. A pronounced peak of slab thickness occurs during the postmidnight (00:00-04:00 LT) period, when the peak electron density is at the lowest level. A large diurnal ratio exists at the equatorial ionization anomaly, and a large night-to-day ratio occurs near the equatorial latitudes and mid-to high latitudes. It is found that the behaviours of the slab thickness and the F2 peak altitude are well correlated at the latitudes of 30-50 • N and during the period of 10:00-16:00 LT. This current study is useful for improvement of the regional model and accurate calculation of the signal delay of radio waves propagating through the ionosphere.

show abstract

Section: Discussionmentioning

confidence: 99%

Climatology of the ionospheric slab thickness along the longitude of 120° E in China and its adjacent region during the solar minimum years of 2007–2009

Huang

Yuan

2015

Ann. Geophys.

View full text Add to dashboard Cite

show abstract

“…The remaining part of the annual anomaly during the daytime and also the south-north asymmetry during the nighttime may be caused by the difference in meridional winds. By using the Hinotori satellite and Sheffield University Plasmasphere Ionosphere Model (SUPIM), Su et al (1998) found that the difference in [O/N2] between December and June, obtained from MSIS-86, reproduces the general behaviour of the observed annual anomaly, but only accounts for 30% of its magnitude. The model calculations suggest that the differences between the solstice values of the neutral wind, resulting from the coupling of the neutral gas and plasma, may also make a significant contribution to the daytime annual anomaly.…”

Section: Explanation Of the Semiannual And Annual Anomaliesmentioning

confidence: 99%

“…Observational evidence indicates that there is no winter anomaly in the topside ionosphere, whereas it is significant in the F-region (e.g. Balan et al, 1998;Torr and Torr, 1973;Su et al, 1998;Zhao et al, 2005;Liu et al, 2007). Moreover, observational evidence also shows that the annual anomaly is very strong in the topside ionosphere, as compared with the bottomside ionosphere (Su et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

“…Balan et al, 1998;Torr and Torr, 1973;Su et al, 1998;Zhao et al, 2005;Liu et al, 2007). Moreover, observational evidence also shows that the annual anomaly is very strong in the topside ionosphere, as compared with the bottomside ionosphere (Su et al, 1998). It is reasonable to imagine that the total electron content (TEC) and the integral of electron density height profile N(h) might have different characteristics as compared with those derived from the NmF2.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Features of annual and semiannual variations derived from the global ionospheric maps of total electron content

et al. 2007

View full text Add to dashboard Cite

Abstract.In the present work we use the NASA-JPL global ionospheric maps of total electron content (TEC), firstly to construct TEC maps (TEC vs. magnetic local time MLT, and magnetic latitude MLAT) in the interval from 1999 to 2005. These TEC maps were, in turn, used to estimate the annualto-mean amplitude ratio, A 1 , and the semiannual-to-mean amplitude ratio, A 2 , as well as the latitudinal symmetrical and asymmetrical parts, A and A of A 1 . Thus, we investigated in detail the TEC climatology from maps of these indices, with an emphasis on the quantitative presentation for local time and latitudinal changes in the seasonal, annual and semiannual anomalies of the ionospheric TEC. Then we took the TEC value at 14:00 LT to examine various anomalies at a global scale following the same procedure. Results reveal similar features appearing in NmF2, such as that the seasonal anomaly is more significant in the near-pole regions than in the far-pole regions and the reverse is true for the semiannual anomaly; the winter anomaly has least a chance to be observed at the South America and South Pacific areas. The most impressive feature is that the equinoctial asymmetry is most prominent at the East Asian and South Australian areas. Through the analysis of the TIMED GUVI columnar [O/N2] data, we have investigated to what extent the seasonal, annual and semiannual variations can be explained by their counterparts in [O/N2]. Results revealed that the [O/N2] variation is a major contributor to the daytime winter anomaly of TEC, and it also contributes to some of the semiannual and annual anomalies. The contribution to the anomalies unexplained by the [O/N2] data could possibly be due to the dynamics associated with thermospheric winds and electric fields.

show abstract

“…Buonsanto (1986) suggested that, at perihelion the greater flux of solar ultraviolet causes greater dissociation of molecular oxygen than aphelion but this hypothesis doesn't explain the totality of the F2-layer asymmetry. Su et al (1998) proposed the dynamical processes cause the annual asymmetry; he analyzed the topside ionosphere at low latitudes. The observation showed a strong annual anomaly at all longitudes concluding that the differences between the solstice values of neutral wind (from coupling of the neutral gas and plasma) may make a significant contribution to daytime and the E × B drift velocity may slightly weaken the annual anomaly during daytime and strengthen the anomaly during the post-sunset period.…”

Section: Introductionmentioning

confidence: 99%

Annual and semiannual variations of vertical total electron content during high solar activity based on GPS observations

Natali

Meza²

2011

Ann. Geophys.

View full text Add to dashboard Cite

Abstract. Annual, semiannual and seasonal variations of the Vertical Total Electron Content (VTEC) have been investigated during high solar activity in 2000. In this work we use Global IGS VTEC maps and Principal Component Analysis to study spatial and temporal ionospheric variability. The behavior of VTEC variations at two-hour periods, at noon and at night is analyzed. Particular characteristics associated with each period and the geomagnetic regions are highlighted.The variations at night are smaller than those obtained at noon. At noon it is possible to see patterns of the seasonal variation at high latitude, and patterns of the semiannual anomaly at low latitudes with a slow decrease towards mid latitudes. At night there is no evidence of seasonal or annual anomaly for any region, but it was possible to see the semiannual anomaly at low latitudes with a sudden decrease towards mid latitudes. In general, the semiannual behavior shows March-April equinox at least 40 % higher than September one. Similarities and differences are analyzed also with regard to the same analysis done for a period of low solar activity.

show abstract

Annual and seasonal variations in the low-latitude topside ionosphere

Cited by 53 publications

References 24 publications

Climatology of the ionospheric slab thickness along the longitude of 120° E in China and its adjacent region during the solar minimum years of 2007–2009

Climatology of the ionospheric slab thickness along the longitude of 120° E in China and its adjacent region during the solar minimum years of 2007–2009

Features of annual and semiannual variations derived from the global ionospheric maps of total electron content

Annual and semiannual variations of vertical total electron content during high solar activity based on GPS observations

Contact Info

Product

Resources

About