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Climatology of the equatorial thermospheric mass density anomaly

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Title: Climatology of the equatorial thermospheric mass density anomaly
Authors: Liu, Huixin Browse this author
Lühr, Hermann Browse this author
Watanabe, Shigeto Browse this author →KAKEN DB
Keywords: equatorial anomaly
thermosphere-ionosphere coupling
thermospheric climatology
Issue Date: 12-May-2007
Publisher: American Geophysical Union
Journal Title: Journal of Geophysical Research
Volume: 112
Issue: a5
Start Page: A05305
Publisher DOI: 10.1029/2006JA012199
Abstract: The equatorial anomaly is an interesting and important feature of the Earth's thermosphere-ionosphere coupling in tropical regions. It is an anomalous latitudinal distribution found in both the ionized and unionized part of the atmosphere. Its equinox configuration consists of a minimum near the dip equator flanked by two maxima on both sides. The ionospheric side of this anomaly, often referred to as the equatorial ionization anomaly (EIA), has long been recognized since the 1930s. However, its thermospheric counterpart was only to be glimpsed by the Dynamic Explorer 2 satellite in the 1970s. A global picture of it has been rather recently revealed by the CHAMP satellite in 2005. In this paper we complement previous studies by investigating the climatology of the equatorial mass anomaly (EMA) in the thermosphere using 4 years of CHAMP measurements. Our analysis has revealed strong variation of the EMA with season and solar flux level. The EMA structure is most prominent around equinox, with a crest-to-trough ratio about 1.05 for F10.7 = 150. Near solstices, it is asymmetric about the dip equator. The density crest attains maximum 1–2 hours earlier and reaches higher values in the summer hemisphere than in the winter hemisphere. The density in EMA regions varies semiannually, with maxima near equinoxes. The latitudinal locations of the EMA crests undergo a seasonal variation, obviously following the movement of the subsolar point. The EMA structure has also been found to become more pronounced at higher solar flux levels. Both the location and magnitude of the EMA crests closely follow those of the EIA in corresponding seasons and solar flux levels, hence demonstrating strong plasma-neutral interaction. Furthermore, two seasonal asymmetries clearly present in the globally averaged density, with the density in March/December being ∼15–20% higher than that in September/June.
Rights: An edited version of this paper was published by AGU. Copyright 2007, American Geophysical Union, JOURNAL OF GEOPHYSICAL RESEARCH, Volume 112
Type: article (author version)
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: Liu Huixin

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