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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers | Copyright
https://doi.org/10.5194/angeo-2018-97
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 29 Aug 2018

Regular paper | 29 Aug 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

Improvements to Predictions of the Ionospheric Annual Anomaly by the International Reference Ionosphere Model

Steven Brown1, Dieter Bilitza1,2, and Erdal Yiğit1 Steven Brown et al.
  • 1George Mason University, Fairfax, Virginia, USA
  • 2Heliospheric Laboratory, NASA Goddard Space Flight Center, Greenbelt, USA

Abstract. The annual anomaly is the ionospheric phenomena in which the globally-averaged electron density is greater in January than it is in July. This anomaly causes the ionospheric solsticial variation – a variation with a periodicity of one year that is in-phase with the January solstice – to be more pronounced over the Northern Hemisphere than the Southern Hemisphere. Predictions of the magnitude of annual anomaly using the International Reference Ionosphere (IRI) model have been shown to be unreliable so far. The objective of our study is to investigate model prediction of the magnitude of the annual ionospheric anomaly using new ionospheric indices as inputs in the IRI model. These new indices improve predictions ionospheric variations that differ over the two hemispheres. We present a retrospective analysis of the IRI predictions of the ionospheric daytime annual anomaly and solsticial variation using a model-data comparison with observations from over 40 ionosondes for high, moderate, and low solar cycle conditions. Our results show that there is an overall 33% underestimation of the magnitude of the annual anomaly when the by the IRI. When the new ionospheric indices as used in the IRI, model predictions underestimate the magnitude of the annual anomaly by 6%. This indicates an improvement of the model predictions when using the new indices. We show that the underestimation of the annual anomaly by IRI is related to a similar underestimation of the magnitude of the ionospheric solsticial variation over the Northern Hemisphere. Based on our results, we infer that the underlying processes of the annual anomaly must vary across each hemisphere.

Steven Brown et al.
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Steven Brown et al.
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Short summary
The ionosphere varies the most over the Northern hemisphere. This is called the annual anomaly. Ionospheric models, such as the International Reference Ionosphere (IRI), underrepresent the anomaly. The ionosphere affects radio waves, so it is important to always improve these models. We show that it is considering the ionosphere's hemispheric behavior is required to improve IRI. We suggest that the annual anomaly is caused by processes which differ over each hemisphere.
The ionosphere varies the most over the Northern hemisphere. This is called the annual anomaly....
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