North-South asymmetry of equatorial ionospheric anomaly computed from the IRI model

Sanjay Kumar

doi:10.4401/ag-8324

Abstract

Using the electron density from the IRI-2016 model and processed results of the in-situ measurements (GRACE and CHAMP) in Xiong et al. (2013), the morphological features of the equatorial ionization anomaly (EIA) such as its magnitude and inter-hemispheric asymmetry have been studied during 2001-2009. The effect of solar activity on ability of the IRI-2016 model to predict the EIA parameters is studied and the results are compared with in-situ measurements from GRACE and CHAMP during high and low solar activity phases. The IRI-2016 generally follows the same latitudinal asymmetry (ACL - Asymmetry of Crest Latitude) at 400 km (the same trend of ACL as for CHAMP) while it tends to be asymmetric towards the North at 480 km (GRACE) (Positive ACL). In addition, during June solstice the IRI-2016 model shows larger departure from observation after 19:00 UT with a larger difference during high solar activity than that during the low solar activity. Also the IRI-2016 model failed to predict significantly North-South asymmetry (southern crest disappears) in the electron density for high solar activity period. This is probably the reason for larger discrepancy of observations and the IRI-2016 model particularly during the summer solstice of the high solar activity period. This suggests that data input in the IRI model particularly in the equatorial- and low-latitude regions are required so that it could better predict the location of EIA crests.

Highlights

The equatorial ionospheric anomaly (EIA) is characterized, in terms of latitudinal distribution of ionization, by a trough at the magnetic equator and crests at about ±17o magnetic latitude and crest to trough ratio of about 1.6 in daytime peak electron density [Appleton, 1946, Balan et al, 2018]
In this paper our aim is to study the seasonal and annual variations of EIA crest parameters as defined by Xiong et al [2013], inter-hemispheric asymmetries properties using the electron density of ionosphere computed from the IRI-2016 model and to compare the results with those reported by Xiong et al [2013] using CHAMP and Gravity Recovery and Climate Experiment (GRACE) observations
In order to study the effect of solar activity on the IRI-2016 model to predict the EIA parameters the period 2001-2009 has been grouped into two parts: 2001-2005 as a moderate activity period and 2005-2009 as low solar activity period

Summary

Introduction

The equatorial ionospheric anomaly (EIA) is characterized, in terms of latitudinal distribution of ionization, by a trough at the magnetic equator and crests at about ±17o magnetic latitude and crest to trough ratio of about 1.6 in daytime peak electron density [Appleton, 1946, Balan et al, 2018]. The perseverance of EIA into the nighttime hours depending on the season and solar activity is known to be produced by the post-sunset enhancement in the eastward electric field produced by the F-region dynamo action. This dynamo action, in turn, results from the eastward component of the F-region thermospheric wind blowing, with the decreasing dawn-to-dusk E-layer Pedersen conductivity distribution [Heelis, 2004]. It contributes to the enhanced ionospheric scintillations effects produced by spread-F/plasma bubbles (depleted electron density region) irregularities on transionospheric radio wave (i.e. GPS signal) propagations [Abdu, 2005]

Objectives

Results

Conclusion