Seasonal and diurnal variations in AMPERE observations of the Birkeland currents compared to modeled results

Coxon, John, Milan, S. E., Carter, J. A., Clausen, L. B. N., Anderson, B. J. and Korth, H. (2016) Seasonal and diurnal variations in AMPERE observations of the Birkeland currents compared to modeled results. Journal of Geophysical Research: Space Physics, 121 (5). pp. 4027-4040. ISSN 2169-9380

[img]
Preview
Text
JGR Space Physics - 2016 - Coxon - Seasonal and diurnal variations in AMPERE observations of the Birkeland currents.pdf - Published Version
Available under License Creative Commons Attribution 4.0.

Download (1MB) | Preview
Official URL: https://doi.org/10.1002/2015JA022050

Abstract

We reduce measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to give the total Birkeland (field-aligned) current flowing in both hemispheres in monthly and hourly bins. We analyze these totals using 6 years of data (2010–2015) to examine solar zenith angle-driven variations in the total Birkeland current flowing in both hemispheres, simultaneously, for the first time. A diurnal variation is identified in the total Birkeland current flowing, consistent with variations in the solar zenith angle. A seasonal variation is also identified, with more current flowing in the Northern (Southern) Hemisphere during Bartels rotations in northern (southern) summer. For months close to equinox, more current is found to flow in the Northern Hemisphere, contrary to our expectations. We also conduct the first test of the Milan (2013) model for estimating Birkeland current magnitudes, with modifications made to account for solar contributions to ionospheric conductance based on the observed variation of the Birkeland currents with season and time of day. The modified model, using the value of ΦD averaged by Bartels rotation (scaled by 1.7), is found to agree with the observed AMPERE currents, with a correlation of 0.87 in the Northern Hemisphere and 0.86 in the Southern Hemisphere. The improvement over the correlation with dayside reconnection rate is demonstrated to be a significant improvement to the model. The correlation of the residuals is found to be consistent with more current flowing in the Northern Hemisphere. This new observation of systematically larger current flowing in the Northern Hemisphere is discussed in the context of previous results which suggest that the Northern Hemisphere may react more strongly to dayside reconnection than the Southern Hemisphere.

Item Type: Article
Additional Information: Funding information: Science and Technology Funding Council (STFC) studentship NERC. Grant Number: NE/L007177/1 STFC. Grant Number: ST/K001000/1
Uncontrolled Keywords: Birkeland currents, dayside reconnection, diurnal variations, field-aligned currents, ionospheric conductance, seasonal variations
Subjects: F300 Physics
F500 Astronomy
F800 Physical and Terrestrial Geographical and Environmental Sciences
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Rachel Branson
Date Deposited: 22 Feb 2022 11:49
Last Modified: 22 Feb 2022 12:00
URI: http://nrl.northumbria.ac.uk/id/eprint/48513

Actions (login required)

View Item View Item

Downloads

Downloads per month over past year

View more statistics