Interhemispheric asymmetry of polar cap patches: Effect of offset between the geographic and magnetic poles
Abstract
Polar cap patches are the regions of increased electron density in the polar cap F region ionosphere. In discussing the generation mechanism, it is important to consider the spatial distribution of 1) the daytime high-density plasma and 2) the high-latitude plasma convection. Taking this into account, if the distance (i.e., offset) between the geographic and geomagnetic (AACGM model) poles is sufficiently large, there should be a period when the entire polar cap is within the dark hemisphere and the intake of daytime high density patches never happens. Thus, it is predicted that the production of patches deeply depends on the offset. However, almost all of the past studies were targeted for patches in the northern hemisphere (NH) where the offset is smaller ( 7°) than that in southern hemisphere (SH) which is 15°. Thus, we reveal the role played by the offset in the patch production process by investigating the interhemispheric asymmetry of patch occurrence characteristics.
In order to perform statistics in both hemispheres, we used all-sky imagers operated at Resolute Bay, Canada (OMTIs: 74.7° N, 265.1°E) and McMurdo, Antarctica (AWI: 77.5° S, 166.4°E) during local time. In addition, to visualize the spatial distribution of the plasma density in the entire polar cap, we employed the GAIA (Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy) model. As a result of statistical analysis, it was found that almost no patches were observed in McMurdo during a few hours from 14 to 17 UT. Similar UT dependence of patch occurrence was not seen in the NH due to the small offset. This indicates the difference in the offset indeed introduces an interhemispheric asymmetry in the climatology of patches. In addition to the analysis of UT dependence, we investigated the effect of the offset on the seasonal distribution by using in-situ plasma density data from the Swarm. We found that the occurrence rate is higher during equinoctial periods, especially in the SH. This tendency can partly be explained by the so-called Russel-McPherron (R-M) effect, but the reason for the slight interhemispheric asymmetry is still unclear. In the presentation, by taking both above two factors into account, we discuss the interhemispheric asymmetry in the seasonal variation of patch occurrence rate.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSM51C2741K
- Keywords:
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- 3369 Thermospheric dynamics;
- ATMOSPHERIC PROCESSESDE: 2431 Ionosphere/magnetosphere interactions;
- IONOSPHEREDE: 2704 Auroral phenomena;
- MAGNETOSPHERIC PHYSICSDE: 2776 Polar cap phenomena;
- MAGNETOSPHERIC PHYSICS