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Midday recovery of the polar-cap absorption of 19-21 March 1990: a case study.

Uljev, V. A. and Shirochkov, A. V. and Moskvin, I. V. and Hargreaves, J. K. (1995) Midday recovery of the polar-cap absorption of 19-21 March 1990: a case study. Journal of Atmospheric and Terrestrial Physics, 57 (8). pp. 905-915.

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Abstract

The effect of the midday recovery of absorption (MDR) during the polar cap absorption (PCA) of 19–21 March 1990 is investigated using data from 25 riometer stations in both hemispheres. The measured variations of absorption are compared with those calculated from a model. Three main aspects are considered: 1. (1) The solar and geophysical conditions under which the effect appears, 2. (2) The essential morphological features of the phenomenon, 3. (3) The relative contributions of (a) diurnal variations in the geomagnetic cut-off energy and (b) an anisotropic pitch-angle distribution of the solar protons to the development of the MDR. The principal morphological features of the MDR effect are found to be as follows: 1. (a) the width of the area affected by MDR is about 10° of invariant latitude, 2. (b) there are two regions, respectively below and above 65° latitude, in which the MDR properties are different, 3. (c) the maximum duration of the MDR effect is about 12 h, 4. (d) there are distinct geomagnetic conjugucy effects in MDR. There are solid reasons to suggest that the MDR at latitude 65–70° is due to the combined influence of a diurnal variation of geomagnetic rigidity, and the pitch-angle anisotropy of the solar protons. The MDR at lower latitudes (Λ = 60–65°) seems to be produced primarily by diurnal variations of the cut-off rigidity.

Item Type: Article
Journal or Publication Title: Journal of Atmospheric and Terrestrial Physics
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Departments:
ID Code: 20499
Deposited By: ep_ss_importer
Deposited On: 09 Dec 2008 12:40
Refereed?: No
Published?: Published
Last Modified: 26 Jul 2012 15:39
Identification Number:
URI: http://eprints.lancs.ac.uk/id/eprint/20499

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