Quality Measure for the Walén Relation. Issue 12 (5th December 2018)

• Record Type: Journal Article
• Authors: Sonnerup, B. U. Ö.; Haaland, S. E.; Paschmann, G.; Denton, R.E.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 12(2018)
• Page Start: 9979
• Page End: 9990
• Publication Date: 2018-12-05
• Subjects: magnetopause -- magnetospheric multiscale -- Walén relation -- reconnection; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2018JA025677
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: A new quality index is proposed for quantitatively assessing the level of Alfvénicity of the flow in the magnetopause and other quasi one‐dimensional plasma/field structures. Perfect Alfvénicity is expressed by the so‐called Walén relation, which describes the agreement of the observed jump in velocity across a suitable portion of the magnetopause and the corresponding jump in Alfvén velocity. In the past, approximate agreement with this relation has been used as an important indicator of ongoing magnetic reconnection. The new index incorporates the effects of deviations in direction as well as in magnitude of the two vectors. Its properties and utility are illustrated by application to a large set of dayside magnetopause crossings by the Magnetospheric Multiscale spacecraft MMS 1. Time series for two of these events are also presented and discussed. Key Points: Single quality index is proposed to quantify the level of agreement of measured magnetic field and plasma data with the Walén relation Index is applied to data from 731 dayside magnetopause crossings by MMS1 MMS statistics for the index are presented and discussed