NDLI: On the value of 'αAR' from Vector Magnetograph data

Content Provider	Springer Nature Link
Author	Leka, K.D.
Copyright Year	1999
Abstract	This investigation is the second of two centering on the parameter α=(∇×B$_{h}$)$_{z}$/B$_{z}$=μ$_{0}$J$_{z}$/B$_{z}$and its derivation from photospheric vector magnetogram data. While α can be evaluated at every spatial position where the vector B is measured, for many reasons it is useful to determine a single value of α to parameterize the magnetic complexity of an entire active region, here called α$_{AR}$(see Leka and Skumanich, 1999). As such, the limitations in today's vector magnetograph data, e.g., finite spatial resolution and limited field of view, may influence any final 'α$_{AR}$' value. We apply three methods of calculating 'α$_{AR}$' to degraded high-spatial-resolution data and find that in general the discrepancies worsen for decreasing resolution compared to the original. We apply the three methods to sub-regions centered on the constituent sunspots for AR 7815. Two of the sub-regions are shown to have magnetic twist with significant magnitude but opposite sign. We show by mosaicing or otherwise combining separate sunspot observations that a measure of α$_{AR}$can be calculated which is consistent with a single large field-of-view observation. Still, the α$_{AR}$≈0 assigned for the entire active region is an average, and does not accurately represent the magnetic morphology of this flux system. To measure the validity of the α$_{AR}$parameterization, we demonstrate that, from each method, a relevant quantity can be calculated which describes the 'goodness of fit' of the resulting α$_{AR}$. Given the spatial variation of α(x,y) over an active region, it is suggested that such a second parameter be used either to indicate uncertainty in α$_{AR}$or as a criterion for data selection, as appropriate.
Starting Page	21
Ending Page	40
Page Count	20
File Format	PDF
ISSN	00380938
Journal	Solar Physics
Volume Number	188
Issue Number	1
e-ISSN	1573093X
Language	English
Publisher	Kluwer Academic Publishers
Publisher Date	1999-01-01
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Astrophysics
Content Type	Text
Resource Type	Article
Subject	Astronomy and Astrophysics Space and Planetary Science

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4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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