Astronomy and Astrophysics – Astronomy
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009spd....40.1407k&link_type=abstract
American Astronomical Society, SPD meeting #40, #14.07; Bulletin of the American Astronomical Society, Vol. 41, p.834
Astronomy and Astrophysics
Astronomy
Scientific paper
A new method for automatically detecting and measuring Polar Coronal Holes in the EUV is presented. We use a series of full solar disk images over solar cycle 23 to measure the perimeter of polar coronal holes as they appear on the limbs. This method utilizes 171, 195, and 304 Å solar images from the Extreme ultraviolet Imaging Telescope (EIT) on SOHO. We are able to more accurately define the size and shape of the polar hole by taking measurements on the limb and making two measurements per image rather than the one used to construct synoptic maps. This method also minimizes line-of-sight obscurations caused by the emitting plasma of the various wavelengths. Perimeter tracking allows for the polar coronal rotation period to emerge organically from the data as 33 days. We have called this the Harvey Rotation rate and count Harvey Rotations starting January 4, 1900. From the measured perimeter we are then able to fit a curve to the data and derive an area within the line of best fit. This method can be adapted to work with any extended data set of full disk solar images. Extending our data set to past NSO full disk spectroheliograms creates a base line of more than three solar cycles. In the future, SDO images will be added to further expand polar hole measurements.
Kirk Michael S.
Pesnell William Dean
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