New NSO Coronal Hole Maps

Karen Harvey (Solar Physics Research Corporation) and Frank Recely (NOAA/SEC) are developing an IDL program to determine the boundaries of coronal holes, using the NSO/KP full-disk He I 1083 nm spectroheliograms and magnetograms. This program will provide a more precise map of the coronal hole boundaries and will be available on the internet more quickly than the method currently in use. It also will provide information on the magnetic fields, size, and location of coronal holes

The products of this program will be 1) a "gif" image of the map of coronal hole boundaries drawn on a Stonyhurst disk; the image size matches the low-resolution NSO He I 1083 nm images; 2) a "fits" image of the coronal map matching the size of the high-resolution full-disk He I 1083 nm spectroheliogram; 3) for each coronal hole, measures of the total magnetic flux, the net magnetic flux, the mean total and net flux density, area in cm and as a fraction of the visible disk, the type of hole (polar, isolated, extension, transient), the heliographic location, and the identification certainty, will be contained in the fits header; and 4) a file listing the coronal hole boundaries in heliographic latitude and longitude at an increment of 3 to 5 degrees. These images and data will be available to the solar community on the NSO anonymous ftp archive. An example of the coronal hole map for 12 October 1996 is shown in the accompanying figure; some of the parameters for the two polar coronal holes on this day are shown in the table below.

Within the next month, we plan to implement this program and produce daily coronal hole maps using current NSO/KP observations. Our plan is then to redo the coronal hole maps for the interval extending from late 1991 (the Yohkoh period) and eventually to complete the maps for the entire NSO/KP full-disk archive period.

Coronal Hole Information Table:

             Basic Info For Coronal Hole Data Base

         Date           = 96/10/12, 15:36:53 UT
         X-Center       = 225.831 X-Radius = 208.741
         Y-Center       = 227.190 Y-Radius = 210.423
         Carr Longitude = 39.830
         Carr Rotation  = 914.898289
         Bzero          = 6.014527
         Semi-Diameter  = 16.029527

                   Parameters: Coronal Hole 1

         Polarity           = negative
         Type               = Polar
         Certainty          = Certain
         Location           = S65 E00
         N/S and E/W Extent = S56/S90 E90/W90
         Area               = 49240.603 X 10-6 hemisphere
         Area               = 14.987 1020 cm2
         TOTAL Magnetic Flux = 44.888 1020 Mx
         NET Magnetic Flux  = -37.077 1020 Mx
         Mean He I 1083 EW  = 28.583 mÅ
         Mean TOT Flux Den  = 2.995 Mx/cm2
         Mean NET Flux Den  = -2.474 Mx/cm2

                  Parameters: Coronal Hole 2

         Polarity            = positive
         Type                = Polar
         Certainty           = Certain
         Location            = N65 E00
         N/S and E/W Extent  = N90/N40 E90/W90
         Area                = 90445.618 X 10-6 hemisphere
         Area                = 27.528 1020 cm2
         TOTAL Magnetic Flux = 111.929 1020 Mx
         NET Magnetic Flux   = 10.271 1020 Mx
         Mean He I 1083 EW   = 30.501 mÅ
         Mean TOT Flux Den   = 4.066 Mx/cm2
         Mean NET Flux Den   = 0.373 Mx/cm2

Karen Harvey