Whole Heliosphere Interval (WHI)

Whole Heliosphere Interval
Combining Multiple Data Sets: The "WHI Mosaic"

(What is the WHI Mosaic?)
(How do we connect to the heliosphere and Earth?)

What is a Carrington Rotation?
WHI is defined as a study of the solar-interplanetary-geospace system originating from Carrington Rotation 2068. Solar people work in Carrington Rotations because the Sun's rotation rate varies with latitude , so a standard solid-body latitute/longitude system does not apply. A solar feature due north of another solar feature will no longer be due north as the sun rotates, so we much devise a coordinate system that will keep us sane but does not overly restrict us.

Therefore, to study the Sun over repeated rotations, we choose a time period (25.38 days) to define as a "rotation." The solar poles rotate slower and equator rotates faster, but we have to start somewhere. We number each consecutive rotation, WHI's is #2068.

The best way to show how a solar rotation translates into a convenient coordinate system is probably by viewing Dave Hathaway's animation showing a magnetogram turning into the "unwrapped" version:
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An excellent example of utility of this system can be found in the Whole Sun Month synoptic map collection. There are maps from multiple coronal altitudes, different wavebands, etc.

The following images are synoptic maps (or synoptic chart, also called a Carrington map) of the solar photospheric magnetic field and EUV Corona for WHI, from the National Solar Observatory's SOLIS and STEREO SECCHI:

AVI (19 MB) GIF (1.8 MB)
The x-axis is labeled "Carrington Longitude," ranging from 0 to 360 per rotation. These can be translated to dates where each longitude was pointing directly at Earth. However, since the Earth also revolves around the Sun, the effective rotation period is 27.27 days, instead of 25.38. (i.e. the Earth has moved since the last rotation, and the sun takes two days to reach that point).

Important Note:Time goes backwards in these maps!

Think about it. The Sun rotates to the right, so longitudes that have already past us have moved to the right, and the new longitudes are to the left. This conflicts with our "time goes from left to right" sensibilities.

The precise time at Earth for Carrington Rotation 2068, Longitude = 360 is 01:18 UT on 20 March, 2008. The longitudes count down in time until Carrington Longitude = 0 occurs at 08:09 UT on 16 April 2008. This also coincides with the beginning of the new rotation, CROT 2069, Longitude = 360. (Note: the dates that STEREO and other missions outside of Earth orbit see those longitudes are different.)

The next question is, "How do we link these solar coordinates to the heliosphere and Earth?"

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The following table gives the dates for all of the Carrington Longitudes for CROT 2068:

Table of Carrington Rotation Dates +

LON = 360 DATE = 2008/03/20 01:18:54
LON = 350 DATE = 2008/03/20 19:33:16
LON = 340 DATE = 2008/03/21 13:47:35
LON = 330 DATE = 2008/03/22 07:52:16
LON = 320 DATE = 2008/03/23 02:06:30
LON = 310 DATE = 2008/03/23 20:20:41
LON = 300 DATE = 2008/03/24 14:34:50
LON = 290 DATE = 2008/03/25 08:39:19
LON = 280 DATE = 2008/03/26 02:53:22
LON = 270 DATE = 2008/03/26 21:07:22
LON = 260 DATE = 2008/03/27 15:21:20
LON = 250 DATE = 2008/03/28 09:35:14
LON = 240 DATE = 2008/03/29 03:39:30
LON = 230 DATE = 2008/03/29 21:53:19
LON = 220 DATE = 2008/03/30 16:07:04
LON = 210 DATE = 2008/03/31 10:20:47
LON = 200 DATE = 2008/04/01 04:24:51
LON = 190 DATE = 2008/04/01 22:38:28
LON = 180 DATE = 2008/04/02 16:52:02
LON = 170 DATE = 2008/04/03 11:05:33
LON = 160 DATE = 2008/04/04 05:19:01
LON = 150 DATE = 2008/04/04 23:22:50
LON = 140 DATE = 2008/04/05 17:36:12
LON = 130 DATE = 2008/04/06 11:49:30
LON = 120 DATE = 2008/04/07 06:02:46
LON = 110 DATE = 2008/04/08 00:06:24
LON = 100 DATE = 2008/04/08 18:19:33
LON = 90 DATE = 2008/04/09 12:32:40
LON = 80 DATE = 2008/04/10 06:45:43
LON = 70 DATE = 2008/04/11 00:58:44
LON = 60 DATE = 2008/04/11 19:02:06
LON = 50 DATE = 2008/04/12 13:15:00
LON = 40 DATE = 2008/04/13 07:27:51
LON = 30 DATE = 2008/04/14 01:40:40
LON = 20 DATE = 2008/04/14 19:43:50
LON = 10 DATE = 2008/04/15 13:56:32
LON = 0 DATE = 2008/04/16 08:09:11

More information on Carrington Coordinates

Whole Heliosphere Interval Combining Multiple Data Sets: The "WHI Mosaic"

Whole Heliosphere Interval
Combining Multiple Data Sets: The "WHI Mosaic"