HMI Data Series hmi.Synoptic_Mr_720s - Synoptic Charts - Radial Field
Data Series General Description
The HMI radial field synoptic maps in the data series hmi.Synoptic_Mr_720s provide magnetic field for each Carrington Rotation starting with CR 2096 in April, 2010.
The maps are constructed from 720s line-of-sight magnetograms (["hmi.M-720s-info"]). Typically central meridian data from 20 magnetograms collected over a 4-hour interval contribute to each longitude in the synoptic map. The maps collected over a 27-day interval are combined to make a synoptic maps with 3600 longitudes and 1440 steps in sine latitude. [http://jsoc.stanford.edu/data/hmi/synoptic/hmi.Synoptic_Mr.2106.png CR 2106] was constructed from observations taken from January 20 - February 16, 2011.
hmi.Synoptic_Mr_720s is the basis for computation of all other HMI synoptic maps.
Steps in Constructing the Synoptic Map
Each 4096*4096 magnetogram is first transformed into a 'radial' field map by dividing by the cosine of the angle from disk center, i.e. we assume that the measured field is the line-of-sight component of a strictly radial field. This is done for perfect magnetograms, i.e. those with the QUALITY keyword equal to zero.
Next the radial image is transformed into a high resolution map in heliographic coordinates. We exclude about 12 pixels near the limb (r < 0.994) to avoid the noisiest observations. To preserve the disc-center resolution we interpolate onto a 5403 * 4320 grid with columns corresponding to 1/30 of a degree in Carrington Longitude and rows corresponding to equal steps of sine latitude. Then each magnetogram is smoothed using a two-dimensional Gaussian with a full width at half max of 9 pixels that is truncated at a full width of 13 pixels. This results in a 1801 by 1440 heliographic map with the resolution of the final synoptic chart where the columns are aligned on 0.1 degree Carrington longitude centers and rows are equally spaced in sine latitude.
- Each point in the final map combines data from 20 transformed radial magnetograms. Good data observed nearest central meridian are averaged. Typically this includes magnetogram data collected within 2 hours of central meridian passage. We perform an additional quality test at each point by excluding observations that are more than 3 standard deviations from the mean of the 30 magnetograms observed near central meridian. Data values observed farther from central meridian are used to replace bad values. The number of magnetograms contributing to each point is recorded in the epts segment of the data series.
Data Series Keywords
The Keywords for any JSOC data series as defined in the JSD can be inspected using the Series Content tab of the lookdata web access tool.
The complete list can also be found [http://hmi.stanford.edu/data/keywords/HMI.Synoptic_Mr_720s.Keywords.pdf here]
Links
[http://jsoc.stanford.edu/jsocwiki/Processing JSOC Wiki Data Products]
[http://hmi.stanford.edu/HMI HMI Home Page]
[http://jsoc.stanford.edu JSOC Home Page]