Noise mask of magnetic field strength for the inverted full-disk vector magnetic field data

The noise mask of the magnetic field strength is a full-disk map that represents the noise of magnetic field strength over the Sun's disk. The noise values at a given location are used in some versions of the disambiguation code to optimize performance.

The noise mask is derived from a group of FD10 full-disk magnetic field strength data. It has been demonstrated that the noise of field strength varies over the Sun's disk, and the pattern of this noise variation changes with the orbital velocity (Vr) of HMI relative to the Sun. Thus it is necessary to generate Vr-dependent noise masks. The method is described below.

Changes of instrument settings took place at several instants (see the list below). When the settings change, the noise appears to change slightly. To reflect such change, a noise mask need to be generated specifically for each time periods. The masks currently available in JSOC are generated using FD10 data from April-June 2012. Thus they can be used for data after 19 January 2012. Based on comprison of samples at Vr=0 over a longer interval, no significant changes in the noise mask were observed to occur between instrument reconfigurations.

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