1. Vector Magnetic Field Synoptic Maps from HMI J Todd Hoeksema, Yang Liu, Xudong Sun & Keiji Hayashi
Carrington Rotation 2106 –
Close-up of AR 11158
Mr 2106
Bt 2106
Bp 2106
Br 2106
The Helioseismic and Magnetic Imager (HMI) project has obtained full-disk vector magnetograms every 12 minutes since beginning of regular operation in May Synoptic maps of the vector magnetic field that cover most of Solar Cycle 24 have now been created. Like previously created line-of-sight synoptic maps, the size in longitude and sine-latitude is 3600 x 1440 pixels. Maps of radial and horizontal field components are created from near-central-meridian observations that combine data from 20 full-disk magnetograms.
We compare the affects on synoptic maps of using different methods for determining the disambiguation in weak-field regions – annealing, random, radial-acute, and potential field. Data in the polar regions is of high quality. We compare these new maps with standard line-of-sight synoptic maps. Next steps include generation of more frequent vector-field synchronic frames.
+1500 G CR
-1500 G
CR 2123 –
Each vector magnetogram is remapped into Carrington coordinates. The twenty high-QUALITY observations nearest central meridian are averaged. About 180 magnetogram pixels observed within 2 hours of CM passage contribute to each synoptic chart pixel at the equator.
For CR 2145 ( ) we compare below the Br, Bt, and Bp components derived using three different disambiguation procedures in the quiet Sun. When choosing a weak-field azimuth that most nearly matches the potential or radial field, systematic effects bias the results because of the greater noise in the transverse field component.
Choosing a random disambiguation where the total field strength is < 150 G provides a better answer.
Synoptic maps for CR 2106 (above). The top right panel shows the radial field inferred from line-of-sight magnetograms. The next three panels show the three vector field components, all with the same color table, one that highlights weak magnetic structures in green and yellow. The panels on the left are a close-up of flare-productive AR #11158 that crossed CM on 14 February. Each longitude is observed at a different time.
The three panels in the top figure (above right) quantitatively compare the noise levels in the components of the quite-Sun field as a function of latitude for CR The upper panel is Br, next Bp and Bt is at the bottom. The potential solution (blue) has higher noise in Br away from the equator. The radial acute (green) shows a similar but broader decrease in noise near the equator. The black line shows a uniformly lower noise level for the random solution, comparable to the profile for the line-of-sight Mr. The center panel shows the same for the phi (E-W) component. The potential solution is uniform and a factor of 2-3 greater than the other methods. The radlal method shows an odd bump near the equator due to a spike in the transverse noise component. The bottom panel, Bp (N-S) shows higher noise for the radial method than the other components. Again the randome method noise level is consistent (and lower). The smaller figure (right) shows the same for CR 2097
CR 2163 –
CR 2181 –
The two figures to the right show the computed coronal neutral line calculated using various synoptic maps. The PFSS is sensitive to large-scale weak-field patterns. The colors are different (see key). A better disambiguation, one that fully anneals all pixels, is shown in black and it matches closely the random (shown in green). Left and right are results for CR 2145 and 2097.