WSA

The WSA model has 3 components. The inner most from the photospheric surface (r = 1 solar radius) to a source surface (r = 2.5 solar radii) is a potential field source surface (PFSS) model of the inner coronal magnetic field. This ingests a map of the surface flux and constructs a potential field solution using a spherical harmonic expansion that matches the photospheric surface flux and also forces the solution to be radial at the source surface.

The second component is a pseudo-potential extension of the field solution from the source surface (2.5 solar radii) to 5 solar radii. This component is based on an approach first implemented by Schatten to add a realistic current sheet base and helmet streamer above the global neutral line, and is referred to as the Schatten Current Sheet (CS) component. It does this by temporarily forcing all radial field values to be positive, solving a potential field problem between 2.5 and 5 solar radii to match the solution from the inner PFSS component at 2.5 solar radiii, then correcting the sign of the radial field. By following this procedure, all fieldlines that are open at the source surface must remain open, but otherwise the field above 2.5 solar radii retains the lowest energy space filling characteristics of a potential field solution. This has the effect of creating a thin current sheet and a helmet streamer above the global neutral line. (Note: some non-radial smoothing of the shape of fieldlines is applied across the boundary between the inner PFSS component and the CS component to prevent unnatural cusps appearing in the fieldlines.)

The third and final component of the WSA model uses the field solution at 5 solar radii to generate a wind speed. The local wind speed is determined from an empirical formula which is a function of the local rate of expansion of the magnetic flux tube compared with that of a purely radial field, and on the distance of the photospheric footpoint of the local field line to the nearest coronal hole boundary.

Parameters

Magnetogram source:

The model can accept photospheric magnetograms from a range of sources. These includes 'synodic' or 'synoptic' maps from the originating observatories (gong_z, gong_b, vsm, kpvt) and ensembles containing 12 realizations from map sequences processed through the ADAPT surface flux evolution model (agong, ahmi, avsm, akpvt).

Magnetogram Type (parameter name MAPTYPE):

MAPTYPE accepts 2 possible settings, 'DU' and 'FR'. The default will be 'DU', which will be used for almost all runs.` This choice has 2 consequences.

(1) The first is that it defines how the longitude coordinate of the maps is interpreted by WSA. In both cases the longitude coordinate in the file runs from 0 to 360 degrees. For 'DU' maps, the sub-earth location at the time of the last observation included in the map construction is located at the center of the map (at 180 degrees). Information in the magnetogram file header is used to relate this to the correct Carrington longitude and rotation number associated with the time of the latest observation. In many cases an 'FR' map will also exist with the same timestamp. For these cases the surface field data is identical to the 'DU' map data, but the longitude coordinate is offset in order to place the sub-earth location at its actual Carrington longitude value. Typically, for ADAPT maps, a both 'DU' and 'FR' maps are created for all available times. (The ADAPT website refers to DU maps as 'Central Meridian Frame' and FR as 'Carrington Frame'.) For the non-ADAPT maps (ie gong_z, gong_b, kpvt, vsm, etc), the 'FR' maps were only created at the end of each Carrington rotation when the sub-earth Carrington longitude was exactly 0. These maps are constructed months after the actual obserrvations, with a uniform time sampling that considers data acquired for a short period beyond the end of that Carrington rotation, and so are not exactly identical to 'DU' maps from the same source constructed right at the end of that Carrington rotation.

(2) When WSA runs it produces a forecast of the wind speed and IMF polarity at the object of interest (see the 'Object' parameter). When 'DU' is chosen, that forecast extends for 24 hours beyond the timestamp associated with the map (ie 24 hours after the time of the last included observation.) When 'FR' is chosen, the forecast extends for a full Carrington rotation time after the time of the last included observation.

Carrington Rotation Number: The data from the different sources covers different time ranges. Note some maps have know bad data issues and the ADAPT maps have not yet been backfilled to cover the full possible time ranges.

kpvt : 1992/05/23 to 2003/07/27 vsm : 2003/07/28 to present gong_z : 2006/09/19 to present : CR_LONGIT 2048_323 to now. gong_b : 2006/09/19 to present : CR_LONGIT 2048_323 to now. agong : 2006/09/19 to present : CR_LONGIT 2048_323 to now. akpvt : 1992/05/23 to 2003/07/27 avsm : 2003/07/28 to present ahmi :

Carrington Longitude:

Should be a 3 digit integer string between 000 and 359, ie 054 or 198 or 002.

Outer radial boundary location of Current Sheet Component:

Accepts 2 possible values. The 'standard' WSA model places this at 5 Solar radii. If this run is intended to generate a coronal field solution for use in an ENLIL model run, this must be set to 21.5 Solar radii.

Images displaying wind speed at outer boundary of the models Current Sheet Component; Wind speed and IMF polarity timelines at L1.

Papers you must cite if you plan to publish the results Arge,C.N. and Pizzo,V.J., JGR, 105,pp 10465-10479, (2000), https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/1999JA000262