Synchronous synoptic maps of the photosphere

Product help

Introduction

These synchronous synoptic maps are maps of the solar photospheric magnetic field and continuum intensity on the full solar sphere, in heliographic (Carrington) longitude and latitude, where data are taken as close as possible to a reference time.

These maps are built from SDO/HMI (NASA Solar Dynamics Observatory mission / Helioseismic and Magnetic Imager) data.

Usual synoptic maps are obtained by accumulating data from the central meridian in consecutive images and letting the Sun rotate in the field-of-view of the observing spacecraft. However, in such maps the data can be as old as one solar rotation period (almost a month), while the structure of the photosphere can change in the matter of a few hours due to the emergence of new Active Regions or the occurrence of eruptions and CMEs. Such maps are then not adequate for testing models or as boundary conditions for numerical simulations of the heliosphere.

In contrast, synchronous synoptic maps capture the state of the photosphere at any given reference time by including data taken as close as possible to this time. In these synchronous maps (as in Auchère et al. 2005), this achieved by:

  • using data from a large fraction of the photosphere (as observed from a given viewpoint) instead of the central meridian only;
  • taking into account a solar differential rotation model to compute synoptic maps from observational data at different times;
  • merging these maps, with weights depending on the difference between the map reference time and the observation time of each map to be merged.

Visualising the latest or nowcast map allows the identification of solar regions such as Active Regions, at all solar longitudes. With further processing, these maps can be used in the following ways:

  • Project this map on a sphere to visualize the Sun as it would be seen from anywhere in the heliosphere.
  • Prepare boundary conditions for numerical simulations of the solar corona and wind.

References:

  • Auchère, F.; Cook, J. W.; Newmark, J. S.; McMullin, D. R.; von Steiger, R.; Witte, M. (2005). Model of the all-sky He II 30.4 nm solar flux. Advances in Space Research, 35, 388-392, doi:10.1016/j.asr.2005.02.036
  • Auchère, F.; Cook, J. W.; Newmark, J. S.; McMullin, D. R.; von Steiger, R.; Witte, M. (2005). The Heliospheric He II 30.4 nm Solar Flux During Cycle 23. Astrophys. J., 625, 1036, doi:10.1086/429869

Technical information

The maps are built daily from SDO/HMI Level 1 data (hmi.m_720s and hmi.ic_720s series), available from the SDO AIA and HMI Joint Science Operations Center (JSOC) about 4 days after the observation.

The central parts of daily SDO/HMI maps (±45° from the central longitude, and more than 0.1 solar radius from the plane of sky), transformed to Carrington coordinates, are added to a queue. In the case of magnetic field, the line-of-sight field is deprojected to a vertical (radial) field. For a given HMI map type and reference time, a time difference between the reference time and the observation time of each image in the queue is computed. From this time difference, the solar differential rotation is applied to the images in the queue (so that they are all transformed to be equivalent to the reference time), and a weight (higher for smaller time differences) is given to each image. The synchronous synoptic map is the result of a weighted average of the images in the queue.

So that the synoptic maps cover the full solar sphere, 30 days of data are included in the queue. Depending on the current time and on the availability of SDO/HMI data before and after the reference time, several product types exist:

  • Archived: when SDO/HMI Level 1 data are available from 15 days before to 15 days after the reference time.
  • Temporary: when the reference time is in the past, but when some required SDO/HMI Level 1 data are not yet available up to 15 days after the reference time.
  • Nowcast: on the current day at 00:00:00Z.
  • Forecast: on the next three days at 00:00:00Z.

The maps are saved as FITS files for data analysis, and as PNG files for display. The colour scale for the magnetic field PNG files is a symmetrical logarithmic scale for positive and negative values between ±100 and ±10⁴ G, with a linear scale between -100 and +100 G. The colour scale for the intensity PNG files is linear between 0 and 62000 DN/s. For each product type, the daily runs of the product generation code produce successive versions of the files, which are saved with incremental version numbers in the archive. FITS files should open with standard FITS tools, but there is a known issue with fv version 5.3, please use a newer version or another tool such as ds9.

Magnetic field maps have units of Gauss and intensity maps have units of DN (data number) per second.

Limitations and caveats of the data

Calibration

Input data has been calibrated by the SDO/HMI instrument team. Magnetic field deprojection assumes that the field is vertical; the SDO/HMI vector magnetic field maps are not used as the full disk inversions have no azimuth disambiguation and the field is less accurate than the line-of-sight field outside of Active Regions. The limb darkening in continuum intensity is not corrected at the moment.

Transient events

The product displays the long-term structure of the photosphere, and transient events occurring at the reference time are not necessarily included. On the other hand, transient events occurring during image observation times different than the reference time can be included, but they are likely to be hidden by the merging process with images observed at different times.

Time evolution of solar structures

While synchronous synoptic maps capture the time evolution of solar structures (such as Active Regions) better than classical synoptic maps on the part of the solar disc that is observed and taken into account at the reference time, they cannot predict the time evolution of structures observed at different times.

Use and functionality of the product

Query form to the archive

The Query menu gives access to a query form, with the following fields:

  • Date range. Please select a date range. The default range covers the full archive. All dates and times are given in UTC.
  • Series: click on the check boxes to select the required data series, corresponding to the SDO/HMI data series used to build the maps.
  • Product types: click on the required product types, and use the Shift or the Ctrl key for multiple selection. Please see above for the definitions of the different product types.
  • Only latest: if checked, only the latest version of each map is shown in list; otherwise, all versions are shown.

If you have an issue with some of the query form input fields, please retry with another browser. The form has been validated with Chrome 98.0 and Firefox 97.0.

In the resulting list, clicking on the Preview thumbnails brings you to a page displaying this map. The download button allows you to download the FITS files with the map data.

Nowcast and forecast pages

The Latest menu gives access to:

  • Nowcast: a page with the latest nowcast maps in each series. You can use the checkboxes on the left to select a limited number of series. Again, clicking on the Preview thumbnails brings you to a page displaying this map, and the download button allows you to download the FITS files with the map data.
  • Forecast: a page with the latest forecast maps in each series, for different forecast horizons (1 to 3 days). You can use the checkboxes on the left to select a limited number of series. The forecast horizon is the time delay between the computation date and the forecast map date (from +1 to +3 days). The maps can be previewed and the data (FITS file) downloaded.

API

An API is available, please consult the appropriate page in the Help menu.