These synchronous synoptic maps are maps of the solar intensity in different Ultra-Violet (UV) and extreme-UV (EUV) wavelength bands on the full solar sphere, in heliographic (Carrington) longitude and latitude, where data are taken as close as possible to a reference time. This allows estimating the EUV radiance (and then the solar activity) anywhere on the Sun (also on the far side), computing the EUV irradiance received at any point in the heliosphere (also outside of Sun-Earth line), and comparing data to models of the solar corona computed for this time. When this reference time is now or in the future, this allows nowcast and even forecast of EUV radiance and irradiance.
These maps are built from SDO/AIA (NASA Solar Dynamics Observatory mission / Atmospheric Imaging Assembly) data.
Usual synoptic maps are obtained by accumulating data (UV/EUV intensity in this case) 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 corona 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 for forecasting EUV radiance or irradiance.
In contrast, synchronous synoptic maps capture the state of the corona 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:
Visualising the latest or nowcast map allow the identification of solar regions such as Active Regions and Coronal Holes, at all solar longitudes. With further processing, these maps can be used in the following ways:
References:
The maps are built daily from SDO/AIA Level 1 data, available from the SDO AIA and HMI Joint Science Operations Center (JSOC) about 4 days after the observation. For the purpose of the synoptic maps generation, these data, given in data numbers (DN), are normalized by exposure time and by the AIA time-dependent degradation factor in each channel.
The central parts of daily SDO/AIA images (±45° from the central longitude, and more than 0.1 solar radius from the plane of sky), transformed to Carrington coordinates, are put into a queue. For a given channel 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/AIA data before and after the reference time, several product types exist:
The maps are saved as FITS files for data analysis, and as PNG files for display. The PNG files colour scale have a power-law normalization — with an exponent gamma = 1/4 — between a minimum and maximum value specific to each channel. For each wavelength channel and 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.
The data calibration relies on the SDO/AIA instrument team-provided correction factor for the time-dependent instrument sensitivity degradation. Furthermore, given that SDO/AIA is a narrow-band imager and not a spectrograph, radiometric calibration (giving radiance in physical units) would rely on assumptions on the plasma emitting the spectral lines included in the channel, and on the precise shape of the wavelength response function in the channel. For this reason, the product is not provided with radiance in physical units.
The product displays the long-term structure of the solar atmosphere, 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.
While synchronous synoptic maps capture the time evolution of solar structures (such as active regions and coronal holes) 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.
The Query menu gives access to a query form, with the following fields:
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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.
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