1.1. About this Guide¶
The purpose of this guide is to provide detailed instructions on how users can find, download, browse, and analyze co-aligned level 2 data obtained with The Interface Region Imaging Spectrograph (IRIS), the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO), and Hinode/SOT level 2 data. The IRIS team at the Lockheed Martin Solar and Astrophysics Laboratory (LMSAL) created new data cubes consisting of the Hinode/SOT and SDO/AIA images co-aligned with the simultaneous IRIS observations. These datasets all have the same IRIS level 2 FITS format, therefore can be accessed and examined using the IRIS SolarSoft software. In this guide, we provide step by step instructions how to access, read, and visualize these newly created co-aligned data cubes. In particular, we describe:
- How to find data using SolarSoft IDL routines;
- How to acquire data sets using either SolarSoft or Heliophysics Coverage Registry (HCR);
- How to read data and visualize them using SolarSoft routines or Crisp Spectral Explorer (CRISPEX).
This guide mostly relies on the IRIS user guide (ITN 26). Hence, we recommend that users have up to date IRIS branch of SolarSoft IDL installation (SSW). ITN 26 details how to install and load IRIS routines if they are not already installed. This guide will be updated and/or expanded as needed.
1.2. Synopsis of the IRIS, Hinode and SDO missions¶
IRIS is a NASA satellite designed to study the solar transition region, i.e., the region between the chromosphere and the corona. The main goal of the IRIS mission is to understand how the upper solar atmosphere is heated from 3000 K in the chromosphere to over one million K in the corona. To achieve this, IRIS takes simultaneous spectra in three passbands, in the near ultraviolet (NUV) from 2783 to 2834 Å and in the far ultraviolet (FUV), from 1332 to 1358 Å (FUV 1) and from 1389 to 1407 Å (FUV 2). In addition, it records slit-jaw images (SJI) using filters whose spectral windows are centered on Mg II k 2796 Å (SJI 2796), the far Mg II h wing at 2832 Å (SJI 2832), 1330 Å (SJI 1330), and 1400 Å (SJI 1400). This way, IRIS samples the Sun from the photosphere up to the transition region, which makes it possible to study the dynamics and energetics of the transition region and its coupling to the other solar atmospheric layers at high spatial and temporal resolutions.
IRIS observations perfectly complement Hinode and SDO observations. The Hinode satellite is a solar mission of the Institute of Space and Astronautical Science (ISAS) of the Japan Aerospace Exploration Agency (JAXA). The Hinode satellite carries three instruments: the Extreme ultraviolet Imaging Spectrometer (EIS), the X-Ray Telescope (XRT) and the Solar Optical Telescope (SOT). The XRT and EIS instruments are dedicated to transient eruptive phenomena and the dynamics of the transition region and corona. On the other hand, the SOT is focused on emergence and evolution of magnetic structures in the solar photosphere and chromosphere. The scientific goals of the Hinode mission are to understand the processes of magnetic field generation and energy transport from the photosphere to the corona, and to determine the mechanisms responsible for eruptive phenomena such as flares and coronal mass ejections.
The SDO mission was developed and launched under NASA’s Living With a Star (LWS) program. This spacecraft carries three instruments: the Atmospheric Imaging Assembly (AIA), the Extreme ultraviolet Variability Explorer (EVE) and the Helioseismic and Magnetic Imager (HMI). AIA is composed of an array of 4 telescopes. They provide full-Sun images of the solar corona in 7 EUV wavelengths every 12 seconds. EVE measures the EUV spectral irradiance while HMI obtains full-disk, high-cadence Dopplergrams, broadband continuum filtergrams, longitudinal and vector magnetograms. The main objectives of the SDO satellite are to investigate the origin of solar activity and understanding of the Sun’s interior. In addition to this, SDO helps us understand coupling between the solar variability and changes in Earths climate.
These three satellites act as a single observatory when coordinated, i.e., when they observe the same region. This gives a unique opportunity to study various solar phenomena at very high temporal (generally sub-minute time resolution) and angular resolution (on the order of 1 or 2 arc seconds), across multiple spectral regions. The coordinated observations allow one to follow the evolution of solar magnetic fields from the photosphere up to the corona and heliosphere. Therefore, it is essential and would be of great scientific interest to gather all coordinated observations obtained by the three satellites, fully process and format them for easy and convenient scientific usage. For this purpose, the IRIS team at LMSAL created new data cubes containing co-aligned simultaneous IRIS, Hinode/SOT and SDO/AIA observations. These datasets all have the same IRIS level 2 FITS format and therefore can be accessed and examined using the IRIS SolarSoft software. In this guide we will give step by step instructions how to access, read and visualize the newly created data.
1.3. Hinode and SDO data cubes co-aligned with IRIS observations¶
The newly created data cubes consist of IRIS observations co-aligned with the simultaneous SDO/AIA and Hinode/SOT filtergrams available for a given time period. Detailed description of co-alignment process can be found in IRIS Technical Note 22, but we include a brief summary below.
IRIS and AIA filtergrams are cross-correlated using the XCEN/YCEN and FOVX/FOVY keywords from IRIS level 2 and AIA level 1.5 data. Because of minor errors in the headers, the current generation of these co-aligned data cubes may have co-alignment errors between SDO/AIA and IRIS observations of up to 5 arcsec, but usually less. To provide context for the IRIS field of view (FOV), the AIA data cubes have a slightly larger FOV than IRIS (±50 arcsec in both x and y directions), and start 10 minutes before the IRIS observations and end 10 minutes later. This way, AIA images cover the entire IRIS observational period and FOV with its surroundings. When necessary, AIA data cubes are corrected for solar rotation tracking and IRIS roll angles. Final AIA data products include the following channels: 94 Å, 131 Å, 171 Å, 193 Å, 211 Å, 304 Å, 335 Å, 1600 Å and 1700 Å. HMI line-of-sight (LOS) magnetograms and intensity maps will be included in future updates of the data cubes.
Similarly, Hinode/SOT and IRIS images are co-aligned using their respective header information. For these co-aligned datacubes, the headers of the Hinode/SOT images are updated with results from cross-correlation between SOT Ca II H images with the AIA 1700 Å channel. This co-alignment does not always work perfectly, errors up to 10-15 arcsec ar possible, but usually much less. As such, the co-alignment between Hinode and IRIS data is not perfect due to uncertainties of the pointing information in the headers of the IRIS and Hinode/SOT data. The offsets can be up to about ±5 arcsec in x and y directions for observations taken near the solar disk center and increase for observations recorded closer to the limb. Therefore, the cubes may need a small co-alignment tuning by the user. This co-alignment imperfection will be addressed in future updates. Similar to the SDO/AIA cubes, the different duration of observational sequences, IRIS roll angles and solar rotation tracking are taken into account. Processed SOT observables are Broadband Filter Imager (BFI) filtergrams (Ca II H 3968 Å, G band 4305 Å and CN band 3883 Å), and Narrowband Filet Imager (NFI) LOS magnetograms along with Stokes I and V images. Future updates will also include SOT Spectro-Polarimeter (SP) data.
Please note that since February 25th, 2016, only SOT-SP observations are available due to the loss of the SOT-FG camera.
The co-aligned SDO/AIA and Hinode/SOT data cubes are formatted in the same way as IRIS level 2 data. This data structure makes it possible to examine all observations using the same IRIS SolarSoft routines. In addition, all cubes can be used along with level 3 IRIS data and examined with CRISPEX.