STORM SIGNALS
From Satellites: RHESSI Spectrograms
Live Data
RHESSI Spectrograms
A complete list of real-time data links is located in the Space Weather Resources section.
These plots are useful because they allow you to see data from 3 missions plotted together, GOES, RHESSI and WIND. This is one way for you to determine if a feature in the RHESSI light curves is artificial or a real flare. In a flare the X-ray emission is seen by both RHESSI and GOES, whereas when RHESSI experiences a result because of the way the instruments work the feature only appears in the RHESSI data. Students can also see when flares are occurring in times that RHESSI isn't recording data because it is in Earth's shadow, or it is flying in the South Atlantic Anomaly, or it is experiencing a data outage. The comparison to the WIND radio spectrogram also allows you to see if the flare was type II/IV indicating the possibility of a CME associated with the flare.
When you select RHESSI Spectrograms you will see a page similar to the one below that plots data from late May 27, 2003 and early May 28, 2003.
Navigation: When the page first opens it will show a recent time interval, but not necessarily the most recent data available.
Click on the year and month you want to examine.
Click on the day of the month in the column numbered
1 - 30 or 31.
The arrows at the top allow you to choose previous time period (back arrow) or the next time period (forward arrow). The outside arrows change the time period by one day. The inner arrows change time by one orbit (a few hours).
Click on the arrows until you get the time period you
want. (Remember, the time is given in Universal Time (UT)
Leave the Rates setting at 'Summary, corrected'.
Interpreting the Plots
The first two plots are light curves. The first is from GOES. The second is from RHESSI and shows the same data plotted in RHESSI Light Curves. (See the tutorial for RHESSI Light Curves for more information.) Notice that there is no increase in x-ray intensity during the end of May 27 even though there was an X-class flare. That flat line in the GOES data looks suspicious! The GOES plot doesn't increase until the event early on May 28. The GOES plot is missing data! The RHESSI data misses the flare on May 28 because it is on the night side of Earth. You can tell RHESSI is on the night side by looking at the RHESSI Light Curve plots (there is a cyan N and a cyan bar). RHESSI does show a flare late on May 27. The green and blue spikes occur because RHESSI has 'shutter' devices called attenuators that open and close to block the detector when the x-ray intensity is high. (Read the Explanation at the bottom of RHESSI Light Curves.) You can confirm that there was a flare by looking for the red F and red bar on the RHESSI Light Curves plots.
The 3rd plot is the RHESSI Spectrogram. The RHESSI Spectrogram represents data in 3-dimensions: time is on the horizontal axis, the energy of the x-ray light is on the vertical axis, and color is used to represent a third dimension - the intensity of the light at a particular energy. A bright color means that many x-rays of that energy are produced. Flares usually produce high intensity across many energy levels (up and down). Artificial events often show bright color at a narrow band of energy (horizontal stripes). The Spectrogram from May 27 shows higher intensity across many energy levels.
TEACHER'S NOTE
Non-solar emission artifacts in the RHESSI data can also be identified readily in the RHESSI spectrograms by the fact they often occur at high energies with no corresponding emission at low energies. (see example image below)
All of this information from these missions is essential to scientists because data from one mission can be evaluated against information from other missions. This gives a more complete picture. Stress this with your students.
The 4th plot shows data of radio emission detected by the WAVES instrument on the NASA Wind satellite. It is also a spectrogram. Time is plotted on the horizontal axis. The energy of the radio light is on the vertical axis. Color is again used to represent the intensity of radio emission. Flares usually produce high intensity across many energy levels (up and down). Artificial events often show bright color at a narrow band of energy (horizontal stripes). The spectrogram form May 27 - 28 shows the characteristics of a flare with a coronal mass ejection. See the tutorial for WIND WAVES for more help interpreting the WAVES data.
TEACHER'S NOTE
Students may be unfamiliar with the description of x-rays and radio as light. All types of electromagnetic emissions are light. Radio emissions are at one end of the electromagnetic spectrum. They have long wavelengths and low frequencies. Radio describes a broad range of frequencies. Next in the electromagnetic spectrum is the band of microwave with shorter wavelengths and higher frequencies. Continuing down the spectrum with shorter and shorter wavelengths and higher frequencies, there is a range of infrared, then the familiar range of visible light, followed by ultraviolet, x-rays and gamma rays. We often describe radio emissions by their frequencies (hertz, megahertz, kilohertz). Infrared, visible and ultraviolet are usually described by their wavelength. And x-rays are often described by their energy. As you can see in the following diagram, wavelength, frequency and energy of electromagnetic emissions are related.
You can find out more about electromagnetic spectrum in the Content Enhancement of Tracking a Solar Storm (Electromagnetic Spectrum and How Astronomers Use EM Spectra). Another good resource is Imagine the Universe - Electromagnetic Spectrum.
- NASA Official: Dr. James Thieman
- Project Manager: Don Robinson-Boonstra
- Website Manager: Bryan Stephenson