The Condegram spiral plot is an illustrative device developed by Dr. Mark Conde,[1] Associate Professor at the University of Alaska, Fairbanks [2] to display space weather data. Space weather effects on Earth are ultimately driven by processes originating with the Sun, many of which are communicated to Earth by the hot plasma which streams out from the Sun, called the solar wind. Solar wind properties such as velocity, density, temperature and magnetic field are dependent upon conditions in the solar atmosphere, and are related either directly or indirectly to space weather effects observed on Earth, such as the aurora.
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As viewed from Earth the rotation period of the Sun is approximately 27 days (see Carrington rotation) near the solar equator (however this period varies with solar latitude). This solar rotation can modulate the solar wind as observed from Earth, by bringing active regions in the Sun’s atmosphere (particularly coronal holes) into and out of alignment with Earth. The condegram spiral plot exploits the close connection between solar wind properties, their effect on space weather, and their modulation by the solar rotation period. A given solar wind parameter (for example velocity) is plotted against a time axis which wraps around a circle (the ordinate therefore points radially outward). The time axis is scaled such that a full revolution around the circle corresponds to 27 days, and the radial distance of the axis from the center of the circle is made to increase with azimuthal angle, allowing the time axis to continue wrapping around the circle in an outward-moving spiral.
The great utility of the plot format is that a line of fixed azimuth (i.e. along a radial line from the center of the circle) essentially tracks a fixed location on the ‘surface’ of the Sun. For example, coronal holes allow fast-moving plasma to escape from the photosphere, which can effect a local increase in the solar wind speed. The solar wind speed will then be modulated by the Sun’s rotation, and hence a condegram spiral plot of solar wind speed would show a recurrent period of elevated speed at a fixed azimuth on the circle. The condegram can then be used as a tool for predicting when space weather effects might be more likely to be observed on Earth, which can be useful to space physics researchers and amateur aurora watchers.
In addition to solar wind parameters (velocity, density, magnetic field), other common condegram parameters include geomagnetic indices and solar spectral fluxes. The plot format has been used to display bulk velocity, density and temperature data from the PLAsma and SupraThermal Ion Composition (PLASTIC)[3][4] instrument aboard the STEREO satellites [5] using software called SPLAT (STEREO PLASTIC Analysis Tool).[6]
![[1]](http://fulcrum.gi.alaska.edu/condegrm/xray_cgm.png){kind=link}