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The CorPITA database, EUV global waves observed in the sun

The CorPITA database
EUV global waves observed in the Sun

It was first published in
VarSITI Newsletter Feb. 2017
David Pérez-Suárez
David Long

Database of global “EIT waves” identified by the
Coronal Pulse Identification and Tracking Algorithm (CorPITA)

David Long and David Pérez-Suárez
Mullard Space Science Laboratory, University College London, UK

Figure 1. An “EIT wave” event observed on 12-May-1997 by the SOHO/EIT instrument. These running difference images (wherein a following image is subtracted from a leading image) are used to highlight the moving pulse and make it easier to identify in single images.

EIT waves” are globally-propagating bright wavelike features associated with a solar eruption that can traverse the solar disk in under an hour (see Figure 1). They were first observed by SOHO/EIT in 1997 (e.g., Moses et al., 1997; Dere et al., 1997; Thompson et al., 1998) but are not yet fully understood. However, they are strongly associated with coronal mass ejections (CMEs) and could provide opportunities to study both the solar corona through which they propagate (via coronal seismology) and the associated CME itself. Although they can be readily identified “by-eye” using moving images, identifying and tracking them over an extended period of time requires extensive image processing of individual images. This approach is complicated by the sheer volume of data provided by the Solar Dynamics Observatory (SDO), which has necessitated development of automated techniques for identifying and tracking dynamic solar features (cf. Martens et al., 2012).

Figure 2. An example of the output from CorPITA, in this case an event from 13-March-2012. The code provides a visual output of the identified pulse (left panel) and a plot of the fitted kinematics of the highest rated arc sector (right panel).

The Coronal Pulse Identification and Tracking Algorithm (CorPITA; Long et al., 2014) was designed to identify, track and analyse global “EIT waves” using SDO images in the 211Å passband. The code is triggered by the start time of a solar flare, using its location as a source and searching for any bright transient feature radiating from there. CorPITA uses a series of overlapping arc sectors to produce intensity profiles which are examined to identify a moving pulse. If a pulse is detected, the algorithm tracks it for as long as possible before measuring its velocity and acceleration in each arc. The derived properties of the pulse are then used to determine a quality rating, which defines the confidence that the detection is a true “EIT wave” pulse. An example of the output provided by CorPITA is shown in Figure 2.

The process of putting the output from the CorPITA code online has begun thanks to a grant awarded by the VarSITI consortium. The grant was used to fund an undergraduate student who began running CorPITA systematically by applying it to 238 “EIT wave” events previously identified by Nitta et al. (2013). This is the first step in compiling a database of “EIT waves” and also provides a benchmark for the effectiveness of the code. The initial database is available online at https://sites.google.com/site/daithisolar/research/corpita, and will be added to as more events are processed.

References:
Dere, K. P., Brueckner, G. E., Howard, R. A., et al., 1997, Solar Physics, 175, 601.
Long, D. M., Bloomfield, D. S., Gallagher, P. T., & Pérez-Suárez, D., 2014, Solar Physics, 289, 3279.
Martens, P. C. H., Attrill, G. D. R., Davey, A. R., et al., 2012, Solar Physics, 275, 79.
Moses, D., Clette, F., Delaboudinière, J.-P., et al., 1997, Solar Physics, 175, 571.
Nitta, N. V., Schrijver, C. J., Title, A. M., & Liu, W., 2013, The Astrophysical Journal, 776, 58.
Thompson, B. J., Plunkett, S. P., Gurman, J. B., et al., 1998, Geophysical Research Letters, 25, 2465.

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