CME-CIR Science Case
The Sun may produce a variety of dynamical phenomena that can be observed to propagate far into the Heliosphere. Among these are powerful expulsions of magnetized plasma from the solar atmosphere into the solar system, known as coronal mass ejections (CMEs). If directed towards Earth they may impact the geomagnetic field, causing a geomagnetic storm, which is particularly dangerous for electrical power grid systems. Another phenomenon which may also cause such a storm (albeit a smaller one than a CME) is a co-rotating interaction region (CIR). CIRs are regions of the solar system where high-speed solar wind crashes into slow speed solar wind, creating a steady shock wave that sweeps around the solar system at the rotation period of the Sun (~30 day rotation period). Since both CMEs and CIRs are potentially damaging, there is an effort to identify and distinguish these phenomena from observational imaging data, mainly from the Heliospheric Imagers (HIs) of the STEREO spacecraft. However, the two phenomena are not easily distinguished in HI and it is difficult to forecast if a CME or CIR will impact Earth. The goal of this workflow is to try and distinguish the characteristics of CMEs and CIRs in imaging observations by using related in-situ observations (in which the two phenomena are easily distinguishable).
In summary, we use in-situ to identify if a CME or CIR is observed; we then use this to detail the characteristics of each phenomena in the imaging observations. Knowing the characteristics of each in the images should aid future imaging identifications of either phenomena.
Our workflow is outlined as follows:
- The initial query is to the stereo_hi_sw_transient list in a particular time range. From this catalogue we extract the longitude of the source of the transient, the longitude error, the start time (launch time of the transient) and the estimated time of arrival. The time of the event is then passed to the HELIO Instrument Location Service (ILS) to extract the Heliocentric Earth Equatorial longitudes of all available instruments.
- If the longitude of the spacecraft matches the launch longitude of the solar wind transient, the spacecraft is checked for the possible in-situ detection of a CME or CIR (all available in-situ catalogues above are checked).
- If a CME or CIR is detected in-situ, both the in-situ data and the imaging data are saved for manual analysis. The procedure is repeated for all detections in the stereo_hi_sw_transient list.
We firstly searched the stereo_hi_sw_transient list in the time range of 2009-05-29 00:00:00 - 2009-05-30 00:00:00 UT (we chose this time range with a priori knowledge that a solar wind transient was identified in STEREO HIs). In this time range, a transient was observed in both STEREO ahead and behind spacecraft, traveling at 309 km/s and 300 km/s, respectively. The stereo_hi_sw_transient catalogue defines an estimated time of arrival (ETA) based on kinematic modelling of the transient observed in each spacecraft. The ETA based on the observations from STEREO A and B are 2009-06-03 06:55:00 UT and 2009-06-03 21:21:00 UT, respectively.
In order to check the possibility of and in-situ detection of this transient, we compare the estimated propagation longitude of the transient and the spacecraft longitude. The transient launch longitude was -7.8 degrees (Stonyhurst Heliographic, with the central meridian on the Sun-Earth line). The longitude of STEREO A was obtained using the HELIO Instrument Location Service (ILS); it was found to be -61 degrees. Given the longitudinal expanse of CMEs at interplanetary distances (>100 degrees), there is a strong possibility of this transient impacting STEREO A (if indeed the transient was a CME). We chose the ETA and STEREO A define a time window of 48 hrs over which to check for an in-situ detection i.e., check for an impact of STEREO A between 2009-06-02T16:55:00 - 2009-06-04T16:55:00 UT. During this time, the stereo_impactplastic_icme catalogue (list of in-situ detections from STEREO) reported a positive detection of a CME at 2009-06-03T16:42 UT. The actual arrival time falls with the ETA window. Hence there is a strong possibility that the solar wind transient observed in images (HI) is the same feature observed by the IMPACT instrument on-board STEREO. In this instance, the workflow is successful in the identification of the solar wind transient observed in HI as a CME, not a CIR.
- "Metaworkflows and Workflow Interoperability for Heliophysics". Dr. Gabriele Pierantoni, Dr. Eoin Carley, IWSG14, June 2014
Dr. Gabriele Pierantoni, Dr. Eoin Carley