Relevance of Murchison Widefield Array Interplanetary Scintillation Observations to Heliospheric Transient Catalogues

TL;DR

This work evaluates how effectively MWA interplanetary scintillation (IPS) observations reproduce and augment heliospheric transient catalogues. By crossmatching 2019 MWA IPS data with CDAW/CACTus CME and STEREO‑A IMPACT/PLASTIC event lists and applying a drag‑based arrival model plus 3D HUXt simulations, the authors quantify the overlap and demonstrate IPS’s ability to reveal events beyond the ecliptic. They identify two representative enhancements (Event A: a CME; Event B: a likely out‑of‑ecliptic SIR) to illustrate how IPS can trace solar wind structures far from Earth that conventional methods may miss. The findings suggest that incorporating MWA IPS data can substantially increase the number of CME and SIR events detected and characterized, improving space weather understanding and forecasting. Significantly, IPS shows promise for continuous heliospheric coverage beyond the ecliptic, enabling remote sensing of events inaccessible to near‑Earth spacecraft.

Abstract

We have conducted a comprehensive comparison of interplanetary scintillation (IPS) observations taken by the Murchison Widefield Array (MWA) with several heliospheric transient event catalogues, over a time period of 7 months during solar minimum. From this analysis we have found that of the 84% of catalogued events that have MWA IPS data available, 68% of them appear in MWA observations. Of the enhancements first identified in IPS observations, only 58% have a potential match with a catalogued event. The majority of enhancements that were identified in the IPS observations were situated greater than 10$^\circ$ from the ecliptic plane. Two such features were selected for detailed analysis, connecting their solar origins to their propagation through the heliosphere. The first of these features was created by a coronal mass ejection (CME), captured over two successive MWA observations and recorded in several catalogues. The second feature has the potential of being a stream interaction region (SIR) travelling out of the ecliptic plane. This particular SIR was not recorded in any catalogue. Thus the MWA shows promise in detecting heliospheric transients that other commonly-used techniques may overlook. These results show the strength of the MWA in having unbridled access to the heliosphere, able to make remote observations of events far out of the ecliptic as it is not restrained to the orbits of spacecraft. We demonstrate how the inclusion of MWA IPS data can potentially boost the number of CME and SIR events that are characterised.

Figures (9)

• Figure 1: The sky coverage of the MWA IPS observations over a 7-month period in 2019. Top panel: Representative target fields of individual observation each in HPC, representing the sky coverage as seen by the MWA. Bottom two panels: The half-power region (light purple lines) of the line-of-sight with the piercepoint highlighted (dark purple circle marker) for the centre of all observations included in the 2019 time period. The line-of-sight is projected into Earth's orbital plane (middle panel) and into the meridional plane containing Earth (bottom panel) both in HCC. The location of Earth and STEREO-A (as found for the central observation; 30-May-2019 08:00 UTC) are added for reference. A total of 735 observations are included.
• Figure 2: Summary of the 17 IPS enhancement events that had a match with a catalogued event, broken down by catalogue; CDAW SOHO LASCO CME catalogue (light green), CACTus LASCO CME catalogue (purple dots), and the STEREO IMPACT/PLASTIC Events list (dark green). The overlap between catalogues are depicted as hatching in their respective colours.
• Figure 3: Daily g-maps in HPC for the two example interplanetary events chosen for further analysis; Event A (top panel) observed on 04-Jul-2019 and 05-Jul-2019, and Event B (bottom panel) observed on 04-Aug-2019. For each event, the centre of their corresponding structure/s are marked as either a cross or plus.
• Figure 4: All panels: A single latitude, and a single timestep from a HUXt simulation. The radial axis is distance from the Sun, but rather than just an equatorial cut, the plot is a projection of the surface of a cone (with the Sun at the apex) into the 2D plane. The location of the simulation CME front is outlined in red. The half-power region of the line-of-sight of the centre arc is shown as a black line, with the piercepoint marked. The base velocity profile of the solar wind velocity (km/s) is given as a colour gradient. Top panels: Latitude of -21$^\circ$, with the left panel showing the timestamp (04-Jul-2019 07:12 UTC) nearest the time of the first observation of Event A (04-Jul-2019 07:17 UTC), whilst the right panel shows the timestamp (05-Jul-2019 07:12 UTC) of the second observation (05-Jul-2019 07:17 UTC). Bottom panel: Latitude of -5$^\circ$ to align with STEREO-A (STA in legend), at the same timestep as top right.
• Figure 5: The location of the CME front from a 3D HUXt simulation projected into the HPC plane, outlined in purple, as compared to the g-maps of Event A. The left panel shows the HUXt simulation at the timestamp (04-Jul-2019 07:14 UTC) nearest the time of the first observation of Event A (04-Jul-2019 07:17 UTC), whilst the right panel shows the timestamp (05-Jul-2019 07:12 UTC) of the second observation (05-Jul-2019 07:17 UTC). The centre point of the enhancement and the projected location of STEREO-A are included for reference.