HELCATS

Recognising radio observations that are associated with heliospheric transients, this work package links, in particular IPS and Type II events to the established Heliospheric Imager observed events.

The work package consists of two tasks.

• Identifying and analysing potentially-geoeffective solar wind events that are observed by both HI and IPS
• Identifying and analysing solar wind transients that are observed by both HI and in Type II radio burst emission

The work package will aim to identify and analyse potentially-geoeffective solar wind events that are observed by both HI and IPS, and use IPS to augment the HI observations. The activity will also identify and analyse solar wind transients that are observed by both HI and in radio, and add value to the HI data by establishing/cataloguing the relationships between them.

Task 1: Identifying and analysing potentially-geoeffective solar wind events that are observed by both HI and IPS

Interplanetary scintillation (IPS) results from inhomogeneities in solar wind/heliospheric outflow (~150 km scale size) crossing the line of sight (LOS) from a distant, point-like astronomical natural radio source to receiving telescopes/antennas on Earth. IPS enables the solar wind velocity, density and turbulence of material flowing across the LOS to be inferred. IPS was the first technique that remotely sensed the heliosphere, and has led to several fundamental discoveries of solar wind structure (some only later confirmed by spacecraft). In the past, IPS was considered to have only modest potential for space weather science based on experimental and instrumental capabilities of the time. Today, these capabilities have been far exceeded due to advances in technology/data analysis/interpretation (e.g. Bisi et al. 2009; Bisi et al. 2010a; 2010b; Fallows et al. 2012; Jackson et al. 2012), making IPS a powerful tool for space weather science and forecasting. The combination of IPS with white-light heliospheric imaging has already been proven to be highly effective for solar wind, CME, and space weather investigations (e.g. Dorrian et al. 2010; Hardwick et al. 2012); this will be capitalised upon here in WP7. The following goals will be achieved in this WP7 objective: 1. Development of a catalogue of CMEs observed using IPS by EISCAT/ESR, LOFAR, and KAIRA/EISCAT_3D during the STEREO mission timeline and comparison with observations from STEREO/HI and COR and LASCO, where appropriate, and where the geometry allows. 2. As 1 but for CIRs and their non-corotating counterparts, Stream Interaction Regions (SIRS). 3. Interaction with the solar wind: (1) investigating effects, if any, on the ambient solar wind due to the events catalogued above (2) investigating the systematic effects, if any, of the ambient solar wind on CMEs/CIRs/SIRs in terms of modification to propagation direction and speed, such that this knowledge can feed into improved space-weather forecasting models. 4. Determining the number of interacting CMEs in HI images, and exploring how IPS may be used to aid interpretation of such complex events including the use of readily-available 3-D computer-assisted tomography where appropriate/sufficient extant IPS data allow (e.g. with IPS data from STELab in Japan).

Task 2: Identifying and analysing solar wind transients that are observed by both HI and in Type II radio burst emission

Solar radio-burst observations cover a broad frequency domain corresponding to different distances from the Sun. The S/ WAVES instruments on STEREO measures radio emission and in-situ plasma waves in the frequency range 2.5 kHz – 16.025 MHz. Radio emissions produced by non-thermal electrons accelerated at the shock front (type II radio bursts) are unique means of studying shock wave propagation. Type II radio bursts appear in dynamic spectra as slowly drifting lanes of enhanced emission decreasing in frequency with distance from the Sun, generated at the local plasma frequency and/or its harmonics. Since frequency is proportional to density, applying a coronal density model allows estimation of the height of the shock signatures. Combining STEREO solar radio-burst, coronagraph and HI observations enables unique study of the propagation of shock waves and their drivers (CMEs), as well as interaction of fast CMEs, all the way from the low corona to 1 AU. This links strongly to the IPS observations. S/WAVES observations impose a lower boundary condition for the HI J-map analysis (Harrison et al. 2012). A key advantage of space-based radio measurements is their effectiveness in tracking CMEs through the interface between coronagraph and HI fields of view, and in analysing examples where fast CMEs interact. The metric Type II radio bursts in conjunction with CME onset are observed using ground-based instruments. We will leverage team participation in ground-based radio observations, e.g. the CALLISTO spectrometer network (10 – 800 MHz), that extend the data down to the low corona, critical in measuring CME kinematics/shock-wave formation near the Sun. The following goals will be achieved in this WP7 objective: 1. Developing a joint catalogue of CMEs observed in HI, and S/WAVES and Wind/WAVES data. 2. Extending the catalogue with ground-based radio observations to examine more closely the source region of each CME. 3. Constructing height-time statistics, and systematically examining usefulness of radio data in constraining modelling of CME lift-off and its impact on CME forecasting. 4. Determining the number of interacting CME events and exploring how radio data can be used to decipher event kinematics and improve forecasting.

Description of work package.

Description of work package.

Description of work package.