ISWAT - International Space Weather Action Teams 

As noted, CHs can be long-lived structures of open magnetic field lines in the solar corona along which the fast solar wind propagates and escapes to interplanetary space over several solar rotations, forming HSSs. HSSs shape the solar wind in interplanetary space, and their interaction with upstream slow solar wind flows generates the SIRs of compressed plasma and magnetic fields in the solar wind. The relevance of SIRs to space weather phenomena is multifaceted. Repeating/recurring SIRs, or CIRs, can significantly affect the evolution/propagation of coronal mass ejections (CMEs) in interplanetary space due to the different interactions between CMEs and fast vs. slow solar wind backgrounds as well as the more-complex HSS and/or SIR-type structures that CMEs can also interact with and sometimes deflect as a result of such interaction.

The pair of shock waves forming at the leading and trailing edges of SIRs/CIRs often trigger phenomena of particle acceleration to quasi-relativistic speeds, generating gradual solar energetic particle (SEP) events (and lower-energy Energetic Particles (EPs)). The high plasma pressure and magnetic fields associated to SIRs/CIRs also trigger recurrent strong geomagnetic storms, making HSSs/SIRs/CIRs major drivers of strong space weather disturbances at Earth and elsewhere in the heliosphere. Improving our current understanding of the origins and evolution/interaction of HSSs and thus the predictions of the HSSs/SIRs/CIRs arrival times, properties, and impact at Earth and other locations in the heliosphere is a critical component to improve predictions of space weather phenomena including the effects on CMEs/SEPs.

Present background heliospheric modelling requires improvements for the overall benefit of our understanding of the heliospheric structures as well as for the prediction of CME transits and impacts throughout the heliosphere and for the prediction of the evolution and impacts of HSSs/SIRs/CIRs.

Presently, the majority of space-weather models and forecast tools use magnetograms to form the background solar wind inside the model.  This often produces mixed results where inaccuracies can seriously affect the propagation of CMEs input into the models, providing less accurate CME arrival times for example.  The accurate reproduction of the background solar wind is therefore essential to not only our understanding of the structures in the heliosphere, but also for the prediction of CME transits throughout the heliosphere and predicting their impacts along with those of HSSs/SIRs/CIRs.  This will lead to improvements in our ability to predict events at Earth and elsewhere that are caused by HSSs/SIRs/CIRs and CMEs (linked to H2 and H4).  Thus, new/additional observations should be experimented with (examples might include  heliospheric observations made using radio, EUV, and/or visible-light wave bands) along with current/new solar wind models to better represent the reality of the heliospheric structures and thus improve the forecasting and model transits of ALL heliospheric structures (including CMEs - again linked to H2 and H4).

• Observations of the outer corona/inner heliosphere for characterizing heliospheric structures and sub-structures over all scales (micro/meso/large).

• Understanding of the turbulence evolution throughout the heliosphere.

• Global modelling of interplanetary magnetic field and solar wind "evolution" in both the inner and outer heliosphere.

• Assessment of modelling capabilities of ambient heliosphere.

• Modelling formation and the evolution of HSSs, SIRs, and CIRs.

• Improve the prediction of relevant fundamental parameters at/near Earth and prospects for other locations in the heliosphere (linked to H4).

• Forecasting the arrival and impact of HSSs/SIRs/CIRs at/near Earth and prospects for other locations in the heliosphere (linked to H4).

• Generating inputs to global space weather roadmaps.