H1: Heliospheric magnetic field and solar wind

Moderator:

Evangelia Samara (NASA GSFC), evangelia.samara@nasa.gov

Co-Moderator:

Nishtha Sachdeva (University of Michigan), nishthas@umich.edu

Advisors:

Mario M. Bisi (UKRI STFC RAL Space, UK), Mario.Bisi@stfc.ac.uk

Martin Reiss (NASA/CCMC, USA), martin.a.reiss@outlook.com

Impact:

Structure of interplanetary space throughout the heliosphere
SIRs/CIRs formation and propagation (including arrival characteristics at targets)
Variability of space environment (preconditioning)
Geospace energy input (impact of HSSs/SIRs/CIRs)

Introduction:

The background solar wind is generally considered to be generated as two “modes”: the slow solar wind (generally thought to originate from closed magnetic-field regions such as above streamer belts, active regions, and potentially from quiet-Sun regions); and the fast solar wind (generally from open magnetic-field lines from above Coronal Holes (CHs) - these can be long lasting in their duration). High-speed stream (HSS) is generally the space-weather term used for a fast solar wind flow traversing the heliosphere. HSSs and the slow solar wind can interact to form stream interaction regions (SIRs) of compressed plasma and magnetic fields throughout the heliosphere and sometimes shear layers are also caused where HSSs and slow solar wind flow more alongside each other rather than interacting with each other. Co-rotating/recurrent SIRs are classified as co-rotating interaction regions (CIRs) that are the major drivers of recurrent strong geomagnetic storms at Earth. Improving our understanding of the background solar wind, the origins of HSSs, and also the evolution and overall global structure in interplanetary space (through observations and state-of-the-art solar wind models as well as improvements to the observations/data used to drive such models) is critical to improving our understanding and prediction of multiple space weather phenomena including CMEs, SEPs, and their impacts at Earth and other locations in the heliosphere (linked to H2 and H4).

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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.

Objectives:

To improve our understanding of the background solar wind structures and improve the background heliospheric modelling to allow for better space weather predictions/forecasts.

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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).

Essential Space Environment Quantities / Forecasting Goals:

Background solar wind plasma and magnetic field properties at Sun-Earth L1 and/or other locations in the heliosphere (linked to H4)
HSSs/SIRs/CIRs arrival times and duration at Sun-Earth L1 and/or other locations in the heliosphere (linked to H4)
HSSs/SIRs/CIRs plasma and magnetic-field properties at Sun-Earth L1 and/or other locations in the heliosphere (linked to H4)

Action topics:

For list of action topics please click "Read more":

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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.

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