Science 

Objectives

 
Background knowledge: 

What is heliophysics?

Click the image labels above or the expanding titles below to see more about each science topic.

PUNCH advances the science of heliophysics. The PUNCH science goal is to determine the cross-scale physical processes that unify the solar corona with the rest of the solar system environment (the heliosphere). The goal divides into two major science objectives:

  • Understand how coronal structures become the ambient solar wind.
  • Understand the evolution of transient structures (such as CMEs) in the young solar wind.

These objectives divide into three specific science topics each, which shape the PUNCH investigation.

Objective 1: Ambient Solar Wind

Objective 1A: Global solar wind flow

 
Background Knowledge: 

What is the solar wind?

Radial-filtered visible light in the outer corona shows 
            highly structured flow. (DeForest et al. 2018)

How does the solar wind flow?

  • Wind speed can be traced using small features in the corona and heliosphere.
  • On global scales, the ambient solar wind is roughly bimodal, with fast and slow streams. This simple description is complicated by shears and complex structure that may dominate the behavior of the solar wind.
  • Structures and boundaries in the corona must ultimately give rise to features in the solar wind. Understanding the correspondence requires global measurements of the flow.
Co-moving averaging subtracts out large-scale transient 
            motions and structure. (DeForest et al. 2018)

Science Working Group 1A Planned Activities

Working group 1A members
  • Measure time-dependent solar wind flow from the outer corona to the inner heliosphere.
  • Identify the changing flow boundaries between solar wind streams in the corona and heliosphere.
  • Determine large-scale flow context necessary to relate coronal structure to in-situ measurements, and to provide ground-truth verification for global simulations.
  • Characterize the global solar wind conditions through which transient structures propagate.

Objective 1B: Solar wind microstructures and turbulence

 
Background Knowledge: 

What is solar wind turbulence?

The transition of radial striae to more clumpy flow (`flocculation') 
            occurs above about 40 solar radii from Sun center. (Deforest et al. 2016)

Where does the corona end and the solar wind begin?

Slow solar wind near Earth is dominated by fluctuations of unknown origin.
  • Do they form mainly from turbulence in the solar wind?
  • Or is the slow solar wind intrinsically intermittent from its origins?
The spatial scales of microstructures observed by STEREO/SECCHI reveal spectral steepening 
            with altitude, suggesting onset of turbulence. With 10× higher sensitivity, PUNCH will fully resolve the hinted inertial 
            range at spatial frequencies up to 5 Gm-1 (200 Mm scale) and to altitudes of 150 Gm.

Science Working Group 1-B Planned Activities

Working group 1B members
  • Track observed coronal microstructures in 3D as they form, evolve and propagate into the heliosphere.
  • Detect the onset of turbulence through spatial spectrum steepening.

Objective 1C: Alfvén Zone: Boundary of the Heliosphere

 
Background Knowledge: 

What is the Alfvén Zone?

Meridional slices colored with solar-wind speed contours 
            for MDI CR 1922 (solar minimum) and MDI CR 1958 (solar maximum. Selected three-dimensional field lines 
            (not two-dimensional projection) are shown in white, and the simulation Alfven surface is shown as 
            solid-black line. The three yellow circles represent distances of 2.5, 10, and 15r, respectively. 
            The size of the displayed box is 17.5r in each direction. From Cohen (2016)
Cohen, 2015

A natural dynamical boundary where the solar wind disconnects from the solar corona

  • Location where speed of the solar wind exceeds that of the fast MHD waves.
  • It is complex and changes with solar magnetic evolution – the “riotous torrent” seen by STEREO indicates there is likely a fractal “Zone” rather than a surface.
  • It has never been observed; models are largely unconstrained.


Science Working Group 1-C Planned Activities

Working group 1C members

Map the evolution of the Alfvén zone by measuring inbound vs. outbound features in image sequences:
  • No measurement of magnetic field is required.
  • Above the Alfvén zone all plasma and wave motion must propagate outwards. Below, motion in both directions is possible.
  • Fourier in/out filtering can be used to identify wave speed directly.

Objective 2: Dynamic Solar Wind

Objective 2A: CME 3D Trajectory, Structure, and Evolution

 
Background Knowledge: 

What are CMEs?

CME observed by Mauna Loa Solar Observatory's MK4 Coronagraph on 2003-02-18, 
            showing rotating substructure close to the Sun. PUNCH will be able to track CME substructure as they evolve and interact with 
            the ambient solar wind. (Gibson and Fan, 2008)

Tracking CMEs’ Evolving Structure in 3D

  • CME magnetic structures are known to change in the solar wind due to distortion, deflection, rotation, CME-CME interactions, and magnetic reconnection/erosion.
  • Current white-light imagers can track only the largest components of CME structure beyond 20 Rsun.
  • We thus know almost nothing about how the sub-structures of CMEs interact with each other or with the solar wind.

CME substructure observed by STEREO/SECCHI

Science Working Group 2-A Planned Activities

Working group 2A members
  • Track CMEs across the solar system in 3D to determine propagation effects including possible deflection.
  • Analyze 3D substructure evolution to relate CME origin to heliospheric structure and geoeffectiveness.
  • Measure CME chirality and relate to measured in-situ magnetic chirality.

Objective 2B: CIR Formation and 3D Dynamics

 
Background Knowledge: 

What are CIRs?

Three views of a CIR simulated by the Enlil model (Odstrcil and Pizzo, 2009)

PUNCH moves beyond a planar perspective on corotating interaction regions (CIRs)

  • Understanding CIR formation and wind/streamer interaction is critical to predicting spiral angle and impact time with the earth.
  • Shock onset in CIRs is not well understood.
  • CIRs are believed to launch strong waves near their source region as pileup begins, but measurements are sparse.
PUNCH is unique in its ability to observe both early and late manifestations of 
            CIRs, enabling analysis of their birth and evolution.

Science Working Group 2-B Planned Activities

Working group 2B members
  • Investigate and analyze early and late manifestations of CIRs from both eastward and westward directed views.

Objective 2C: Shock 3D Dynamics & Morphology

 
Background Knowledge: 

What are shocks?

PUNCH resolves shock-turbulence interaction. Shown are 3 
            Enlil models of a hypothetical CME in the solar wind on 3 different numerical grids (angular resolution 
            indicated). Yellow dot=Earth. High-resolution simulation shows instabilities at the leading edge, yielding 
            corrugated density structures.

Punch provides a cross-scale picture of shock dynamics

  • Simulations suggest that CME are strongly affected by turbulent instabilities across their shocks.
  • Corrugations of shock fronts may be responsible for the acceleration of solar energetic particles (SEPs) and type II radio bursts.
  • The current generation of coronagraphs and heliospheric imagers are not designed to capture shock evolution, interactions and possible instabilities, due to sensitivity and motion blur effects.
  • PUNCH observes global shock structure and resolves shock-turbulence interactions.
SOHO/LASCO C3 CME difference image reveals distortion at shock 
            front caused by variation in propagation speed (Tappin & Simnett, 1997)

Science Working Group 2-C Planned Activities

Working group 2C members
  • Develop a data-driven, cross-scale picture of shock formation and turbulence using spatial irregularities and brightness variations.