Evolution of the heliospheric magnetic field Space and Atmospheric Electricity group Department of Meteorology Evolution of the heliospheric magnetic field Mathew Owens

HMF: big Questions (that I probably won’t answer today) What are the physical processes by which the the heliospheric magnetic field (HMF) evolve? What is the relation to solar wind release and acceleration? How do long- and short- time scales couple, and does this result in any long-term predictability? How can these processes be used to diagnose the solar dynamo? What are the implications for stellarspheres and stellar winds? The HMF magnetically couples the Sun and planets, channels SEPs, shields from GCRs and can be reconstructed over millennia, providing the strongest constraints on the solar dynamo

Context: HMF variability

3D structure of HMF ULysses

PFSS solutions Magnetic field polarity at coronal source surface

OPEN SOLAR FLUX FU=  |BR| r2 cos() dd Flux threading the coronal source surface FU=  |BR| r2 cos() dd +/2 2 -/2 0 “closed” field line “open” field lines e.g., Balogh et al., 1995

Open solar flux view of the ecliptic OSF Total HMF

In-situ measurements Owens et al., JGR, 2008

Inner Heliosphere Sampling A strong case for orbiter (% Probe)!

Space-age variations

Suprathermal electrons Tracers of HMF topology Solar wind electrons consist of a thermal core, which accounts for most of the electrons by number, and a suprathermal tail. The suprathermal population is highly anisotropic with regards to the magnetic field direction. Strahl and halo. [Hammond et al., 1996] [Stverak et al., 2009]

OSF evolution relating in situ and remote observations Owens and Crooker, JGR, 2006 Sheeley et al., 2007

Closed HMF Primarily ICMEs aT 1 AU Composition

Suprathermal electron scattering see poster by georgina graham

Non-CME closed flux? Closed flux outside CMEs close to the Sun (but not identifiable at1 AU)? HELIOS data (e.g., Owen, Mattini, Graham, Stansby, Salem) Unique, but not ideal for these kinds of study Remote observations of rising loops? Sun

HMF inversions in-situ observations

Aside: Flux excess [Lockwood et al., 2009] Flux at R – Flux at L1 R [AU] [Lockwood et al., 2009]

Coronal source c.f. “Q parameter”

Pseudostreamers interchange reconnection and the slow wind

Slow wind source Latitudes accessible to orbiter [Owens et al., 2014]

Orbiter? Coordinated observations… ….Between Orbiter instruments: Remote sensing and in situ How “representative” is a single-point measurement? How can we interpret 2D images of 3D structures? …With other spacecraft (Probe, DSCOVR) Remote and in-situ obs Mulitpoint in-situ obs Mulitploint remote obs Sample range of heliocentric distances Disentangle structures of solar origin and those formed in transit High latitude (>20 degrees) observations

Extra slides

HMF inversions e.g., Crooker et al., 2004

Photospheric flux Top: e.g., David Hathaway, MSFC Top plot. Each vertical slice is the a magnetogram, averaged over all longitude and binned by latitude Introduce idea of solar wind dragging solar field out into interplanetary space: The heliosphere

Modelling the corona Left: Riley et al Modelling the corona Left: Riley et al., 2006 Right: Eclipse photograph, Carlos & Espenak, 1995.

ULYSSES |BR| ecliptic d R Balogh et al., 1995; Smith et al., 2001; Lockwood et al., 2000 d |BR| ecliptic R |BRE| Ulysses showed that everywhere |BR|(d/R)2 = |BRE| Thus total unsigned magnetic flux leaving the sun = 4R2 |BRE|

Flux ropes Q: Does the CME flux rope form in transit or exist prior to launch? CME initiation mechanisms SWx forecasting implications Q: How much flux/helicity is transported from the corona by CMEs? Role of CMEs in solar cycle evolution of heliosphere Compare flux/helicity in AR with that in ICME. Compare composition with ICME with coronal flux systems

Non-cloud icmes Q: What are non-flux rope ICMEs? Eruption without FR? FR destroyed in transit? FR not encountered? Is there a increase in the fraction of non-FR ICMEs with distance? Do structured CMEs result in FRs in situ? Image from cane 2012 on forbush decreases

Large-scale structure ICMEs remain (partly) magnetically connected to Sun Critical for the “open flux” contribution of CMEs Q: Is connectivity affected by pre-launch topology? Q: What is the extent of the “identifiable” ICME? Q: Over what length-scales are similar signatures seen?

Small-scale transients Q: How do “blobs” relate to CMEs? Spectrum of similar phenomenon or fundamentally different beasts? What do “blobs” look like before solar wind processing? Are small flux ropes present that can’t survive to 1 AU? Do they contain counterstreaming electrons which are subsequently lost?

ICME kinematics Q: To what extent are CMEs deflected from radial propagation? Primarily in corona by CH flux? What about by fast wind in heliosphere? True centre of mass deflection or distortion of CME edges? Q: Where and how does the bulk of ICME deceleration occur? CMEs tend towards solar wind speed But evidence of deceleration in HI field of view is weak (or model dependent).

Shocks and SEPs Q: What controls SEP production? Fundamental difference in impulsive and gradual SEPs? Properties of near-Sun shocks Existence of suprathermal seed particles Transport/release of SEPs Shock connectivity

Requirements (?) “Low” resolution (~minutes) in situ data (plasma, B, suprathermal electrons, composition) sufficient for most “transient” science? Low res data throughout mission (including cruise) preferable to high resolution data over limited periods Exceptions: Shocks. Blobs. How to predict timing of these? Radio-based event trigger? Streamer belt encounter? High cadence in situ observations need not be coordinated with high cadence remote sensing? Schedule remote sensing observations for quadrature with L1, etc. How can we address the questions I’ve mentioned? What are the major science questions I omitted?