A Whole-Heliosphere View of the Solar Wind

Hale LectureAmerican Astronomical Society

5/24/2010

Marcia NeugebauerUniversity of Arizona

A Better Title:

The Things that Happen to the Solar Wind After it Leaves the Sun

The Complex Solar Atmosphere

The Sun creates both slow and fast solar wind

But, it’s a complicated process

Model of open and closed field lines

(Wang et al., 2007)

The Source-Surface Model

(Cravens, 1997)

Major Processes in the Solar Wind

• Expansion• Collision• Reconnection• Pickup (mass loading)

• All of which leads to: – Turbulence– The interstellar medium

Expansion

First Adiabatic Invariant(Conservation of Magnetic Moment )

= mw2/2B T/B = constant

As B , expect T , and T||/ T

Magnetic moment versus distance

(Tu, 1988)

Magnetic Moment versus Distance from Sun

Tperp/Tpar vs βpar for protons < 600 /V km s

Contours of max growth rate inωcp

Proton cyclotron

Parallelfirehose

Mirror instability

Obliquefirehose

(Hellinger et al., 2009)

Proton Distribution functions

(Marsch et al., 1981)

Dis

tanc

e fr

om S

un -

->

Solar wind speed -->

The Strange Behavior of Alpha Particles

• Abundance highly variable• na/np = 0 - .03 in slow wind (~0 at HCS)• na/np = .04-.05 in fast wind• Greatly enhanced in CMEs (up to 0.40!)

• Hotter than protons• Ta/Tp = 4 to 6 in fast wind• Approaches isothermal in slow wind

• Faster than protons• Vap up to 100 km/s in fast wind • Vap -> 0 in dense, slow wind

• Anisotropic and double peaked

Vap vs Distance in Fast Wind

(Neugebauer et al., 1996)

Collision

Magnetized Plasmas Don’t Easily Mix

Note Boundaries Between Winds from Streamers & Coronal Holes

(Gosling et al., 1978)

Some Stream Interfaces are Stable over Many AU

Tangential discontinuities between plasmas fromdifferent sources

Also called the heliospheric current sheet

Heliospheric Current Sheets, Embedded in the Slow Wind, are Also Stable

Solar Maximum Solar MinimumDeclining Activity

Result of the Solar Dipole Tilt(Ballerina Skirt)

(Jokipii & Thomas, 1981)

Solar Rotation Creates Corotating Interaction Regions

(Pizzo, 1978)

Signatures of a CIR at

~5 AU

(Lazarus et al., 1999)

SI at density drop

HCS on Day 138

Coronal Mass Ejections

Interplanetary CMEs

(Richardson, 1997)

Interaction Regions at Solar Max and Min

Evolution of Interaction

regions from

1 to 60 AU

Formation of MIRs

(Wang & Richardson, 2003)

Ecliptic plane view of pileup out to 100 AU

Effect of GMIRs on Cosmic Rays

(Burlaga et al., 2003)

Anti-Correlation of Sunspots and Cosmic Rays

Reconnection

Petschek Reconnection Mechanism

(Gosling, 2005)

Reconnection Exhaust Fans

(Gosling, 2010)

Bifurcated structure

Opposite V//B

Decreased B, Increased V, T

Observed even for small angle changes

Created by turbulence?

Pickup

Pick-up is sometimes associated with

Mass Loading

Non-Solar Sources of Solar Wind Ions

• Atoms and ions– Interstellar medium– Dust– Comets– Planets

• Dust– Comets and Asteroids– Interstellar medium– Jupiter

The Pick-up Process

B

U

In solar-wind frame In inertial frame

Photoionization adds mass to wind.

Charge exchange creates fast neutral and slow ion.

Both processes provide drag on wind.

Proton Spectrum with Pickup Ions

(Gloeckler et al., 2001)

Inner Source of Pick-up Ions

(Gloeckler et al., 2001)

High-Energy Tails of H and He

(Gloeckler, 2003)

Effect of Pickup Ions on the Wind

• Photoionization adds mass • Charge exchange may conserve mass

– Results in a fast neutral atom and a slow ion

• Both processes result in:– Acceleration of slow ions up to Vsw – Drag– Hot ions with Vth Vsw

Slow-Down of Solar Wind due to Pick-up Ions

Turbulence

OGO 5Density fluctuations(Neugebauer, 1976)

f/fpg

Helios 2Field vector spectra

(Bruno & Carbone, 2005)

Power Spectra

2-D Simulation of MHD Turbulence

(Greco et al., 2010)

Field lines + Current density (gray shade)

Current sheets generated locally

Reconnection heats plasma

The End of the Road

(Approach to Alaska’s Bridge to Nowhere)

Interaction with the Interstellar Medium

Model of Outer Heliosphere

Anomalous Cosmic Rays at TS and in Heliosheath

(Courtesy A. Cummings, 2010)

“The Ribbon”

Summary

• A lot of interesting physics in the solar wind• Several unsolved issues

– Turbulent processes– Relaxation of anisotropic and multi-beams– Physics of high-energy tails– Acceleration of ACR– Prevalence of reconnection– Stability/sources of discontinuities

• Applications to many other astrophysical settings