Historical Perspective from Helios

HistoricalHistorical PerspectivePerspective FromFrom HeliosHelios

IanIan G.G. RichardsonRichardson

CodeCode 672,672, NASA/GoddardNASA/Goddard SpaceSpace FlightFlight CenterCenter andand GPHI/DepartmentGPHI/Department ofof Astronomy,Astronomy, UniversityUniversity ofof Maryland,Maryland, CollegeCollege ParkPark

Gerd Wibberenz 15 November, 1930 – 28 May, 2017

Near Bozemann, Montana, 1996 Orbits of Helios 1 and 2

US-German Mission

Orbit ~0.3 to ~1 AU

Helios 2 orbit major axis leads Helios 1 by ~40° longitude

~12 Solar constants at 0.29 AU;

Maximum Speed: 252,000 km/hr (Helios 2)

(cp: PSP 724,000 km/hr)

HELIOS Spacecraft HELIOS 1 Launch

Helios 1 Launch: December 10, 1974 Spin axis perpendicular to Deactivated: February 18, 1985 the ecliptic Helios 2 Launch: January 15, 1976 Deactivated: December 23, 1979 Sloping side walls, reflective solar cells and Contemporary with Skylab, IMPs 7/8, ISEE- mirrors, to reduce thermal 3 (L1), Pioneer 10/11, Voyager 1/2 (Outer load near the Sun heliosphere); Spanned solar cycle 21. Experiments on Board the HELIOS Spacecraft E1: Plasma Detector and Analyzer (Rosenbauer; MPI-Aeronomie)

E2: Fluxgate Magnetometer for Field Fluctuations (Neubauer; University of Cologne) E3: Fluxgate Magnetometer for Average Fields (Ness; NASA Goddard SFC) E4: Search Coil Magnetometer (Neubauer; University of Cologne)

E5: Plasma and Radio Wave Spectrometer (Gurnett; University of Iowa)

E6: Cosmic Ray Telescope (Kunow; Christian-Albrecht University, Kiel, Germany) E7: Cosmic Ray Telescopes, X-Ray Monitor (Trainor; NASA Goddard SFC) Identical/similar to instruments on IMPs 7/8, Pioneer 10/11, Voyager 1/2 E8: Detectors for Low Energy Cosmic Rays (Keppler; MPI-Aeronomie)

E9: Zodiacal Light Photometer (Leinert; MPI-Astronomie)

E10: Micrometeorite Detector and Analyzer (Fechtig; MPI-Kernphysik) From “10 Jahre HELIOS” (1984)

Vp 1) Are transitions in solar wind properties Helios 1 Launch (e.g., speed) relatively gradual near the np Sun and steepen in the heliosphere due Tp to dynamical stream interactions?

2) Are the transitions relatively abrupt near the Sun (distinct slow/fast stream sources) and then relax/are eroded in the heliosphere?

<= Helios 1 observations during 5 solar rotations after launch.

0.31 AU Leading edges of corotating streams tend to steepen closer to the Sun

Suggests that hypothesis (2) is correct.

Differences in many solar wind properties reflect their origin as slow/fast solar wind at the Sun Rosenbauer et al., 1977 HELIOS Longitudinal Speed Gradients at High Speed Stream Leading Edges vs. Heliocentric Distance

Speed gradient, km/s per degree Individual Summary of Observations Observations

Radial Distance 0.3-1 AU Schwenn, 1990

Largest speed gradients are within ~0.5 AU of the Sun

Remarkable Differences in the Solar Wind Speed Structure as the HELIOS Spacecraft Separated in Heliolatitude in Early 1976

Separation > 5°

Schwenn et al., 1981

Latitudinal Structure is Related to the Coronal Hole Configuration at the Sun

Vsw

Coronal Coronal Hole Brightness

High and lower resolution simulations of the radial Schwenn et al., 1978 solar wind speed at 30 Rs (Riley et al., 2012)

B Examples of solar wind proton velocity distributions as a function of increasing solar wind speed (left 0.96 AU 360 km/s 0.95 AU 474 km/s 0.98 AU 717 km/s to right) and decreasing heliocentric distance (top to bottom)

Cuts are in the V-B plane. 0.42 AU 359 km/s 0.50 AU 463 km/s 0.54 AU 618 km/s (Marsch et al., 1982)

0.32 AU 360 km/s 0.39 AU 0.29 AU 781 km/s 494 km/s New HELIOS Solar Wind Database (David Stansby, Imperial College)

The new solar wind data set includes the perpendicular and parallel proton temperatures, which show some significant differences with the previous single temperature.

See Poster!

Derived from data in the HELIOS plasma and magnetic field archive compiled by Chadi Salem (http://helios-data.ssl.berkeley.edu/) See related poster! ftp://apollo.ssl.berkeley.edu/pub/helios- data/E1_experiment/New_proton_corefit_data_2017/ Configuration of Interplanetary Coronal Mass Ejection and Upstream shock

Shock

Sheath ICME

Zurbuchen & Richardson, 2006 “Confident Associations” Between Two Solwind CMEs and Two Shocks (+ICMEs) at Helios 1 in May, 1981 Solwind Coronagraph: Two CMEs above East Limb

Helios 1 Orbit (0.3-1 AU), Helios 1 Shock Shock V 1979-1982 Solar Wind, n 0.66 AU, ICME T E95º ICME p

Solwind Sheeley et al., 1985 Coronagraph “Solar Orbiter will make comprehensive in-situ measurements of the fields and plasmas (particularly composition) of ICMEs following their release and, critically, prior to their processing during propagation in the heliosphere.”

Solar Orbiter - Exploring the Sun-heliosphere Connection, ESA/SRE(2009)5, December 2009

Interaction of Two ICMEs Observed at ~0.3 AU Interaction of two shocks/ICMEs

Clearly not pristine ICMEs!

Shock of second ICME is running into the first ICME

Shock Sh ICME ICME

20 hours

ICME-Driven Shock Speeds at < 1.0 AU Inferred From Doppler Scintillation and/or Helios Observations

Lines join the same event ●= Helios

Shocks from Filament Eruptions

Cane et al. 1986; Also Woo at al., 1985; Woo, 1988

Clear deceleration/acceleration within 0.3 AU => ICMEs observed by SO are unlikely to be “pristine”, little effected by interaction with the solar wind. Radial Dependence of ICME Parameters at 0.3- 1.0 AU (Helios 1 and 2)

Results from Richardson, 2014 and Forsyth et al., 2006; See also Bothmer and Schwenn, 1998; Liu et al., 2005; Wang et al., 2005; Totten et al., 1995... The Structure and Origin of Magnetic Clouds in the Solar Wind (Bothmer and Schwenn, 1998)

Used HELIOS observations of magnetic clouds to suggest a relationship between the configuration of flux ropes in magnetic Li et al., 2011 clouds and the structure of filaments at the Observed solar cycle Sun. variation in the rates of NS and SN magnetic clouds Solar cycle variation in the fraction of south turning north vs. north turning south flux rope fields. Nearby Spacecraft May Observe Different Magnetic Field Structures in the Same ICME Helios 1: Magnetic Cloud Helios 2: Non-cloud ICME Shock ICME Shock ICME B

θ B

φ B

T p Filament eruption at ~E50º

β Helios 1, near n eruption longitude, saw a MC; V Helios 2 saw a non-cloud ICME Cosmic Rays

Cane, Richardson & Wibberenz, 1997 ICME Configurations Inferred From Combining Observations from HELIOS and Other Spacecraft

Loop structure of a magnetic cloud

Interaction of three shocks and ICMEs (April, 1979)

Burlaga et al., 1990

Burlaga et al., 1987

Many Multi-Spacecraft Observations of Solar Energetic Particle Events Using HELIOS and Other Spacecraft

Trainor and Van Hollebeke, 1984 Kallenrode et al., 1993

Radial and Longitudinal Solar Energetic Particle Variations Based on HELIOS and IMP 8 Observations (Lario et al., 2006)

Fit to:

j=j (R/a)nexp(-k(φ-φ )2) o o

e.g., Peak intensity at 27-37 MeV:

~R-1.95±0.25

“Extreme Propagation” of SEP Events (Extended in Longitude, Rapid Propagation to Poorly-Connected Spacecraft; Cliver et al., 1995)

“Coronal propagation” speeds ~250-500 km/s

Suggestive of association with propagating shocks in the corona (e.g., Morton waves?)

Multi-Spacecraft Observations of Solar Flare Particles in the Inner Heliosphere (Wibberenz and Cane, 2006)

Helios 1 e-, He (0.31 AU)

IMP 8 e-, He

Multiple impulsive SEP Impulsive electron events can extend further events are evident in longitude than suggested by single point closer to the Sun that observations are not resolved at 1 AU. Tracking Impulsive Event Electrons by Triangulation of a Type III Radio Burst With HELIOS and ISEE-3

Gurnett and Anderson, 1984 Kayser and Stone, 1984

Association of Recurrent Particle Events with High-Speed Streams From Coronal Holes

1 solar rotation IMP 8

Mason and Sanderson, 1999, adapted from Scholer et al., 1979 Positive Radial Gradient in Recurrent Event Intensity at 0.3 - ~4 AU (Helios/IMP/Pioneer) (Van Hollebeke et al., 1978)

Acceleration region is NOT at the Sun.

Pioneer 11 Interplanetary ~100%/AU acceleration at a few AUs IMP suggested.

Helios

Use of the HELIOS E6 Plastic Anti-coincidence Guard as a Galactic Cosmic Ray Detector

Plastic Anti-Coincidence Guard GCR decrease at a stream interface

Richardson, 2004

Multi-Spacecraft Observations of Forbush Decreases Using HELIOS E6 and IMP-8 GME Anti-coincidence Guard Counting Rates

Helios 2, 0.4 AU, W5º

IMP 8, 1 AU,

Smaller Fd

(Count rates normalized)

Richardson and Cane, 2011, after Cane, 2000, Zurbuchen and Richardson, 2006 Galactic Cosmic Ray Intensities at HELIOS and Pioneer 10 (at 12- 23 AU) in 1976-1980 (ascending phase of solar cycle 21)

Pioneer 10 Positive radial gradient;

Structures observed first at HELIOS then at HELIOS Pioneer (outward propagating)

Trainor and Van Hollebeke, 1984)

Observing Solar Wind Density Structures With the HELIOS Zodiacal Light Photometers

Jackson, 1991 => SMEI, STEREO heliospheric imagers, etc

Summary

The HELIOS spacecraft made pioneering observations of the inner heliosphere in to ~0.29 AU that are invaluable for planning for SO and PSP.

They hint of interesting latitudinal variations that will be better studied with SO with its higher incination orbit.

Sharper distinctions between solar wind types, rapid decelerations of fast ICMEs at smaller radial distances, and new details of the acceleration and propagation of SEPs, will likely be observed by PSP.