Observations of spectral shapes of suprathermal H +, He + and He ++ G. Gloeckler Department of Atmospheric, Oceanic and Space Sciences University of Michigan, Ann Arbor, MI Workshop on Inner Heliosphere Physics ACE, Wind SOHO and STEREO in-situ investigations Breakout Session D Pickup Ions and Building the Energetic Particle Reservoir Nonantum Resort, Kennebunkport, ME June 8-11, 2010

Summary of observations of spectral shapes of suprathermal protons, He + and He ++ Presented by Decker, Gloeckler, Hill and Popecki at the Second meeting of the ISSI International Team on Tails and ACRs International Space Science Institute, Bern, Switzerland May 25-29, 2010

Summary of observations of suprathermal tails by Decker (V1, V2 ), Gloeckler (ACE, Ulysses ), Hill (Cassini ) and Popecki (STEREO ) In the majority of cases observed suprathermal tails are -5 (-1.5) power laws with a rollover at some higher speed (energy) that is variable (we call these the common spectra) These common spectra are observed for H +, He + and He ++ when no local shocks are observed (quiet times and polar coronal holes) during disturbed periods upstream and especially downstream of shocks in the heliosheath Deviations from the common spectral shape are observed particularly in disturbed conditions. However, in all cases that can be studied in detail, the deviations are accompanied by strong anisotropies, even at low energies, suggesting that the particles are accelerated elsewhere and propagate to the observing site. Anisotropic velocity distributions in the solar wind frame will affect spectral shapes and full, instrument-dependent Compton-Getting are required to yield the true solar wind frame spectra

Suprathermal Tails observed in Large Spatially Homogenous Regions in the Solar System Decker, Roelof, Krimigis and Hill JHU/APL V1 and V2 spectra are identical power law with spectral index –1.45±0.05 HeliosheathPolar Coronal Hole The red curve is a -5 power law with a gentle exponential rollover (e-folding speed of w = 3)

Suprathermal Tails observed in Large Spatially Homogenous Regions in the Solar System In the solar wind frame the suprathermal tail spectrum has the form f (v ) = f o v –5 exp[–(v/v o ) 1.26 ], where v o = cm/s w ≈ 40 Pickup protons GCRs Quiet times at 1 AU Rollover could be exponential or power steeper power law 15

Power Law Fits to Cassini CHEMS Suprathermal (flux vs. energy) Spectra in the SW Frame He + H+H+ Matt Hill – Interim Analysis 2010 May 25 He ++

Suprathermal Tails observed in the Disturbed Solar Wind Upstream and downstream of a CIR reverse shock During the 5-day time period between two forward shocks In the solar wind frame the suprathermal tail spectra have the form f (v ) = f o v –5 exp[–(v/v o ) 1.2 ], where v o = cm/s (~1.7 MeV) Note: for compression ratio r = 3.6  dsh = 4.15 Horizontal error bars indicate systematic uncertainties in transforming from the spacecraft to solar wind frames (which depend on the spin- wind angle and anisotropies in the solar wind frame)

Conclusions The most common spectral shape for the suprathermal particles, found in many disparate plasma conditions, is a power law with spectral index of -5 and a gradual exponential rollover, with a varying rollover energy. When statistics permit, the common spectral shape is observed on time scales ~1 hour. The common spectral shape occurs in regions for which no shocks are present, indicating that the principle acceleration mechanism for the common spectral shape cannot be diffusive shock acceleration. The common spectral shape occurs downstream of all shocks we studied, independent of the shock strength. Deviations from the common spectral shape are observed particularly in disturbed conditions. However, in all cases that can be studied in detail, the deviations are accompanied by strong anisotropies, even at low energies, suggesting that the particles are accelerated elsewhere and propagate to the observing site. The data are consistent with the common spectral shape being the source spectrum, and deviations from the common spectral shape due to propagation effects.

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