CaltechAUTHORS
  A Caltech Library Service

Analysis of suprathermal tails using hourly-averaged proton velocity distributions at 1 AU

Gloeckler, G. and Fisk, L. A. and Mason, G. M. and Roelof, E. C. and Stone, E. C. (2012) Analysis of suprathermal tails using hourly-averaged proton velocity distributions at 1 AU. In: Physics of the heliosphere: a 10 year retrospective. AIP Conference Proceedings. No.1436. American Institute of Physics , Melville, NY, pp. 136-143. ISBN 978-0-7354-1026-8. https://resolver.caltech.edu/CaltechAUTHORS:20160420-112640844

[img] PDF - Published Version
See Usage Policy.

1734Kb

Use this Persistent URL to link to this item: https://resolver.caltech.edu/CaltechAUTHORS:20160420-112640844

Abstract

We obtain hourly values of tail densities and of power law indices, γ, of suprathermal (speeds above 2.48 times the solar wind speed) protons from power law fits to hourly velocity distribution functions in the solar-wind-frame. ACE/SWICS and ULEIS data, which often include very low counting statistics, are used to derive hourly proton phase space densities. We find that during part of the recent deep solar minimum (first 82 days in 2009): (a) the spectrum averaged over the entire 82 day period reveals the bulk and the halo solar wind components, interstellar pickup protons (seldom seen at 1 AU), and the common Fisk and Gloeckler (F&G) suprathermal tail (v^(−5) in velocity v with an exponential rollover at some higher speed); (b) hourly values of the tail densities range from ~1•10^(−6) to ~3•10^(−3) cm^(−3) and vary by a factor of ~2-10 over periods of hours as well as in a quasi-periodic manner by factors of 20 to 50 over 4 to 10 days; (c) about 95% of the nearly 2000 hourly spectra have complex shapes and that are not power laws; (d) about half of the ~5% of the hourly spectra that are monotonically decreasing with increasing speed (e.g. exponentials or Max-wellians, or F&G) are observed at times of high tail densities (>−5•10^(−5) cm^(−3)) where the spectra have the common F&G shapes; (e) each of the six sharp (few day long), large (tail density > 5•10^(−4) cm^(−3)) increases observed during this time period is associated with solar wind compression regions; (f) the eight shocks recorded locally that were not contained in compression regions did not produce signif-icant increases in the tail densities. We conclude that during times of low solar activity the higher energy portions of locally accelerated suprathermal tail spectra are often obscured by significant contributions from remotely accelerated particles whose spectra below (1-3)•10^8 cm/s are modified (modulated) by propagation from this remote acceleration region. In those instances where strong acceleration occurs locally, the observed tail spectra have the common F&G spectral shapes.


Item Type:Book Section
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1063/1.4723601DOIArticle
http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.4723601PublisherArticle
ORCID:
AuthorORCID
Mason, G. M.0000-0003-2169-9618
Roelof, E. C.0000-0002-2270-0652
Stone, E. C.0000-0002-2010-5462
Additional Information:© 2012 American Institute of Physics. Published: 21 May 2012. This work was supported in part by NASA Grant 44A-1085637 (ACE) and by NSF Grant AGS-1043012. We thank E. Möbius and especially P. Bochsler for discussions of analysis of low count data. This paper benefited substantially from discussions held at the meetings of the International Team on -5 Tails and ACRs of the International Space Science Institute in Bern, Switzerland.
Group:Space Radiation Laboratory
Funders:
Funding AgencyGrant Number
NASA44A-1085637
NSFAGS-1043012
Subject Keywords:Particle acceleration, suprathermal tails
Series Name:AIP Conference Proceedings
Issue or Number:1436
Classification Code:PACS: 96.50.Pw, 96.50.Qx, 95.50.Ci, 96.50.Ya
Record Number:CaltechAUTHORS:20160420-112640844
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20160420-112640844
Official Citation:Analysis of suprathermal tails using hourly-averaged proton velocity distributions at 1 AU Gloeckler, G. and Fisk, L. A. and Mason, G. M. and Roelof, E. C. and Stone, E. C., AIP Conference Proceedings, 1436, 136-143 (2012), DOI:http://dx.doi.org/10.1063/1.4723601
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:66315
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:20 Apr 2016 18:35
Last Modified:09 Mar 2020 13:19

Repository Staff Only: item control page