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Title: TRACKING THE SOLAR CYCLE THROUGH IBEX OBSERVATIONS OF ENERGETIC NEUTRAL ATOM FLUX VARIATIONS AT THE HELIOSPHERIC POLES

Abstract

With seven years of Interstellar Boundary Explorer ( IBEX ) observations, from 2009 to 2015, we can now trace the time evolution of heliospheric energetic neutral atoms (ENAs) through over half a solar cycle. At the north and south ecliptic poles, the spacecraft attitude allows for continuous coverage of the ENA flux; thus, signal from these regions has much higher statistical accuracy and time resolution than anywhere else in the sky. By comparing the solar wind dynamic pressure measured at 1 au with the heliosheath plasma pressure derived from the observed ENA fluxes, we show that the heliosheath pressure measured at the poles correlates well with the solar cycle. The analysis requires time-shifting the ENA measurements to account for the travel time out and back from the heliosheath, which allows us to estimate the scale size of the heliosphere in the polar directions. We arrive at an estimated distance to the center of the ENA source region in the north of 220 au and in the south a distance of 190 au. We also find a good correlation between the solar cycle and the ENA energy spectra at the poles. In particular, the ENA flux for the highest IBEX energy channel (4.3more » keV) is quite closely correlated with the areas of the polar coronal holes, in both the north and south, consistent with the notion that polar ENAs at this energy originate from pickup ions of the very high speed wind (∼700 km s{sup −1}) that emanates from polar coronal holes.« less

Authors:
;  [1];
  1. University of Montana, Missoula, MT 59812 (United States)
Publication Date:
OSTI Identifier:
22661454
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 833; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCURACY; CORRELATIONS; ENERGY SPECTRA; HELIOSPHERE; KEV RANGE; MAGNETOHYDRODYNAMICS; PLASMA PRESSURE; SOLAR CYCLE; SOLAR WIND; SPACE VEHICLES; SUN; TIME RESOLUTION; VARIATIONS

Citation Formats

Reisenfeld, D. B., Janzen, P. H., Bzowski, M., E-mail: dan.reisenfeld@umontana.edu, E-mail: paul.janzen@umontana.edu, E-mail: bzowski@cbk.waw.pl, and others, and. TRACKING THE SOLAR CYCLE THROUGH IBEX OBSERVATIONS OF ENERGETIC NEUTRAL ATOM FLUX VARIATIONS AT THE HELIOSPHERIC POLES. United States: N. p., 2016. Web. doi:10.3847/1538-4357/833/2/277.
Reisenfeld, D. B., Janzen, P. H., Bzowski, M., E-mail: dan.reisenfeld@umontana.edu, E-mail: paul.janzen@umontana.edu, E-mail: bzowski@cbk.waw.pl, & others, and. TRACKING THE SOLAR CYCLE THROUGH IBEX OBSERVATIONS OF ENERGETIC NEUTRAL ATOM FLUX VARIATIONS AT THE HELIOSPHERIC POLES. United States. doi:10.3847/1538-4357/833/2/277.
Reisenfeld, D. B., Janzen, P. H., Bzowski, M., E-mail: dan.reisenfeld@umontana.edu, E-mail: paul.janzen@umontana.edu, E-mail: bzowski@cbk.waw.pl, and others, and. Tue . "TRACKING THE SOLAR CYCLE THROUGH IBEX OBSERVATIONS OF ENERGETIC NEUTRAL ATOM FLUX VARIATIONS AT THE HELIOSPHERIC POLES". United States. doi:10.3847/1538-4357/833/2/277.
@article{osti_22661454,
title = {TRACKING THE SOLAR CYCLE THROUGH IBEX OBSERVATIONS OF ENERGETIC NEUTRAL ATOM FLUX VARIATIONS AT THE HELIOSPHERIC POLES},
author = {Reisenfeld, D. B. and Janzen, P. H. and Bzowski, M., E-mail: dan.reisenfeld@umontana.edu, E-mail: paul.janzen@umontana.edu, E-mail: bzowski@cbk.waw.pl and others, and},
abstractNote = {With seven years of Interstellar Boundary Explorer ( IBEX ) observations, from 2009 to 2015, we can now trace the time evolution of heliospheric energetic neutral atoms (ENAs) through over half a solar cycle. At the north and south ecliptic poles, the spacecraft attitude allows for continuous coverage of the ENA flux; thus, signal from these regions has much higher statistical accuracy and time resolution than anywhere else in the sky. By comparing the solar wind dynamic pressure measured at 1 au with the heliosheath plasma pressure derived from the observed ENA fluxes, we show that the heliosheath pressure measured at the poles correlates well with the solar cycle. The analysis requires time-shifting the ENA measurements to account for the travel time out and back from the heliosheath, which allows us to estimate the scale size of the heliosphere in the polar directions. We arrive at an estimated distance to the center of the ENA source region in the north of 220 au and in the south a distance of 190 au. We also find a good correlation between the solar cycle and the ENA energy spectra at the poles. In particular, the ENA flux for the highest IBEX energy channel (4.3 keV) is quite closely correlated with the areas of the polar coronal holes, in both the north and south, consistent with the notion that polar ENAs at this energy originate from pickup ions of the very high speed wind (∼700 km s{sup −1}) that emanates from polar coronal holes.},
doi = {10.3847/1538-4357/833/2/277},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 833,
place = {United States},
year = {2016},
month = {12}
}