Expansion of High Speed Solar Wind Streams from Coronal Holes through the Inner Heliosphere. (arXiv:1811.11605v1 [astro-ph.SR])

Expansion of High Speed Solar Wind Streams from Coronal Holes through the Inner Heliosphere. (arXiv:1811.11605v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Garton_T/0/1/0/all/0/1">Tadhg M. Garton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Murray_S/0/1/0/all/0/1">Sophie A. Murray</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gallagher_P/0/1/0/all/0/1">Peter T. Gallagher</a>

Coronal holes (CHs) are regions of open magnetic flux which are the source of
high speed solar wind (HSSW) streams. To date, it is not clear which aspects of
CHs are of most influence on the properties of the solar wind as it expands
through the Heliosphere. Here, we study the relationship between CH properties
extracted from AIA (Atmospheric Imaging Assembly) images using CHIMERA (Coronal
Hole Identification via Multi-thermal Emission Recognition Algorithm) and HSSW
measurements from ACE (Advanced Composition Explorer) at L1. For CH
longitudinal widths $Deltatheta_{CH}<$67$^{circ}$, the peak SW velocity ($v_{max}$) is found to scale as $v_{max}~approx~330.8~+~5.7~Deltatheta_{CH}$~km~s$^{-1}$. For larger longitudinal widths ($Deltatheta_{CH}>$67$^{circ}$), $v_{max}$ is found to
tend to a constant value ($sim$710~km~s$^{-1}$). Furthermore, we find that the
duration of HSSW streams ($Delta t$) are directly related to the longitudinal
width of CHs ($Delta t_{SW}$~$approx$~0.09$Deltatheta_{CH}$) and that their
longitudinal expansion factor is $f_{SW}~approx 1.2~pm 0.1$. We also derive
an expression for the coronal hole flux-tube expansion factor, $f_{FT}$, which
varies as $f_{SW} gtrsim f_{FT} gtrsim 0.8$. These results enable us to
estimate the peak speeds and durations of HSSW streams at L1 using the
properties of CHs identified in the solar corona.

Coronal holes (CHs) are regions of open magnetic flux which are the source of
high speed solar wind (HSSW) streams. To date, it is not clear which aspects of
CHs are of most influence on the properties of the solar wind as it expands
through the Heliosphere. Here, we study the relationship between CH properties
extracted from AIA (Atmospheric Imaging Assembly) images using CHIMERA (Coronal
Hole Identification via Multi-thermal Emission Recognition Algorithm) and HSSW
measurements from ACE (Advanced Composition Explorer) at L1. For CH
longitudinal widths $Deltatheta_{CH}<$67$^{circ}$, the peak SW velocity
($v_{max}$) is found to scale as
$v_{max}~approx~330.8~+~5.7~Deltatheta_{CH}$~km~s$^{-1}$. For larger
longitudinal widths ($Deltatheta_{CH}>$67$^{circ}$), $v_{max}$ is found to
tend to a constant value ($sim$710~km~s$^{-1}$). Furthermore, we find that the
duration of HSSW streams ($Delta t$) are directly related to the longitudinal
width of CHs ($Delta t_{SW}$~$approx$~0.09$Deltatheta_{CH}$) and that their
longitudinal expansion factor is $f_{SW}~approx 1.2~pm 0.1$. We also derive
an expression for the coronal hole flux-tube expansion factor, $f_{FT}$, which
varies as $f_{SW} gtrsim f_{FT} gtrsim 0.8$. These results enable us to
estimate the peak speeds and durations of HSSW streams at L1 using the
properties of CHs identified in the solar corona.

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