932 research outputs found
Deciphering Solar Magnetic Activity: On Grand Minima in Solar Activity
The Sun provides the energy necessary to sustain our existence. While the Sun
provides for us, it is also capable of taking away. The weather and climatic
scales of solar evolution and the Sun-Earth connection are not well understood.
There has been tremendous progress in the century since the discovery of solar
magnetism - magnetism that ultimately drives the electromagnetic, particulate
and eruptive forcing of our planetary system. There is contemporary evidence of
a decrease in solar magnetism, perhaps even indicators of a significant
downward trend, over recent decades. Are we entering a minimum in solar
activity that is deeper and longer than a typical solar minimum, a "grand
minimum"? How could we tell if we are? What is a grand minimum and how does the
Sun recover? These are very pertinent questions for modern civilization. In
this paper we present a hypothetical demonstration of entry and exit from grand
minimum conditions based on a recent analysis of solar features over the past
20 years and their possible connection to the origins of the 11(-ish) year
solar activity cycle.Comment: 9 pages - submitted to Frontiers in Solar and Stellar Physic
The Inconvenient Truth About Coronal Dimmings
We investigate the occurrence of a CME-driven coronal dimming using unique
high resolution spectral images of the corona from the Hinode spacecraft. Over
the course of the dimming event we observe the dynamic increase of non-thermal
line broadening in the 195.12Angstrom emission line of Fe XII as the corona
opens. As the corona begins to close, refill and brighten, we see a reduction
of the non-thermal broadening towards the pre-eruption level. We propose that
the dynamic evolution of non-thermal broadening is the result of the growth of
Alfven wave amplitudes in the magnetically open rarefied dimming region,
compared to the dense closed corona prior to the CME. We suggest, based on this
proposition, that, as open magnetic regions, coronal dimmings must act just as
coronal holes and be sources of the fast solar wind, but only temporarily.
Further, we propose that such a rapid transition in the thermodynamics of the
corona to a solar wind state may have an impulsive effect on the CME that
initiates the observed dimming. This last point, if correct, poses a
significant physical challenge to the sophistication of CME modeling and
capturing the essence of the source region thermodynamics necessary to
correctly ascertain CME propagation speeds, etc.Comment: 4 pages, 3 figures, submitted to ApJ - rerouted to ApJ
The Spectroscopic Footprint of the Fast Solar Wind
We analyze a large, complex equatorial coronal hole (ECH) and its immediate
surroundings with a focus on the roots of the fast solar wind. We start by
demonstrating that our ECH is indeed a source of the fast solar wind at 1AU by
examining in situ plasma measurements in conjunction with recently developed
measures of magnetic conditions of the photosphere, inner heliosphere and the
mapping of the solar wind source region. We focus the bulk of our analysis on
interpreting the thermal and spatial dependence of the non-thermal line widths
in the ECH as measured by SOHO/SUMER by placing the measurements in context
with recent studies of ubiquitous Alfven waves in the solar atmosphere and line
profile asymmetries (indicative of episodic heating and mass loading of the
coronal plasma) that originate in the strong, unipolar magnetic flux
concentrations that comprise the supergranular network. The results presented
in this paper are consistent with a picture where a significant portion of the
energy responsible for the transport of heated mass into the fast solar wind is
provided by episodically occurring small-scale events (likely driven by
magnetic reconnection) in the upper chromosphere and transition region of the
strong magnetic flux regions that comprise the supergranular network.Comment: 25 pages, accepted to appear in the Astrophysical Journal. Supporting
movies can be found in http://download.hao.ucar.edu/pub/mscott/papers/ECH
- …