Results 151 to 160 of about 1,446 (180)

Coronal holes and the solar wind

2002
Abstract Coronal holes are the darkest regions of the ultraviolet and X-ray Sun, both on the disk and above the limb. Coronal holes are associated with rapidly expanding open magnetic fields and the acceleration of the high-speed solar wind. This paper reviews measurements of the plasma properties of coronal holes and how these measurements have been
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Polar coronal holes and solar cycles

Solar Physics, 1979
The relationship between the geomagnetic activity of the three years preceding a sunspot minimum and the peak of the next sunspot maximum confirms the polar origin of the solar wind during one part of the solar cycle. Pointing out that the polar holes have a very small size or disappear at the time of the polar field reversal, we suggest a low latitude
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Observations of Doppler Shifts in a Solar Polar Coronal Hole

The Astrophysical Journal, 1997
Using observations from the Solar Ultraviolet Measurements of Emitted Radiation experiment flown on the Solar and Heliospheric Observatory spacecraft, we have measured Doppler wavelength shifts in the north polar coronal hole in the 1032 and 1038 A emission lines of O VI and the 1036 and 1037 A emission lines of C II relative to chromospheric emission ...
Warren, H., Mariska, J., Wilhelm, K.
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Acceleration of the High Speed Solar Wind in Coronal Holes

Space Science Reviews, 1999
We outline a theory for the origin and acceleration of the fast solar wind as a consequence of network microflares releasing a spectrum of high frequency Alfven waves which heat (by cyclotron absorption) the corona close to the Sun. The significant features of our model of the fast wind are that the acceleration is rapid with the sonic point at around ...
Axford, W., McKenzie, J., Sukhorukova, G., Banaszkiewicz, M., Czechowski, A., Ratkiewicz, R.   +5 more
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Models for Solar Coronal Holes.

1978
Abstract : This report summarizes several investigations of coronal holes and quiet regions. Temperature-density models for those regions have been derived from EUV observations. It is found that the coronal temperature, density, and temperature gradient are lower in coronal holes than in quiet regions.
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The effects of coronal holes on the propagation of solar energetic protons

Radiation Measurements, 1999
The accurate prediction of the start of a Solar Energetic Particle Event (SEP) is a high priority for space weather forecasters. The Space Environment Center (SEC) has recorded parameters related to SEPs since 1976, and that list includes a total of 134 events for the period 1976-1997.
J M, Kunches, R D, Zwickl
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Coronal Holes in Solar Cycles 21 to 23

Solar Physics, 2013
We present identifications of coronal holes (CHs) from observations in the He i 10 830 A line made at Kitt Peak Observatory (from 1975 to 2003) and in the EUV 195 A wavelength with SOHO/EIT (from 1996 to 2012). To determine whether a feature is a CH we have developed semi-automatic techniques for delineating CH borders on synoptic charts and for ...
A. Tlatov, K. Tavastsherna, V. Vasil’eva   +2 more
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Solar cycle dependence of polar coronal holes

Solar Physics, 1993
A study has been made of the polar coronal holes in relation to solar cycle activity. Important results obtained are: (i) the peak of the frequency distribution of coronal hole size shifts towards lower values as the solar cycle advances towards maximum, this being true for both the north and south polar holes, (ii) coronal hole size decreases with the
T. K. Das, T. N. Chatterjee, A. K. Sen
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Coronal Holes and Solar Mass Loss

1981
During the declining phase of solar activity, and possibly at other phases, solar mass loss occurs in the form of high speed streams in the solar wind. These streams originate in low density, low temperature coronal regions, called “holes.” The physical properties of the wind streams and the holes will be discussed.
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A 600-day periodicity in solar coronal holes

Nature, 1992
CORONAL holes are large-scale structures of lower density and temperature in the solar corona. They appear as large dark features in X-ray and radio images, and as bright areas in infrared He I images of the Sun. The longest series of data is the He I (10,830 A) observations published within Hα synoptic charts1.
P. S. Mclntosh, R. J. Thompson, E. C. Willock   +2 more
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