Search Publications
Observations of ultraviolet emission lines in solar coronal holes on the disk with SUMER on SOHO
Dammasch, Ingolf E.; Wilhelm, Klaus; Xia, Lidong
The Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrograph and other instruments on the Solar and Heliospheric Observatory (SOHO) have observed many solar polar coronal holes (PCHs) during the minimum of the sunspot cycle in 1996 and 1997. Based on the results obtained for PCHs, investigations of near-equatorial coronal holes (EC…
Constraints on ion outflow speeds and electron distribution function in the corona derived from sumer electron temperatures and SWICS ion fractions
Esser, R.; Edgar, R. J.
It has been a puzzle for quite some time that spectroscopic measurements in the inner corona indicate electron temperatures far too low to produce the ion fractions observed in the in situ solar wind. In the present paper we show that in order to reconcile the two sets of measurements, a number of conditions have to exist in the inner corona: 1) t…
Sumer observations of solar transition region structures and dynamics
Dammasch, Ingolf E.; Wilhelm, Klaus
Several raster scans of the UV/EUV spectrometer SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on SOHO (the Solar and Heliospheric Observatory of ESA and NASA) in quiet-Sun regions were used to study the region between the chromosphere and the corona, i.e., the transition region with a temperature range between ≈ 30 000 K and 400 000 …
Characterization of the polar plumes from high cadence LASCO-C2 observations
Llebaria, A.; Lamy, P.; Thernisien, A.
In order to understand the spatio-temporal characteristics of polar plumes, we analyzed a sequence of continuous observations obtained with the SOHO/LASCO-C2 coronagraph over a period of 3 days with a time resolution of 10 minutes. We generated the time intensity diagram (TID) where the radiance of the plumes is displayed as a function of their an…
The rising phase of solar cycle 23 as seen by Ulysses
Marsden, R. G.
Following its highly successful survey of the latitudinal structure of the heliosphere under near-minimum solar activity conditions, the Ulysses space-probe embarked in 1998 on a second out-of-ecliptic orbit of the Sun. This second high-latitude survey will culminate near solar maximum, offering a unique opportunity to study the polar regions of t…
A discussion of recent evidence for solar irradiance variability and climate
Kuhn, Jeff; Fröhlich, Claus; Sofia, Sabatino +2 more
One of the over-arching questions, among others, to be addressed by studying Sun-Earth connections is: "Is the climate changing in a way we can understand and predict?" The Earth's climate is the result of a complex and incompletely understood system of external inputs and interacting parts. Climate change can occur over a range of time scales, ma…
The acceleration and release of solar energetic particles in events from April 20 - May 9, 1998
Simnett, G. M.
The most active period in X-rays of the current solar cycle to date (August 1998) occurred from April 23 - May 9, 1998, when there were four X-class flares and two more which exceeded M6. All were likely to have been from AR 8210 (two were occulted and thus didn't have positive identification, although the coronal Yohkoh images were consistent wit…
Non-axisymmetrical distributions of solar magnetic activity and irradiance
Benevolenskaya, E. E.
Active longitudes play an important role in spatial organization of solar activity. These zones associated with complexes of solar activity may persist for 20-40 consecutive rotations, and may be caused by large-scale non-axisymmetrical components of the global magnetic field. These zones of the field concentrations are 20°-40° wide and during sub…
Solar activities associated with interplanetary magnetic flux ropes
Marubashi, K.; Watanabe, T.; Watari, S.
A smoothly rotating interplanetary magnetic field with duration on the order of a day has been detected in solar wind observations. This structure is called an "interplanetary magnetic flux rope." Here, we studied the relationship between interplanetary magnetic flux ropes observed by Ulysses when it was near the solar limb and coronal mass ejecti…
Coronal mass ejections and emerging flux
Chen, P. F.; Shibata, K.; Fang, C. +1 more
This paper reviews our recent progress in the numerical study of coronal mass ejections (CMEs) based on flux rope model, which shows that when the reconnection-favored emerging flux appears either within or on the outer edge of the filament channel, the flux rope would lose its equilibrium, and be ejected, while a current sheet is formed below the…