Search Publications
FIP Effect in the Solar Upper Atmosphere: Spectroscopic Results
Feldman, U.
Recent spectroscopic measurements from instruments on the Solar and Heliospheric Observatory (SOHO) find that the coronal composition above a polar coronal hole is nearly photospheric. However, similar SOHO observations show that in coronal plasmas above quiet equatorial regions low-FIP elements are enhanced by a factor of ≈ 4. In addition, the pr…
Fractionation of SI, NE, and MG Isotopes in the Solar Wind as Measured by Soho/Celias/MTOF
Bochsler, P.; Geiss, J.; Galvin, A. B. +9 more
Using the high-resolution mass spectrometer CELIAS/MTOF on board SOHO we have measured the solar wind isotope abundance ratios of Si, Ne, and Mg and their variations in different solar wind regimes with bulk velocities ranging from 330 km/s to 650 km/s. Data indicate a small systematic depletion of the heavier isotopes in the slow solar wind on th…
O5+ in High Speed Solar Wind Streams: SWICS/Ulysses Results
Wimmer-Schweingruber, Robert F.; Gloeckler, George; Geiss, Johannes +3 more
Recent observations with UVCS on SOHO of high outflow velocities of O5+ at low coronal heights have spurred much discussion about the dynamics of solar wind acceleration. On the other hand, O6+ is the most abundant oxygen charge state in the solar wind, but is not observed by UVCS or by SUMER because this helium-like ion has …
Corotating Particle Events
Simnett, G. M.; Kunow, H.; Horbury, T. +8 more
The corotating particle events give us a unique opportunity to probe the three-dimensional structures of the heliosphere. This is especially true if we have observations over a period of extreme stability of the CIRs, such as existed over the recent solar minimum. We discuss how the observations fit into the context of current heliospheric magneti…
Solar EUV and UV Emission Line Observations Above a Polar Coronal Hole
Wilhelm, K.; Bodmer, R.
The roll manoeuvre of SOHO on September 3, 1997 provided the opportunity to study the northern coronal hole with SUMER slits in east-west orientation, so that polar plumes and inter-plume lanes could be observed simultaneously. A preliminary analysis of the observations shows that lines emitted by ions with the lowest formation temperatures (with …
Elemental Abundances in Coronal Structures
Kohl, John L.; Noci, Giancarlo; Raymond, John C. +1 more
A great deal of evidence for elemental abundance variations among different structures in the solar corona has accumulated over the years. Many of the observations show changes in the relative abundances of high- and low-First Ionization Potential elements, but relatively few show the absolute elemental abundances. Recent observations from the SOH…
Composition and Opacity in the Solar Interior
Turck-Chieze, Sylvaine
Detailed abundances of elements from hydrogen up to iron are necessary to perform a precise model of the solar structure. Most of them have been deduced from photospheric observed values, some others from the meteoritic composition. Nowadays, thanks to helioseismic constraints, they seem more and more under control.
UVCS/SOHO: The First Two Years
Cranmer, S. R.; Noci, G.; Kohl, J. L.
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) has observed the extended solar corona between 1 and 10 R· for more than two years. We review spectroscopic and polarimetric measurements made in coronal holes, equatorial streamers, and coronal mass ejections, as well as selected non-solar targets. UVCS/SOHO has provided a great amount of …
Structure of the Solar Wind and Compositional Variations
Bochsler, P.
The composition of the solar wind is largely determined by the composition of the source material, i.e. the present-day composition of the outer convective zone. It is then modified by the processes which operate in the transition region and in the inner corona. In situ measurements of the solar wind composition give a unique opportunity to obtain…
Sensitivity of Low Frequency Oscillations to Updated Solar Models
Provost, J.; Berthomieu, G.; Morel, P.
A large number of acoustic frequencies have already been detected, leading to a "seismic" model of the Sun rather close to the actual standard solar models. The core however is not yet well constrained by these observations and frequencies of low degree, low frequency modes which penetrate deeply into the solar core are needed. We present here a s…