Search Publications
Reconstruction of solar irradiance variations in cycle 23: Is solar surface magnetism the cause?
Solanki, S. K.; Krivova, N. A.; Unruh, Y. C. +1 more
A model of solar irradiance variations is presented which is based on the assumption that solar surface magnetism is responsible for all total irradiance changes on time scales of days to years. A time series of daily magnetograms and empirical models of the thermal structure of magnetic features (sunspots, faculae) are combined to reconstruct tot…
Active longitudes in sunspot activity: Century scale persistence
Usoskin, I. G.; Berdyugina, S. V.
A novel analysis of sunspot group data for the past 120 years reveals that sunspots in both northern and southern hemispheres are formed preferably in two persistent active longitudes separated by 180°. In the Carrington reference frame, the active longitudes continuously migrate in phase with respect to the Carrington meridian with a variable rat…
Solar active regions: SOHO/CDS and TRACE observations of quiescent coronal loops
Mason, H. E.; Del Zanna, G.
This study focuses on the diagnostic capabilities of the TRACE and SOHO-CDS instruments to describe the physical characteristics of quiescent solar active regions. In particular we concentrate on the 1 MK loops, best seen in the TRACE EUV 173 Å passband. These are high-lying structures which can remain stable over timescales of hours to days. We p…
Formation and development of shock waves in the solar corona and the near-Sun interplanetary space
Mann, G.; Classen, H. -T.; Aurass, H. +1 more
At the Sun, shock waves are produced either by flares and/or by coronal mass ejections (CMEs) and are regarded as the source of solar energetic particle events. They can be able to generate solar type II radio bursts. The non-radial propagation of a disturbance is considered away from an active region through the corona into the interplanetary spa…
Hot coronal loop oscillations observed with SUMER: Examples and statistics
Solanki, S. K.; Curdt, W.; Innes, D. E. +3 more
We give an extensive overview of Doppler shift oscillations in hot active region loops obtained with SUMER. The oscillations have been detected in loops sampled 50-100 arcsec off the limb of the Sun in ultraviolet lines, mainly Fe Xix and Fe Xxi, with formation temperature greater than 6 MK. The spectra were recorded along a 300 arcsec slit placed…
Slow-mode standing waves observed by SUMER in hot coronal loops
Solanki, S. K.; Marsch, E.; Curdt, W. +2 more
We report the first detection of postflare loop oscillations seen in both Doppler shift and intensity. The observations were recorded in an Fe Xix line by the SUMER spectrometer on SOHO in the corona about 70 min after an M-class flare on the solar limb. The oscillation has a period of about 17 min in both the Doppler velocity and the intensity, b…
Dynamics of solar coronal loops. I. Condensation in cool loops and its effect on transition region lines
Peter, H.; Hansteen, V. H.; Müller, D. A. N.
We report numerical calculations of the condensation of plasma in short coronal loops, which have several interesting physical consequences. Firstly, we propose a connection between small, cool loops (T < 106 K), which constitute one of the basic components of the solar transition region, and prominences, in the sense that the same p…
Coronal dimming and the coronal mass ejection onset
Simnett, G. M.; Harrison, R. A.; Bryans, P. +1 more
A set of five observations of extreme-ultraviolet (EUV) coronal dimming associated with coronal mass ejection (CME) activity is examined. Using spectroscopic data, plasma characteristics across a broad range of temperatures from 20 000 K to 2 million K are determined. The dimming events are found to coincide in time, and to coincide spatially, wit…
A self-consistent treatment of radiation in coronal loop modelling
Mason, H. E.; Bradshaw, S. J.
We perform a hydrodynamic simulation of a cooling coronal loop and calculate the time-dependent ion populations of the most abundant elements of the solar atmosphere at each time-step. We couple the time-dependent ion balance equations to the hydrodynamic equations in order to treat the energy loss through radiation in a self-consistent way by all…
Modelling the rotational modulation of the Sun as a star
Barge, P.; Llebaria, A.; Pagano, I. +2 more
We analyse the time variability of the total solar irradiance (TSI) as measured by VIRGO/SoHO in order to model the variability of the Sun as a star. Apart from the phases near the minimum at the beginning of activity cycle 23, the period of the rotational modulation is significantly different from the solar synodic period as a consequence of the …