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Possible solar cycle variations in the convection zone
Basu, Sarbani; Antia, H. M.
Using data from the Global Oscillations Network Group (GONG) that covers the period from 1995 to 1998 we study the change in frequencies of solar oscillations with solar activity. From these frequencies we attempt to determine any possible variation in solar structure with solar activity. We do not find any evidence of a change in the convection z…
Near-Surface Flow Fields Deduced Using Correlation Tracking and Time-Distance Analyses
Duvall, T. L., Jr.; De Rosa, Marc; Toomre, Juri
Near-photospheric flow fields on the Sun are deduced using two independent methods applied to the same time series of velocity images observed by SOI-MDI on SOHO. Differences in travel times between f modes entering and leaving each pixel measured using time-distance helioseismology are used to determine sites of supergranular outflows. Alternativ…
The potential of solar high-degree modes for structure inversion
Christensen-Dalsgaard, J.; Basu, Sarbani; Rabello-Soares, M. C. +1 more
It is likely that precise and reliable frequencies of high-degree modes will soon be available from the SOI/MDI experiment. Here we examine the ability of such modes (with l>300) to resolve the solar structure in the near-surface region. In particular, we investigate inversions to determine the adiabatic exponent Γ1 as a test of the …
An Erupting Active Region Filament: Three-Dimensional Trajectory and Hydrogen Column Density
Penn, M. J.
From 15:33 through 16:02 UT on 13 June 1998, observations of an erupting filament as it crossed solar disk center were obtained with the NSO/KPVT and SOHO/CDS instruments as part of the SOHO Joint Observing Program 70. Context observations show that this event was the eruption of the north-east section of a small active region filament associated …
Helmet Streamers with Triple Structures: Simulations of resistive dynamics
Wiegelmann, Thomas; Schindler, Karl; Neukirch, Thomas
Recent observations of the solar corona with the LASCO coronagraph on board of the SOHO spacecraft have revealed the occurrence of triple helmet streamers even during solar minimum, which occasionally go unstable and give rise to large coronal mass ejections. There are also indications that the slow solar wind is either a combination of a quasi-st…
Magnetic field gradient and flare: study of a small flare in NOAA 8038
Mathew, Shibu K.; Ambastha, Ashok
Active region NOAA 8038 was observed from 10 to 13 May, 1997 using the USO solar video magnetograph. During this period, the active region was mostly inactive, and gave rise to only a single notable flare of 1N/C1.3 class on May 12, 1997/04:45 UT. The flare occurred in a weak field location, but new emerging fluxes were observed prior to the flare…
New Approach to Study Extended Evolution of Supergranular Flows and Their Advection of Magnetic Elements
De Rosa, Marc; Toomre, Juri; Lisle, Jason
Using velocity and magnetogram data extracted from the full-disk field of view of MDI during the 1999 Dynamics Program, we have studied the dynamics of small-scale magnetic elements (3-7 Mm in size) over time periods as long as six days while they are readily visible on the solar disk. By exploiting concurrent time series of magnetograms and Doppl…
Solar Cycle Variations of Large-Scale Flows in the sun
Basu, Sarbani; Antia, H. M.
Using data from the Michelson Doppler Imager (MDI) instrument on board the Solar and Heliospheric Observatory (SOHO), we study the large-scale velocity fields in the outer part of the solar convection zone using the ring diagram technique. We use observations from four different times to study possible temporal variations in flow velocity. We find…
Electro-Mechanical Coupling Between the Photosphere and Transition Region
Tarbell, T. D.; Shine, R.; Ryutova, M.
We study the response of the chromosphere and transition region to dynamic changes in the photospheric network magnetic fields. We present results from simultaneous measurements taken by TRACE in chromospheric and transition region (C iv) images, high-resolution magnetograms taken by MDI, and spectra of chromospheric (C ii) and transition region l…
Measuring Magnetic Oscillations in the Solar Photosphere: Coordinated Observations with MDI, ASP and MWO
Ulrich, R. K.; Norton, A. A.
A comprehensive observing effort was undertaken to simultaneously obtain full Stokes profiles as well as longitudinal magnetogram maps of a positive plage region on 8 December, 1998 with the Michelson Doppler Imager, the Advanced Stokes Polarimeter and Mt. Wilson Observatory magnetograph. We compare 1.2'' spatially-averaged signals of velocities a…