Wednesday, May 7, 2008, 4:00 pm, Physics & Astrophysics Conf.Room 232:
Numerical simulations of MHD waves in coronal loops
Marcin Gruszecki (Maria Curie Skladowska
University of Lublin)
Abstract:
Magnetic loops are the main building blocks of the solar corona, that
are able to sustain various kinds of waves and oscillations. The waves
may play an important role in the heating of the loops, as was first
suggested by Ionson (1978), and also can be used as a diagnostic tool
of
loop parameters (e.g., Nakariakov and Ofman 2001).
The hot coronal loops were detected to oscillate mainly in a slow
magnetosonic mode (Wang et al. 2002). Cool loops primarily sustain
fast
magnetosonic kink oscillations which are observed in two polarizations:
horizontal (Aschwanden et al. 1999, Nakariakov et al. 1999, Van
Doorsselaere et al. 2007) and vertical (Wang & Solanki 2004). The
detection and identification of magnetohydrodynamic (MHD) waves and
oscillations has made MHD coronal seismology a viable diagnostic tool
for the determination of unknown parameters of the corona (Uchida 1970,
Roberts et al. 1984).
In my work I consider to the observationally determined signatures of
the vertical oscillations (Wang & Solanki 2004). I modelled the
oscillation by taking into account a simple two dimensional geometry
of
a coronal loop arcade in which loop oscillations are excited by
localized pulses in the lower atmosphere.
Wednesday, May 21, 2008, 4:00 pm, Physics & Astrophysics Conf.Room 232:
Combined Analysis of Solar Neutrino and Solar Irradiance
Data:
Indications of an Inhomogeneous, Fluctuating, Slowly
Rotating Core,
and Suggestions of an Inner Tachocline, an Inner Dynamo,
and a
Second Solar Cycle
Peter Sturrock (Stanford)
Abstract. A search for any particular feature in any single solar
neutrino dataset is unlikely to establish variability of the solar
neutrino flux since the count rates are very low. It helps to combine
datasets, and in this talk I examine data from both the Homestake and
GALLEX experiments. These show evidence of modulation with a
frequency of 11.85 yr-1, which could be indicative of rotational
modulation originating in the solar core. I find that precisely the
same frequency is prominent in power spectrum analyses of the ACRIM
irradiance data for the Homestake and GALLEX time intervals. These
results suggest that the solar core is inhomogeneous and rotates with
sidereal frequency 12.85 yr-1. I find, by Monte Carlo calculations,
that the probability that the neutrino data would match the
irradiance data in this way by chance is only a few parts in 10,000.
This rotation rate is significantly lower than that of the inner
radiative zone (13.97 yr-1) as recently inferred from analysis of
Super-Kamiokande data, suggesting that there may be a second, inner
tachocline separating the core from the radiative zone. This opens
up
the possibility that there may be an inner dynamo that could produce
a strong internal magnetic field and a second solar cycle. Analysis
of ACRIM data points to the existence of such a cycle with frequency
0.92 yr-1.