Abstract.The discrepancies between theoretically predicted and observed frequencies of solar global oscillations (e.g. pand f -modes) have attracted major attention in the past decades. The f -mode is essentially a surface wave hence the mode frequencies are less likely to be influenced by the solar stratification. Most probably then the discrepancies are the result of some near surface mechanism(s) such as interactions with surface or sub-surface magnetic fields and flows. In the following we explore whether the small-scale photospheric magnetic fields, sometimes also called the magnetic carpet, may be part of the explanation for the apparent frequency paradox.

Parker's interface dynamo is generalized to the case when a homogeneous flow is present in the high-diffusivity (upper) layer in the lateral direction (i.e. perpendicular to the shear flow in the lower layer). This is probably a realistic first representation of the situation near the bottom of the solar convective zone, as the strongly subadiabatic stratification of the tachocline (lower layer in the interface dynamo) imposes a strong upper limit on the speed of any meridional flow there. Analytic solutions to the eigenvalue problem are presented for the cases of vanishing diffusivity contrast and infinite diffusivity contrast, respectively. Unlike the trivial case of a homogeneous system, the ability of the meridional flow to reverse the propagation of the dynamo wave is strongly reduced in the interface dynamo. In particular, in the limit of high diffusivity contrast relevant to the solar case it is found that a meridional flow of realistic amplitude cannot reverse the direction of propagation of the dynamo wave. The implications of this result for the solar dynamo problem are discussed.Comment: 5 pages, 3 figures; MNRAS, in pres

We examine the effect of random horizontal flows on the dispersion relation of high-degree solar f modes. We follow the approach of Murawski and Roberts (Astron. Astrophys. 272, 595, 1993), addressing some limitations of that paper, and extending the results to include damping and to apply for a general turbulent spectrum. We find a reduction in frequency below the classical result that is about three times that observed. For large wavenumber the damping rate is larger than the frequency correction by a factor of the order of the nondimensional wavenumber, which appears to be consistent with observation.

Parker's analytic Cartesian interface dynamo is generalized to the case of a shear layer of finite thickness and low resistivity ("tachocline"), bounded by a perfect conductor ("radiative zone") on the one side, and by a highly diffusive medium ("convective zone") supporting an $\alpha$-effect on the other side. In the limit of high diffusivity contrast between the shear layer and the diffusive medium, thought to be relevant for the Sun, a pair of exact dispersion relations for the growth rate and frequency of dynamo modes is analytically derived. Graphic solution of the dispersion relations displays a somewhat unexpected, non-monotonic behaviour, the mathematical origin of which is elucidated. The dependence of the results on the parameter values (dynamo number and shear layer thickness) is investigated. The implications of this result for the solar dynamo problem are discussed.Comment: 11 pages, 4 figures Geophys. Astrophys. Fluid Dyn., in pres

In this paper we introduce a new approach to study the interaction of solar eigenoscillations, with particular emphasis on the f-mode, with random inhomogeneities caused by flows and magnetic field near the solar surface. We present an initial value method to derive a general dispersion relation for a class of models where the magnetic atmosphere is overlying an arbitrary static solar interior. In these models the interior part is treated parametrically and does not need to be specified before we obtain the dispersion relation. In order to demonstrate the applicability of the proposed method, an analytical solution of the dispersion relation is given for an incompressible interior with constant density. Subject headingg s: MHD -Sun: atmosphere -Sun: helioseismology -Sun: magnetic fields