Kristóf Petrovay

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A review of solar cycle prediction methods and their performance is given, including forecasts for cycle 24. The review focuses on those aspects of the solar cycle prediction problem that have a bearing on dynamo theory. The scope of the review is further restricted to the issue of predicting the amplitude (and optionally the epoch) of an upcoming solar(More)
The precise nature of photospheric flows, and of the transport effects they give rise to, has been the subject of intense debate in the last decade. Here we attempt to give a brief review of the subject emphasizing interdisciplinary (solar physics—turbulence theory) aspects, key open questions, and recent developments.
Helioseismic measurements indicate that the solar tachocline is very thin, its full thickness not exceeding 4 % of the solar radius. The mechanism that inhibits differential rotation to propagate from the convective zone to deeper into the radiative zone is not known, though several propositions have been made. In this paper we demonstrate by numerical(More)
A simple way to couple an interface dynamo model to a fast tachocline model is presented, under the assumption that the dynamo saturation is due to a quadratic process and that the effect of finite shear layer thickness on the dynamo wave frequency is analoguous to the effect of finite water depth on surface gravity waves. The model contains one free(More)
In contrast to the situation with the geodynamo, no breakthrough has been made in the solar dynamo problem for decades. Since the appearance of mean-field electrodynamics in the 1960's, the only really significant advance was in the field of flux tube theory and flux emergence calculations. These new results, together with helioseismic evidence , have led(More)
1 Following an earlier proposal by Choudhuri (2003) for the origin of twist in the magnetic fields of solar active regions, we model the penetration of a wrapped up background poloidal field into a toroidal magnetic flux tube rising through the solar convective zone. The rise of the straight, cylindrical flux tube is followed by numerically solving the(More)
The mean value of the normalized current helicity αp = B · (∇ × B)/B 2 in solar active regions is on the order of 10 −8 m −1 , negative in the northern hemisphere, positive in the southern hemisphere. Observations indicate that this helicity has a subsurface origin. Possible mechanisms leading to a twist of this amplitude in magnetic flux tubes include the(More)
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