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The parking maneuver of a passenger car is known by bench and vehicle testers to sometimes produce brake squeal, even though the brake system is otherwise quiet. This phenomenon is examined in this work. Pressure foil measurements at the pad caliper contact and acceleration measurements are done on a real break system in order to better understand the mechanisms of the forward–backward driving maneuver. The contact area at the caliper is under a large change during a forward and backward driving maneuver. The measurements motivate linear and nonlinear simulations. A proposal has been made to include the linear effects of parking into the standard robustness analysis with the complex eigenvalues calculation. A time integration of the full nonlinear system shows a possible stable limit cycle, when the brake pad moves from the leading to the trailing side, like in a parking maneuver. This growth of amplitude is not anticipated from the complex eigenvalue analysis (CEA), because no instable eigenvalue is found in the linearized equation of motion at that working point. This subcritical flutter-type behavior is known for small models in the literature and is examined in this paper with a more realistic brake system. It is found that the resulting error of the linearization cannot be neglected. Furthermore, different initial conditions are analyzed to narrow the zone of attraction of the stable limit cycle and the decrease of the critical friction value due to this kind of bifurcation behavior.

UARS SOLSTICE data have been subjected to Fourier and wavelet analyses in order to search for the signature of the solar rotation law in the disk‐integrated irradiance of UV lines. Lyman‐α, Mg II, and Ca II data show a different behaviour. In the SOLSTICE data there are significant temporal variations of the rotation rate of the UV tracers over 5—6 years. Often several distinct rotation periods appear almost simultaneously. Beside the basic period around 27 days there are signals at 32—35 days corresponding to the rotation rate at very high latitudes. For more than 5 years during another period of the solar cycle the rotational behaviour is quite different; there is an indication of differential rotation of active regions in these Ca II ground‐based data. The data contain a wealth of information about the solar differential rotation, but it proves difficult to disentangle the effects of the different emitting sources.

The influence of turbulence on the frequencies of free acoustic modes in convection zones is considered. The frequencies are modified via the speed of sound by the turbulence-induced alterations of the effective pressure: (i) by the correlated fluctuations of temperature and density and (ii) the pressure part of the Reynolds stress. The two effects shift the frequency of low 1 gmodes in opposite directions. In addition, the correlation of the density fluctuations with the random velocitythe eddy-mass flow -is also relevant. It is, in a steady state, balanced by a vertical mean velocity. The balance results in a rather small net effect completely disappearing for highly nonradial oscillations. Both effects of the density fluctuations produce a redshiJl of the low 1 p-mode frequencies. The Reynolds stress, however, makes a blueshijt of the frequencies relative to that computed for a laminar gas. This effect dominates for subsonic turbulences. The applied second-order correlation-approximation, however, only holds for the lowest frequencies, where the KORONAS (solar minimum) data are indicating a blueshift. Of part.icular importance for t,he present concept is the expected cycle-variations of the lineshifts, i.e. the consideration of the rnagnet.ic modification of the various contributions. Observations may show whether the suggested modifications of the solar oscillation theory are correct.