SUNSPOT VELOCITY CORRELATIONS - ARE THEY DUE TO REYNOLDS STRESSES OR TO THE CORIOLIS-FORCE ON RISING FLUX TUBES

Observations have consistently pointed out that the longitudinal and l atitudinal motions of sunspots are correlated. The magnitude of the co variance was found to increase with latitude, and its sign was found t o be positive in the N-hemisphere and negative in the S-hemisphere. Th is correlation was believed to be due to the underlying turbulence whe re the sunspot flux tubes are anchored, and the covariance had the rig ht sign and magnitude needed to explain the transfer of angular moment um toward the equator through Reynolds stresses. Here we present an al ternate explanation for these sunspot velocity correlations: It is bel ieved that the dynamo operates in a thin overshoot layer beneath the b ase of the convection zone, and the flux tubes generated there produce sunspots at the photosphere. By studying the dynamics of flux tubes e merging from the base of the convection zone to the photosphere, we sh ow that these velocity correlations of sunspots could be merely a cons equence of the effect of Coriolis force on rising flux tubes. The effe ct of the Coriolis force, as demonstrated by even a back-of-the-envelo pe calculation, is to push the faster rotating spots equatorward and t he slower rotating spots poleward, giving rise to a correlation in the ir longitudinal and latitudinal velocities, which is positive in the N -hemisphere and negative in the S-hemisphere. The increase in the corr elation with latitude is due to the increase in magnitude of the Corio lis force. Hence we show that these velocity correlations might have n othing to do with the Reynolds stresses of the underlying turbulence. We present analyses of observations, and show that the covariances of plages are an order of magnitude higher than the sunspot covariances. If plages and sunspots share the same origin, and if their horizontal velocity correlations are wholly due to the effect of Coriolis force o n rising flux tubes, then the study of their dynamics suggests that th e flux tubes that form plages should have diameters of a couple of tho usand km at the base of the convection zone and remain intact until th ey reach the photosphere, whereas sunspots should be formed by a colle ction of small flux tubes (each measuring about a hundred km in diamet er), that rise through the convection zone as individual elements and coalesce when they emerge through the photosphere.