Solar-cycle variation of the rotational shear near the solar surface

Helioseismology has revealed that the angular velocity of the Sun increases with depth in the outermost 35 Mm of the Sun. Recently, we have shown that the logarithmic radial gradient ($\rm d\ln\Omega/\rm d\ln r$) in the upper 10~Mm is close to $-1$ from the equator to $60^\circ$ latitude.We aim to measure the temporal variation of the rotational shear over solar cycle 23 and the rising phase of cycle 24 (1996-2015). We used f mode frequency splitting data spanning 1996 to 2011 from the Michelson Doppler Imager (MDI) and 2010 to 2015 from the Helioseismic Magnetic Imager (HMI). In a first for such studies, the f mode frequency splitting data were obtained from 360-day time series. We used the same method as in our previous work for measuring $\rm d\ln\Omega/d\ln r$ from the equator to $80^\circ$ latitude in the outer 13~Mm of the Sun. Then, we calculated the variation of the gradient at annual cadence relative to the average over 1996 to 2015. We found the rotational shear at low latitudes ($0^\circ$ to $30^\circ$) to vary in-phase with the solar activity, varying by $\sim \pm 10$\% over the period 1996 to 2015. At high latitudes ($60^\circ$ to $80^\circ$), we found rotational shear to vary in anti-phase with the solar activity. By comparing the radial gradient obtained from the splittings of the 360-day and the corresponding 72-day time series of HMI and MDI data, we suggest that the splittings obtained from the 72-day HMI time series suffer from systematic errors. We provide a quantitative measurement of the temporal variation of the outer part of the near surface shear layer which may provide useful constraints on dynamo models and differential rotation theory.Comment: 5 pages, 6 figure

Simulation with Fluctuating and Singular Rates

Abstract. In this paper we present a method to generate independent samples for a general random variable, either continuous or discrete. The algorithm is an extension of the Acceptance-Rejection method, and it is particularly useful for kinetic simulation in which the rates are fluctuating in time and have singular limits, as occurs for example in simulation of recombination interactions in a plasma. Although it depends on some additional requirements, the new method is easy to implement and rejects less samples than the Acceptance-Rejection method

Near-polytropic simulations with a radiative surface

Studies of solar and stellar convection often employ simple polytropic setups using the diffusion approximation instead of solving the proper radiative transfer equation. This allows one to control separately the polytropic index of the hydrostatic reference solution, the temperature contrast between top and bottom, and the Rayleigh and Peclet numbers. We extend such studies by including radiative transfer in the gray approximation using a Kramers-like opacity with freely adjustable coefficients. We study the properties of such models and compare them with results from the diffusion approximation. We use the Pencil Code, which is a high-order finite difference code where radiation is treated using the method of long characteristics. The source function is given by the Planck function. The opacity is written as kappa=kappa_0 rho^a T^b, where b is varied from -3.5 to +5, and kappa_0 is varied by four orders of magnitude. We consider sets of one dimensional models and perform a comparison with the diffusion approximation. Except for the case where b=5, we find one-dimensional hydrostatic equilibria with a nearly polytropic stratification and a polytropic index close to n=(3-b)/(1+a), covering both convectively stable (n>3/2) and unstable (n<3/2) cases. For b=3 and a=-1, the value of n is undefined a priori and the actual value of $n$ depends then on the depth of the domain. For large values of $\kappa_0$, the thermal adjustment time becomes long, the Peclet and Rayleigh numbers become large, and the temperature contrast increases and is thus no longer an independent input parameter, unless the Stefan Boltzmann constant is considered adjustable. Proper radiative transfer with Kramers-like opacities provides a useful tool for studying stratified layers with a radiative surface in ways that are more physical than what is possible with polytropic models using the diffusion approximation.Comment: 16 pages, 17 figures, submitted to A&

Comparison of technetium-99m IgG with technetium-99m red blood cells labeling in cardiac blood-pool scintigraphy: A preliminary study

This first clinical prospective study was conducted to use of technetium-99m immunoglobulin G (99mTc-IgG) as compared with autologous 99mTc-red blood cells (RBC) in gated blood pool ventriculography. We studied 12 patients who referred to us for a possible diagnosis of liver hemangioma or infection. Six patients underwent gated planar blood pool (GPBP) acquisition using 99mTc-RBC and 6 GPBP acquisition using 99mTc-IgG. The use of 99mTc-IgG in cardiac blood pool studies provided comparable images to 99mTc-RBC. In conclusion, 99mTc-IgG, which is readily available and needs only a single injection, may be an attractive alternative to 99mTc-RBC for the estimation of various cardiac function parameters like left ventricular function