Ring diagram analysis of solar oscillation power spectra obtained from Michelson Doppler Imager data is carried out to study the velocity fields in the outer part of the solar convection zone. The three-dimensional power spectra are fitted to a model that has a Lorentzian profile in frequency and includes the advection of the wave front by horizontal flows in order to obtain the two components of the subsurface flows as a function of the horizontal wave number and radial order of the oscillation modes. This information is then inverted using the optimally localized averages method and regularized least squares method to infer the variation in horizontal flow velocity with depth. The average rotation velocity at different latitudes obtained by this technique agrees reasonably with helioseismic estimates made using frequency-splitting data. The shear layer just below the solar surface appears to consist of two parts, with the outer part measuring up to a depth of 4 Mm where the velocity gradient does not show any reversal up to a latitude of 60°. In the deeper part the velocity gradient shows reversal in sign around a latitude of 55°. The zonal flow velocities inferred in the outermost layers appear to be similar to those obtained by other measurements. A meridional flow from equator poleward is found. It has a maximum amplitude of about 30 m s-1 near the surface, and the amplitude is nearly constant in the outer shear layer.
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机译：对从迈克尔逊多普勒成像仪数据获得的太阳振荡功率谱进行了环图分析，以研究太阳对流区外部的速度场。将三维功率谱拟合到一个模型，该模型的频率具有洛伦兹分布，并包括水平流对波前的平流，以便获得地下流的两个分量作为水平波数和径向函数的函数振荡模式的顺序。然后使用最佳局部平均法和正则化最小二乘法对这些信息进行反演，以推断水平流速随深度的变化。通过该技术获得的不同纬度的平均转速与使用分频数据得出的高地震估计值合理地吻合。太阳表面正下方的剪切层似乎由两部分组成，外部部分的深度最大为4 Mm，在该深度处，速度梯度在纬度为60°时没有任何反转。在较深的部分，速度梯度在55°纬度附近显示出符号反转。在最外层推断出的纬向流速似乎与通过其他测量获得的流速相似。发现从赤道极向的子午流。它在地表附近的最大振幅约为30 m s-1，在外剪切层中振幅几乎恒定。
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