Accurate Mapping of the Torsional Oscillations: a Trade-Off Study between Time Resolution and Mode Characterization Precision

Abstract

One salient result of global helioseismology is the mapping of the so-called torsional oscillations below the solar surface. These subsurface flows are inferred by inverting rotational frequency splitting sets of global modes. These flows extend down to a depth of at least 0.8 R, and are likely associated with the activity cycle of our star. To better understand the mechanisms that drive the solar cycle we need to accurately map these flows, and characterize precisely their penetration depth and their temporal behavior.

We present a study of the spatial (depth and latitude) and temporal variations of the solar rotation rate associated with the torsional oscillation based on state-of-the-art mode fitting of time series of various lengths of MDI observations, namely 1456-, 728-, 364- and 182-day long time series. Such approach allows us to better estimate how much significant information can be extracted from the different time spans and hence trade off time resolution for precision in the inverted profiles resulting from the different mode sets.