The Quasi-biennial-oscillation-type Signals in the Subsurface Flow Fields during Solar Cycles 23 and 24

Abstract

We studied the presence and spatiotemporal evolution of quasi-biennial oscillations (QBOs) in the rotation-rate residuals at target depths of 0.90R (circle dot), 0.95R (circle dot), and 0.99R (circle dot) and at low- (0 degrees-30 degrees), mid- (30 degrees-50 degrees), and high-latitudinal (50 degrees-70 degrees) bands. To achieve these objectives we used data from the Michelson Doppler Imager on the Solar and Heliospheric Observatory and the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory, covering solar cycles 23 and 24, respectively. The results show that there are QBO-like signals in each latitudinal band and depth; however, they are affected by higher-amplitude and longer-timescale variations. The QBO-like signals found in each target depth and latitudinal bands show different spatiotemporal evolution. The amplitudes of variations of the rotation-rate residuals in the QBO timescale increase with increasing depth.