As mode lifetimes get shorter and spatial leaks get closer in frequency, individual p-modes can only be resolved up to some degree l (around 150). At higher degrees, individual modes blend into ridges and the power distribution of the ridge masks the true underlying mode frequency. To recover the underlying mode frequency from fitting the ridge, an accurate model of the amplitude of the peaks that contribute to the ridge power distribution is needed. Using full-disk data from the Michelson Doppler Imager data on the Solar and Heliospheric Observatory, we present and discuss the differences between the observations and the spatial leakage calculation (including the horizontal component) and estimate the horizontal-to-vertical displacement ratio for medium-degree modes using sectoral modes for different observational periods. We show how time variations in the instrument calibration affect the spatial leakage and discuss their importance in the spatial leakage calculation. By constructing a physically motivated model (rather than some ad hoc correction scheme) can we hope to produce an unbiased determination of the high-degree modes in the near future.
SOHO 10/GONG 2000 Workshop: Helio- and Asteroseismology at the Dawn of the Millennium
- Pub Date:
- January 2001
- SUN: OSCILLATIONS