Energy Distribution of Solar Oscillation Modes Inferred from Space-based Measurements

Abstract

We have measured the energy distribution of solar p- and f-mode oscillations of angular degree and temporal frequency in the range 100<l<800 and 2<ν(mHz)<4 using helioseismology data from the Solar Oscillations Investigation-Michelson Doppler Imager instrument on the Solar and Heliospheric Observatory satellite. At temporal frequency ν~3 mHz, the surface velocity power per oscillation mode increases slightly with angular degree between l=100 and l=200 but decreases rather steeply with l above l=200, in approximate agreement with earlier findings from ground-based measurements. From this we infer that the time-averaged energy per mode, which is theoretically related to the modal surface velocity power, decreases steeply with l, at fixed frequency, over the entire observed l-range. Specifically, at ν=3.1 mHz, the energy per mode drops by a factor of ~10 between l=150 and l=650, a circumstance not quantitatively understood at present.