ENERGY DISTRIBUTION OF SOLAR OSCILLATION MODES INFERRED FROM SPACE-BASED MEASUREMENTS

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.