Width and Energy of Solarp‐Modes Observed by Global Oscillation Network Group

Abstract

We present measurements of mode width, Γ, and mean square velocity power, , derived from all currently processed 108 day Global Oscillation Network Group (GONG) time series and discuss their implications for p-mode excitation and damping. Assuming stochastic excitation, we estimate the energy per mode, E, and the energy supply rate, dE/dt. For modes with l = 9-150, the mean square velocity power and the mode energy peak at about 3.15 mHz reaching values of ≈ 1.4 × 103 cm2 s-2 and E ≈ 2.2 × 1028 ergs. The energy supply rate reaches a maximum value of dE/dt ≈ 2.5 × 1023 ergs s-1 near 3.6 mHz. The mode width shows the familiar plateau between 2.5 and 3.1 mHz with a near 2.9 mHz, which is strongest for l ≈ 40. This dip is most prominent during solar cycle minimum and disappears with increasing magnetic activity. The energy supply rate decreases on average by about 2.7% from the previous activity minimum to the currently highest level of activity. The solar cycle variation of dE/dt shows no frequency dependence, which is in marked contrast to the other mode parameters. The mode parameters are adequately represented by power laws in several frequency ranges, for example, dE/dt ~ ν6.89±0.07 for 2.4 mHz ≤ ν < 3.0 mHz and dE/dt ~ ν-5.62±0.27 for 3.75 mHz ≤ ν < 4.5 mHz. The solar cycle variation of these parameters can then be expressed as changes of a few percent in the power-law exponents and multipliers. Our results agree reasonably well with previous studies of Birmingham Solar-Oscillations Network and Big Bear Solar Observatory data.