Observation of, and temporal variations in, solar p-mode multiplet frequency asymmetries at ℓ=2

The predominant contribution to the frequency splitting of low-l solar p modes arises from the rotation of the solar interior and this lifts the frequency degeneracy in l to give a symmetric pattern where the observed (synodic) separation between adjacent m (i.e. for \Deltam\=1) is similar to400 nHz. Magnetic fields can also contribute to the splitting, but they do so in such a way as to introduce asymmetries in the arrangement of the components within each multiplet. In disc-integrated data this effect may become apparent when lgreater than or equal to2. Here, we attempt to extract estimates of the frequency asymmetries at l=2 from the analysis of disc-integrated data collected by the ground-based Birmingham Solar Oscillations Network (BiSON) and the GOLF instrument on board the ESA/NASA SOHO satellite. Our analyses demonstrate that we have evidence for there being non-zero asymmetries present (significance approximate to3-4sigma) during an epoch coincident with high levels of surface activity close to the maximum of solar cycle 23. The asymmetries are indistinguishable from zero at minimum levels of activity near the cycle 22/23 boundary. We also compare the observed asymmetries with those calculated from a model that is based upon the recent predictions of Moreno-Insertis & Solanki. While the level of agreement between the two is found to be reasonable, the observations suggest (though with poor constraints placed upon this) that the influence on the mode frequencies of high-latitude activity may not be as strong as in the model.