| Abstract: | Standing oscillations with multiple periods have been found in a number of atmospheric structures on the Sun.The ratio of the period of the fundamental to twice the one of its first overtone,P_1/2P_2,is important in applications of solar magneto-seismology.We examine how field-aligned flows impact P_1 /2P_2 of standing modes in solar magnetic cylinders.For coronal loops,the flow effects are significant for both fast kink and sausage modes.For kink modes,they reduce P_1 /2P_2 by up to 17% relative to the static case even when the density contrast between the loop and its surroundings approaches infinity.For sausage modes,the reduction in P_1 /2P_2 due to flow is typically 5.5% compared with the static case.However,the threshold aspect ratio,only above which can trapped sausage modes be supported,may increase dramatically with the flow magnitude.For photospheric tubes,the flow effect on P_1/2P_2 is not as strong.However,when applied to sausage modes,introducing field-aligned flows offers more possibilities in interpreting the multiple periods that have recently been measured.We conclude that field-aligned flows should be taken into account to help better understand what causes the departure of P_1/2P_2 from unity. |
