选址与日冕观测组知识库

We present observations of multimode (fundamental and harmonic) oscillations in a loop system, which appear to be simultaneously excited by a GOES C-class flare. Analysis of the periodic oscillations reveals that (1) the primary loop with a period of P-a approximate to 4 minutes and a secondary loop with two periods of Pa approximate to 4 minutes and Pb approximate to 2 minutes are detected simultaneously in closely spaced loop strands; (2) both oscillation components have their peak amplitudes near the loop apex, while in the second loop the low-frequency component Pa dominates in a loop segment that is two times larger than the high-frequency component Pb; (3) the harmonic mode Pb shows the largest deviation from a sinusoidal loop shape at the loop apex. We conclude that multiple harmonic modes with different displacement profiles can be excited simultaneously even in closely spaced strands, similar to the overtones of a violin string.