Excitation of oscillations in photospheric flux tubes through buffeting byexternal granules

We examine the excitation of transverse (kink) and longitudinal (sausage) w aves in magnetic flux tubes by granules in the solar photosphere. The inves tigation is motivated by the interpretation of network oscillations in term s of flux tube wavers. We model the interaction between a granule, with a s pecified transverse velocity, and a vertical flux tube in terms of the Klei n-Gordon equation, which we solve analytically as an initial value problem for both wave modes, assuming the same external impulse. The calculations s how that for magnetic field strengths typical of the network, the energy fl ux in transverse waves is higher than in longitudinal waves by an order of magnitude, in agreement with the chromospheric power spectrum of network os cillations observed by Lites, Rutten, & Kalkofen. But for weaker fields, su ch as those that might be found in internetwork regions, the energy fluxes in the two modes are comparable. This result implies that if there are inte rnetwork oscillations in magnetic flux tubes, they must show the cutoff per iods of both longitudinal and transverse modes at 3 minutes and at 7 minute s or longer. We also find that granules with speeds of about 2 km s(-1) can efficiently excite transverse oscillations in frequent short-duration (typ ically 1 minute) bursts that can heat the corona.