A recent study by Nakariakov et al .
pointed out that the dispersion relation of MHD sausage mode oscillations has been incorrectly applied to coronal loops , neglecting the highly dispersive nature of the phase speed and the long-wavelength cutoff of the wave number .
In the light of these new insights we revisit previous observations that have been interpreted in terms of MHD sausage mode oscillations in coronal loops and come to the following conclusions : ( 1 ) Fast sausage MHD mode oscillations require such a high electron density imposed by the wave number cutoff that they can only occur in flare loops ; ( 2 ) In the previously reported radio observations ( \nu \approx 100 MHz to 1 GHz ) with periods of P \approx 0.5 - 5 s , the fast sausage MHD mode oscillation is likely to be confined to a small segment ( corresponding to a high harmonic node ) near the apex of the loop , rather than involving a global oscillation over the entire loop length .
The recent microwave and soft X-ray observations of fast periods ( P \approx 6 - 17 s ) by Asai et al .
and Melnikov et al. , however , are consistent with fast sausage MHD oscillations at the fundamental harmonic .