A simultaneous observation of large-scale periodic TIDs in both hemispheres following an onset of auroral disturbances

A study has been undertaken on the position of the auroral sources of large-scale TIDs (LS TIDs) in both hemispheres. A selected case study, herewith presented, refers to an onset of an auroral substorm at the equatorward edges of the southern and northern auroral zones which preceded the occurrence of periodic variations in virtual height (h′F) of the F-region in the Southern and Northern Hemispheres. The variations in h′F had characteristics typical of large-scale TIDs propagating equatorwards with a velocity of about 800 m s⁻¹, and with a constant period of 135 min in both hemispheres. The horizontal wavefront of LS TIDs was observed in mid-latitudes to be in excess of 7000 km. The LS TIDs were found to be in phase at the stations which are equidistant from the auroral sources. From this it was concluded that the periodic LS TIDs were likely to produce a constructive interference effect at the points of their encounter near the equator.It was concluded that the sources of LS TIDs in both hemispheres were elongated along the L-shell with L-value between 4 and 5, and had a large longitudinal extent, exceeding 60°. The source locations were consistent with the positions of the belts of energetic particle precipitations as inferred from the standard riometer and magnetometer data. The large quasi-linear extent of the source is consistent with the wide horizontal wavefronts of LS TIDs as well as with a large distance of their propagation.