Locating TID sources with a north-south chain of rapid-run ionosondes in western Québec


  • M. G. Morgan


Three rapid-run ionosondes placed mutually 150 km apart for determination of the vector motion of traveling ionospheric disturbances, near L = 3.3 in northern New Hampshire and Vermont, were augmented with three more ionosondes laid out northward near L = 4.0. 4.5, and 6.0 in western Québec along the predominant direction (north-northwest) from which daytime TID's arrive at the New Hampshire-Vermont network. Observations were made for the 3-month period March, April, May 1982. In a preliminary analysis, records have been reduced by our “slit-scanner” technique to produce continuous displays of virtual height at selected frequencies moderately below the F layer critical. These isofrequency waveforms show a high degree of correlation among the three network stations, with propagation time delays from which speed and direction of TID travel can be deduced. An example, from 1980 observations, is shown of remarkable correlation over many daytime hours of the waveforms obtained by the network stations with that obtained by a sounder placed 1500 km downstream in the predominant direction (south-southeast) toward which the TID's go. On the other hand, sources have now been found to be located as little as 200 km upstream from the network. TID's and their causative gravity waves propagate northward from these sources as well as southward. The sources are evidently narrow in north-south extent for they frequently exist between the stations, spaced some 275 km apart, without causing absorption of ionosonde signals at either adjacent station. However, when they are located at an ionosonde station, they cause complete loss of echoes, thereby confirming that they are zones of energetic particle precipitation. They are believed to be due to precipitation from the outer radiation belt.