ALTERNATING-CODE EXPERIMENT FOR PLASMA-LINE STUDIES

We present results of the first plasma-line measurement of the incoher ent spectrum using the alternating-code technique with the EISCAT VHF radar. This technique, which has earlier mostly been used to measure h igh-resolution E-region ion-line spectra, turned out to be a very good alternative to other techniques for plasma-line measurements. The exp eriment provides simultaneous measurement of the ion line and downshif ted and upshifted plasma-line spectra with an altitude resolution of 3 km and a temporal resolution of 10 s. The measurements are taken arou nd the peak of the F region, but not necessarily at the peak itself, a s is the case with the long-pulse technique. The condition for success is that the scale height should be large enough such that the backsca ttered signal from the range extent of one gate falls inside the recei ver filter. The data are analyzed and the results are combined with th e results of the ion-line data analysis to estimate electron mean drif t velocity and thereafter electric currents along the line of sight of the radar using both the standard dispersion relation assuming a Maxw ellian electron velocity distribution and the more recent model includ ing a heat-flow correction term.