Introduction Plasmagram records Velocity-field effect Observing a fce+ echo Of all measurement programs used by RPI, program 38 offers the best spectral resolution at low frequencies for observing the PGH echoes. The program sends a 3.2 ms pulse at each frequency and advances the frequency by 300 Hz every 5 minutes, from 6 kHz to 62 kHz. The figures below show successive plasmagrams produced by program 38 taken on the same orbit on August 15, 2004. As fce increases, meaning that the proton gyrofrequency fci also increases, the median echo delay time drops. The virtual range limit of 4.2Re in the first plasmagram prevents us from seeing the second echo at 2Tp, although it probably exists as can be seen from the second plasmagram. Three PGH echoes appear in the last plasmagram, although the diminished amplitude of the echo at 3Tp makes it almost indistinguishable. Several features of this set are typical of most other observed echoes. As IMAGE approaches lower altitudes and fce increases, multiple echoes can be seen on the same because the delay time decreases. Echoes at farther delays, however, tend to have lower amplitudes and eventually become too weak to be recognizable. When more time elapses, the energized protons may lose the plasma memory effect and make echoes at higher nTp unlikely. The echoes also cover a range of bandwidths and curvatures, and an inverse relationship exists between bandwidth and curvature as can be expected. (a) Echo observed on August 15, 2004 at 21:59:55. The value of fpe is 185 kHz. (b) Echoes observed on August 15, 2004 at 22:16:38. The value of fpe is 208 kHz. (c) Echoes observed on August 15, 2004 at 22:23:55. The value of fpe is 227 kHz. ............................................................................................. Records of fce+ echoes May 2004 June 2004 July 2004 August 2004* March 2005 April 2005 May 2005 July 2005 August 2005* * Offers the best spectral resolution because program 38 was run.