Strong and well-defined single-hop whistlers have been observed on L=4.0 at the mid-latitude subauroral station Sanae, Antarctica, between 1000 and 1100 UT (or LT) on June 16, 1986, when Kp~2- amid a magnetically quiet period extending over several weeks. These single-hop whistlers were followed often by diffused echo whisters 6¿1 s later. A significant correlation has been found between the arrival times of the single-hop whistlers and 30-MHz riometer absorption events, using point statistics. A superposed epoch analysis of the cross-correlated events, using the instants of maxima of the intergrated VLF signals as zeroth time, yields a maximum absorption of 30-MHz cosmic radio noise of ~0.04 dB with a delay of 3¿2 s and decay time to half maximum of ~10 s. This correlation is evaluated by calculations of the energy spectrum of electrons precipitated into the atmosphere by gyroresonance interaction of whistler mode waves with radiation belt electrons, using the results of the computer-simulated test particle program of Chang and Inan (1985). The temporal variation of the electron density in the upper atmosphere due to the whistler-induced electron precipitation spectrum is derived as a function of altitude, taking into account electron-ion production and recombination rates. The resulting enhanced riometer absorption maximizes at ~7¿10-3 dB, based on the average power spectral density of the input wave packet and the average plasmaspheric density distribution used by Chang and Inan (1985).

Variations in the magnitude of the equatorial wave magnetic field intensities, and approximations made in calculating the riometer absorptions, impose an order of magnitude uncertainty on the calculated value and hence consistency with the observed 0.04-B-averaged absorption maximum, which is just above the sensitivity limit of a riometer with a wide-angle antenna. Furthermore, these calculations depend on the trapped electron energy spectrum and pitch angle distribution accepted for the calculations and on features of whistlers related to convection electric field variations, which could not be identified from available recordings. In the evaluation of the observed correlations between riometer absorptions and whistlers it must also be taken into account that the VLF receiver, having a wide viewing window, is receiving VLF emissions via many ducts. Hence the electron precipitation region associated with a particular VLF signal may not necessarily coincide with the field of view of the wide-angle riometer antenna. ¿American Geophysical Union 1991