INTERPRETING ELECTRON TEMPERATURE CHANGES IN THE LOWER IONOSPHERE
COCO, DAVID STEPHEN
Doctor of Philosophy
The electron temperature changes due to 3, 5 and 430 MHz radio wave heating in the lower ionosphere are measured using incoherent scatter diagnostic techniques and are also calculated from heating/cooling theory. The experiments were performed at Arecibo Observatory using the new HF heating facility and the Arecibo Observatory 430 MHz incoherent backscatter system. In order to interpret the incoherent scatter results a spectral parameter library is developed which gives the spectral width, the spectral maximum and the bandlimited power of the incoherent scatter spectrum for a wide range of ionospheric parameters. There are two collisional formulations which have been widely used to reduce incoherent scatter data in the D and E regions: Dougherty and Farley (1963) and Waldteufel (1970). To determine which collisional formulation should be used, we examine the results of recent Arecibo experiments performed in an unheated ionosphere. A comparison of the measured electron-neutral collision frequency values derived from the two different collisional formulations to the predicted model values show excellent agreement for the Dougherty and Farley formulation but less than satisfactory agreement for the Waldteufel formulation. Using the Dougherty and Farley formulation we determine electron temperature changes from the measured heated-to-ambient spectral parameter ratios. In comparing the measured electron temperature changes to the predicted changes for 430 MHz heating we find a large discrepancy throughout the D and E regions: the measured electron temperature changes are much less than the predicted. The discrepancy in the 75-100 km region can be removed by increasing the model O(,2) rotational cooling rate by a factor of 10, while the discrepancy below 75 km can be removed by a factor of 4 increase. The cooling rate increases, however, are not the only possible explanation for the discrepancies. Two other effects, the non-Maxwellian electron velocity distribution and heat conduction, could remove the discrepancies if the magnitude of their effects were significantly increased in the model. The discrepancies could also be removed by using a f('2.18) frequency scaling law for the predicted heating rather than the currently accepted f('2) law, but there are no physical explanations to support this modification. The 3 and 5 MHz heating results are in satisfactory agreement with the model if D region absorption is taken into account and, thus, do not support the increased cooling rates suggested by the 430 MHz results. The agreement of these results, however, would not be significantly affected by the other suggested modifications. The heating due to the 52 (mu)sec diagnostic pulse is also measured. The diagnostic pulse heating at 70 km is found to increase the electron temperature by a factor of 2.85 (+OR-) 1.35 above ambient. Although the error estimates are large, this increase is in agreement with the predictions of the model.