APPENDIX C OHMIC HEATING OF THE D-REGION High power radio waves can cause the electron temperature in the lower D-region to increase to many times its ambient value, whenever the flux exceeds a critical value: where is in MHz and is in . becomes . Thus, where the MPTS produces a flux of it will be an increase of the critical value. Calculations such as those in reference 3 indicate that a flux of this magnitude will raise the electron temperature to a value on the order of 1000°K. For it would be an increase of the critical value and the associated electron temperature would be raised to a value on the order of 2000°K. In assessing the effects of the temperature rise, it must be remembered that the electrons are a minor constituent of the D-region since there are neutral molecules for each electron. Since the neutral molecules remain at the same temperature, the energy per unit volume of the D-region is not significantly changed. The two most important effects of the increase in electron temperature are: (1) a change in the chemistry of the ionosphere which reduces the rate of recombination of electrons and ions and thus increases the electron density; and (2) an increase in the electron collision frequency. The increase in electron-collision frequency will increase the absorption of radio waves with and decrease the absorption in the opposite limit. This effect will be localized to signals which pass through the heated cylinder whose diameter is on the order of five km. This effect might interfere with specific receivers but it would not effect any geographically - widespread communication systems. It might effect individual receivers of LORAN if they were located close to the heated region since the electron temperature rise would extend all the way down to low altitudes where the rf radar frequency equals the electron-collision frequency, and the electron density is much less than the LORAN critical density.
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