A UHF cross‐modulation D region heating experiment with aeronomic implications

Abstract

A unique wave interaction experiment employing the Arecibo 2.0‐MW, 430‐MHz radar as disturbing or heating transmitter has been performed. The purpose of this experiment was to evaluate UHF electron heating effects and to extend the wave interaction technique to higher than usual heights (˜100 km). The heater beam used was much smaller in angular extent than the probing or wanted beam, yielding an unfavorable geometric weighting factor and making the experiment very sensitive to reflection properties of the E region. Nonetheless, wave interaction was easily detected using a completely digital signal processing technique. Comparison of experimental wave interaction results with a numerical model of the process indicates that lower thermosphere electron cooling rates are possibly too small by a factor of 4. Power spectra of the 3.155 MHz wanted signal (reflected from E region) amplitude fluctuations for ‘quiet’ and ‘disturbed’ days are also given.

Diagnosing radio plasma heating in the polar summer mesosphere using cross modulation: Theory and observations

“…Indeed, it is noted in section 3 of Fejer [1970] that an experiment using a narrow transmitting beam “was too directional for pulsed cross‐modulation measurements because the fading wanted echo arrives from a cone whose opening angle usually exceeds the width of the transmitted beam”. Sulzer et al [1982] had a particularly severe example of this effect because their heater beam was the very narrow 430 MHz Arecibo radar beam.…”

“…The purely vertical propagation case studied so far corresponds to a half‐angle approaching zero. Sulzer et al [1982] adopted another approach based on a Fresnel zone theory of the reflected diagnostic wave. Figure 6 is similar to Figure 5 but compares the model results for a set of half‐angles for Cases 1 and 2 to the corresponding observations.…”

“…The present model includes the self‐absorption of the high‐power HF heating wave which was neglected in these models, probably due to the lower powers used. The numerical model described by Georges [1966] does include this effect but it is not clear whether the model used by Sulzer et al [1982] did so. The present model also has some refinements in the radio absorption calculation and in the use of more recent electron cooling rates.…”

A short history of geophysical radar at Arecibo Observatory

“…In a rather unique use of the log-periodic feed Sulzer et al (1982) used the heater HF transmitter at 12 kW peak power level and 3.155 MHz frequency to provide the probing or "wanted" pulse for a D-region cross-modulation experiment where the 430 MHz radar performed as the heater transmitter. This "inverted role" system successfully demonstrated wave interaction (cross-modulation) and is the only known example of UHF (430 MHz) heating of the ionosphere D-region.…”

“…Today Arecibo Observatory is used for atmospheric and ionospheric studies, planetary radar astronomy, and radio astronomy. It remains the most sensitive such facility and has been or is being used over a frequency range from about 3 MHz (on-dish high frequency (HF) heating; Sulzer et al, 1982) through about 10 GHz (radio astronomy).…”