In recent years methods of producing controlled modifications of the ionosphere by use of high‐intensity radio‐frequency waves have been proposed; some have been tried with inconclusive results. The present paper describes detection of significant (∼30%) changes in the electron temperature in the F2 region produced by absorption of radio‐frequency energy propagated at or near the local ionospheric plasma frequency. The radio‐frequency source is the 1‐Mw cw transmitter and ∼16° beamwidth antenna array described in the accompanying paper by Utlaut [1970]. As shown by the calculations of Meltz and LeLevier [1970], electron temperature increases of ∼35% can be expected within a few tens of seconds after the transmitter, tuned to within 1% of f0F2, is turned on.
Observations of the free atomic sodium layer near 90 km have been made as part of performance tests on a tunable dye‐laser radar. Altitude profiles of the layer obtained during parts of four nights in the fall of 1971 are consistent with those obtained by other groups but show two interesting additional features. The first is a sharp decrease in density that terminates the layer on the bottom side at a variable altitude near the mesopause. This decrease appears to become sharp only some time after twilight, suggesting that the sodium consumption mechanism undergoes a change as the nighttime chemistry is established. The second feature is a fourfold increase in sodium‐layer content during a 4‐hour period surrounding the transit of the radiant of the Geminids meteor shower on the night of December 13–14, 1971, when the shower was at its peak.
A Fabry-Perot spectrometer has been used at Arecibo, Puerto Rico, for measurement of the Doppler line width of [0 I] 6300-A emission in the night airglow. The temperature of the nighttime F region was obtained simultaneously from this technique and from analysis of data from incoherent scatter radar. In a
SUMMARYThirty night-time observations of the stratosphericaerosol were made between October 1972 and March 1974, using a ground-based ruby lidar (laser radar) at Menlo Park, California (37.5"N 122.2"W). Vertical profiles of scattering ratio and particulate backscattering coefficient were obtained by reference to a level of assumed negligible particulate backscattering.The observation period preceded the major stratospheric penetration of the Fuego volcanic eruption and was evidently one of minimal volcanic influence. Nevertheless, there was appreciable variation among observations, including significant vertical movement of the scattering ratio peak near the time of the 1973 stratospheric warming. Maximum scattering ratios ranged between 1.08 and 1.19, indicating a decline in particulate backscattering by approximately an order of magnitude since the maximum observed shortly after the 1963 eruption of the Agung volcano. This decline in backscattering is shown to agree with the overall trend in twilight scattering and particle data, from balloons, during the same period. On a single night, sequential observations with ruby (694 nm) and dye (589 nm) laser transmitters were made, showing significant scattering-ratio differences, due primarily to the wavelength dependence of molecular back-scattering.An optical model, consistent with a number of stratospheric measurements made in the early 1970s by a variety of techniques, is used to convert the lidar-measured backscattering values to other quantities. In this manner, good agreement is demonstrated between particle mass values inferred from lidar and aircraft filter measurements made on the same date. Values for turbidity and particulate optical thickness are similarly derived from the lidar data, giving values considerably smaller than those measured by searchlight in 1964-1965. To assist in radiative transfer calculations for the nonvolcanic period, a table of these optical thickness values is provided. Between 10 and 30 km, the lidar-derived nonvolcanic particulate optical thicknesses are 0.005 and 0.004 for wavelengths of 550 and 700 nm, respectively.
Remote measurements of calibrated samples of SO2 and O3 have been achieved with a lidar using ultraviolet signals produced by a tunable dye laser and a nonlinear crystal. The operating wavelengths for these measurements were 292.3 and 293.3 nm for SO2 and 292.3 and 294.0 nm for O3. The atmosphere in front of and behind the chamber acted as a distributed reflector to send laser light back through the chamber to a receiver near the laser. The laser measurements agreed well with in situ measurements. Integration of eight laser pulses at each of two wavelengths allowed the determination of SO2 concentration with an uncertainty equivalent to ±0.6 ppm in 100 m for low concentrations. For O3, the corresponding uncertainty limit was ±1.2 ppm in 100 m. The measurement errors are primarily attributable to variations in atmospheric backscattering intensity during the experiment, since the different wavelengths were radiated sequentially rather than simultaneously. The sensitivity of a system transmitting more favorable wavelengths at intervals separated by less than 1 min is estimated to be near ±0.1 ppm in 100 m for both SO2 and O3.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.