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Radars operating in the frequency band between 2 MHz and several hundred megahertz are capable of supplying a large data base of measurements of turbulent energy dissipation rates in the middle atmosphere. So far this has not been achieved; only occasionally have such radars been used to produce estimates of turbulence intensities. In order to encourage a greater emphasis on this aspect of radar studies of the middle atmosphere, this review summarizes the various techniques which can be used to measure turbulent energy dissipation rates. It is shown how absolute measurements of backscatter cross section can be used to measure turbulence intensities. A new theory is presented which shows that the power backscattered from the mesosphere depends on the turbulent energy dissipation rate, the electron density gradient, the neutral density scale height, the total electron density and the temperature gradient. The effects of turbulence on the width of signal spectra received by these radars are discussed, and it is shown how turbulence intensities may be extracted from spectral width measurements. The importance of removing nonturbulent processes which also broaden the width of the power spectra, such as wind shear broadening and beam width broadening, are stressed.

The vertical eddy diffusivity K due to atmospheric turbulence with spatial scales of 10ø-102 m has been computed from the echo power spectral width observed by the middle and upper atmosphere radar for almost every month from January 1986 to December 1988. The method of analysis follows Lilly et al. [1974], $ato and Woodman [ ], and Hocking [1983a[ , 1988, and the contamination due to beam broadening, vertical shear, and transience has been removed. Although observations for horizontal wind speeds larger than approximately 40 m/s, such as occur near the tropopause jet stream in winter, have been omitted because of excessive beam broadening, sufficient numbers of observations have been accumulated to produce a reasonable climatology for the upper troposphere and lower stratosphere (6-20 km altitude) and for the mesosphere (60-82 km altitude). The monthly median of K shows a local maximum near the tropopause jet stream altitude. It becomes larger in the mesosphere, increasing gradually with height. Maxima of K are observed in winter near the tropopause and in summer in the mesosphere, and the seasonal variability of K reaches approximately an order of magnitude. A semiannual variability is apparent in the mesosphere with minima in the equinoctial seasons. effects of seasonal and meridional variations [Johnson and Wilkins, 1965; Justus, 1973; McElroy et al., 1974; Shimazaki and Ogawa, 1974; Crutzen, 1974; Johnston et al., 1976; Ogawa and $himazaki, 1975; Blum and $chuchardt, 1978; Massie and Hunten, 1981; Allen et al., 1981; $trobel et al., 1987]. Such an ad hoc description has also been used in dynamical models of gravity-wave dissipation [Matsuno, Paper number 94JD00911. 0148-0227/94/94JD-00911 $05.00 1982]. Chemically deduced values of K are often affected by the lifetime of each constituent and include not only the true diffusion effect due to microscale turbulence but also an advection effect due to the meridional circulation [Strobel, 1989; Mcintyre, 1989] and/or planetary waves [cf. Matsuno, 1980; Holton, 1981]. Since Lindzen [1981] proposed his well-known parameterization scheme for K due to purely monochromatic internal gravity waves, modelers have incorporated it into their models [e.g., Holton, 1982; Garcia and Solomon, 1985].Recently, mesosphere-stratosphere-troposphere (MST) and mesosphere/lower-thermosphere (MLT) radars have provided a powerful measurement technique for determination of K over a quite broad altitude range, with far better temporal resolution than previously afforded with the other techniques. There are two main procedures which may be used to infer K. Firsfly, we may estimate characteristics of the target scattering the radio wave from the radar echo power intensity [Gage et al., 1980;Balsley and Garello, 1985;Sato et al., 1985]. We then use relationships between the refractive index gradient and the turbulence parameters [e.g., Tatarski, 1971] to infer K, but the accuracy of this method decreases when temperature and humidity are not known with high resolution. Alternatively, we can e...

Abstract. Experimental studies of the temperature and pressure dependence of the ambipolar diffusion coefficient in the mesopause region have been undertaken by studying meteor trail decay times with radars at a variety of sites in North America, with latitudes between 75N and 35N. The site at Resolute Bay, Canada, has proven especially useful, due to the wide range of mesopause temperatures experienced at that site between summer and winter. Theoretical predictions have been confirmed, and an algorithm is outlined which permits meteor decay times to be used to determine absolute measurements of mesospheric temperatures.

Abstract. The current primary radar method for determination of atmospheric momentum fluxes relies on multiple beam studies, usually using oppositely directed coplanar beams. Generally VHF and MF radars are used, and meteor radars have never been successfully employed. In this paper we introduce a new procedure that can be used for determination of gravity wave fluxes down to time scales of 2-3 h, using the SKiYMET meteor radars. The method avoids the need for beam forming, and allows simultaneous determination of the three components of the wind averaged over the radar volume, as well as the variance and flux components u 2 , v 2 , w 2 , u v , u w and v w , where u refers to the fluctuating eastward wind, v refers to the fluctuating northward wind, and w refers to the fluctuating vertical wind. Data from radars in New Mexico and Resolute Bay are used to illustrate the data quality, and demonstrate theoretically expected seasonal forcing.

[1] Imaging measurements of a bright wave event in the nighttime mesosphere were made on 14 November 1999 at two sites separated by over 500 km in the southwestern United States. The event was characterized by a sharp onset of a series of extensive wavefronts that propagated across the entire sky. The waves were easily visible to the naked eye, and the entire event was observed for at least 5 1 2 hours. The event was observed using three wide-angle imaging systems located at the Boston University field station at McDonald Observatory (MDO), Fort Davis, Texas, and the Starfire Optical Range (SOR), Albuquerque, New Mexico. The spaced imaging measurements provided a unique opportunity to estimate the physical extent and time history of the disturbance. Simultaneous radar neutral wind measurements in the 82 to 98 km altitude region were also made at the SOR which indicated that a strong vertical wind shear of 19.5 ms À1 km À1 occurred between 80 and 95 km just prior to the appearance of the disturbance. Simultaneous lidar temperature and density measurements made at Fort Collins, Colorado, $1100 km north of MDO, show the presence of a large ($50 K) temperature inversion layer at the time of the wave event. The observations indicated that the event was most probably due to an undular mesospheric bore, a relatively uncommon disturbance which has only recently been reported [Taylor et al., 1995a]. Evidence is also shown to suggest that a large east-west tropospheric frontal system lying over the northern United States was the origin of the disturbance.

We compare Tropospheric Emission Spectrometer (TES) version 2 (V002) nadir ozone profiles with ozonesonde profiles from the Intercontinental Chemical Transport Experiment Ozonesonde Network Study, the World Ozone and Ultraviolet Data Center, the Global Monitoring Division of the Earth System Research Laboratory, and the Southern Hemisphere Additional Ozonesonde archives. Approximately 1600 coincidences spanning 72.5°S–80.3°N from October 2004 to October 2006 are found. The TES averaging kernel and constraint are applied to the ozonesonde data to account for the TES measurement sensitivity and vertical resolution. TES sonde differences are examined in six latitude zones after excluding profiles with thick high clouds. Values for the bias and standard deviation are determined using correlations of mean values of TES ozone and sonde ozone in the upper troposphere (UT) and lower troposphere (LT). The UT biases range from 2.9 to 10.6 ppbv, and the LT biases range from 3.7 to 9.2 ppbv, excluding the Arctic and Antarctic LT where TES sensitivity is low. A similar approach is used to assess seasonal differences in the northern midlatitudes where the density and frequency of sonde measurements are greatest. These results are briefly compared to TES V001 ozone validation work which also used ozonesondes but was carried out prior to improvements in the radiometric calibration and ozone retrieval in V002. Overall, the large number of TES and sonde comparisons indicate a positive bias of approximately 3–10 ppbv for the TES V002 nadir ozone data set and have helped to identify areas of potential improvement for future retrieval versions.

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