GEOPHYSICAL RESEARCH LETTERS, VOL. 21, NO. 14, PAGES 1539-1542, JULY 1, 1994 Gravity wave activity inthe upper. stratosphere. and lower mesosphere observed wth the Rayleigh lidar at Tsukuba, Japan Y. Murayama, • T. Tsuda, and R. Wilson • Radio Atmospheric Science Center, Kyoto University, Kyoto, Japan H. Nakane, S. A. Hayashida, N. Sugimoto, I. Matsui,andY. Sasano The National Institute for Environmental Studies, Tsulcuba, Japan Abstract. We delineatedthe climatological character- istics of the potential energy of gravity waves, E•,, us- ing Rayleigh lidar observations made in 1990--1991 at Tsukuba, Japan (36øN, 140øE).Tendency of large and small values of E•, in winterand summer, respectively, was detected in the upper stratosphere (30-45 kin), suggesting annualvariationwith a winter maximum. This annualcy- cle seemed to be consistent with lidar observations made in France and UK [Wilson et al., 1991; Mitchell et al., 1991]. The obtained E•, values in the upperstratosphere and lower mesosphere (45-60 kin) wererather similar to the Frenchdata, despite the large scatterof the Tsukuba v•lues. Introduction Studies on the climatological characteristics of gravity waves, such as their seasonal and latitudinal variations, were commenced by employing a globaldata-base of rock- etsonde measurements [Hirota, 1984]. Recentground- based observations with atmospheric radarsandlidarshave greatly contributed to studies of gravity waves, due to the advantage of continuous monitoring with good time-height resolution, whichrevealed variations with altitude, latitude and season [e.g.,Vincent and Fritts, 1987; Tsuda et al., 1990,1993; Senff and Gardner, 1991; Wilson et al., 1991]. Usingstatisticalanalysis of the monthly MU radar obser- vations over Shigaraki, Japan (35øN, 136øE) for fouryears, Murayamaet al. [1993] revealed annualvariation of the gravity waveenergy with a winter maximum in the lower stratosphere, while in the upper mesosphere, the semian- nuM variation with peaks in summerand winter was de- tected by Tsudaet al. [1990]. Senft and Gardner [1991] also showed the semiannual component of the gravitywave activity in the mesopause region from Na lidar observations at Urbana. Rayleigh lidar observations also provided density and temperature profilesat about 30-80 kin, with good time •Now at Communications Research Laboratory,Tokyo, Japan 2Now at Service d•A•ronomie du CNRS, Universit• Paris (3, France Copyright 1994 by the American Geophysical Union. Paper number 93GL02693 0094-8534/94/93 GL-02693 $03.00 and height resolutions [e.g., Chanin and Hauchecorne, 1981; Mitchell et al., 1991; Senft et al., 1993],which are useful in complementing MST radar observations, with which one is normally unable to measure the wind fields between 25 and 60 kin. The kineticenergy of gravitywaves can be derivedfrom the wind velocityvariance with MST radar observations, whilelidar observations of the density and temperature fluctuations allow the determination of the available potential energy. The Rayleigh lidar obser- vations could interpolate radar studies on gravity wavecli- matology, resulting in the annualvariationof gravity wave potentialenergy in the upper stratosphere [Wilson et al., 1991;Mitchellet al., 1991]. Wilsonet al. [1991] showed that the variation in the lower mesosphere was rather fea- tureless. In this study we employed a data-base obtained with the Rayleigh lidar at the National Institute for Environmental Studies (NIES) at Tsukuba, Japan(36øN,140øE) [Sugi- moto et al., 1989;Nakane et al., 1992a, hi, for studies of the statistical behavior of the potentialenergy of gravity waves in the stratosphere andmesosphere (30-60kin). We further compare the results with lidar observations madeat the Observatoire de Haute Provence (OHP) (44 ø N, 6 ø E) and Biscarosse (BIS)(44ø N, 1 ø W)[Wilson et al., 1991], as well as the results at Aberystwyth, UK [Mitchell et al., 1991]. Lidar Observations and Data Processing Lidar observations at NIES were started in 1988, the de- tails of the lidar system and basic experimental procedures beingdescribed elsewhere [Sugimoto et al., 1989;Nakane et al., 1992b]. The atmospheric density wasderived from the Rayleigh scattering intensity with a 351 nm laserwith height and time resolutions of 0.15 km and 10 rain, re- spectively, and the temperature profile was further inferred with the hydrostatic assumption of an ideal gas. The observation periodsare illustrated in Figure 1, the observations beingconducted only at night, with intervals ranging from a few to 10 hours. Note that the observations were more frequently conducted in winter months due to the better weather conditions than in summer. The upper limit of the heightrange for each profile was determined by investigating the statistical behavior of the received signal. Note that we did not include a profile which showed great variation near the stratopause, which seemedto include the effect of the enhanced activity of planetary waves [Wilson, private communication ]. We first averaged the profiles for one hour, and defined a background profile p(z) by using the least-squares fit of 1539