GEOPHYSICAL RESEARCH LETTERS, VOL. 22, NO. 20, PAGES 2841-2844, OCTOBER 15, 1995 ALOHA-93 measurements of intrinsic AGW characteristics usingairborne airglow imager and groundbased Na Wind/Temperature lidar G. R. Swenson Lockheed Research andDevelopment M. J. Taylor andP. J. Espy, Utah State University C. Gardner and X. T ac University of Illinois Abstract. Monochromatic Acoustic Gravity Waves (AGWs) with periods < 1 hourare a prevalent feature in themesospheric airglow layers. These waves are importantdynamically and energetically to the region where their temporal and spatial morphologyare not well established. The purposeof this study is establishthe intrinsic AGW characteristics over an extended region(as flown by the NCAR Electraaircraft)andto present the data in terms of the predicted spectral domain defined by the Brunt-Vaisala frequency and the diffusive filtering limit proposed by Gardner [1994]. On October21, 1993, observations were made from the NCAR Electra aircraft duringa 6 hour flight in a largetriangle N andW of Maui, for a inte..gral distance of ~3000 kin. The entire area observed [~1M km z] had a monochromatic AGW propagating toward th•NW and the western half had a SW propagating wave superimposed. These waves were also observed with the Michelson interferometer on the aircraft and an airglow imager at the Haleakala location during this time. Intrinsic phasevelocities were computed where the Na Wind/Temperature (w/r) lidar at Haleakalaprovideda measure of the mean wind to compensate phase velocities observedwith the imager. The data were tabulated and plottedin an AGW spectral reference frame and compared to cutoff conditions predicted by diffusive filtering theory. Introduction Horizontal wavelengthstructure has been observed with airglowimagers from ground based sites but the Electra flights providea new capability to observe the geographical extent of structure and to investigate wave sources. Monochromatic AGW features with periods lessthan 1 hour are an ever present phenomena in airglow structure at upper mesosopheric altitudes. Taylor et al. [1987] andSwenson andMende [1994] (and references)provide data examplesof monochromatic AGW structure, a frequentlyreported feature. In order to extractthe intrinsic parameters of an AGW, the measurement of the horizontalwavelength and extrinsic period are required, wherethe extrinsic (apparent) AGW periodis corrected for the background wind at the altitude throughwhich the AGW is propagating [Hines and Tarasick, 1987]. Historically, horizontalwavelength and the observed period have typically beenmeasured but coincident background wind data needed to calculate the intrinsic phase speedhave been lacking. The ALOHA-93 observations of October21 provide a measurement of the intrinsic AGW parameters over a large spatial region. Copyright 1995 by theAmerican Geophysical Union. Papernumber 95GL02579 0094-8534/95/95GL-02579503.00 The purpose of this intrinsicAGW wave parameters study is to (1) providea sampling from a relativelylarge geographic region and (2), to tabulate and presentthe observations in an 'AGW' spectralreference frame (domain). The statistical sample from this flight is usedin a separate studyalong with other data by Swenson et al. [this issue]to predict the upper limit to which the monochromatic waves observed in the 80- 105 km altitude region are capable of propagating and transferring their energy to the atmosphere. The AGW intrinsicparameters calculated here are plotted in the spectral reference framepredicted by diffusive filteringtheory[Gardner, 1994]. A goal is to begin the compilationof a data base to establish a spectral domain of monochromatic AGW observations to validate spectral models. As a data base evolves, the spectral character of monochromatic AGWs can be ascertained and eventually a 'spectral climatology' can be established. This is important in order to validate AGW models as well as to provide an input into global circulation studies where AGW inputarerequired. On October 21, a six hour triangular flight covered an extended regionNW of Haleakala, Maui while simultaneously, data was acquired from all-sky imagery and lidar systems on Haleakala. On the Electra aircraft, measurementswere made with a Michelson Interferometer [OH (3,1) band], an all-sky airglow imager, and the Na densitylidar. The aspects of the ^LOHA-93 campaign, the instrumentation and the observational and data analysis methods reportedin this paper are summarized by Gardner [this issue]and Swenson and Espy [this issue] and references. The details of the horizontal and verticalwave number spectra inferred from the airglowimager and Na lidar data are presented by Gardneret al. [this issue]. This paper summarizes the nature of the monochromatic features, which were extensive throughout the flight, for the airglow data measured from the aircraft, and Haleakala. The apparent phase velocity (Cobs) can be measured with the aircraftimager by observing a given AGW phase front for 10- 20 minutes to establish wave positionversustime. Changes in phasefront position,corrected for aircraft velocity, yield the observedphase velocity, i.e. Cobs. The Na lidar on Haleakalameasured the mean winds at airglow altitudes. The intrinsic phase velocity (Cin)for the aircraft measurements were thencomputed by Cin= Cobs - U, whereU= the component of wind normal to the AGW phasefronts. For this study, the Haleakala Na lidar measurement of wind [Xinet al., this issue] was used for the calculation of U. The AGW dispersion relationship wasused to calculate •.zfromCin (described above) andmeasured •.hß This is usefulfor comparison of 'measured' spectral data to theoretical spectral predictions of these waves. The intrinsic wave data was then tabulated and plotted in an AGW spectraldomain plot with boundaryconstraints of the Brunt-Vaisala periodand molecular diffusion [Gardner, 1994]. 2841