Atmospheric Variability Experiment (AVE) Project is a historical digital data set archived at the National Climatic Data Center (NCDC). During February 1964, the Marshall Space Flight Center supported an observational program in which rawinsonde data were collected from a network of 30 stations in the southeastern U.S. at intervals of 3 hours or less. This program, called Project AVE (Atmospheric ... Variability Experiment), presents, for the first time, data with a high degree of time resolution over a spatially and temporally extensive network. Part I of this report - Acquisition and Reduction of the Project AVE Data -is intended primarily as a documentation of the acquisition, checking, and processing of the data. Various printout and tape formats of the data are described, and a complete summary of the data available at each station and the location of known remaining errors are provided in appendices. The hourly parameters included in these data are surface, boundary layer, and upper level humidity, vapor pressure, temperature, precipitation, pressure, and winds. A wind computation scheme designed to extract as much detailed wind information as possible from AVE's unique angle data is discussed. Mesoscale wind features with amplitudes exceeding 2 ms-1 and 3 degrees should be resolvable at elevation angles approaching 12 degrees, while macroscale wind data are provided to about 6 degrees. Estimates of the accuracy of the thermodynamic and wind data are presented and comparisons with routine data made. These indicate that the extra care and precision used in evaluating the AVE data result in increased accuracy over data routinely available. Part II - Atmospheric Variability and Mesoscale Structure of the Atmosphere as Revealed by the Project AVE Data -presents results of first studies utilizing these data. Analysis of pressure-height and temperature on constant pressure charts at 3-hourly intervals shows that large scale features (wavelengths greater than 600 km) with amplitudes only half the values of commonly cited observational uncertainties exhibit space and time continuity. Examination of 3-hourly tendencies of important meteorological variables indicate that they typically exceed measurement uncertainties, may often be inadequately represented by interpolation of 12-hourly observations, and exhibit appreciable spatial variation. Time sections in the lower troposphere constructed from 90-minute soundings reveal features on scales seldom seen by the meteorologist; horizontal dimensions are on the mesoscale and vertical wavelength characteristically about 1 km. Such features can account for appreciable temporal variability on short time scales. Finally, it is demonstrated that the AVE detailed wind data resolve, in some detail, theme so scale wind structure of the lower stratosphere noted by various investigators. Observations of these features at two stations permitted their wavelength to be estimated at 600 km, and their motion, relative to the surface, to be approximately along the direction of the mean wind but at about half its speed.