Variances of the normalized power, the angle of arrival, and temporal spectra were obtained from millimeter-wave propagation experiments. For their interpretation the existing theory for monochromatic spherical wave propagation through an anisotropic weakly turbulent medium had been expanded such that anisotropy of the refractive index fluctuations transverse to the propagation path is taken into account. The comparison of experimental and theoretical results provides path-averaged estimates for the outer scale L0 in vertical and horizontal directions within the first few hundred meters above ground. Thus a determination of the atmospheric anisotropy is feasible, and it is found to be related to the atmospheric stability. The values obtained for L0 in vertical and horizontal directions are compatible with those presented in the literature. We found that the size and the anisotropy of L0 depend significantly on atmospheric conditions and vary accordingly widely in time.