Intra‐annual variation in large‐scale moisture fields

To identify better the annual cycle in the northern hemisphere fields of integrated water vapor and its flux, we have separated 5 years of upper‐air rawinsonde station data into four composite seasonal quarters. Maps and zonal means of the fields attest to the intensity of the summer‐winter contrast, increasing and sharpening prior estimates of this difference based on semester definitions of these seasons. Interestingly, results for the transition seasons of spring and of autumn are not identical but rather tend to resemble their antecedents, reflecting in part the importance of the ocean's thermal inertia. Our study should prove useful as a basis for comparison with results expected during the next decade from analyses of the Global Weather Experiment.