Gravity Wave Influences On Mesoscale Divergence:An Observational Case Study

Characteristics of tropospheric low-frequency gravity waves are diagnosed in radiosonde soundings from the Tropical Warm Pool-International Cloud Experiment near Darwin, Australia. The waves have typical vertical wavelengths of about 4 km, horizontal wavelengths of about 600 km, and intrinsic periods of about 12 hr. These scales match those of the vertical, horizontal, and temporal variability found in area-averaged horizontal wind divergence over the same domain. Vertical profiles of divergence show wave-like structures with variability of the order of 2 (Formula presented.) 10 (Formula presented.) s (Formula presented.) in the free troposphere. The results for Darwin are similar to previously reported observed mesoscale patterns of divergence/convergence over the tropical Atlantic. The findings imply that tropical divergence on spatial scales of a few hundred kilometers, which is known to influence the organization of convection, may be forced by gravity waves.