High-Resolution Observations of Mammatus in Tropical Anvils

Abstract

Unprecedented high-resolution observations of mammatus from a profiling 94-GHz Doppler radar during the NASA Cirrus Regional Study of Tropical Anvils and Cirrus Layers?Florida Area Cirrus Experiment (CRYSTAL?FACE) are presented. Because of its high sensitivity and temporal and spatial resolution, the cloud radar used was able to resolve the fine structure of individual mammatus clouds and record significant vertical Doppler velocity perturbations (?6 to +1 m?s?1). Strong perturbations of the Doppler velocity within the mammatus as it extends below the main cirrus cloud base are captured by the radar observations. Upward motions in the periphery of descending mammatus cores are documented. Areas of intense, small-scale turbulent mixing near the cirrus cloud base are identified using the Doppler spectrum width. Power spectra analysis of the mean Doppler velocity field supports the presence of gravity waves and the development of higher-frequency structures near the cirrus anvil base, where the mammatus clouds are observed. The observations provide strong evidence for dynamical forcing from coherent vertical motions 500 m above the cloud base contributing to the mammatus formation. The results are discussed in the context of suggested theories for mamma formation and morphology.