Testing convective transport on short time scales: Comparisons with mass divergence and ozone anomaly patterns about high rain events

Abstract

High rain events in the western tropical Pacific were identified using the Tropical Rainfall Measuring Mission (TRMM) 3B42 gridded rainfall data set. Horizontal wind measurements from radiosonde arrays, cloud top frequency measurements from CALIPSO, and ozonesonde measurements from SHADOZ were used to construct anomaly patterns of divergence, cloud top frequency, and ozone mixing ratio about the high rain events. The observed divergence anomaly pattern was compared with patterns produced by the Goddard Earth Observing System version 4 (GEOS-4) and GEOS-5 assimilated meteorological data sets. The midlevel (∼6 km) divergence dipole seen in observations, consisting of a local maximum in divergence 8 h before peak rainfall and a local maximum in convergence 8 h after peak rainfall, is not represented in the GEOS-4 or GEOS-5 meteorology. The ozone anomaly pattern shows ozone decreases at midlevels (3-8 km) up to 16 h prior to peak rainfall. These decreases occur in association with increases in the frequency of midlevel cloud tops and are due to increased detrainment from cumulus congestus clouds. The observed ozone anomaly pattern was compared with anomaly patterns produced by the GEOS-Chem chemical transport model, driven by GEOS-4 and GEOS-5 assimilated winds and temperatures. The GEOS-Chem simulations also exhibit negative ozone anomalies at midlevels in association with high rain events. However, these anomalies are nearly symmetric about peak rainfall, rather than strongest prior to peak rainfall. The upper level negative ozone anomalies of the models are more persistent than the observations. These results help characterize some of the difficulties of meteorological data sets in capturing the layered character of tropical convective outflow and its timing with respect to high rain events. Copyright 2012 by the American Geophysical Union.