Variability of Tropical Elongated Convergence Zones

University Of California-Irvine, Irvine CA

Investigators

Abstract

Intertropical convergence zones (ITCZs) are narrow, zonally elongated regions of enhanced precipitation which can be identified near the equator over all ocean basins in time-averaged plots of precipitation, cloudiness, and surface wind convergence. In addition, an elongated region of enhanced mean precipitation known as the South Pacific Convergence Zone (SPCZ) extends across the Western Pacific to the south of the equator, with a somewhat southeastward orientation. This project examines the variability in the aereal coverage and location of these features using a novel spatial-temporal statistical model that will be applied to various datasets including a recently available high-resolution 30-year satellite dataset. The statistical method is a Markov random field (MRF) model, which identifies pixels contained in an ITCZ based on the clustering of ITCZ pixels in space and time. The MRF model is used to examine the variability of ITCZs caused by transient phenomena including easterly waves, extratropical disturbances, and the Madden-Julian Oscillation (MJO). Research on the impact of extratropical disturbances focuses in particular on the role of these disturbances in creating the conditions for intense moisture transport in "atmospheric rivers". Research on easterly waves seeks to determine the proportions of such waves which propagate through an ITCZ without interaction, become immersed in the ITCZ, or result in the breakup of a well-formed ITCZ. Other issues of interest include the formation of double-ITCZs, parallel to each other on either side of the equator, which occur in nature but are greatly exaggerated in many climate models, and the relationship between ITCZs and underlying sea surface temperatures. In addition to the MRF model and other observational diagnostic tools, the project uses a regional climate model (RCM) to simulate ITCZ behavior. The behavior of ITCZs is of practical importance as well as theoretical interest, as ITCZ variability is associated with El Nino events, the MJO, and atmospheric rivers, all of which have implications for severe weather in the United States. In addition, the work provides education and training for two graduate students, who will be trained in both atmospheric science and statistical modeling, thereby contributing to the development of an interdisciplinary science workforce. The two students also participate in an outreach and education program for elementary and middle school children, known as the Climate Literacy Empowerment and iNquiry program.