The Role of Inertial Instability and Boundary-Layer Processes in Equatorial Monsoon Regions

Northwest Research Associates, Incorporated, Seattle WA

Investigators

Abstract

Much of the rain that falls in the deep tropics is concentrated in the inter-tropical convergence zone (ITCZ). The dynamics that determine the distribution of convective rainfall near the equator, such as the position of the inter-tropical convergence zone (ITCZ), are not well understood. Global climate models (GCMs) often fail to capture the observed distribution, and it is sensitive to details of model parameterizations. Observational evidence suggests that a fundamental fluid dynamical instability, inertial instability, is important for this problem. Here the problem of the position of the ITCZ will be addressed by focusing on the role of inertial instability within the boundary layer - the atmospheric layer near the ground - and interactions between inertial instability and boundary-layer turbulence and convection. Dynamical hypotheses will be tested using boundary-layer parameterizations driven by data. The key data are scatterometer (QuikSCAT) derived winds and wind stresses. Processes inferred from the observational studies will be tested in a set of model experiments. Three major tasks will be carried out: 1) Analyses of observational data to investigate the relationship between the inertial instability - specifically the location of the line of zero absolute vorticity - and the location of the ITCZ. 2) Analyses of the force balances within the boundary layer, and the transition from advective to Ekman (drag dominated) regimes across the line of zero absolute vorticity. 3) Analyses of the time scales of inertial instability and the processes that contribute to the position of the ITCZ on different timescales Broader impacts of this research are in its potential to drive improved representations of tropical circulations in global models, improved understanding of the Indian monsoon and of the genesis of tropical cyclones, and in the application of some methods to related problems that involve modeling sub-grid scale processes. A new investigator will be trained and an undergraduate will participate in the research through cooperation with the University of Washington.