POSTPONED, new date TBA; Sack Lunch Seminar (SLS) – Alex Gonzalez (WHOI)

Title: Dynamical importance of the trade wind inversion in suppressing the southeast Pacific Inter-Tropical Convergence Zone (ITCZ)

Abstract:
Sea surface temperature (SST) gradients are a primary driver of low-level wind convergence associated with the Inter-Tropical Convergence Zone (ITCZ) through their hydrostatic relationship to the surface pressure force (PGF). To what extent temperature gradients above the surface have an effect on ITCZ convergence through their modulation of the surface PGF is not well understood, which could be important in tropical regions with a strong trade wind inversion (TWI), such as the east Pacific Ocean. In this study, we show evidence of a dynamical link between the TWI and east Pacific ITCZ in a series of simulations using an idealized boundary layer model (SBLM). SBLM simulations using the full, surface to 850 hPa, virtual temperature profile produce a realistic northern hemisphere ITCZ. However, SST-only simulations tend to produce excessive equatorial cold tongue-driven divergence and off-equatorial convergence, a double ITCZ-like structure. Subsequent SBLM simulations and investigations of virtual temperature gradients at different pressure levels highlight the importance of temperature gradients weakening with height everywhere, especially from the equator to 15 degrees south, where there is anomalous divergence south of the equator due to an elevated cold anomaly and anomalous convergence on the equator due to an elevated warm anomaly both associated with the TWI and stratocumulus clouds. Thus, the TWI and stratocumulus clouds can help enable a more northern hemisphere dominant ITCZ. In this way, we provide evidence of a dynamical link between double ITCZs and low clouds, which both are problematic in present-day Earth System Models.

About this Series: The Atmospheres, Ocean and Climate Sack Lunch Seminar Series is an informal seminar series within PAOC that focuses on more specialized topics than the PAOC Colloquium. Seminar topics include all research concerning the science of atmospheres, ocean and climate. The seminars usually take place on Wednesdays from 12-1pm. The presentations are either given by an invited speaker or by a member of PAOC and can focus on new research or discussion of a paper of particular interest. Contact: sacklunch-committee@mit.edu for more information and Zoom password