Bala, E.

Knippertz, P.

Voigt, A.

English

KITopen

EGU2020-18239https://doi.org/10.5194/egusphere-egu2020-18239EGU General Assembly 2020© Author(s) 2022. This work is distributed underthe Creative Commons Attribution 4.0 License.An MSE budget view on seasonal and CO2-induced ITCZ shifts in theTRAC-MIP model ensembleElzina Bala1, Aiko Voigt1,2, and Peter Knippertz11Karlsruhe Institute of Technology (KIT), Institute of Meteorology and Climate Research, Troposphere, Germany(elzinabala@gmail.com)2Lamont-Doherty Earth Observatory, Columbia University, New York, New York, USAOne of the grand challenges of climate is predicting and modeling tropical rainfall. Here, weaddress a specific problem of this grand challenge, namely how does the vertical structure of theatmosphere affect the tropical circulation and the position of the ITCZ during the seasonal cycleand in response to increased CO2. The tropical circulation can be described by the column-integrated budget of moist static energy (MSE). We use this framework in the TRAC-MIP modelensemble to investigate the role of the vertical structure of the tropical atmosphere in setting theanti-correlation between the ITCZ location and the atmospheric energy transport.TRACMIP "The Tropical Rain belts with an Annual cycle and Continent - Model IntercomparisonProject" is a set of idealized simulations that are designed to study the tropical rain belt responseto past and future forcings. TRACMIP includes 13 comprehensive CMIP5-class atmosphere modelsand one simplified atmospheric model. Importantly, TRACMIP includes a slab ocean withprescribed ocean heat transport. This leads to a closed surface energy balance and forces theannual-mean ITCZ to be north of the equator, consistent with today’s climate.We use the MSE budget framework to diagnose the seasonal evolution of vertical velocity from theenergetic terms in the MSE budget equation. We obtain a diagnostic expression for the verticalvelocity. By means of the MSE budget framework we estimate the efficiency of exporting energyfrom the atmospheric column, which is defined as the gross moist stability (GMS). The GMScharacterizes the stability of the tropical troposphere related to moist convective processes in thetropospheric column. We use the MSE and GMS analysis to disentangle the impact of deep andshallow circulations on energy transport, vertical velocity and hence precipitation in an objectivemanner.Through this work we aim to elucidate to what extent model uncertainty in simulations of futureITCZ changes are caused by model differences in the vertical structure of the atmosphere. We alsohope to use the results to advance our understanding of the tropical climate and to assess theplausibility of simulated changes in tropical rainfall.Powered by TCPDF (www.tcpdf.org)

An MSE budget view on seasonal and CO2-induced ITCZ shifts in the TRAC-MIP model ensemble

https://publikationen.bibliothek.kit.edu/1000128897/141040615

An MSE budget view on seasonal and CO2-induced ITCZ shifts in the TRAC-MIP model ensemble

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