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Publication Date
1 July 2015

The Tropical Inversion will Strengthen in a Warming Climate

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The lowest few kilometers of the tropical marine atmosphere are frequently capped by an inversion layer. Under this inversion lie several types of boundary layer clouds. A key factor controlling the amount of the clouds is the strength of the inversion. A stronger inversion suppresses the mixing of boundary layer air with warmer and drier air in the free-troposphere, leading to a shallower, moister and cloudier boundary layer. In this study, we examine the realism of the tropical inversion and the response of inversion strength to anthropogenic forcing simulated in 18 CMIP5 models.

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Impact

Given the strong link between low-cloud cover (LCC) and EIS, LCC ought to increase, due to a EIS increase. One study by Caldwell et al. (2012) supports this view. In their study, imposing CMIP3-model-simulated large-scale changes on a mixed layer model yields an increase in LCC. They attributed this increase primarily to the EIS increase. Furthermore, increases in EIS cause LCC to increase (albeit less strongly than observed) in many fully coupled atmosphere-ocean models (CMIP3 and CMIP5, see Qu et al. 2014). Nevertheless, LCC changes in those models are less impacted by the EIS increase than they are by other cloud controlling factors (e.g., an increase in SST). A recent study using Large-Eddy Simulations also concludes that the EIS rise may be less important to the overall LCC change than other factors, namely the increases in moisture transport through the boundary layer which are fundamentally tied to the warmer temperature in the boundary layer (Bretherton and Blossey 2014). Even so, the EIS change may still play a significant role in coupled model simulations at least in two ways. First, it may contribute to the fast cloud response and thus modulate effective GHG radiative forcing (see Webb et al. 2012). Second, due to its intrinsic nonlinearity, the EIS change may contribute to the nonlinearity of the tropical low-cloud feedback (see Williams et al. 2008 and Andrews et al. 2012). 

Point of Contact
Xin Qu
Institution(s)
University of California Los Angeles (UCLA)
Funding Program Area(s)
Acknowledgements
Publication