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Journal Article

Quantifying convective aggregation using the tropical moist margin's length

MPS-Authors

Leutwyler,  David
Precipitating Convection, The Atmosphere in the Earth System, MPI for Meteorology, Max Planck Society;

/persons/resource/persons226395

Windmiller,  Julia
Precipitating Convection, The Atmosphere in the Earth System, MPI for Meteorology, Max Planck Society;

External Resource

https://github.com/tbeucler/2019_WMI
(Supplementary material)

Fulltext (public)

2020MS002092.pdf
(Publisher version), 4MB

Supplementary Material (public)
There is no public supplementary material available
Citation

Beucler, T., Leutwyler, D., & Windmiller, J. (2020). Quantifying convective aggregation using the tropical moist margin's length. Journal of Advances in Modeling Earth Systems, e2020MS002092, pp. acc. article online. doi:10.1029/2020MS002092.


Cite as: http://hdl.handle.net/21.11116/0000-0006-EC6A-A
Abstract
On small scales, the tropical atmosphere tends to be either moist or very dry. This denes two states that, on large scales, are separated by a sharp margin, well identied by the antimode of the bimodal tropical column water vapor distribution. Despite recent progress in understanding physical processes governing the spatiotemporal variability of tropical water vapor, the behavior of this margin remains elusive, and we lack a simple framework to understand the bimodality of tropical water vapor in observations. Motivated by the success of coarsening theory in explaining bimodal distributions, we leverage its methodology to relate the moisture eld's spatial organization to its time evolution. This results in a new diagnostic framework for the bimodality of tropical water vapor, from which we argue that the length of the margin separating moist from dry regions should evolve toward a minimum in equilibrium. As the spatial organization of moisture is closely related to the organization of tropical convection, we hereby introduce a new convective organization index (BLW) measuring the ratio of the margin's length to the circumference of a welldened equilibrium shape. Using BLW, we assess the evolution of selfaggregation in idealized cloudresolving simulations of radiativeconvective equilibrium and contrast it to the time evolution of the Atlantic Intertropical Convergence Zone (ITCZ) in the ERA5 meteorological reanalysis product. We nd that BLW successfully captures aspects of convective organization ignored by more traditional metrics, while offering a new perspective on the seasonal cycle of convective organization in the Atlantic ITCZ