Organization of deep convection into squall lines

The organization of deep convection into squall lines is not represented in global climate models, despite being among the biggest storms on Earth and having a huge impact on precipitation and extremes in tropical regions such as the Sahel or the Amazon [1, 2]. The overarching goal of this project is to parameterize the occurrence of squall lines in the general circulation model LMDZ, and their impact on their environment. Since the interaction between wind shear and cold pools is essential in squall line formation and maintenance [3], we plan to take advantage of the cold pool scheme [4] already implemented in LMDZ.

Regarding the occurrence of squall lines, we hypothesize that it can be predicted based on the domain-mean wind profile and the cold pool properties, diagnosed from the cold pool scheme.

Regarding the impact of squall line in their environment, we hypothesize that squall lines impact the vertical profile of diabatic heating [5], either through entrainment in convective updrafts [6] or through the rate of rain evaporation [7]. We also hypothesize that the larger rate of rain evaporation strengthens cold pools favoring more likely and more intense convection [8]. Entrainment and rate of rain evaporation can be varied in the convective scheme of LMDZ [9] through tunable parameters.

To test these hypotheses, we analyse simulations from the cloud-resolving model SAM in radiative-convective equilibrium configuration with various wind shear and large-scale ascent conditions.

Ultimately, the representation of squall lines should improve the simulation of precipitation distribution, variability and extremes in tropical regions such as the Sahel or the Amazon.

 

 

[1] R. Roca, J. Aublanc, P. Chambon, T. Fiolleau, N. Viltard, J. Clim. 27, 4952–4958 (2014).

[2] R. Roca, T. Fiolleau, Com. Earth & Env. 1, 18 (2020).

[3] R. Rotunno, J.B. Klemp, M.L. Weisman, J. Atmos. Sci., 45(3), 463-485 (1988).

[4] J.-Y. Grandpeix, J.-P. Lafore, J. Atmos. Sci., 67, 881–897 (2010).

[5] U. Anber, S. Wang, A. Sobel, J. Atmos. Sci., 71, 2976–2993 (2014).

[6] T. Becker, C. S. Bretherton, C. Hoehenegger, B. Stevens, Geophys. Research Lett. 45, 455–462 (2018).

[7] J. P. Lafore, J. L. Redelsperger, G. J. Jaubert, Atmos. Sci., 45(22), 3483-3500 (1988).

[8] G. G. Rooney, A. J. Stirling, R. A. Stratton, M. Whitall, Quart. J. Royal. Meteoro. Soc. 148, 962–980 (2021).

[9] K. A. Emanuel, J. Atmos. Sci. 48, 2313–2329 (1991).