Land–Atmosphere coupling sensitivity to GCMs resolution: a multimodel assessment of local and remote processes in the Sahel hot spot

Muller, O. V., Vidale, P. L. ORCID: https://orcid.org/0000-0002-1800-8460, Vanniere, B. ORCID: https://orcid.org/0000-0001-8600-400X, Schiemann, R. ORCID: https://orcid.org/0000-0003-3095-9856, Senan, R., Haarsma, R. J. and Jungclaus, J. H. (2021) Land–Atmosphere coupling sensitivity to GCMs resolution: a multimodel assessment of local and remote processes in the Sahel hot spot. Journal of Climate, 34 (3). pp. 967-985. ISSN 1520-0442 doi: 10.1175/jcli-d-20-0303.1

Abstract/Summary

Land–atmosphere interactions are often interpreted as local effects, whereby the soil state drives local atmospheric conditions and feedbacks originate. However, nonlocal mechanisms can significantly modulate land–atmosphere exchanges and coupling. We make use of GCMs at different resolutions (low ~1° and high ~0.25°) to separate the two contributions to coupling: better represented local processes versus the influence of improved large-scale circulation. We use a two-legged metric, complemented by a process-based assessment of four CMIP6 GCMs. Our results show that weakening, strengthening, and relocation of coupling hot spots occur at high resolution globally. The northward expansion of the Sahel hot spot, driven by nonlocal mechanisms, is the most notable change. The African easterly jet’s horizontal wind shear is enhanced in JJA due to better resolved orography at high resolution. This effect, combined with enhanced easterly moisture flux, favors the development of African easterly waves over the Sahel. More precipitation and soil moisture recharge produce strengthening of the coupling, where evapotranspiration remains controlled by soil moisture, and weakening where evapotranspiration depends on atmospheric demand. In SON, the atmospheric influence is weaker, but soil memory helps to maintain the coupling between soil moisture and evapotranspiration and the relocation of the hot spot at high resolution. The multimodel agreement provides robust evidence that atmospheric dynamics determines the onset of land–atmosphere interactions, while the soil state modulates their duration. Comparison of precipitation, soil moisture, and evapotranspiration against satellite data reveals that the enhanced moistening at high resolution significantly reduces model biases, supporting the realism of the hot-spot relocation.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/95707
Identification Number/DOI	10.1175/jcli-d-20-0303.1
Divisions	Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Uncontrolled Keywords	Atmospheric Science
Publisher	American Meteorological Society
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