06 Jul 2021

06 Jul 2021

Review status: this preprint is currently under review for the journal ESD.

Sensitivity of land-atmosphere coupling strength to perturbations of early-morning temperature and moisture profiles in the European summer

Lisa Lea Jach, Thomas Schwitalla, Oliver Branch, Kirsten Warrach-Sagi, and Volker Wulfmeyer Lisa Lea Jach et al.
  • Institute of Physics and Meteorology, University of Hohenheim, Stuttgart, Germany

Abstract. Land-atmosphere coupling can have a crucial impact on convective initiation. Yet, uncertainty remains in the analyses of the atmospheric segment of the coupling between land surface wetness and the triggering of deep moist convection, particularly over Europe. One reason for this is a lack of suitable data. To overcome this limitation, we perturb early-morning temperature and moisture profiles from a regional climate simulation covering the period 1986–2015 over Europe to create a spread in atmospheric conditions. Applying the ‘Convective Triggering Potential – low-level Humidity Index’ framework, we analyze whether and how strongly the coupling strength and the predominance of positive versus negative feedbacks are sensitive to modifications in the atmospheric conditions.

The results show that the hotspot region in northeastern Europe, in which strong feedbacks are likely to occur, is insensitive to temperature and moisture changes, but the number of potential feedback days varies by up to 20 days per season in dependence of the atmospheric background conditions. Temperature modifications rather control differences in the coupling strength in the north of the domain, while moisture changes dominant the control in the south. In the north of the hotspot region, a predominance for positive feedbacks (deep convection over wet soils) remains, but a switch of the dominant feedback class between positive feedbacks and a transition zone (convection over any soil, but usually shallow convection) occurred from the Alps to around the Black Sea. This indicates a dependence of the dominant feedback class on temperature and relative humidity in this region.

Lisa Lea Jach et al.

Status: open (until 29 Aug 2021)

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Lisa Lea Jach et al.

Lisa Lea Jach et al.


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Short summary
The land surface can influence the occurrence of local rainfall through different feedback mechanisms. In Europe, this happens most frequently in summer. Here, we examine how differences the average atmospheric conditions change where and how often the land surface can influence rainfall. The results indicate that the differences barely change that the surface influence is strongest over Scandinavia and Eastern Europe, but they can change the frequency of feedback events.