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

Abstract

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.

Observation‐Driven Characterization of Soil Moisture‐Precipitation Interactions in the Central United States

“…Despite the general scientific consensus that diurnal soil moisture feedbacks play an important role in shaping regional hydroclimatology, prior studies show less agreement as to the feedbacks' sign and strength. Modelingand observation-based studies have found evidence for either or both wet and dry soil feedbacks to precipitation in many global regions (Graf et al, 2021;Guillod et al, 2015;Huggannavar & Indu, 2020;Jach et al, 2021;Klein & Taylor, 2020;Vecellio et al, 2019). The inconsistencies between studies are attributable to multiple factors, such as (a) the paucity of high-quality observations from vadose zone to boundary layer and the consequential reliance on regional-to global-scale models, (b) the challenge of establishing causality of a soil moisture feedback to precipitation in the face of many confounding factors, and (c) the frequent inference of feedback sign and strength from a single metric applied to a relatively large spatial area.…”