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| Titel |
How did soil dryness intensify recent European heatwaves? |
| VerfasserIn |
Diego Miralles, Ryan Teuling, Chiel van Heerwaarden, Jordi Vilà-Guerau de Arellano |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091068
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| Publikation (Nr.) |
 EGU/EGU2014-5337.pdf |
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| Zusammenfassung |
| In August 2010 a mega-heatwave hit large parts of Eastern Europe and Russia, breaking the
historical records from the 2003 event in Western Europe. While such heatwaves are
predicted to become common by the end of this century, our understanding of the physics
behind these phenomena is still imperfect, and so is their representation in climate models. In
this presentation we will provide new evidence of how land-atmosphere feedbacks contribute
to the development of the extreme temperatures based on satellite observations,
climate model reanalyses data (ERA Interim), balloon sounding measurements, soil
moisture-temperature coupling diagnostics and mechanistic modelling of the lower
atmosphere.
Results of our analyses show that in both European mega-heatwaves, persistent synoptic
conditions favored evaporation and intensified soil desiccation. As a consequence of soil
dryness, a deep residual atmospheric boundary layer (ABL) developed, which allowed the
multi-day storage of heat coming from: (a) large-scale horizontal advection, (b) intense
warming from the land surface associated to the increasingly dry soils, and (c) enhanced
warm air entrainment from the top of the ABL (which counteracted the dilution effect of the
gradually deeper layer). This progressive storage of heat in the residual ABL played a crucial
role in the escalation of temperatures, and therefore in the regulation and intensification of
land feedbacks.
Soil moisture deficits have both direct and indirect effects in all these processes,
effects that have not been scrutinized separately in previous model studies. This
suggests the need of revisiting the traditional view of the soil moisture-temperature
coupling during mega-heatwaves, in which only the direct impact of dry soils on the
surface energy balance is explicitly considered. Reinforced by our findings, a more
complete conceptualization can be provided, with dry soils enhancing diurnal warm air
entrainment and leading to the formation of persistent residual layers that favor the
progressive storage of atmospheric heat. These positive feedbacks provide a plausible
answer to why temperatures become increasingly higher as heatwaves evolve, and
why they reach values so far outside the expected range of variability. We suggest
therefore, that both land-surface memory and multi-day ABL development need
to be simultaneously considered for timely prediction of future mega-heatwaves. |
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