Unravelling the transport of moisture into the Saharan Air Layer using passive tracers and isotopes

The subtropical free troposphere plays a critical role in the radiative balance of the Earth. However, the complex interactions controlling moisture in this sensitive region and, in particular, the relative importance of long-range transport compared to lower-tropospheric mixing, remain unclear. Thi...

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Main Authors: Dahinden, Fabienne, Aemisegger, Franziska, Wernli, Heini, Pfahl, Stephan
Format: Article in Journal/Newspaper
Language:English
Published: 2023
Subjects:
Online Access:https://refubium.fu-berlin.de/handle/fub188/40654
https://doi.org/10.17169/refubium-40375
https://doi.org/10.1002/asl.1187
id ftfuberlin:oai:refubium.fu-berlin.de:fub188/40654
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spelling ftfuberlin:oai:refubium.fu-berlin.de:fub188/40654 2024-01-21T10:08:23+01:00 Unravelling the transport of moisture into the Saharan Air Layer using passive tracers and isotopes Dahinden, Fabienne Aemisegger, Franziska Wernli, Heini Pfahl, Stephan 2023 11 Seiten application/pdf https://refubium.fu-berlin.de/handle/fub188/40654 https://doi.org/10.17169/refubium-40375 https://doi.org/10.1002/asl.1187 eng eng https://refubium.fu-berlin.de/handle/fub188/40654 http://dx.doi.org/10.17169/refubium-40375 doi:10.1002/asl.1187 https://creativecommons.org/licenses/by/4.0/ atmospheric humidity moisture sources moisture transport Saharan Air Layer stable water isotopes turbulent mixing ddc:551 doc-type:article 2023 ftfuberlin https://doi.org/10.17169/refubium-4037510.1002/asl.1187 2023-12-24T23:26:13Z The subtropical free troposphere plays a critical role in the radiative balance of the Earth. However, the complex interactions controlling moisture in this sensitive region and, in particular, the relative importance of long-range transport compared to lower-tropospheric mixing, remain unclear. This study uses the regional COSMO model equipped with stable water isotopes and passive water tracers to quantify the contributions of different evaporative sources to the moisture and its stable isotope signals in the eastern subtropical North Atlantic free troposphere. In summer, this region is characterized by two alternating large-scale circulation regimes: (i) dry, isotopically depleted air from the upper-level extratropics, and (ii) humid, enriched air advected from Northern Africa within the Saharan Air Layer (SAL) consisting of a mixture of moisture of diverse origin (tropical and extratropical North Atlantic, Africa, Europe, the Mediterranean). This diversity of moisture sources in regime (ii) arises from the convergent inflow at low levels of air from different neighbouring regions into the Saharan heat low (SHL), where it is mixed and injected by convective plumes into the large-scale flow aloft, and thereafter expelled to the North Atlantic within the SAL. Remarkably, this regime is associated with a large contribution of moisture that evaporated from the North Atlantic, which makes a detour through the SHL and eventually reaches the 850–550 hPa layer above the Canaries. Moisture transport from Europe via the SHL to the same layer leads to the strongest enrichment in heavy isotopes (δ2H correlates most strongly with this tracer). The vertical profiles over the North Atlantic show increased humidity and δ2H and reduced static stability in the 850–550 hPa layer, and smaller cloud fraction in the boundary layer in regime (ii) compared to regime (i), highlighting the key role of moisture transport through the SHL in modulating the radiative balance in this region. Article in Journal/Newspaper North Atlantic Freie Universität Berlin: Refubium (FU Berlin) Detour ENVELOPE(-63.913,-63.913,-65.021,-65.021)
institution Open Polar
collection Freie Universität Berlin: Refubium (FU Berlin)
op_collection_id ftfuberlin
language English
topic atmospheric humidity
moisture sources
moisture transport
Saharan Air Layer
stable water isotopes
turbulent mixing
ddc:551
spellingShingle atmospheric humidity
moisture sources
moisture transport
Saharan Air Layer
stable water isotopes
turbulent mixing
ddc:551
Dahinden, Fabienne
Aemisegger, Franziska
Wernli, Heini
Pfahl, Stephan
Unravelling the transport of moisture into the Saharan Air Layer using passive tracers and isotopes
topic_facet atmospheric humidity
moisture sources
moisture transport
Saharan Air Layer
stable water isotopes
turbulent mixing
ddc:551
description The subtropical free troposphere plays a critical role in the radiative balance of the Earth. However, the complex interactions controlling moisture in this sensitive region and, in particular, the relative importance of long-range transport compared to lower-tropospheric mixing, remain unclear. This study uses the regional COSMO model equipped with stable water isotopes and passive water tracers to quantify the contributions of different evaporative sources to the moisture and its stable isotope signals in the eastern subtropical North Atlantic free troposphere. In summer, this region is characterized by two alternating large-scale circulation regimes: (i) dry, isotopically depleted air from the upper-level extratropics, and (ii) humid, enriched air advected from Northern Africa within the Saharan Air Layer (SAL) consisting of a mixture of moisture of diverse origin (tropical and extratropical North Atlantic, Africa, Europe, the Mediterranean). This diversity of moisture sources in regime (ii) arises from the convergent inflow at low levels of air from different neighbouring regions into the Saharan heat low (SHL), where it is mixed and injected by convective plumes into the large-scale flow aloft, and thereafter expelled to the North Atlantic within the SAL. Remarkably, this regime is associated with a large contribution of moisture that evaporated from the North Atlantic, which makes a detour through the SHL and eventually reaches the 850–550 hPa layer above the Canaries. Moisture transport from Europe via the SHL to the same layer leads to the strongest enrichment in heavy isotopes (δ2H correlates most strongly with this tracer). The vertical profiles over the North Atlantic show increased humidity and δ2H and reduced static stability in the 850–550 hPa layer, and smaller cloud fraction in the boundary layer in regime (ii) compared to regime (i), highlighting the key role of moisture transport through the SHL in modulating the radiative balance in this region.
format Article in Journal/Newspaper
author Dahinden, Fabienne
Aemisegger, Franziska
Wernli, Heini
Pfahl, Stephan
author_facet Dahinden, Fabienne
Aemisegger, Franziska
Wernli, Heini
Pfahl, Stephan
author_sort Dahinden, Fabienne
title Unravelling the transport of moisture into the Saharan Air Layer using passive tracers and isotopes
title_short Unravelling the transport of moisture into the Saharan Air Layer using passive tracers and isotopes
title_full Unravelling the transport of moisture into the Saharan Air Layer using passive tracers and isotopes
title_fullStr Unravelling the transport of moisture into the Saharan Air Layer using passive tracers and isotopes
title_full_unstemmed Unravelling the transport of moisture into the Saharan Air Layer using passive tracers and isotopes
title_sort unravelling the transport of moisture into the saharan air layer using passive tracers and isotopes
publishDate 2023
url https://refubium.fu-berlin.de/handle/fub188/40654
https://doi.org/10.17169/refubium-40375
https://doi.org/10.1002/asl.1187
long_lat ENVELOPE(-63.913,-63.913,-65.021,-65.021)
geographic Detour
geographic_facet Detour
genre North Atlantic
genre_facet North Atlantic
op_relation https://refubium.fu-berlin.de/handle/fub188/40654
http://dx.doi.org/10.17169/refubium-40375
doi:10.1002/asl.1187
op_rights https://creativecommons.org/licenses/by/4.0/
op_doi https://doi.org/10.17169/refubium-4037510.1002/asl.1187
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