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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ftethz:oai:www.research-collection.ethz.ch:20.500.11850/628392 2024-02-11T10:06:07+01:00 Unravelling the transport of moisture into the Saharan Air Layer using passive tracers and isotopes Dahinden, Fabienne Aemisegger, Franziska Wernli, Heini id_orcid:0 000-0001-9674-4837 Pfahl, Stephan id_orcid:0 000-0002-9872-6090 2023-12 application/application/pdf https://hdl.handle.net/20.500.11850/628392 https://doi.org/10.3929/ethz-b-000628392 en eng Wiley info:eu-repo/semantics/altIdentifier/doi/10.1002/asl.1187 info:eu-repo/semantics/altIdentifier/wos/001048531700001 info:eu-repo/grantAgreement/SNF/Projekte MINT/164721 http://hdl.handle.net/20.500.11850/628392 doi:10.3929/ethz-b-000628392 info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International Atmospheric Science Letters, 24 (12) atmospheric humidity Moisture sources Moisture transport Saharan air layer Stable water isotopes Turbulent mixing info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion 2023 ftethz https://doi.org/20.500.11850/62839210.3929/ethz-b-00062839210.1002/asl.1187 2024-01-22T00:52:55Z 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 (d(2)H correlates most strongly with this tracer). The vertical profiles over the North Atlantic show increased humidity and d(2)H 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. ISSN:1530-261X Article in Journal/Newspaper North Atlantic ETH Zürich Research Collection Detour ENVELOPE(-63.913,-63.913,-65.021,-65.021) |
institution |
Open Polar |
collection |
ETH Zürich Research Collection |
op_collection_id |
ftethz |
language |
English |
topic |
atmospheric humidity Moisture sources Moisture transport Saharan air layer Stable water isotopes Turbulent mixing |
spellingShingle |
atmospheric humidity Moisture sources Moisture transport Saharan air layer Stable water isotopes Turbulent mixing Dahinden, Fabienne Aemisegger, Franziska Wernli, Heini id_orcid:0 000-0001-9674-4837 Pfahl, Stephan id_orcid:0 000-0002-9872-6090 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 |
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 (d(2)H correlates most strongly with this tracer). The vertical profiles over the North Atlantic show increased humidity and d(2)H 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. ISSN:1530-261X |
format |
Article in Journal/Newspaper |
author |
Dahinden, Fabienne Aemisegger, Franziska Wernli, Heini id_orcid:0 000-0001-9674-4837 Pfahl, Stephan id_orcid:0 000-0002-9872-6090 |
author_facet |
Dahinden, Fabienne Aemisegger, Franziska Wernli, Heini id_orcid:0 000-0001-9674-4837 Pfahl, Stephan id_orcid:0 000-0002-9872-6090 |
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 |
publisher |
Wiley |
publishDate |
2023 |
url |
https://hdl.handle.net/20.500.11850/628392 https://doi.org/10.3929/ethz-b-000628392 |
long_lat |
ENVELOPE(-63.913,-63.913,-65.021,-65.021) |
geographic |
Detour |
geographic_facet |
Detour |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_source |
Atmospheric Science Letters, 24 (12) |
op_relation |
info:eu-repo/semantics/altIdentifier/doi/10.1002/asl.1187 info:eu-repo/semantics/altIdentifier/wos/001048531700001 info:eu-repo/grantAgreement/SNF/Projekte MINT/164721 http://hdl.handle.net/20.500.11850/628392 doi:10.3929/ethz-b-000628392 |
op_rights |
info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International |
op_doi |
https://doi.org/20.500.11850/62839210.3929/ethz-b-00062839210.1002/asl.1187 |
_version_ |
1790603596199362560 |