Unravelling the transport of moisture into the Saharan Air Layer using passive tracers and isotopes
Abstract 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 unc...
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crwiley:10.1002/asl.1187 2024-06-02T08:11:05+00:00 Unravelling the transport of moisture into the Saharan Air Layer using passive tracers and isotopes Dahinden, Fabienne Aemisegger, Franziska Wernli, Heini Pfahl, Stephan Deutsche Forschungsgemeinschaft Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung 2023 http://dx.doi.org/10.1002/asl.1187 https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/asl.1187 en eng Wiley http://creativecommons.org/licenses/by/4.0/ Atmospheric Science Letters volume 24, issue 12 ISSN 1530-261X 1530-261X journal-article 2023 crwiley https://doi.org/10.1002/asl.1187 2024-05-03T10:59:58Z Abstract 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 (δ 2 H correlates most strongly with this tracer). The vertical profiles over the North Atlantic show increased humidity and δ 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. Article in Journal/Newspaper North Atlantic Wiley Online Library Detour ENVELOPE(-63.913,-63.913,-65.021,-65.021) Atmospheric Science Letters |
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Wiley Online Library |
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crwiley |
language |
English |
description |
Abstract 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 (δ 2 H correlates most strongly with this tracer). The vertical profiles over the North Atlantic show increased humidity and δ 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. |
author2 |
Deutsche Forschungsgemeinschaft Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung |
format |
Article in Journal/Newspaper |
author |
Dahinden, Fabienne Aemisegger, Franziska Wernli, Heini Pfahl, Stephan |
spellingShingle |
Dahinden, Fabienne Aemisegger, Franziska Wernli, Heini Pfahl, Stephan Unravelling the transport of moisture into the Saharan Air Layer using passive tracers and isotopes |
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 |
publisher |
Wiley |
publishDate |
2023 |
url |
http://dx.doi.org/10.1002/asl.1187 https://rmets.onlinelibrary.wiley.com/doi/pdf/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_source |
Atmospheric Science Letters volume 24, issue 12 ISSN 1530-261X 1530-261X |
op_rights |
http://creativecommons.org/licenses/by/4.0/ |
op_doi |
https://doi.org/10.1002/asl.1187 |
container_title |
Atmospheric Science Letters |
_version_ |
1800757112894128128 |