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Response of the North African summer monsoon to precession and obliquity forcings in the EC-Earth GCM

Response of the North African summer monsoon to precession and obliquity forcings in the EC-Earth GCM
Response of the North African summer monsoon to precession and obliquity forcings in the EC-Earth GCM


We investigate, for the first time, the response of the North African summer monsoon to separate precession and obliquity forcings using a high-resolution state-of-the-art coupled general circulation model, EC-Earth. Our aim is to better understand the mechanisms underlying the astronomical forcing of this low-latitude climate system in detail. The North African monsoon is strengthened when northern hemisphere summer insolation is higher, as is the case in the minimum precession and maximum obliquity experiments. In these experiments, the low surface pressure areas over the Sahara are intensified and located farther north, and the meridional pressure gradient is further enhanced by a stronger South Atlantic high pressure area. As a result, the southwesterly monsoon winds are stronger and bring more moisture into the monsoon region from both the northern and southern tropical Atlantic. The monsoon winds, precipitation and convection also extend farther north into North Africa. The precession-induced changes are much larger than those induced by obliquity, but the latter are remarkable because obliquity-induced changes in summer insolation over the tropics are nearly zero. Our results provide a different explanation than previously proposed for mechanisms underlying the precession- and, especially, obliquity-related signals in paleoclimate proxy records of the North African monsoon. The EC-Earth experiments reveal that, instead of higher latitude mechanisms, increased moisture transport from both the northern and southern tropical Atlantic is responsible for the precession and obliquity signals in the North African monsoon. This increased moisture transport results from both increased insolation and an increased tropical insolation gradient.
Paleoclimate modelling, Astronomical forcing, Milankovitch cycles, North African monsoon
0930-7575
279-297
Bosmans, J.H.C.
20249d98-78a4-49c4-9bc0-880cecef0662
Drijfhout, S.S.
a5c76079-179b-490c-93fe-fc0391aacf13
Tuenter, E.
33b282bc-c149-4ae1-92a9-cff714101d30
Hilgen, F.J.
a6acc962-bc4d-42b4-b8fa-a012f1301a11
Lourens, L.J.
61c02597-1860-45e5-9b78-a1473c7c86dd
Bosmans, J.H.C.
20249d98-78a4-49c4-9bc0-880cecef0662
Drijfhout, S.S.
a5c76079-179b-490c-93fe-fc0391aacf13
Tuenter, E.
33b282bc-c149-4ae1-92a9-cff714101d30
Hilgen, F.J.
a6acc962-bc4d-42b4-b8fa-a012f1301a11
Lourens, L.J.
61c02597-1860-45e5-9b78-a1473c7c86dd

Bosmans, J.H.C., Drijfhout, S.S., Tuenter, E., Hilgen, F.J. and Lourens, L.J. (2015) Response of the North African summer monsoon to precession and obliquity forcings in the EC-Earth GCM. Climate Dynamics, 44 (1-2), 279-297. (doi:10.1007/s00382-014-2260-z).

Record type: Article

Abstract



We investigate, for the first time, the response of the North African summer monsoon to separate precession and obliquity forcings using a high-resolution state-of-the-art coupled general circulation model, EC-Earth. Our aim is to better understand the mechanisms underlying the astronomical forcing of this low-latitude climate system in detail. The North African monsoon is strengthened when northern hemisphere summer insolation is higher, as is the case in the minimum precession and maximum obliquity experiments. In these experiments, the low surface pressure areas over the Sahara are intensified and located farther north, and the meridional pressure gradient is further enhanced by a stronger South Atlantic high pressure area. As a result, the southwesterly monsoon winds are stronger and bring more moisture into the monsoon region from both the northern and southern tropical Atlantic. The monsoon winds, precipitation and convection also extend farther north into North Africa. The precession-induced changes are much larger than those induced by obliquity, but the latter are remarkable because obliquity-induced changes in summer insolation over the tropics are nearly zero. Our results provide a different explanation than previously proposed for mechanisms underlying the precession- and, especially, obliquity-related signals in paleoclimate proxy records of the North African monsoon. The EC-Earth experiments reveal that, instead of higher latitude mechanisms, increased moisture transport from both the northern and southern tropical Atlantic is responsible for the precession and obliquity signals in the North African monsoon. This increased moisture transport results from both increased insolation and an increased tropical insolation gradient.

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More information

Published date: January 2015
Keywords: Paleoclimate modelling, Astronomical forcing, Milankovitch cycles, North African monsoon
Organisations: Physical Oceanography

Identifiers

Local EPrints ID: 374956
URI: https://eprints.soton.ac.uk/id/eprint/374956
ISSN: 0930-7575
PURE UUID: 4a7a10a3-e0a5-4990-adb2-2071f4d06769

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Date deposited: 06 Mar 2015 13:34
Last modified: 17 Jul 2017 21:21

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Contributors

Author: J.H.C. Bosmans
Author: S.S. Drijfhout
Author: E. Tuenter
Author: F.J. Hilgen
Author: L.J. Lourens

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