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Mechanisms for African easterly wave changes in simulations of the mid-Holocene
- Bian, Jianpu (author)
- Räisänen, Jouni (author)
-
- Zhang, Qiong, 1971- (author)
- Stockholms universitet,Institutionen för naturgeografi
- (creator_code:org_t)
- 2023-03-07
- 2023
- English.
- In: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 61:7-8, s. 3165-3178
- Journal article (peer-reviewed)
Abstract
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- The mid-Holocene was a warm period with significantly amplified precipitation in North Africa, and a northward shifted Western African Monsoon during boreal summer. We conduct simulations for the pre-industrial and mid-Holocene periods to investigate the connection between summer rainfall variability and changes of African easterly waves (AEWs) during the mid-Holocene. Summer rainfall increases and migrates northward during the mid-Holocene, but the magnitude of change fails to reconcile the discrepancy with mid-Holocene proxy evidence, possibly due to no prescribed vegetation change in our simulations. The spectrum of summer rainfall over the Sahel and West Africa reveals enhanced synoptic time scale (3-to-6 days) variability during the mid-Holocene, which is consistent with the enhanced AEW activity influence. Specifically, the southern AEW track strengthens and migrates poleward during the mid-Holocene period, which modulates summer rainfall over the Sahel and West Africa. By comparison, the northern AEW track changes less and produces a minor contribution to rainfall changes in those regions. We find enhanced baroclinic and barotropic instabilities to promote the AEW activity during the mid-Holocene, with a doubling of the eddy kinetic energy of the meridional wind from that in PI, and baroclinic energy conversion plays a more important role. Stronger low-level meridional thermal gradients increase moisture flux from the Atlantic Ocean to inland.The amplified AEW activity, together with promoted moist convection and increased precipitation, results in a northern shift of the summer rainfall band during the mid-Holocene.
Subject headings
- NATURVETENSKAP -- Geovetenskap och miljövetenskap -- Meteorologi och atmosfärforskning (hsv//swe)
- NATURAL SCIENCES -- Earth and Related Environmental Sciences -- Meteorology and Atmospheric Sciences (hsv//eng)
- NATURVETENSKAP -- Geovetenskap och miljövetenskap -- Klimatforskning (hsv//swe)
- NATURAL SCIENCES -- Earth and Related Environmental Sciences -- Climate Research (hsv//eng)
Keyword
- African easterly waves
- Mid-Holocene
- Summer rainfall
- Baroclinic and barotropic instability
- Wave-mean flow interaction
Publication and Content Type
- ref (subject category)
- art (subject category)
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