Thursday, 14 January 2021

Jet Stream History

Jet Stream History 

Where was the jet stream during the Younger Dryas? And how do you map it? And how does it matter? Read all about it HERE and HERE.

The Younger Dryas was a period of cooling at the end of the last glaciation - 12.9 to 11.7 thousand years ago. It would be no surprise if the jet stream had something to do with it but how do you map the jet stream?

Answer:- look at the glaciers of the period; identify the equilibrium line altitude (ELA) where ablation (mass lost) equals accumulation (mass gain); from that draw a map of precipitation across Europe 12,000 years ago. Simple! The sources tell you how to do it. 

Western Europe and the eastern Mediterranean were wetter than now. The bit in between was drier. And from this you can map the jet stream. 

Current computer models of the climate do not show this. To have confidence in predictions of future climate we need models which model the past with some degree of accuracy. Work such as described above helps in this.

Equilibrium Line Altitude  elevation surface for the Younger Dryas.

The ELA surface should be viewed as “theoretical” (ELAthl) because glaciers can only form where the topography is higher than the ELAthl surface. For example, there are no glaciers in SE England or the low countries. Black dots show the location of palaeoglacier reconstruction sites. The FIS and the West Highlands icefield are shown, but the ice mass in the Alps is not shown due to incomplete knowledge of its geometry at this time.

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