group meeting 5.7.2009 wen-yen. vienna trip views
TRANSCRIPT
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Group Meeting5.7.2009
Wen-Yen
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Vienna Trip
Views
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Foods
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EGU
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Paper Review :
Amplification of obliquity forcing
through mean annual and seasonal
atmospheric feedbacks
S.-Y. Lee and C.J. Poulsen 2008
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Main Ideas
• Benthic δ records indicating that global ice volume has modulated by Earth’s axial tilt(obliquity).
• In this paper, use a coupled ocean-atmosphere general circulation model to quantify changes in continental snowfall associated with mean annual and seasonal insolation forcing due to a change in obliquity.
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• There were 2 experimental sets.
• Boundary conditions were set to modern values.
• Each experiments was integrated for 200 years and the model results were averaged over last 50 model years.
Experimental Design
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Experimental Design
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Results – insolation difference
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Results – snowfall response25.0 cm↑
10.9 cm↑
14.1 cm↑
+78%
+22%
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Results – N.H. winter snowfall
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Results – N.H. summer snowfall
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Results – N.H. summer snowfall
Different heating between low- and high-latitude (Fig. 5) let baroclinicity increases (especially in △TOTAL). N.H. transient eddies increase with baroclinicity leading to a 200% increase in summer poleward transient eddy vapor transport at 45N and an enhancement in the total vapor transport.
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• Local reductions in air temperature enhance precipitation as snowfall.
• An intensification of the winter meridional insolation gradient strengthens zonal circulation (e.g. the Aleutian low), promoting greater vapor transport from ocean to land and snow precipitation.
• An increase in the summer meridional insolation gradient enhances summer eddy activity, increasing vapor transport to high-latitude regions.
Results
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• Climate mechanisms amplify the climate response to obliquity forcing, and both “mean annual” and “seasonal” changes in the distribution of insolation play important roles.
• The model results suggest that these climate feedbacks can not be sufficiently large to account for the spectral nature of the ice volume record.
Summary
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THE ENDThank You