glace: the global land-atmosphere coupling experiment. part i: overview
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GLACE: The Global Land-Atmosphere Coupling Experiment. Part I: Overview. Wenxian Zhang School of Earth and Atmospheric Sciences Georgia Institute of Technology. Background. Precipitation Land surface moisture Numerical models vs. observations AGCMs Model dependence. Background. - PowerPoint PPT PresentationTRANSCRIPT
GLACE: The Global Land-Atmosphere Coupling Experiment.
Part I: Overview
Wenxian ZhangSchool of Earth and Atmospheric Sciences
Georgia Institute of Technology
Background
• Precipitation Land surface moisture
• Numerical models
vs. observations
• AGCMs
• Model dependence
Background
• Land-atmosphere coupling strength• K02: Four-model intercomparison (Koster et al.,
2002) - Four independent AGCM modeling groups - One-month simulation - The same time series of surface prognostic variables - Quantification of the response of precipitation - A marked disparity in the coupling strength
Motivations
• To quantify the land-atmosphere coupling strength of the twelve AGCMs
- Participation from a wider range of models
- Separation of the effects of “fast” and “low”
reservoirs
- Effect on air temperature• To document the coupling strengths of the
participating models for future study
Experimental Design
• Three ensemble
- Write
- Read
- Subsurface• Sixteen members• 1 June – 31 August
1994• The same SST
Ω Diagnostic
• Time series of six-day totals• P(t): 14 six-day totals for each simulation• :The ensemble mean time series
• :The temporal standard deviation• :The standard deviation of the ensemble mean time series
( )P t
16
1
1( ) ( )
16 ii
P t P t
p
P
Ω Diagnostic
• The degree to which the sixteen precipitation time series generated by the ensemble members are similar
• The relative contributions of boundary forcing and internal chaotic variability to the generation of precipitation
2 2
2
16
15
PP
pP
Ω Diagnostic
Figure 2 of Koster et al., 2002: Time series of precipitation produced by NSIPP’s R ensemble. (top) Grid cell for which Ω is high. (bottom) Grid cell for which Ω is low