Improving the Scientific Foundation for Atmosphere-Land-Ocean Simulations Report of a Workshop (2005) / Chapter Skim
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Appendix B Input from Workshop Invitees
Appendix B Input from Workshop Invitees
Pages 34-55
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From page 34... ...
And some address fundamental problems in the atmospheric and climate communities that hinder advancements in modeling. ATMOSPHERIC GRAVITY WAVE EFFECTS IN GLOBAL MODELS Joan Alexander, Colorado Research Associates Gravity waves are a major mode of geophysical variability on scales of O ~ 101000 km in stably stratified fluids.
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From page 35... ...
Mechanistic model studies show that planetary wave refraction and vacillation cycles are very sensitive to winter stratosphere wave drag via the mean flow. Monthly-mean latitude-height wind distributions are generally used to assess the fitness of a particular gravity wave parameterization in model tuning, yet mechanistic model studies show that slight variations in gravity wave drag can give very similar mean-wind distributions while giving very different stratosphere warming frequencies because of this wind sensitivity.
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From page 36... ...
As described above, there is a wealth of data that detect gravity waves, but it is a rare set of data that can provide sufficient information simultaneously on the wave momentum flux as well as the propagation properties of the waves, and no such data exist on the global scale. As with other physical processes, we must use models to aid in the interpretation of datasets, recognizing the observational limitations, to infer the wave properties needed to constrain parameterizations.
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From page 37... ...
Parameterization developments are behind the model needs but will eventually be sufficient, probably before the needs are considered top priority. LAND-ATMOSPHERE INTERACTIONS: HYDROLOGIC CYCLES Alan Betts, Atmospheric Research I believe major progress has been made in the past few years in understanding and evaluating the coupling of physical processes over land in global models (Betts, 2004; Betts and Viterbo, 2005; Koster et al., 2004; Lawrence and Slingo, 2004)
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From page 38... ...
· Identify links/causes in either data assimilation or representation of physical processes, using data as a guide. · Basic research on new representations of physics, in parallel with pragmatic improvements, again tied to data.
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From page 39... ...
The slow processes are the "climate" of the carbon cycle and are inextricably linked to the rest of the climate system. An important strategy in carbon cycle science is to observe variations in carbon compounds in the atmosphere and ocean and use them to understand underlying processes that govern sources and sinks.
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From page 40... ...
This is a generic requirement for subgrid-scale physical parameterizations in climate models, not a particular requirement for carbon cycle science. There is an emerging consensus in the carbon science community that diagnostic modeling and data assimilation provide a framework for leveraging
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From page 41... ...
. Cultural issues that hamper progress in carbon cycle parameterization include the traditional divides between observationalists and modelers, as well as perhaps more unique divides between modelers of fast versus slow processes.
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From page 42... ...
tend to be viewed as tools toward reducing these biases and uncertainties. Since it is often unclear which physical processes are responsible for particular biases and sensitivity uncertainty, there has been a serious lack of focus on improving the fundamental physical soundness of convective parameterizations and an emphasis on tuning physical parameterizations to produce realistic climate simulations.
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From page 43... ...
Precipitation is a critical variable, but in the global climate modeling context is not parameterized in terms of surface variables. Radiative fluxes at the surface do involve surface variables, but the principal source of variability (and uncertainty)
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Carbon Cycle program has (in my opinion) too much emphasis on observations to constrain oceanic PCO2.
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From page 45... ...
km or larger, and the vertical grid resolution is tens to a hundred meters. At this resolution the subgrid ocean processes that need to be parameterized can be divided into two categories: · mesoscale eddy fluxes due to balanced motions generated through instabilities of the mean circulation and · microscale turbulent processes due to unbalanced turbulent motions such as breaking internal waves, shear instabilities, double diffusion, or boundary layer mixing near the surface and bottom.
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From page 46... ...
Recently a CPT has been funded to develop new approaches to mesoscale eddy parameterizations at the ocean boundaries, based on better dynamical understanding and analysis of available observations. The physics of microscale turbulence in the oceanic boundary layers is the subject of a vast literature and parameterizations exist.
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From page 47... ...
Much work remains to properly parameterize double-diffusive mixing, with theoretical, experimental, observational, and numerical approaches needed. These and other ocean mixing processes are discussed in a white paper titled "Coupling Process and Model Studies of Ocean Mixing to Improve Climate Models -- A Pilot Climate Process Modeling and Science Team" (Schopf et al., 2003)
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From page 48... ...
. Now, most models carry total cloud water (and sometimes either cloud cover or higher moments of the cloud water distribution)
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From page 49... ...
However, as pointed out by Somerville and Remer (1984) , the assumption of temperature-dependent water content leads to a strong negative feedback on climate change due to the increase in global cloud albedo that accompanies global warming.
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From page 50... ...
Due to the complexity of the cloud problem, progress will depend not only on a complexity hierarchy of models but also on a scale hierarchy in which the behavior of microphysical parcel models, eddy- and cloud-resolving, regional, and global models are connected. A first principles microphysical calculation of hydrometeor growth in a single deep convective updraft is roughly as complicated as a climate calculation with a GCM.
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How important is this? CHALLENGES IN RATIONAL CLIMATE SCIENCE Bjorn Stevens, University of California, Los Angeles The challenge in representing physical processes in coupled atmosphereland-ocean models is foremost a political, not a scientific, one.
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From page 52... ...
From a physical perspective, the challenge is how to exploit technological advances in an attempt to improve the physical basis for the representation of physical processes in A-L-O models. An indispensable strategy is to use observations to identify regimes (i.e., recurrent patterns)
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From page 53... ...
In the marine boundary layers, surface gravity waves are critical components. They are visible signatures of coupling between the atmosphere
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From page 54... ...
closures that represent bulk features of the ABL and OBL, boundary layer depth, surface fluxes, and entrainment rates. In general, bulk boundary layer parameterizations are not well tested and can break catastrophically for certain flows -- for example, stable boundary layers.
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From page 55... ...
2003. Coupled process and model studies of ocean mixing to improve climate models: A pilot Climate Process Modeling and Science Team.
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