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| Titel |
Insights from extremum principles:\\The effects of diffusivity parameters on entropy budgets within an ocean-atmosphere-ice model |
| VerfasserIn |
M. Sonnewald, K. I. C. Oliver, J. Dyke |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064430
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| Zusammenfassung |
| Entropy budgets can potentially offer new and valuable insights into the dissipation of energy
in the climate system. Previous studies that assumed entropy produced via the latitudinal flux
of heat in the Earth’s atmosphere was at a maximum have given good agreement with
empirical data. Here, we extend such approaches to a four box ocean-atmosphere-ice model.
We test the hypothesis that the Earth system is in a state of maximum entropy production with
respect to the flux of heat within, and from low to high latitudes via the oceans and
atmosphere. Extending a model developed by Jochem Marotzke, we calculate the total
internal entropy production (the sum of entropy production associated with the
four ocean and atmosphere boxes), and go on to decompose this into the low/high
latitude oceanic and low/high latitude atmospheric boxes (latitudinal), as well as
ocean/atmosphere boxes (vertical). By adjusting rates of diffusivity between low
and high latitude ocean (kO) and atmosphere (kA) boxes we construct an entropy
landscape.
When adjusting kO and kA to maximize total system entropy production (kO = 3.3Ã1014WK-1 and kA =
3.2Ã1014WK-1) the model produces low latitude ocean temperatures within 3°C
and high latitude ocean temperature within 1°C of observed values. This compares
favourably to empirically determined values for kO and kA which produce ocean
temperatures within 5°C for low latitudes and 3°C for high latitudes, and both models are
within standard deviation for observational data.
The landscape of internal entropy production created by the oceanic and atmospheric
diffusivity was found to be fairly smooth, with non-linearities primarily due to ice albedo. We
note that the total internal entropy production in the modelled climate system is maximised
by a lower internal ocean entropy production than that produced using empirically
determined parameters. Vertical entropy production over the entire parameter space is
dominated by lower latitude interactions. However, total system entropy production is
maximized with values of kO approximately 50% higher than empirically derived values.
These are within a regime where higher latitude vertical interactions can have a significant
impact on total vertical entropy production, due to a discontinuity arising from ice extent and
thus albedo changes. Atmospheric internal entropy production (significantly larger than
oceanic internal entropy production) is strongly determined by kO. We interpret this as a
result of the ocean’s role as a heat reservoir, and the atmosphere as the main transport
mechanism. |
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