Status: this preprint was under review for the journal ACP. A revision for further review has not been submitted.
The Nonequilbrium Thermodynamics of Atmospheric Blocking
Andrew Jensen
Abstract. Two strong NE Pacific blocking events that occurred nearly one year apart and in the same region are examined here by methods from nonequilbrium thermodynamics. In a nonequilibrium setting, the time variation of entropy is a sum of two parts: the external entropy supply and the internal entropy production. The internal entropy production and external entropy supply (the surface entropy supply) are calculated and compared to recent trends in the region that encompassed both blocking events. The entropy production and entropy surface supply were found to be high during both blocking events. However, the surface conditions during the events were markedly different. The surface conditions during the first event were dominated by the NE Pacific sea surface temperature anomaly known as the Blob, while the other event was less influenced. In particular, the surface entropy supply increased from January to February for the first event. The entropy production decreased slightly but any negative entropy flows from extratropical cyclones were offset by the increasing surface entropy supply, maintaining the blocking event. On the other hand, the second event had no large changes in the surface entropy supply or entropy production during its lifetime even though it was similar to the first event in many respects. The use of entropy as a convenient variable to examine the mechanisms that maintain blocking events is considered.
Received: 09 Jun 2016 – Discussion started: 29 Jun 2016
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Further studies of the fundamental physics of blocking are needed since they are still incompletely understood. To examine the physical processes, an approach based on nonequilibrium thermodynamics is used. This approach to blocking highlights the thermodynamics, which are often not considered in depth. Results indicate that a thermodynamic perspective of blocking can be characterized by significant entropy production and surface entropy fluxes which may sustain blocking events against demise.
Further studies of the fundamental physics of blocking are needed since they are still...
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