The Role of Transients in Weather Regimes and Transitions

Brian Reinhold Department of Meteorology, Arrhenius Laboratory, University of Stockholm, Stockholm, Sweden

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Shuting Yang Department of Meteorology, Arrhenius Laboratory, University of Stockholm, Stockholm, Sweden

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Abstract

Transition of weather regimes is examined in a highly simplified model. Two completely distinct internal methods of transition are identified. The first is a synoptically triggered large-scale instability, while the second is an energy inconsistency between the large-scale and synoptic scales that does not allow the two scales to equilibrate. In the atmosphere, the first case appears as a sudden propagation and damping (or vice versa) of the large-scale pattern with no obvious warning, while the second is consistent with the synoptician's description of a regime being disrupted by a single catastrophic event such as explosive cyclogenesis. The first method is always fast (on a synoptic time scale), while the second does not have to be, though often is. By examining what causes the regimes to fail, one can better understand the role of the transients during all phases of weather regimes.

Abstract

Transition of weather regimes is examined in a highly simplified model. Two completely distinct internal methods of transition are identified. The first is a synoptically triggered large-scale instability, while the second is an energy inconsistency between the large-scale and synoptic scales that does not allow the two scales to equilibrate. In the atmosphere, the first case appears as a sudden propagation and damping (or vice versa) of the large-scale pattern with no obvious warning, while the second is consistent with the synoptician's description of a regime being disrupted by a single catastrophic event such as explosive cyclogenesis. The first method is always fast (on a synoptic time scale), while the second does not have to be, though often is. By examining what causes the regimes to fail, one can better understand the role of the transients during all phases of weather regimes.

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