THE ROLE OF TRANSIENTS IN WEATHER REGIMES AND TRANSITIONS

Transition of weather regimes is examined in a highly simplified model . Two completely distinct internal methods of transition are identifie d. The first is a synoptically triggered large-scale instability, whil e the second is an energy inconsistency between the large-scale and sy noptic scales that does not allow the two scales to equilibrate. In th e atmosphere, the first case appears as a sudden propagation and dampi ng (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 explos ive cyclogenesis. The first method is always fast (on a synoptic time scale), while the second does not have to be, though often is. By exam ining what causes the regimes to fail, one can better understand the r ole of the transients during all phases of weather regimes.