Energetics of Winter Troughs Entering South America

Abstract

The energetics and behavior of midtropospheric troughs over the Southern Hemisphere and their re lationship with South America surface cyclogenesis were studied during the winters of 1999-2003. All surface cyclogenesis situations over Uruguay and adjacent areas associated with 500-hPa troughs were analyzed. The atmospheric circulation associated with type-B and type-C cyclones form the basis for two composites: composite B (with 25 cases) and composite C (with 13 cases). The results showed that the midtropospheric troughs were more intense in composite C than in composite B before the surface cyclogenesis and that the opposite occurred during the surface cyclogenesis. The baroclinic conversion was dominant in both com posites. In composite B. the ageostrophic flux convergence (AFC) contributed positively to the intensification of the surface cyclone since it imported energy into the area before the cyclogenesis started. But in composite C, the AFC served as a sink because it exported energy. Based on these results, it can be concluded that (i) the trough was crucial for the cyclogenesis; (ii) the variables in the mid-and upper levels did not differ signifi cantly from one composite to another; (iii) the northerly heat and moisture flow acted as a preconditioning for the cyclogenesis, mainly for composite C; (iv) the baroclinic conversion dominated the energetics: and (v) the AFC had only a secondary role, contributing negatively to the development of the cyclone in composite C and positively to the initial development in composite B.

The Energy Cycle Associated to the Pacific Walker Circulation and Its Relationship to ENSO

“…Here the energetics anomalies are triggered at about the same time as ENSO, leaving an open interpretation as to how the changes are transmitted to the energetics in the first place. As pointed out in earlier work ( [9][10][11][12][13][14][15][16][17][18][21][22][23]) the Rossby wave propagation can be influenced by the state of the energetics, as it draws energy from the environment, but the energetics is in turn also influenced by the weather anomalies.…”

“…Once warm air rises and relatively cold air sinks, respectively, over the western and eastern equatorial Pacific basin there is a continuous conversion between potential and kinetic energy; however, what maintains the apparently continuous generation of the kinetic energy reservoir at the expense of available potential energy had not been quantified yet. The importance of measuring the energy reservoirs and the way they are transformed into another kind of energy (potential to kinetic or vice-versa) has been emphasized in many studies of open ( [9][10][11][12][13][14][15][16]) and closed ( [17][18][19][20][21][22][23]) domains. Thus, in order to quantify the generation of potential energy, the conversion between potential and kinetic energy, and the sources and sinks of available potential and kinetic energy, the present study focuses on the atmospheric energetics involved in the WC and its behavior for strong ENSO phases.…”

Energetics of a Southeastern Pacific cut‐off low

“…Although there is a conceptual model to explain the formation of COLs, what causes the formation and maintenance of these systems is not understood yet. In contrast, the formation of mid-latitude disturbances in the atmosphere has been explained by baroclinic, barotropic, non-modal instabilities and wave energy propagation, or downstream development (Nielsen-Gammon, 1995;Piva et al, 2010).…”

Development of a Front Identification Scheme for Compiling a Cold Front Climatology of the Mediterranean

“…FTS is based on Eulerian changes of the 10 m meridional wind component (v) which is valuable in diagnosing various aspects of frontal behavior [8,28]. The criteria for identification are [19]: (a) at a time t, grid points are flagged where the wind changes from the southwestern quadrant (westerly zonal wind u > 0, southerly meridional wind v > 0) to the northwestern quadrant (westerly zonal wind u > 0, northerly meridional wind v < 0) between subsequent time points t and (t + 6 h), (b) the change of the meridional wind dv exceeds a specific threshold value dv crit during the same 6 h period.…”