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

Abstract

In this paper we study the Lorenz energy cycle of the Walker circulation associated with ENSO. The robust formulation of the energetics allows drawing a clear picture of the global energy and conversion terms associated with the three dimensional domains appropriate to qualify the large scale transfers that influence, and are influenced by, the anomalies during ENSO. A clear picture has emerged in that El Niño and La Niña years have approximately opposite anomalous energy fluxes, regardless of a non-linear response identified in the potential energy fields (zonal and eddy). During El Niños the tropical atmosphere is characterized by an increase of zonal available potential energy, decrease of eddy available potential energy and decrease of kinetic energy fields. This results in weaker upper level jets and a slowingdown of the overall Walker cell. During La Niñas reversed conditions are triggered, with an acceleration of the Walker cell as observed from the positive anomalous kinetic energy. The potential energy in the Walker circulation domain during the cold phase is also reduced. An equally opposite behavior is also experienced by the energy conversion terms according to the ENSO phase. The behavior of anomalous energetics seems to be triggered at about the same time when ENSO starts to manifest for both the positive and negative phases, suggesting a coupled mechanism in which atmospheric and oceanic anomalies interact and feed back onto each other.

An Analysis of the Energetics of Tropical and Extra-Tropical Regions for Warm ENSO Composite Episodes

“…Our results, therefore, suggest that El Niño episodes may be able to show a growth in the display of AZ, which in turn is associated with an intensifying meridional temperature gradient. Also based on these results, the AZ energy rise observed in the tropical atmosphere is in agreement with the results found by Veiga et al (2013). Figure 3b shows the production of zonal kinetic energy (KZ), which was intensified by about 2.39% (zone 2), 8.54% (zone 3), and 14.76% (zone 4) and decreased by about 5.03% (zone 1).…”

“…More, Veiga et al, 2013 focused their findings on the results obtained for two-dimensional analysis (pressure levels vs. time), while this work is based on the temporal variation of integrated energy components in the atmospheric volume. The main purpose behind the selected regions is to quantify and evaluate the impact of strong El Niño events on the energetics of remote (far from the EL Niño domain) areas.…”

“…Differently from Veiga et al, 2013, who conducted the study for the tropical region that encompassed only the limits of the Walker circulation (latitude 5°N and 10°S, longitude 120°E and 80°W), in this paper, the study is conducted for regions located in tropical and extratropical regions. More, Veiga et al, 2013 focused their findings on the results obtained for two-dimensional analysis (pressure levels vs. time), while this work is based on the temporal variation of integrated energy components in the atmospheric volume.…”

“…Today, through energetics, there are many studies in order to investigate the impact in the general circulation caused by emission of aerosols by active volcanoes (Silva and Satyamurty, 2013), monsoons (Krishnamurti et al, 1998;Gutierrez et al, 2009), ENOS events (Veiga et al, 2013), by increasing the concentration of greenhouse gases (Bohr, 1995;Deckers and von Storch 2010, 2012, among others.…”

“…Gutierrez et al (2009), who studied the South American rainy season, observed after application of multivariate Empirical Orthogonal Function (EOF), that depending on which component of Lorenz Cycle was more pronounced at each phase of the South American Monsoon System could be used as an indicator of the onset of the rainy season. Veiga et al (2013), using the energy flow charts of a limited area, analyzed the energy cycle in a region overlooked by the Walker Circulation and its relationship with strong episodes of ENSO. They concluded that for a composite of El Niño events the tropical atmosphere is characterized by an increase in zonal potential energy, a decrease of eddy potential energy, and a reduction in kinetic energy fields.…”