The Lorenz energy cycle: trends and the impact of modes of climate variability

Abstract

The atmospheric circulation is driven by heat transport from the tropics to the polar regions, embedding energy conversions between available potential and kinetic energy through various mechanisms. The processes of energy transformations related to the dynamics of the atmosphere can be quantitatively investigated through the Lorenz energy cycle formalism. Here we examine these variations and the impacts of modes of climate variability on the Lorenz energy cycle by using reanalysis data from the Japanese Meteorological Agency (JRA-55). We show that the atmospheric circulation is overall becoming more energetic and efficient. For instance, we find a statistically significant trend in the eddy available potential energy, especially in the transient eddy available potential energy in the Southern Hemisphere. We find significant trends in the conversion rates between zonal available potential and kinetic energy, consistent with an expansion of the Hadley cell, and in the conversion rates between eddy available potential and kinetic energy, suggesting an increase in mid-latitudinal baroclinic instability. We also show that planetary-scale waves dominate the stationary eddy energy, while synoptic-scale waves dominate the transient eddy energy with a significant increasing trend. Our results suggest that interannual variability of the Lorenz energy cycle is determined by modes of climate variability. We find that significant global and hemispheric energy fluctuations are caused by the El Nino-Southern Oscillation, the Arctic Oscillation, the Southern Annular Mode, and the meridional temperature gradient over the Southern Hemisphere.

Trends in the tropospheric general circulation from 1979 to 2022

“…Comparison with earlier studies is hampered by differences in formulation of the energy equations, in the reanalyses used, in the length of the period studied and in dataprocessing details. The time series for kinetic energy shown here compares reasonably well with that reported recently by Ma et al (2021) for JRA-55. Agreement is less good for available potential energy for reasons that are unclear.…”

“…Manney et al (2021) have shown that although there are appreciable seasonal and regional variations in the re-lationships between jet-stream speeds and El Niño events, subtropical jet speeds tend to be higher than normal during these events. Ma et al (2021) found significant correlations between the sea-surface temperature fluctuations that characterize El Niño and La Niña and components of the atmospheric energy cycle derived from JRA-55. Lorenz (1955) noted that TPE is not a good measure of the amount of energy available for conversion to kinetic energy under adiabatic flow.…”

“…It does not take water vapour into account and so cannot give an indication of the energy available to increase kinetic energy through latent-heat release. Following Lorenz' original derivation, the terms involving T do not include the time-averaging used in subsequent studies such as that of Ma et al (2021) to enable separation of APE into stationary and transient components.…”

Formation and Maintenance Mechanisms of the Subseasonal Eastern Pacific Pattern: Energetics Analysis

“…Finally, it should be noted that this study has examined the energetics of the EP pattern as a regional atmospheric system, while some recent studies examined the features of the Lorenz energy cycle for the global atmospheric circulation during the modern satellite era since 1979 (e.g., Kim & Kim, 2013;Ma et al, 2021;Pan et al, 2017). It is found that the global atmospheric circulation is overall becoming more energetic and efficient, characterized by significant trends in the conversion rates between zonal APE and zonal KE, and between eddy APE and eddy KE (Ma et al, 2021;Pan et al, 2017). Whether or not similar trends exist in the energy conversions/generations for the EP pattern or some other well-known atmospheric teleconnection patterns, such as the Arctic Oscillation, North Atlantic Oscillation and the Pacific-North American pattern, will be an interesting topic for future study.…”

“…Finally, it should be noted that this study has examined the energetics of the EP pattern as a regional atmospheric system, while some recent studies examined the features of the Lorenz energy cycle for the global atmospheric circulation during the modern satellite era since 1979 (e.g., Kim & Kim, 2013;Ma et al, 2021;Pan et al, 2017). It is found that the global atmospheric circulation is overall becoming more energetic and efficient, characterized by significant trends in the conversion rates between zonal APE and zonal KE, and between eddy APE and eddy KE (Ma et al, 2021;Pan et al, 2017).…”