Examination of the global lorenz energy cycle using MERRA and NCEP-reanalysis 2

Yeon-Hee Kim,Maeng-Ki Kim

doi:10.1007/s00382-012-1358-4

Abstract

In this study, the global Lorenz atmospheric energy cycle is evaluated using the Modern Era Retrospective analysis for Research and Applications (MERRA) and the National Center for Environmental Prediction and the Department of Energy (NCEP R2) reanalysis datasets over a 30-year period (1979–2008) for the annual, JJA, and DJF means. The energy cycle calculated from the two reanalysis datasets is largely consistent, but the energy cycle determined using the MERRA dataset is more active than that determined from the NCEP R2 dataset. For instance, with regard to the annual mean, the general discrepancy between the energy components in the global integral is about 5 %, whereas the discrepancy between the conversion components is about 16 %, with the exception of C(PM, KM), which has a different sign in the global integrals. The latitude-altitude cross-section indicates that the difference in the energy cycle of the two reanalysis datasets is larger in the southern hemisphere than in the northern hemisphere. The conversion rates of mean available potential energy to mean kinetic energy [C(PM, KM)] and eddy available potential energy to eddy kinetic energy [C(PE, KE)] are also calculated using two formulations (so-called ‘v·grad z’ and ‘ω·α’) for the two reanalysis datasets. The differences in the conversion rate between the two reanalysis datasets for the global integral are not appreciable for the two formulations.

Highlights

Lorenz (1955) proposed the energy cycle as a mechanism to enable easy understanding of atmospheric circulation from the perspective of energy conversion by considering the physical processes involved, from the generation of potential energy by solar energy to the dissipation of kinetic energy
PM is converted into eddy-available potential energy (PE) by the growing baroclinic disturbances, and PE is converted into eddy kinetic energy (KE) based on the baroclinic instability, which is induced by the sinking of colder air and the rising of warmer air by the eddies
We evaluate the Lorenz atmospheric energy cycle using a new reanalysis dataset, MERRA (Rienecker et al 2011), from the point of view of the global integral and latitude-altitude cross-sections of the global energy components (PM, PTE, PSE, KM, KTE, and KSE) and conversion components [C(PM, PTE), C(PM, PSE), C(PTE, KTE), C(PSE, KSE), C(KTE, KM), C(KSE, KM), C(PSE, PTE), C(KSE, KTE), and C(PM, KM)]

Summary

Introduction

Lorenz (1955) proposed the energy cycle as a mechanism to enable easy understanding of atmospheric circulation from the perspective of energy conversion by considering the physical processes involved, from the generation of potential energy by solar energy to the dissipation of kinetic energy. Li et al (2007) and Marques et al (2009) examined the global atmospheric energy cycle based on monthly evaluations using two reanalysis datasets (NCEP R2 and ERA-40) covering the 23 years from 1979 to 2001. Marques et al (2010) compared three reanalysis datasets (NCEP R2, ERA-40, and JRA-25) using global energy analysis for all seasons. They found that the Lorenz energy cycles of the three datasets were similar, but that appreciable differences appeared mainly in the southern hemisphere and that the magnitudes of the energy and conversion terms tended to follow the hierarchy of ERA-40 [ JRA-25 [ NCEP-R2. We investigate the Lorenz energy cycle from a climatology perspective based on the two reanalysis datasets to fully characterize the energy cycle in MERRA and compare it with that in NCEP R2

Data and methodology

Results

Conclusions