Wind kinetic energy climatology and effective resolution for the ERA5 reanalysis

Abstract

ERA5 represents the state of the art for atmospheric reanalyses and is widely used in meteorological and climatological research. In this work, this dataset is evaluated using the wind kinetic energy spectrum. Seasonal climatologies are generated for 30° latitudinal bands in the Northern Hemisphere (periodic domain) and over the North Atlantic area (limited-area domain). The spectra are also assessed to determine the effective resolution of the reanalysis. The results present notable differences between the latitudinal domains, indicating that ERA5 is properly capturing the synoptic conditions. The seasonal variability is adequate too, being winter the most energetic, and summer the least energetic season. The limited area domain results introduce a larger energy density and range. Despite the good results for the synoptic scales, the reanalysis’ spectra are not able to properly reproduce the dissipation rates at mesoscale. This is a source of uncertainties which needs to be taken into account when using the dataset. Finally, a cyclone tropical transition is presented as a case study. The spectrum generated shows a clear difference in energy density at every wavelength, as expected for a highly-energetic status of the atmosphere.

Horizontal kinetic energy analysis of tropical transition simulations with the WRF and HARMONIE‐AROME models

“…This is mainly noticed in the synoptic range, and it has already been mentioned by Bolgiani et al . (2022), presenting results in line with Skamarock (2004). This is as expected, as jet streams and planetary‐scale waves belong to upper levels and the higher synoptic energy density steepens the curve.…”

“…Figure 1 shows the 500 hPa wind HKE spectra for the averaged (42 hr before to 30 hr after the TT) simulation of each of the four TTs simulated with WRF at their respective D01 and D02. As a reference of the energy levels “fed” to the limited‐area model, the ERA5 September–November climatology for the North Atlantic basin (Bolgiani et al ., 2022), with a resolution of 27.0 km, is also shown. It becomes immediately clear that each increase in resolution enhances the k −5/3 transition in the curves, as expected by the Lindborg (1999, eq.…”

“…The energy spectrum of each simulation is computed following the basic methodology set by Skamarock (2004) and the more specific methodology already applied in previous studies by Bolgiani et al . (2022). First, the wind‐speed field is derived using the horizontal components u and v .…”

“…Nastrom and Gage (1985) use potential temperature in their study, and Cho et al . (1999) derive the energy spectra from trace gases; however, horizontal kinetic energy (HKE) derived from wind speed is the variable used most because of its simplicity and the availability of observations (Nastrom and Gage, 1985; Skamarock, 2004; Bolgiani et al ., 2022).…”

“…Before evaluating the meteorological characteristics of these simulations, possible limitations must be assessed, as we are dealing with high‐resolution simulations, verging on the design limits of the models. Thus, the first step was to generate a seasonal climatology of the HKE spectra (Bolgiani et al ., 2022), both for the Northern Hemisphere (periodic domain) and for the North Atlantic area (limited‐area domain) using the fifth generation of the European Centre for Medium‐Range Weather Forecasts (ECMWF) Atmospheric Reanalysis (ERA5; Hersbach et al ., 2020). The results exhibit that ERA5 is properly capturing the synoptic conditions with remarkable differences between the latitudinal domains.…”