Abstract

Abstract. Climate reanalyses provide a plethora of global atmospheric and surface parameters in a consistent manner over multi-decadal timescales. Hence, they are widely used in many fields, and an in-depth evaluation of the different variables provided by reanalyses is a necessary means to provide feedback on the quality to their users and the operational centres producing these data sets, and to help guide their development. Recently, the European Centre for Medium-Range Weather Forecasts (ECMWF) released the new state-of-the-art climate reanalysis ERA5, following up on its popular predecessor ERA-Interim. Different sets of variables from ERA5 were already evaluated in a handful of studies, but so far, the quality of land-surface energy partitioning has not been assessed. Here, we evaluate the surface energy partitioning over land in ERA5 and concentrate on the appraisal of the surface latent heat flux, surface sensible heat flux, and Bowen ratio against different reference data sets and using different modelling tools. Most of our analyses point towards a better quality of surface energy partitioning in ERA5 than in ERA-Interim, which may be attributed to a better representation of land-surface processes in ERA5 and certainly to the better quality of near-surface meteorological variables. One of the key shortcomings of the reanalyses identified in our study is the overestimation of the surface latent heat flux over land, which – although substantially lower than in ERA-Interim – still remains in ERA5. Overall, our results indicate the high quality of the surface turbulent fluxes from ERA5 and the general improvement upon ERA-Interim, thereby endorsing the efforts of ECMWF to improve their climate reanalysis and to provide useful data to many scientific and operational fields.

Highlights

  • The partitioning of available energy at the land surface into sensible and latent heat exerts a strong control on atmospheric boundary layer (ABL) dynamics and informs on the coupling strength between land and atmosphere

  • This study evaluated the surface energy partitioning over land in European Centre for MediumRange Weather Forecasts (ECMWF)’s latest reanalysis ERA5 by assessing the quality of the surface latent heat flux, surface sensible heat flux, and Bowen ratio at different spatiotemporal scales and using different validation approaches

  • Different in situ validation data sets – including eddy-covariance, river discharge, and balloon sounding data – were used to validate the reanalysis fields, and Global Land Evaporation Amsterdam Model (GLEAM) and CLASS4GL were adopted as modelling tools to evaluate the surface energy partitioning in both reanalyses

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Summary

Introduction

The partitioning of available energy at the land surface into sensible and latent heat exerts a strong control on atmospheric boundary layer (ABL) dynamics and informs on the coupling strength between land and atmosphere. It translates variations in the state of the land surface (e.g. soil moisture) into changes in the state of the atmosphere (e.g. cloud formation, near-surface air temperature, and the ABL height), both in local and remote locations (Teuling et al, 2017; Miralles et al, 2016; Guillod et al, 2015; Taylor et al, 2012; Seneviratne et al, 2010).

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