Comparison of convective parameters derived from ERA5 and MERRA2 with rawinsonde data over Europe and North America

Mateusz Taszarek,Harold E Brooks,Victor Gensini,Natalia Pilguj,John T Allen,Piotr Szuster

doi:10.1175/jcli-d-20-0484.1

Abstract

AbstractIn this study we compared 3.7 mln rawinsonde observations from 232 stations over Europe and North America with proximal vertical profiles from ERA5 and MERRA2 to examine how well reanalysis depicts observed convective parameters. Larger differences between soundings and reanalysis are found for thermodynamic theoretical parcel parameters, low-level lapse rates and low-level wind shear. In contrast, reanalysis best represents temperature and moisture variables, mid-tropospheric lapse rates, and mean wind. Both reanalyses underestimate CAPE, low-level moisture and wind shear, particularly when considering extreme values. Overestimation is observed for low-level lapse rates, mid-tropospheric moisture and the level of free convection. Mixed-layer parcels have overall better accuracy when compared to most-unstable, especially considering convective inhibition and lifted condensation level. Mean absolute error for both reanalyses has been steadily decreasing over the last 39 years for almost every analyzed variable. Compared to MERRA2, ERA5 has higher correlations and lower mean absolute errors. MERRA2 is typically drier and less unstable over central Europe and the Balkans, with the opposite pattern over western Russia. Both reanalyses underestimate CAPE and CIN over the Great Plains. Reanalyses are more reliable for lower elevations stations and struggle along boundaries such as coastal zones and mountains. Based on the results from this and prior studies we suggest that ERA5 is likely one of the most reliable available reanalysis for exploration of convective environments, mainly due to its improved resolution. For future studies we also recommend that computation of convective variables should use model levels that provide more accurate sampling of the boundary-layer conditions compared to less numerous pressure levels.

Highlights

Understanding the spatiotemporal climatology of severe convective storm environments has primarily been achieved through atmospheric reanalyses (Brooks et al 2003, 2007; Gensini and Ashley 2011; Grams et al 2012; Tippett et al 2012; Allen et al 2015; Rädler et al 2018; Chen et al 2020; Taszarek et al 2020)
Thermodynamic parcel-related parameters are better represented by ERA5, with higher correlations and lower mean absolute error (MAE) compared to MERRA-2 (Fig. 3, Table 2)
MAE is lower for m layer (ML) CAPE (283 and 331 J kg21 for ERA5 and MERRA-2), compared to the MU version (378 and 414 J kg21), which can be explained by climatologically higher values of the latter

Summary

Introduction

Understanding the spatiotemporal climatology of severe convective storm environments has primarily been achieved through atmospheric reanalyses (Brooks et al 2003, 2007; Gensini and Ashley 2011; Grams et al 2012; Tippett et al 2012; Allen et al 2015; Rädler et al 2018; Chen et al 2020; Taszarek et al 2020). Thermodynamic parcel-related parameters are better represented by ERA5, with higher correlations and lower MAE compared to MERRA-2 (Fig. 3, Table 2).

Results

Conclusion