Global coastal low‐level wind jets revisited through the new ERA5 reanalysis

Abstract

AbstractThe recent ECMWF (European Centre of Medium‐Range Weather Forecasts) reanalysis product (ERA5) is a 3D‐atmospheric dataset of unparalleled value to advance the characterization and understanding of the main global coastal low‐level jet (CLLJ) systems, due to its finer resolution (horizontal and vertical) and hourly output. Regional climate studies have revealed the added value of higher spatial and temporal resolutions of models and reanalyses for the representation of CLLJs, which play an important role in the definition of the regional climate along the Eastern Boundary Current Systems. ERA5 reveals an improvement in the representation of the wind speed and temperature vertical profiles within the boundary layer in CLLJ regions. This improvement enables a better representation of CLLJs and therefore a new view on their features. ERA5 show larger CLLJ frequencies of occurrence and larger wind speed intensities, when compared with previous reanalysis. The maximum frequency of occurrence ranges from 20% in the West Australian and 73% in the Oman CLLJs, in the summer season, which constitutes an increase of 10% compared to ERA‐Interim. Moreover, a shift for higher wind speeds is also found, where the maximum wind speed approach 30 m·s−1. Typically, CLLJs are found below 500 m above sea level, where the finer vertical discretization results clearly in a better description of the CLLJ peak height. Regarding the diurnal cycles of CLLJs frequency of occurrence, ERA5 exposes higher peaks and larger amplitudes, where the maximum hourly frequency is about 38% in the Oman CLLJ and the diurnal amplitude can vary between 7 and 14%. The diurnal maximum and minimum frequency of CLLJ occurrence can be found between 1900 and 2200 UTC, and between 1000 and 1400 LST, respectively. The momentum and temperature budget profiles reveal significant differences between CLLJ regions and emphasize the relevance of local processes in its occurrences.