Global climatology of low-level-jets: occurrence, characteristics, and
meteorological drivers
Abstract
Low-level jets (LLJs), wind speed maxima in the lower troposphere,
impact several environmental and societal phenomena. In this study we
take advantage of the spatially and temporally complete meteorological
dataset from ERA5 to present a global climatology of LLJs taking into
consideration their formation mechanisms, characteristics and trends
during the period of 1992-2021. The global mean frequency of occurrence
was of 21% with values of 32% and 15% for land and ocean. We
classified the LLJs into three regions: non-polar land (LLLJ), polar
land (PLLJ) and coastal (CLLJ). Over LLLJ regions, the average frequency
of occurrence was of 20%, with 75% of them associated with a
near-surface temperature inversion i.e. associated with inertial
oscillation at night. Over PLLJ regions the LLJs were also associated
with a temperature inversion, but were much more frequent (59%),
suggesting other driving mechanisms than the nocturnal inversion. They
were also the lowest and the strongest LLJs. CLLJs were very frequent in
some hotspots, specially on the west coast of the continents, with
neutral to unstable stratification close to the surfaces, that became
more stably stratified with increasing height. We found distinct
regional trends in both the frequency and intensity of LLJs, potentially
leading to changes in the emission and transport of dust aerosols, polar
ice and moisture over the world. However, it is currently unclear the
evolution of the trends with global warming and what the implications
are for climate and weather extremes. Future studies will investigate
long-term trends for LLJs and the associated implications.