  Winds play an essential role in the climate system. In this study, we analyze
the global pattern of the diurnal cycle of surface (10 m) winds from the ERA5
reanalysis data. We find that over the land and especially over sand dune
regions, the maximal wind speed and wind drift potential (DP) occur during the
hours around midday. However, over the ocean, the wind also peaks at night.
Using the sensible heat flux, we show that the weaker winds over land at night
are due to a nocturnal cooling that decouples upper atmospheric levels and
their associated stronger winds from the surface -- nocturnal cooling is much
smaller over the ocean. We also analyze wind data from more than 400
meteorological stations in the USA and find a similar diurnal trend as in the
reanalysis data. The timing (during the day) of the maximum wind speed has not
varied much over the past 70 years. Yet, the wind speed, wind power, and wind
drift potential exhibit significant increases with time over the ocean and, to
a much lesser degree, over the land and sand dune regions. We compare the USA
and Europe DP and wind speed of the ERA5 to that of meteorological stations and
find that the ERA5 significantly underestimates real winds; however, the
temporal patterns of the two are similar.
