The diurnal cycle and temporal trends of surface winds

TL;DR

This study examines the global diurnal cycle of surface winds using ERA5 reanalysis and station data, revealing land-ocean differences, temporal stability in timing, and recent increases in wind metrics, with ERA5 underestimating actual winds.

Contribution

It provides a comprehensive analysis of the diurnal wind cycle globally, compares reanalysis with station data, and documents temporal trends and discrepancies in wind estimates.

Findings

Maximal wind speeds occur around midday over land and dunes.

Over oceans, wind peaks at night, influenced by nocturnal cooling.

Wind speed and power have increased over the past 70 years.

Abstract

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.