Surface-Layer Wind Shear and Momentum Transport From Clear-Sky to Cloudy Weather Regimes Over Land

Journal Article (2021)
Author(s)

A. M. Koning (TU Delft - Atmospheric Remote Sensing)

L. Nuijens (TU Delft - Atmospheric Remote Sensing)

F. C. Bosveld (Royal Netherlands Meteorological Institute (KNMI))

A. Pier Siebesma (Royal Netherlands Meteorological Institute (KNMI), TU Delft - Atmospheric Remote Sensing)

P. A. van Dorp (Whiffle)

HJJ Jonker (Whiffle, TU Delft - Atmospheric Remote Sensing)

Research Group
Atmospheric Remote Sensing
Copyright
© 2021 A.M. Koning, Louise Nuijens, F. C. Bosveld, A.P. Siebesma, P. A. van Dorp, H.J.J. Jonker
DOI related publication
https://doi.org/10.1029/2021JD035087
More Info
expand_more
Publication Year
2021
Language
English
Copyright
© 2021 A.M. Koning, Louise Nuijens, F. C. Bosveld, A.P. Siebesma, P. A. van Dorp, H.J.J. Jonker
Research Group
Atmospheric Remote Sensing
Issue number
21
Volume number
126
Pages (from-to)
1-18
Reuse Rights

Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons.

Abstract

This study investigates how wind shear and momentum fluxes in the surface- and boundary layer vary across wind and cloud regimes. We use a 9-year-long data set from the Cabauw observatory complemented by (8.2 × 8.2 (Formula presented.)) daily Large Eddy Simulation (LES) hindcasts. An automated algorithm classifies observed and simulated days into different cloud regimes: (a) clear-sky days, (b) days with shallow convective clouds rooted in the surface layer, with two ranges of cloud cover, and (c) non-convective cloud days. Categorized days in observations and LES do not always match, particularly the number of non-convective cloud days are underestimated in the LES, which likes to develop convection. However, the climatology and diurnal cycle of winds for each regime are very similar in LES and observations, strengthening our confidence in LES’ skill to reproduce certain clouds for certain atmospheric states. Along-wind momentum flux profiles are similar across all regimes, but large cloud cover (convective and non-convective) days have larger total momentum flux distributed over a deeper layer, with up to 30% of the surface flux still present near cloud base. The clear-sky and especially shallow cumulus regime with low cloud cover have notably larger crosswind momentum fluxes in the boundary layer. Surface-layer wind shear at daytime is smallest in the shallow cumulus regimes, having deeper boundary layers and a steady increase in surface layer wind speed during daytime. Compared to clear-sky days at a similar stability, convective cloud regimes have smaller surface-layer wind shear and larger surface friction than estimated by Monin-Obukhov Similarity Theory.