Wind speed response of marine non-precipitating stratocumulus clouds over a diurnal cycle in cloud-system resolving simulations Journal Article uri icon



  • Abstract. Observed and projected trends in large scale wind speed over the oceans prompt the question: how might marine stratocumulus clouds and their radiative properties respond to future changes in large scale wind speed? Wind speed drives the surface fluxes of sensible heat, moisture, and momentum, and thereby acts on cloud liquid water path (LWP) and cloud radiative properties. We present an investigation of the dynamical response of non-precipitating, overcast marine stratocumulus clouds to different wind speeds, all else equal. In cloud-system resolving simulations, we find that higher wind speed leads to faster boundary layer growth and stronger entrainment. The dynamical driver is enhanced buoyant production of turbulence kinetic energy (TKE) from latent heat release in cloud updrafts. LWP is enhanced during the night and in the morning at higher wind speed, and more strongly suppressed later in the day. Wind speed hence accentuates the diurnal LWP cycle by expanding the morning – afternoon contrast. The higher LWP at higher wind speed does not, however, enhance cloud top cooling because in clouds with LWP ⪆ 50 g m−2, long wave emissions are very insensitive to LWP. This leads to the more general conclusion that in sufficiently thick stratocumulus clouds, additional boundary layer growth and entrainment due to a boundary layer moistening arises by stronger production of TKE from latent heat release in cloud updrafts, rather than from enhanced longwave cooling. We find furthermore that large scale wind modulates boundary layer decoupling. At nighttime and at low wind speed during daytime, it enhances decoupling in part by faster boundary layer growth and stronger entrainment, and in part because circulation driven by shear from large scale wind in the sub-cloud layer hinders vertical moisture transport between the surface and cloud base. With increasing wind speed, however, in decoupled daytime conditions, shear-driven circulation due to large scale wind takes over from buoyancy-driven circulation in transporting moisture from the surface to cloud base, and thereby reduces decoupling and helps maintain LWP. The cloud radiative effect (CRE) responds to changes in LWP and cloud fraction, and higher wind speed translates to a stronger diurnally averaged CRE. However, the sensitivity of the diurnally averaged CRE to wind speed decreases with increasing wind speed.;

publication date

  • October 21, 2015

has restriction

  • green

Date in CU Experts

  • July 5, 2021 9:57 AM

Full Author List

  • Kazil J; Feingold G; Yamaguchi T

author count

  • 3

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