How large-scale subsidence affects stratocumulus transitions

How large-scale subsidence affects stratocumulus transitions

van der Dussen, J.J. (TU Delft Atmospheric Physics; TU Delft Atmospheric Remote Sensing)
de Roode, S.R. (TU Delft Atmospheric Physics)
Siebesma, A.P. (TU Delft Atmospheric Physics; TU Delft Atmospheric Remote Sensing; Royal Netherlands Meteorological Institute (KNMI))

2016-01-21

Some climate modeling results suggest that the Hadley circulation might weaken in a future climate, causing a subsequent reduction in the large-scale subsidence velocity in the subtropics. In this study we analyze the cloud liquid water path (LWP) budget from large-eddy simulation (LES) results of three idealized stratocumulus transition cases, each with a different subsidence rate. As shown in previous studies a reduced subsidence is found to lead to a deeper stratocumulus-topped boundary layer, an enhanced cloud-top entrainment rate and a delay in the transition of stratocumulus clouds into shallow cumulus clouds during its equatorwards advection by the prevailing trade winds. The effect of a reduction of the subsidence rate can be summarized as follows. The initial deepening of the stratocumulus layer is partly counteracted by an enhanced absorption of solar radiation. After some hours the deepening of the boundary layer is accelerated by an enhancement of the entrainment rate. Because this is accompanied by a change in the cloud-base turbulent fluxes of moisture and heat, the net change in the LWP due to changes in the turbulent flux profiles is negligibly small.

OA-Fund TU Delft

http://resolver.tudelft.nl/uuid:0f0da3bb-64c0-4cce-822f-2d022fb4d66e

https://doi.org/10.5194/acp-16-691-2016

1680-7316

Atmospheric Chemistry and Physics (online), 16 (2), 691-701

Institutional Repository

journal article

© 2016 J.J. van der Dussen, S.R. de Roode, A.P. Siebesma