Single-Column Model Simulations of Subtropical Marine Boundary-Layer Cloud Transitions Under Weakening Inversions
R.A.J. Neggers (Universität zu Köln, Royal Netherlands Meteorological Institute (KNMI))
Andrew S. Ackerman (NASA Goddard Institute for Space Studies)
W. M. Angevine (University of Colorado - Boulder, National Oceanic and Atmospheric Administration)
Eric Bazile (Meteo France)
I. Beau (Meteo France)
P. N. Blossey (University of Washington)
I. A. Boutle (Met Office)
C. de Bruijn (Royal Netherlands Meteorological Institute (KNMI))
A cheng (National Oceanic and Atmospheric Administration)
J. van der Dussen (TU Delft - Civil Engineering & Geosciences, TU Delft - Civil Engineering & Geosciences)
J. Fletcher (University of Leeds, University of Washington)
S. Dal Gesso (Royal Netherlands Meteorological Institute (KNMI), Universität zu Köln)
A. Jam (Meteo France)
H Kawai (Meteorological Research Institute)
S. K. Cheedela (Max Planck Institute for Meteorology)
V. E. Larson (University of Wisconsin-Milwaukee)
Marie Pierre Lefebvre (Meteo France)
A. P. Lock (Met Office)
N. R. Meyer (University of Wisconsin-Milwaukee)
S. R. de Roode (TU Delft - Civil Engineering & Geosciences)
WC de Rooy (Royal Netherlands Meteorological Institute (KNMI))
I Sandu (European Centre for Medium Range Weather Forecasts)
H Xiao (Pacific Northwest National Laboratory, University of California)
K. M. Xu (NASA Langley Research Center)
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Abstract
Results are presented of the GASS/EUCLIPSE single-column model intercomparison study on the subtropical marine low-level cloud transition. A central goal is to establish the performance of state-of-the-art boundary-layer schemes for weather and climate models for this cloud regime, using large-eddy simulations of the same scenes as a reference. A novelty is that the comparison covers four different cases instead of one, in order to broaden the covered parameter space. Three cases are situated in the North-Eastern Pacific, while one reflects conditions in the North-Eastern Atlantic. A set of variables is considered that reflects key aspects of the transition process, making use of simple metrics to establish the model performance. Using this method, some longstanding problems in low-level cloud representation are identified. Considerable spread exists among models concerning the cloud amount, its vertical structure, and the associated impact on radiative transfer. The sign and amplitude of these biases differ somewhat per case, depending on how far the transition has progressed. After cloud breakup the ensemble median exhibits the well-known “too few too bright” problem. The boundary-layer deepening rate and its state of decoupling are both underestimated, while the representation of the thin capping cloud layer appears complicated by a lack of vertical resolution. Encouragingly, some models are successful in representing the full set of variables, in particular, the vertical structure and diurnal cycle of the cloud layer in transition. An intriguing result is that the median of the model ensemble performs best, inspiring a new approach in subgrid parameterization.