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  • Author or Editor: A. C. M. Beljaars x
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A. A. M. Holtslag
,
G. Svensson
,
P. Baas
,
S. Basu
,
B. Beare
,
A. C. M. Beljaars
,
F. C. Bosveld
,
J. Cuxart
,
J. Lindvall
,
G. J. Steeneveld
,
M. Tjernström
, and
B. J. H. Van De Wiel

The representation of the atmospheric boundary layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2-m temperature and 10-m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, the authors review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art as well as findings and recommendations from three intercomparison studies held within the Global Energy and Water Exchanges (GEWEX) Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the stable boundary layer and the diurnal cycle over land in clear-sky conditions. For this purpose, single-column versions of weather and climate models have been compared with observations, research models, and large-eddy simulations. The intercomparison cases are based on observations taken in the Arctic, Kansas, and Cabauw in the Netherlands. From these studies, we find that even for the noncloudy boundary layer important parameterization challenges remain.

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A. J. Illingworth
,
H. W. Barker
,
A. Beljaars
,
M. Ceccaldi
,
H. Chepfer
,
N. Clerbaux
,
J. Cole
,
J. Delanoë
,
C. Domenech
,
D. P. Donovan
,
S. Fukuda
,
M. Hirakata
,
R. J. Hogan
,
A. Huenerbein
,
P. Kollias
,
T. Kubota
,
T. Nakajima
,
T. Y. Nakajima
,
T. Nishizawa
,
Y. Ohno
,
H. Okamoto
,
R. Oki
,
K. Sato
,
M. Satoh
,
M. W. Shephard
,
A. Velázquez-Blázquez
,
U. Wandinger
,
T. Wehr
, and
G.-J. van Zadelhoff

Abstract

The collective representation within global models of aerosol, cloud, precipitation, and their radiative properties remains unsatisfactory. They constitute the largest source of uncertainty in predictions of climatic change and hamper the ability of numerical weather prediction models to forecast high-impact weather events. The joint European Space Agency (ESA)–Japan Aerospace Exploration Agency (JAXA) Earth Clouds, Aerosol and Radiation Explorer (EarthCARE) satellite mission, scheduled for launch in 2018, will help to resolve these weaknesses by providing global profiles of cloud, aerosol, precipitation, and associated radiative properties inferred from a combination of measurements made by its collocated active and passive sensors. EarthCARE will improve our understanding of cloud and aerosol processes by extending the invaluable dataset acquired by the A-Train satellites CloudSat, Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and Aqua. Specifically, EarthCARE’s cloud profiling radar, with 7 dB more sensitivity than CloudSat, will detect more thin clouds and its Doppler capability will provide novel information on convection, precipitating ice particle, and raindrop fall speeds. EarthCARE’s 355-nm high-spectral-resolution lidar will measure directly and accurately cloud and aerosol extinction and optical depth. Combining this with backscatter and polarization information should lead to an unprecedented ability to identify aerosol type. The multispectral imager will provide a context for, and the ability to construct, the cloud and aerosol distribution in 3D domains around the narrow 2D retrieved cross section. The consistency of the retrievals will be assessed to within a target of ±10 W m–2 on the (10 km)2 scale by comparing the multiview broadband radiometer observations to the top-of-atmosphere fluxes estimated by 3D radiative transfer models acting on retrieved 3D domains.

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