Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
21 Mar 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Top-down and Bottom-up aerosol-cloud-closure: towards understanding sources of uncertainty in deriving cloud radiative flux
Kevin J. Sanchez1,2, Greg C. Roberts1,2, Radiance Calmer2, Keri Nicoll3,4, Eyal Hashimshoni5, Daniel Rosenfeld5, Jurgita Ovadnevaite6, Jana Preissler6, Darius Ceburnis6, Colin O'Dowd6, and Lynn M. Russell1 1Scripps Institution of Oceanography, University of California, San Diego, CA
2Centre National de Recherches Météorologiques, Toulouse, France
3Department of Meteorology, University of Reading, UK
4Department of Electronic and Electrical Engineering, University of Bath, UK
5The Hebrew University of Jerusalem, Israel
6School of Physics and Centre for Climate and Air Pollution Studies, National University of Ireland Galway, Ireland
Abstract. Top-down and bottom-up aerosol-cloud-radiative flux closures were conducted at the Mace Head atmospheric research station in Galway, Ireland in August 2015. This study is part of the BACCHUS (Impact of Biogenic versus Anthropogenic emissions on Clouds and Climate: towards a Holistic UnderStanding) European collaborative project, with the goal of understanding key processes affecting aerosol-cloud-radiative flux closures to improve future climate predictions and develop sustainable policies for Europe. Instrument platforms include ground-based, unmanned aerial vehicles (UAV), and satellite measurements of aerosols, clouds and meteorological variables. The ground-based and airborne measurements of aerosol size distributions and cloud condensation nuclei (CCN) concentration were used to initiate a 1D microphysical aerosol-cloud parcel model (ACPM). UAVs were equipped for a specific science mission, with an optical particle counter for aerosol distribution profiles, a cloud sensor to measure cloud extinction, or a 5-hole probe for 3D wind vectors. UAV cloud measurements are rare and have only become possible in recent years through the miniaturization of instrumentation. These are the first UAV measurements at Mace Head. ACPM simulations are compared to in-situ cloud extinction measurements from UAVs to quantify closure in terms of cloud radiative flux. Two out of seven cases exhibit sub-adiabatic vertical temperature profiles within the cloud, which suggests that entrainment processes affect cloud microphysical properties and lead to an overestimate of simulated cloud radiative flux. Including an entrainment parameterization and explicitly calculating the entrainment fraction in the ACPM simulations both improved cloud-top radiative closure. Entrainment reduced the difference between simulated and observation-derived cloud-top radiative flux (δRF) by between 30 W m−2 and 40 W m−2. After accounting for entrainment, satellite-derived cloud droplet number concentrations (CDNC) were within 30 % of simulated CDNC. In cases with a well-mixed boundary layer, δRF is less than 25 W m−2 after accounting for cloud-top entrainment, compared to less than 50 W m−2 when entrainment is not taken into account. In cases with a decoupled boundary layer, cloud microphysical properties are inconsistent with ground-based aerosol measurements, as expected, and δRF is as high as 88 W m−2, even after accounting for cloud-top entrainment. This work demonstrates the need to take in-situ measurements of aerosol properties for cases where the boundary layer is decoupled as well as consider cloud-top entrainment to accurately model stratocumulus cloud radiative flux.

Citation: Sanchez, K. J., Roberts, G. C., Calmer, R., Nicoll, K., Hashimshoni, E., Rosenfeld, D., Ovadnevaite, J., Preissler, J., Ceburnis, D., O'Dowd, C., and Russell, L. M.: Top-down and Bottom-up aerosol-cloud-closure: towards understanding sources of uncertainty in deriving cloud radiative flux, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-201, in review, 2017.
Kevin J. Sanchez et al.
Kevin J. Sanchez et al.
Kevin J. Sanchez et al.


Total article views: 353 (including HTML, PDF, and XML)

HTML PDF XML Total BibTeX EndNote
245 89 19 353 7 21

Views and downloads (calculated since 21 Mar 2017)

Cumulative views and downloads (calculated since 21 Mar 2017)

Viewed (geographical distribution)

Total article views: 353 (including HTML, PDF, and XML)

Thereof 351 with geography defined and 2 with unknown origin.

Country # Views %
  • 1



Latest update: 26 Apr 2017
Publications Copernicus