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dc.contributor.authorSanchez, Kevin J.
dc.contributor.authorRoberts, Gregory C.
dc.contributor.authorCalmer, Radiance
dc.contributor.authorNicoll, Keri
dc.contributor.authorHashimshoni, Eyal
dc.contributor.authorRosenfeld, Daniel
dc.contributor.authorOvadnevaite, Jurgita
dc.contributor.authorPreissler, Jana
dc.contributor.authorCeburnis, Darius
dc.contributor.authorO'Dowd, Colin
dc.contributor.authorRussell, Lynn M.
dc.identifier.citationSanchez, 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 shortwave radiative flux, Atmos. Chem. Phys., 17, 9797-9814,, 2017en_IE
dc.description.abstractTop-down and bottom-up aerosol-cloud shortwave 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 shortwave radiative flux closures to improve future climate predictions and develop sustainable policies for Europe. Instrument platforms include ground-based unmanned aerial vehicles (UAVs)(1) 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 1-D 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 five-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 shortwave 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 shortwave 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 shortwave radiative flux (delta RF) by between 25 and 60Wm(-2). After accounting for entrainment, satellite-derived cloud droplet number concentrations (CDNCs) were within 30% of simulated CDNC. In cases with a well-mixed boundary layer, delta RF is no greater than 20Wm(-2) after accounting for cloud-top entrainment and up to 50Wm(-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 delta RF is as high as 88Wm(-2), even high (> 30Wm(-2)) 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.en_IE
dc.description.sponsorshipThe research leading to these results received funding from the European Union’s Seventh Framework Programme (FP7/2007-2013) project BACCHUS under grant agreement no. 603445. EU H2020 project ACTRIS-2 under the grant agreement no. 654109 is also acknowledged for supporting the Mace Head Atmospheric Research Station. Keri Nicoll acknowledges a NERC Independent Research Fellowship (NE/L011514/1). Darius Ceburnis acknowledges the Irish EPA (2012-CCRP-FS.12). Jana Preissler acknowledges the Irish EPA (2015-CCRP-FS.24). Radiance Calmer acknowledges financial support from Météo France. Kevin J. Sanchez acknowledges the Chateaubriand Fellowship. We thank École Nationale de l’Aviation Civile (ENAC) for assistance with construction and operation of the UAVs. The authors also acknowledge Kirsten Fossum for the collection of SMPS data. We applied a sequence-defines-credit approach for the sequence of authorship.en_IE
dc.publisherEuropean Geosciences Union (EGU)en_IE
dc.relation.ispartofAtmospheric Chemistry And Physicsen
dc.rightsAttribution-NonCommercial-NoDerivs 3.0 Ireland
dc.subjectMACE HEADen_IE
dc.subjectMIXED LAYERSen_IE
dc.subjectACE 1en_IE
dc.titleTop-down and bottom-up aerosol-cloud closure: towards understanding sources of uncertainty in deriving cloud shortwave radiative fluxen_IE
dc.contributor.funderEuropean Union’s Seventh Framework Programme (FP7/2007-2013)
dc.contributor.funderEU H2020
dc.local.contactDarius Ceburnis, School Of Physics, Room 215a Arts/Science Building, Nui Galway. 2496 Email:

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