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Volume 18, issue 8
Atmos. Chem. Phys., 18, 5821-5846, 2018
https://doi.org/10.5194/acp-18-5821-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Atmos. Chem. Phys., 18, 5821-5846, 2018
https://doi.org/10.5194/acp-18-5821-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Apr 2018

Research article | 26 Apr 2018

Aerosol midlatitude cyclone indirect effects in observations and high-resolution simulations

Daniel T. McCoy1, Paul R. Field1,2, Anja Schmidt1,3,4, Daniel P. Grosvenor1,5, Frida A.-M. Bender6, Ben J. Shipway2, Adrian A. Hill2, Jonathan M. Wilkinson2, and Gregory S. Elsaesser7 Daniel T. McCoy et al.
  • 1School of Earth and Environment, Institute of Climate and Atmospheric Science, University of Leeds, Leeds, LS2 9JT, UK
  • 2Met Office, Fitzroy Rd, Exeter EX1 3PB, UK
  • 3Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK
  • 4Department of Geography, University of Cambridge, Downing Place, Cambridge CB2 3EN, UK
  • 5National Centre for Atmospheric Science (NCAS), University of Leeds, Leeds, LS2 9JT, UK
  • 6Department of Meteorology and Bolin Centre for Climate Research, Stockholm University, Stockholm, 106 91, Sweden
  • 7Department of Applied Physics and Applied Mathematics, Columbia University and NASA Goddard Institute for Space Studies, New York, NY, USA

Abstract. Aerosol–cloud interactions are a major source of uncertainty in inferring the climate sensitivity from the observational record of temperature. The adjustment of clouds to aerosol is a poorly constrained aspect of these aerosol–cloud interactions. Here, we examine the response of midlatitude cyclone cloud properties to a change in cloud droplet number concentration (CDNC). Idealized experiments in high-resolution, convection-permitting global aquaplanet simulations with constant CDNC are compared to 13 years of remote-sensing observations. Observations and idealized aquaplanet simulations agree that increased warm conveyor belt (WCB) moisture flux into cyclones is consistent with higher cyclone liquid water path (CLWP). When CDNC is increased a larger LWP is needed to give the same rain rate. The LWP adjusts to allow the rain rate to be equal to the moisture flux into the cyclone along the WCB. This results in an increased CLWP for higher CDNC at a fixed WCB moisture flux in both observations and simulations. If observed cyclones in the top and bottom tercile of CDNC are contrasted it is found that they have not only higher CLWP but also cloud cover and albedo. The difference in cyclone albedo between the cyclones in the top and bottom third of CDNC is observed by CERES to be between 0.018 and 0.032, which is consistent with a 4.6–8.3Wm−2 in-cyclone enhancement in upwelling shortwave when scaled by annual-mean insolation. Based on a regression model to observed cyclone properties, roughly 60% of the observed variability in CLWP can be explained by CDNC and WCB moisture flux.

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Short summary
Here we use a combination of global convection-permitting models, satellite observations and the Holuhraun volcanic eruption to demonstrate that aerosol enhances the cloud liquid content and brightness of midlatitude cyclones. This is important because the strength of anthropogenic radiative forcing is uncertain, leading to uncertainty in the climate sensitivity consistent with observed temperature record.
Here we use a combination of global convection-permitting models, satellite observations and the...
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