Do deep-convective aerosol effects resolve climate enigmas?
It would help reconcile some conflicts in climate-change evidence if aerosols had a stronger negative forcing than the most likely range as assessed by e.g. the IPCC. A number of mechanisms have been suggested whereby aerosol (CCN) affect cloud properties. One idea motivated by recent observations is that CCN numbers limit cloud formation and growth in areas where background concentrations are particularly low, i.e., remote ocean regions. A related one is that CCN can invigorate deep convection by delaying the onset of rain so that more water freezes, producing more high-level cloud. New observational and multiscale modeling evidence is presented indicating that observed correlations between aerosol and cloud cover and height can arise from purely meteorological factors and that a strong microphysical effect is uniikely. On the other hand, model simulations do suggest that CCN can subtly alter convection in shallow-to-deep transition regions in a way that would produce a nontrivial global indirect negative forcing. This mechanism is likely to have been overlooked by typical observational and model studies, which focus mainly on shallower cloud types.
16 May 2016, 14:15 (Monday, 4th week, Trinity 2016)
Atmospheric, Oceanic and Planetary Physics, off Parks Road OX1 3PU
Dobson Lecture Room
Steve Sherwood (University of New South Wales)
Department of Physics
Andrew Wells (Atmospheric, Oceanic & Planetary Physics, University of Oxford; & Wolfson College)
Philip Stier (AOPP)
Geophysical & Nonlinear Fluid Dynamics Seminars
Members of the University only