title: Role of updraft velocity in temporal variability of global cloud hydrometeor number.
abstract: Understanding how dynamical and aerosol inputs affect the temporal variability of hydrometeor formation in climate models will help to explain sources of model diversity in cloud forcing, to provide robust comparisons with data, and, ultimately, to reduce the uncertainty in estimates of the aerosol indirect effect. This variability attribution can be done at various spatial and temporal resolutions with metrics derived from online adjoint sensitivities of droplet and crystal number to relevant inputs. Such metrics are defined and calculated from simulations using the NASA Goddard Earth Observing System Model, Version 5 (GEOS-5) and the National Center for Atmospheric Research Community Atmosphere Model Version 5.1 (CAM5.1). Input updraft velocity fluctuations can explain as much as 48% of temporal variability in output ice crystal number and 61% in droplet number in GEOS-5 and up to 89% of temporal variability in output ice crystal number in CAM5.1. In both models, this vertical velocity attribution depends strongly on altitude. Despite its importance for hydrometeor formation, simulated vertical velocity distributions are rarely evaluated against observations due to the sparsity of relevant data. Coordinated effort by the atmospheric community to develop more consistent, observationally based updraft treatments will help to close this knowledge gap.
authors.affiliation: School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332;
authors.forename: Sylvia C
authors.initials: SC
authors.lastname: Sullivan
authors.affiliation: Goddard Earth Sciences Technology and Research, Morgan State University, Baltimore, MD 21251;
authors.forename: Dongmin
authors.initials: D
authors.lastname: Lee
authors.affiliation: Climate and Radiation Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771;
authors.forename: Lazaros
authors.identifier: 0000-0001-6061-6905
authors.initials: L
authors.lastname: Oreopoulos
authors.affiliation: School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332; School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332; Institute for Environmental Research and Sustainable Development, National Observatory of Athens, 15236 Palea Penteli, Greece; Foundation for Research and Technology - Hellas, 26504 Patras, Greece athanasios.nenes@gatech.edu.
authors.forename: Athanasios
authors.initials: A
authors.lastname: Nenes
keywords: attribution; clouds; global models; sensitivity; vertical velocity