School of Meteorology

Cloud-aerosol interactions in fields of organizing shallow cumuli

Dr. Thijs Heus
Institute for Geophysics and Meteorology, University of Cologne, Germany

18 February 2014, 4:00 PM

National Weather Center, Room 1313
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Coffee / Cookies @ 3:30 PM

Despite decades of studies, cloud-aerosol interactions remain a notoriously difficult topic. These interactions are particularly important for trade-wind cumulus clouds, which often barely precipitate. Many of the postulated cloud-aerosol interactions involve precipitation to limit for instance the cloud size or the cloud life time. However, if the precipitation exceeds a certain threshold, it will feedback on the cloud field through cold pools and mesoscale organization. Such mesoscale responses have mostly been ignored so far in the discussion of aerosol indirect effects.

In this study, we use high-resolution (25 m in all directions), large-domain (50-km width), long-duration (48 hours) large eddy simulations to quantify the indirect effects of aerosols through the lifetime, size, and depth of cumulus clouds. Six idealized simulations are conducted for the Rain In Cumulus over the Ocean (RICO) inter-comparison case as the baseline. Using an in-house developed cloud tracking algorithm, we are able to directly calculate the cloud life time and cloud size distributions. As it turns out, the occurrence and timing of the mesoscale organization plays a crucial role in assessing the aerosol indirect effects for these fields of cumulus clouds. We found that the pathway towards organization differs significantly between the different cases, with the moist and pristine cloud ensembles organizing much faster than the dry and polluted ones. It is concluded that an accurate assessment of the changes in cloud lifetime and size can only be made when distinguishing between the organized and the randomly distributed situations.

For accommodations based on disability, or more details, please call 325-6561. All visitors without NOAA or University of Oklahoma identification must register at the registration desk on arrival. Visitor parking is available for all University visitors. However, faculty/staff/students must have a current multi-purpose parking permit. Additional parking is available at the Lloyd Noble Center (LNC) for those individuals who do not have a parking permit. You do not need a permit to park in one of 1,200 spaces reserved for CART bus riders, although you must ride the CART shuttle to park in the reserved area. This area is on the north central side of the Lloyd Noble Center. Elsewhere at the LNC, permits are required.

The University of Oklahoma is a smoke-free / tobacco-free campus.

School of Meteorology Seminar Series website