Convectively Forced Gravity Wave Drag

Ake Johansson


Gravity waves are a ubiquitous feature of the earth’s atmosphere. They appear on virtually all space and time scales, with a rich variability in its properties dependent on not only the spatial and temporal scales but also on the ambient atmosphere. A substantial part of the gravity wave spectrum is not resolved by present day NWP and climate models. One important aspect of the unresolved waves is that they exert a drag force on the resolved scales when and where they brake. Gravity waves generated by subgrid scale orography have been parameterized in NWP and climate models for over 20 years, with beneficial results. However, there are many other mechanisms whereby gravity waves are generated. One such mechanism is the perturbations to the stable atmosphere above convective clouds caused by deep cumulus convection. Scientists from Korea have recently addressed this issue by developing and testing a parameterization scheme for convectively forced gravity wave drag.

The Korean parameterization scheme (Chun and Baik 1998) has been adapted and tested in the NCEP GFS and CFS models. Results will be presented for both weather and climate aspects.