Work package leader:
Øyvind Saetra (Norwegian Meteorological institute)
Other key investigators:
Alastair Jenkins, Harald Schyberg, Jón Egill Kristjánsson, Erik Kolstad, Idar Barstad, Stanislav Ermakov, Irna Repina, Anna Sjöblom, Trond Iversen.
Background
Methods for treating sea-state dependent momentum fluxes in coupled wave-atmosphere models are currently implemented in some operational weather forecasting systems (Janssen et al., 2001). Also the moist fluxes are believed to be sea-state dependent, although experimental evidence for this has proven difficult to obtain. However, a recent study by Brut et al. (2005) presents observations that support this idea. For wind speeds near hurricane force, the surface zone becomes embedded in sea-spray. Some speculate that under such conditions, the traditional formulations for air-sea fluxes no longer apply, and this is also supported by some field and theoretical studies (Powell et al., 2003; Makin, 2005; Kudryavtsev, 2005; Bye and Jenkins, 2006). Release of latent heat in convective towers is another important part of the energy budget. In most present NWP models the convection is parameterized, and the feedback mechanisms will be governed by the selected scheme, with schemes based on moisture convergence favouring a CISK-type, while CAPE-based schemes are more prone to the WISHE type of intensification (van Delden et al., 2003). In the wintertime Arctic, the Arctic lower troposphere is very stable, and subsequently strong lee effects are common behind the mountains of e.g. Greenland and Svalbard.
Research plan
Observations of turbulent fluxes will be carried out and used to investigate the sea-state dependency of the air-sea fluxes and the turbulence in the planetary boundary layer, under high wind speed conditions. The observations will guide model improvement and validation; see attachment for models used. For improved treatment of the surface and the boundary layer, atmosphere models will be coupled to an ocean wave model. From the observations, attempts will be made to document the southward extension of Arctic fronts and to investigate possible interactions between Arctic fronts and polar lows. The influence of model resolution on simulations of polar lows and arctic fronts will be investigated. Also, the role of latent heat release, the treatment of convection, and the formulation of cloud microphysics will be investigated. Data from the intensive observational campaigns will be of invaluable importance for validating the models, for instance the aircraft measurements, which include dropsondes and wind/humidity LIDAR (Weissmann and Cardinali, 2006) will provide useful information. In the 2007 campaign we will investigate to what extent the forecasting challenges associated with Greenland’s orography can be met be adding more observations or by improving the parameterization of orographic influences in the models.