MMM SEMINAR NCAR
Assuming that both the mesoscale observing network and high-resolution forecast models continue to improve, how much can we expect to improve forecasts at short range and small scales? The classical results of Lorenz (1969) suggest that regardless of the number of observations and the quality of forecast models, flows with many scales of motion may have finite, intrinsic limits of predictability, owing to the increase of error growth rates as scale decreases. Other turbulence-closure models indicate a more subtle situation: predictability appears to be intrinsically limited in three-dimensional turbulence, but not in the forward cascading inertial range of two-dimensional turbulence. Increased computational capabilities now allow direct investigation of the growth of forecast differences in flows that truly span multiple scales of motion. The atmospheric mesoscale represents a particularly interesting case, as it is complicated by the importance of moist convection and lies at the transition between regimes that (at least in some qualitative respects) resemble two-dimensional and three-dimensional turbulence. I will review the concept of an intrinsic limit of predictability and discuss recent efforts to quantify and understand error growth in simulations of baroclinic waves with explicitly resolved moist convection and in high-resolution simulations of quasigeostrophic turbulence.
Thursday, April 15, 2004,
3:30 PM
NCAR-Foothills
Laboratory
3450 Mitchell Lane
Bldg 2 (Room 1022)