| Turbulent boundary layers form when fluid flow passes a material surface. Geophysical boundary layers include airflow over ground or water surfaces and oceanic currents over the sea bottom or adjacent to the wavy top surface. The atmospheric boundary layer may be as deep as 1-2 km with daytime surface heating but as thin as a few meters or tens of meters on weak-wind, clear nights with significant surface cooling. Momentum is tranferred through this boundary layer from moving air to stationary or mobile surfaces through surface drag. Transfer of heat, moisture, carbon dioxide, and other greenhouse gases between the Earth's surface and the atmosphere also occurs through the atmospheric boundary layer. NorthWest Research Associates has become a center for boundary layer research and is conducting research on a variety of boundary layer topics with funding from many different agencies. Some of the projects are highlighted below: |
Ed has 4 primary research areas, all tied together by his fundamental interest in turbulent transfer processes in the atmospheric boundary layer. These 4 areas:
Ed has done theoretical work and modeling in all 4 areas; his experimental work has concentrated on the 2nd, 3rd, and 4th areas. The following figures are from some of Ed's field projects...fig. 1 | fig. 2 | fig. 3 |
Larry Mahrt is analyzing new data from networks of fast response wind sensors to study the time-space relationships of mesoscale motions in the stable nocturnal boundary layer, their horizontal transport and their influence on turbulence. With weak winds and strong nocturnal stratification, contaminants may locally reach high concentrations due to very weak vertical mixing. The example animation, based on the CASES99 network for a 30-minute period, shows simulated particles released into an observed wind field. The blue particles reveal the instantaneous distribution of particles; the smaller white specs show the accumulated particle count since the beginning of the animation. Due to unpredictable sudden shifts in the wind direction, the accumulated particle distribution tends to be concentrated in three streaks. Additional animations can be found at http://moonset.coas.oregonstate.edu/ by clicking on "animations". |
Insight into complex atmospheric dynamics often derives from the study of reduced models. David Schecter (Seattle Division) is currently investigating the mechanisms by which chaotic flows self-organize in 3-layer atmospheres that include basic representations of cumulus convection and air-sea interaction. Knowledge gained from this study will contribute to our understanding of how and why climate variation may affect hurricane formation, intensity and frequency. The attendant figure illustrates the evolution of quasi two-dimensional (2D) turbulence in the lower troposhere of a reduced model with tropical parameters. Bright and dark shades represent positive and negative values of relative vorticity; the color-map in each plot is recentered and rescaled to span the instantaneous extremes. Ideal 2D processes, such as vortex merger and filamentation, control the early stage of flow development. In time, deep cumulus convection (regulated by air-sea interaction) transforms a few distinguished cyclones into hurricanes. These hurricanes eventually merge and generate peripheral filaments, which provide the seeds for future convective votices. One of our goals is to better understand the interplay between cumulus convection and 2D mechanisms of self-organization. This work is supported primarily by NSF grant ATM-0750660, entitled "Diabatic Ekham Turbulence." |