Common Variability in the Stable Atmospheric Boundary Layer on Small Space and Time Scales

Northwest Research Associates, Incorporated, Seattle WA

Investigators

Abstract

A regular nighttime occurrence is the development of a stable boundary layer, which is a shallow, near-calm layer of air near the Earth’s surface. However, despite the air seemingly being calm, there are ongoing motions which have important impacts on near-ground temperatures and the dispersion of pollutants. This research award provides support for the analysis of existing observational data on stable boundary layer motions, with a fresh look at how they can be tracked and how that information can be used to improve numerical weather models. A specific use case that this award will address, in consultation with local field managers, is vineyards in the Pacific Northwest where frosts and freezes have a significant impact. The research under this award will expand understanding of small-scale, non-stationary motions, their interaction with surface heterogeneity, and their stochastic behavior. The focus is on submeso motions, which are formally defined to include motions on scales just larger than the largest turbulent eddies and up to scales normally considered to be the smallest mesoscale motions (2km). A sequence of case studies of different types of small-scale motions will be constructed using data from 9 prior field campaigns and a package of different analysis methods that has been developed by the researcher. The main objectives of the proposal are to: 1) Quantify the submeso time and space variability of the temperature, the wind vector, and turbulent fluxes and relate these variations to the forcing variables, 2) Track propagating modes across networks of data and examine their interaction with surface-based phenomena due to gentle topography and the impact of this interaction on turbulent fluxes, 3) Formulate probability distributions for short-term (non-turbulent) variations of the temperature and wind direction for low wind speeds and relate the characteristics of the distributions to the forcing variables, and 4) Reanalyze the behavior of the fluxes and corresponding transfer coefficients in the bulk formula for low wind speeds based on time averaging and based on spatial averaging across the networks and improve formulation of the transfer coefficients for low wind speeds. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.