Three ASMD Scientists Author Paper Exploring Turbulent Mixing Methods in HYSPLIT

November 2019

“The evaluation of mixing methods in HYSPLIT using measurements from controlled tracer experiments” was recently accepted by Atmospheric Environment and will appear in the journal’s December 15 issue. The study, authored by Fong (Fantine) Ngan, Christopher Loughner, and Ariel Stein, focuses on evaluating the turbulent mixing methods available in HYSPLIT and their impacts on dispersion results compared to two controlled tracer experiments.

In this first-of-its-kind study the authors conducted dispersion simulations using HYSPLIT with four different mixing methods (Belijaars-Holtslag, Kantha-Clayson, turbulent kinetic energy, and turbulent exchange coefficient), producing different mixing profiles in varying scenarios with no one mixing option consistently outperforming the others. The manuscript discusses the uncertainties inherent in using different mixing methods and concludes that HYSPLIT users can select a mixing option according to their scenario and availability of meteorological fields and use different mixing options to generate dispersion ensembles.

The figure at right illustrates computed vertical velocity variance profiles (a-d) which, in simpler terms, measure the strength of mixing in the boundary layer. These profiles are compared with a measurement located 800 meters away from the source location (e) – the release location of the pollutant, or tracer. Colored lines indicate different hours and black lines represent an averaged vertical velocity variance for a three-hour window (12-15 MST) on October 5, 2013.

Five graphic results of the variance of turbulent mixing. a-d indicate the 4 mixing methods and e is an actual observation. Different colors for 1200, 1300, 1400 & 1500, & a black line for three hour average from 12-15 MST on 10/5/13.
Computed vertical velocity variance profiles from Project Sagebrush phase 1, intense observation period 2, conducted at the Idaho National Laboratory. Credit: NOAA