Evaluation of STILT Features Incorporated into HYSPLIT

NOAA’s Hybrid Single Particle Lagangian Integrated Trajectory (HYSPLIT) model is one of the most widely used atmospheric dispersion and trajectory model. The Stochastic Time-Inverted Lagrangian Transport (STILT) model, which has traditionally been used to estimate greenhouse gas emissions, is based on an old version of HYSPLIT and includes additional complex routines. These additional features include 1) a vertical interpolation scheme specific for interpolating Weather Research and Forecasting (WRF) meteorological model output onto the HYSPLIT domain; 2) a more detailed scheme for estimating boundary layer height; 3) the Hanna turbulence parameterization scheme; 4) an algorithm for calculating a Lagrangian vertical timescale varying in space and time; 5) a more complex mean advection and turbulent transport option; and 6) two new convection schemes. These complex STILT features have been integrated into HYSPLIT. An in-depth evaluation will be presented of the current and newly added HYSPLIT routines with observations from tracer release experiments to quantify model biases and uncertainties under different meteorological regimes (i.e., stable, unstable). This presentation will highlight differences and similarities between HYSPLIT runs performed with the current model options versus the more complex STILT routines.