Movie: Forward Trajectories over the Eastern US from 6/01/91 to 9/01/91

Description:

Forward trajectories from 20 receptor sites evenly distributed over the Eastern US. The trajectories extend for three days after their release from each source during 6/01/91 through 9/01/91. The source release time, in Eastern Standard Time (EST), is located at the bottom of the movie, and has a four hour time increment. The transport of each source airmass is simulated by three trajectories. The squares along each trajectory identify the location of the airmass every four hours along its pathway from the source.

Purpose:

This movie can be used as a resource to provide meteorological context to the interpretation of air quality data. The trajectories identify the pathway of airmasses that originate at specific locations, and can be used to identify stagnating and recirculating airmasses.

Method:

The back trajectories were calculated using the CAPITA Monte Carlo model, and Eulerian wind fields generated from the National Meteorological Centers Nested Grid Model, with 180 km resolution. Three particles were released from each site at four hour time increments and tracked backwards for three days.

Interpretation:

Transport in the atmosphere is a random process resulting from turbulent mixing in the atmospheric boundary layer. The mixing processes are generally very efficient during the day causing individual airmasses to lose their identity and become a part of a larger regional airmass. Consequently, a receptor airmass is made up of sub airmasses that may have had very different transport histories from each other. This phenomenon is simulated by using three particles to trace the transport route or each airmass. As shown in the movie, each particle follows its own pathway which maybe very different from the others.