U.S. Air Quality

Poor Ozone and the Low Level Jet

Charles Piety at UMCP and the folks in Bill Ryan's Philadelphia Air Quality Forecasting group have set out a warning for the next two days that the ozone will be rising into the Unhealthy range as temperatures warm and we get flow from the south/southwest.

We are running the lidar all night on Saturday morning and Sunday morning because warnings have been issued for a Low Level Jet (LLJ) each night (probably stronger on Sunday morning).

What's a LLJ? When a strong east-west pressure gradient sets up with high pressure to the east, strong nighttime winds can arise flowing northward. Tonight's pressure map from the RUC model shows such a pressure situation with the high to the east of the Appalachian mountains. The Jet will manifest itself as strong winds (10-20 m/s) at a very low altitude (300-800m).

Why do we care in terms of air quality? These events are great conduits of pollution and pollution precursors from the south. For some reading, you can link to the paper by K. Zhang of UMCP, "Numerical Investigation of Boundary Layer Evolution and Nocturnal Low Level Jets: Local versus Non- local PBL Schemes".

It is now 1:20 AM EDT here in Baltimore and we may be seeing a sign of a LLJ in the lidar data here at UMBC at 400m. More coffee..more coffee.

Posted by Ray Hoff at June 17, 2006 12:44 AM