Regional observations of the nocturnal low level jet over the mid-Atlantic

A nocturnal low level jet (LLJ) is commonly observed east of the Appalachians during the warm season. Under high pressure conditions to the Southeast and with the sudden cessation of turbulence around sunset, the wind can accelerate to supergeostrophic speeds in a shallow layer at the top of the nocturnal inversion. These same conditions are known to trap pollutants, precursors to ozone formation, and particulate matter. At night these pollutants and particles are confined to the residual layer and can be transported long distances by the LLJ at night, and mixed down to the surface the next day. Data from multiple profilers east of the Appalachians (MADIS CAP profiler network) and an acoustic SODAR at Millersville University were used to identify several LLJ occurrences during the warm seasons of 2008 and 2009. This study focused on persistence of LLJ events, those that were observed on at least three consecutive nights by no fewer than three profilers. Surface observations of ozone and particulate matter were used to identify the surface level response to transport and mixing. In addition to the wind profiler and surface measurements, supplementary tools such as HYSPLIT back trajectories and the WRF model are used for a detailed analysis of a notable event that occurred in June 2008. This study uses a regional profiling network to demonstrate the importance of the LLJ on the nocturnal transport of ozone and particulate matter and its influence on daytime surface concentrations.