HR: 16:45h
AN: A34A-04    [Abstracts]
TI: Nocturnal Secondary Ozone Maxima over the Mid-Atlantic U.S. from Shear Induced Turbulence in the Low Level Jet
AU: * Taubman, B F
EM: btaubman@meteo.psu.edu
AF: Pennsylvania State University, Department of Meteorology, University Park, PA 16802
AU: Thompson, A M
EM: anne@met.psu.edu
AF: Pennsylvania State University, Department of Meteorology, University Park, PA 16802
AU: Joseph, E
EM: ejoseph@howard.edu
AF: Howard University, Department of Physics and Astronomy, Washington, DC 20059
AU: Michaels, S M
EM: smm519@psu.edu
AF: Pennsylvania State University, Department of Meteorology, University Park, PA 16802
AU: Zhang, S
EM: shunli@atmos.umd.edu
AF: University of Maryland, Department of Atmospheric and Oceanic Sciences, College Park, MD 20742
AU: Piety, C A
EM: charles@atmos.umd.edu
AF: University of Maryland, Department of Atmospheric and Oceanic Sciences, College Park, MD 20742
AB: The Mid-Atlantic nocturnal low level jet (LLJ) is a potentially important mechanism for the regional transport of pollutants and precursor species between major urban areas in the Mid-Atlantic U.S. The species within the LLJ are transported in a thin layer above the nocturnal inversion and may mix down to the surface, thereby impacting air quality, via two pathways: 1) solar heating induced vertical mixing upon erosion of the nocturnal inversion, or 2) shear induced turbulent mixing overnight. We provide the first direct evidence that shear induced turbulence mixes ozone transported in the LLJ down to the surface overnight. We launched several ozonesonde/GPS radiosonde packages overnight in August, 2005 from the Howard University Atmospheric Science site in Beltsville, MD to characterize the chemistry and dynamics of the LLJ. Wind maxima of 10-15 m/s occurred in a thin layer between 300 and 800 m. The wind in the jet was generally southwesterly whereas the flow above the jet was slower (4 m/s) and more westerly. Ozone values up to 100 ppbv were observed in the same layer as the jet and were distinct from the rest of the residual layer values. However, the ozone maxima were at a slightly higher altitude than the wind maxima, a fact that appears to be due to ozone within the center of the jet mixing down to the surface via shear induced turbulence. This occurrence is corroborated by the NOAA CASTNET ozone measurements in Beltsville, MD that measured secondary ozone maxima up to 60 ppbv at the surface during the same time period as the LLJ. Additional evidence is provided by the MM5, which was able to resolve downward vertical velocities of 3-5 cm/s at altitudes consistent with those of the observed wind maxima. In addition to ozone, this mechanism is capable of mixing precursor species and particulate matter to the surface during the nighttime and requires detailed representation in models and better experimental characterization.
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0368 Troposphere: constituent transport and chemistry
DE: 3307 Boundary layer processes
DE: 3329 Mesoscale meteorology
DE: 3355 Regional modeling
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005