Synoptic influences on springtime tropospheric O3 and CO over the North American export region observed by TES J. Hegarty, H. Mao, and R. Talbot Institute for the Study of Earth, Oceans and Space, Climate Change Research Center, University of New Hampshire, Durham, New Hampshire 03824, USA
Abstract. The relationship between synoptic circulation patterns over the western
North Atlantic Ocean in spring (March, April, and May) and tropospheric
O3 and CO was investigated using retrievals from the Tropospheric
Emission Spectrometer (TES) for 2005 and 2006. Seasonal composites of TES
retrievals reprocessed to remove the artificial geographic structure added
from the a priori revealed a channel of slightly elevated O3 (>55 ppbv) and CO (>115 ppbv) at the 681 hPa retrieval level between
30° N and 45° N extending from North America out over the Atlantic
Ocean. Ozone and CO in this region were correlated at r=0.22 with a slope
value of 0.13 mol mol−1 indicative of the overall impact of
photochemical chemical processes in North American continental export.
Composites of TES retrievals for the six predominant circulation patterns
identified as map types from sea level pressure fields of the NCEP FNL
analyses showed large variability in the distribution of tropospheric
O3. Map types MAM2 and MAM3 featuring cyclones near the US east coast
produced the greatest export to the lower free troposphere with O3>65 ppbv and a relatively well-defined O3-CO correlation (slope
values near 0.20 mol mol−1). The ensembles of HYSPLIT backward
trajectories indicated that the high O3 levels were possibly a result
of pollutants lofted to the free troposphere by the warm conveyor belt (WCB)
of a cyclone. An important finding was that pollutant export occurred in the
main WCB branch to the east of the cyclone and in a secondary branch
circling to the back of the cyclone center. Conversely, a map type featuring
a large anticyclone dominating the flow over the US east coast (MAM6)
restricted export with O3 levels generally <55 ppbv and CO levels
generally <110 ppbv. There was also evidence of stratospheric intrusions
particularly to the north of 45° N in the 316 hPa composites
predominately for MAM1 which featured a large cyclone near Newfoundland.
However, the concurrence of these intrusions with pollutant export,
specifically in the southwestern North Atlantic Ocean, made it difficult to
delineate their respective contributions to the 681 hPa O3 composites.
Citation: Hegarty, J., Mao, H., and Talbot, R.: Synoptic influences on springtime tropospheric O3 and CO over the North American export region observed by TES, Atmos. Chem. Phys., 9, 3755-3776, doi:10.5194/acp-9-3755-2009, 2009.