A meteorological overview of the MILAGRO field campaigns J. D. Fast1, B. de Foy2,*, F. Acevedo Rosas3, E. Caetano4, G. Carmichael5, L. Emmons6, D. McKenna6, M. Mena5, W. Skamarock6, X. Tie6, R. L. Coulter7, J. C. Barnard1, C. Wiedinmyer6, and S. Madronich6 1Pacific Northwest National Laboratory, Richland, WA, USA 2Molina Center for Energy and the Environment, La Jolla, CA, USA 3Comisión Nacional del Agua, USMN-GRGC, Boca del Río, Veracruz, México 4Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, México City, México 5University of Iowa, Iowa City, IA, USA 6National Center for Atmospheric Research, Boulder, CO, USA 7Argonne National Laboratory, Argonne, IL, USA *now at: Saint Louis University, Saint Louis, MO, USA
Abstract. We describe the large-scale meteorological conditions that affected
atmospheric chemistry over Mexico during March 2006 when several field
campaigns were conducted in the region. In-situ and remote-sensing
instrumentation was deployed to obtain measurements of wind, temperature,
and humidity profiles in the boundary layer and free atmosphere at four
primary sampling sites in central Mexico. Several models were run
operationally during the field campaign to provide forecasts of the local,
regional, and synoptic meteorology as well as the predicted location of the
Mexico City pollutant plume for aircraft flight planning purposes. Field
campaign measurements and large-scale analyses are used to define three
regimes that characterize the overall meteorological conditions: the first
regime prior to 14 March, the second regime between 14 and 23 March, and the
third regime after 23 March. Mostly sunny and dry conditions with periods of
cirrus and marine stratus along the coast occurred during the first regime.
The beginning of the second regime was characterized by a sharp increase in
humidity over the central plateau and the development of late afternoon
convection associated with the passage of a weak cold surge on 14 March.
Over the next several days, the atmosphere over the central plateau became
drier so that deep convection gradually diminished. The third regime began
with the passage of a strong cold surge that lead to humidity, afternoon
convection, and precipitation over the central plateau that was higher than
during the second regime. The frequency and intensity of fires, as
determined by satellite measurements, also diminished significantly after
the third cold surge. The synoptic-scale flow patterns that govern the
transport of pollutants in the region are described and compared to previous
March periods to put the transport into a climatological context. The
complex terrain surrounding Mexico City produces local and regional
circulations that govern short-range transport; however, the mean synoptic
conditions modulate the thermally-driven circulations and on several days
the near-surface flow is coupled to the ambient winds aloft.
Citation: Fast, J. D., de Foy, B., Acevedo Rosas, F., Caetano, E., Carmichael, G., Emmons, L., McKenna, D., Mena, M., Skamarock, W., Tie, X., Coulter, R. L., Barnard, J. C., Wiedinmyer, C., and Madronich, S.: A meteorological overview of the MILAGRO field campaigns, Atmos. Chem. Phys., 7, 2233-2257, doi:10.5194/acp-7-2233-2007, 2007.