Transport of smoke from the Central American Fires of 1998

Abstract

During the spring of 1998, smoke produced by biomass burning in Central America was transported northward, where it eventually affected the United States. The Total Ozone Mapping Spectrometer (TOMS) aerosol index is used in this study to measure biomass-burning aerosols and analyze the event. Comparison between the TOMS aerosol product and air parcel trajectories computed from assimilated winds verifies that the trajectories adequately represent the smoke transport. Analysis of the TOMS data and the trajectories indicate that the source region of the smoke is influenced by two prevailing transport regimes: one northward and one westward. The transport alternates between the two flow patterns which is also evident in mean wind fields calculated for corresponding time periods. In order to determine whether the 1998 transport was unusual, a twenty-year transport climatology is computed using assimilated winds. Statistical analysis of the transport shows that May 1998 and the climatology contain similar patterns of northward and westward flow regimes in the area surrounding the smoke's source. The northward flow regime in 1998, however, was among the strongest of the twenty-year period analyzed. The vertical flux of air parcels was also unusual during May 1998 with convergence near 800 mb whereas, in the climatology, the vertical motion is usually upwards throughout the lower troposphere. In addition to unusually strong northward transport in 1998, the smoke production in the source region was large compared to the Nimbus 7 TOMS aerosol product climatology for 1979 to 1992.