Atmospheric boundary-layer structure observed during a haze event due to forest-fire smoke

Markus Pahlow, Jan Kleissl, Marc B. Parlange, John M. Ondov, David Harrison

Research output: Contribution to journalArticleResearchpeer-review

35 Citations (Scopus)

Abstract

During a haze event in Baltimore, U.S.A. from July 6 to 8, 2002, smoke from forest fires in the Québec region (Canada), degraded air quality and impacted upon local climate, decreasing solar radiation and air temperature. The smoke particles in and above the atmospheric boundary layer (ABL) served as a tracer and provided a unique opportunity to investigate the ABL structure, especially entrainment. Elastic backscatter lidar measurements taken during the haze event distinctly reveal the downward sweeps (or wisps) of smoke-laden air from the free atmosphere into the ABL. Visualisations of mechanisms such as dry convection, the entrainment process, detrainment, coherent entrainment structures, and mixing inside the ABL, are presented. Thermals overshooting at the ABL top are shown to create disturbances in the form of gravity waves in the free atmosphere aloft, as evidenced by a corresponding ripple structure at the bottom of the smoke layer. Lidar data, aerosol ground-based measurements and supporting meteorological data are used to link free atmosphere, mixed-layer and ground-level aerosols. During the peak period of the haze event (July 7, 2002), the correlation between time series of elastic backscatter lidar data within the mixed layer and the scattering coefficient from a nephelometer at ground level was found to be high (R=0.96 for z=324 m, and R=0.89 for z=504 m). Ground-level aerosol concentration was at a maximum about 2 h after the smoke layer intersected with the growing ABL, confirming that the wisps do not initially reach the ground.

Original languageEnglish
Pages (from-to)53-70
Number of pages18
JournalBoundary-Layer Meteorology
Volume114
Issue number1
DOIs
Publication statusPublished - Jan 2005
Externally publishedYes

Keywords

  • Atmospheric boundary layer
  • Baltimore PM Supersite
  • Entrainment
  • Forest fire
  • Haze event
  • Lidar

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