科研之友
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摘要
In the framework of the Saharan Mineral Dust Experiment (SAMUM) airborne High Spectral Resolution Lidar and in situ measurements of the particle size, aerosol mixing state and absorption coefficient were conducted. Here, the properties of mineral dust and tropical biomass burning layers in the Cape Verde region in January/February 2008 are investigated and compared with the properties of fresh dust observed in May/June 2006 close the Sahara. In the Cape Verde area, we found a complex stratification with dust layers covering the altitude range below 2 km and biomass burning layers aloft. The aerosol type of the individual layers was classified based on depolarization and lidar ratios and, in addition, on in situ measured Angstrom exponents of absorption (a) over circle (ap). The dust layers had a depth of 1.3 +/- 0.4 km and showed a median ($) over circle (ap) of 3.95. The median effective diameter D(eff) was 2.5 mu m and the dust layers over Cape Verde yielded clear signals of aging: large particles were depleted due to gravitational settling and the accumulation mode diameter was shifted towards larger sizes as a result of coagulation. The tropical biomass layers had a depth of 2.0 +/- 1.1 km and were characterized by a median ($) over circle (ap) of 1.34. They always contained a certain amount of large dust particles and showed a median Deff of 1.1 mu m and a fine mode D(eff,fine) of 0.33. The dust and biomass burning layers had a median aerosol optical depth (AOD) of 0.23 and 0.09, respectively. The median contributions to the AOD of the total atmospheric column below 10 km were 75 and 37%, respectively.
- 出版日期2011-9
