OPTICAL-PROPERTIES OF SAHARAN DUST DURING ACE-2

The Aerosol Robotic Network (AERONET) of automatic Sun/sky radiometers collected data on Tenerife, Canary Islands, in June-July 1997 during the second Aerosol Characterization Experiment (ACE 2). Initially, two instruments were deployed at Izana observatory (2360 m above sea leve l) and one at a mountain station Teide (3570 m above sea level). Repea tability of the calibration constants (Langley method) for all instrum ents was less than 0.5%. Aerosol optical depths measured by colocated sunphotometers and column size distributions, retrieved from spectral sky radiance data, were in good agreement. Later, one of the instrumen ts was relocated at sea level. On July 8, 17, and 25, Saharan dust out breaks were observed. Diurnal variations of spectral aerosol optical d epth are presented. Relative diurnal stability of Saharan dust optical properties has been observed. Volume size distributions at various he ights (sea level and 2360 m above sea level) show that the main portio n of coarse particles is situated above 2360 m level. Measurements on July 25 showed how incoming dust has changed the magnitude and spectra l dependence of aerosol optical depth and volume spectra of columnar a erosol. Mean optical depth and Angstrom parameter values for Saharan d ust outbreaks during the ACE 2 experiment agree well with the Atlantic Ocean and Bermuda data obtained during the Tropospheric Aerosol Radia tive Forcing Observational Experiment (TARFOX) in July 1996, as well a s with previously reported Atlantic Ocean results. Also, there is a go od agreement between ACE 2 data for Saharan air masses and data obtain ed on certain sites of the AERONET network.