[1] During the dry season airborne campaign of the Southern African Regional Science Initiative (SAFARI 2000), coordinated observations were made of massive thick aerosol layers. These layers were often dominated by aerosols from biomass burning. We report on airborne Sun photometer measurements of aerosol optical depth (l = 0.354-1.557 mm), columnar water vapor, and vertical profiles of aerosol extinction and water vapor density that were obtained aboard the University of Washington's Convair-580 research aircraft. We compare these with ground-based AERONET Sun/sky radiometer results, with ground based lidar data (MPL-Net), and with measurements from a downward pointing lidar aboard the high-flying NASA ER-2 aircraft. Finally, we show comparisons between aerosol optical depths from the Sun photometer and those retrieved over land and over water using four spaceborne sensors (TOMS, MODIS, MISR, and ATSR-2).

Abstract.A 13-year analysis (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) of the NO 2 vertical column densities derived from ground-based (GB) instruments and satellites has been carried out over the Izaña NDACC (Network for the Detection of the Atmospheric Composition Change) subtropical site. Ground-based DOAS (differential optical absorption spectroscopy) and FTIR (Fourier transform infrared spectroscopy) instruments are intercompared to test mutual consistency and then used for validation of stratospheric NO 2 from OMI (Ozone Monitoring Instrument) and SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY). The intercomparison has been carried out taking into account the various differences existing in instruments, namely temporal coincidence, collocation, sensitivity, field of view, etc. The paper highlights the importance of considering an "effective solar zenith angle" instead of the actual one when comparing direct-sun instruments with zenith sky ones for a proper photochemical correction. Results show that NO 2 vertical column densities mean relative difference between FTIR and DOAS instruments is 2.8 ± 10.7 % for a.m. data. Both instruments properly reproduce the NO 2 seasonal and the interannual variation. Mean relative difference of the stratospheric NO 2 derived from OMI and DOAS is −0.2 ± 8.7 % and from OMI and FTIR is −1.6 ± 6.7 %. SCIAMACHY mean relative difference is of 3.7 ± 11.7 and −5.7 ± 11.0 % for DOAS and FTIR, respectively. Note that the days used for the intercomparison are not the same for all the pairs of instruments since it depends on the availability of data. The discrepancies are found to be seasonally dependent with largest differences in winter and excellent agreement in the spring months (AMJ). A preliminary analysis of NO 2 trends has been carried out with the available data series. Results show increases in stratospheric NO 2 columns in all instruments but larger values in those that are GB than that expected by nitrous oxide oxidation. The possible reasons for the discrepancy between instruments and the positive trends are discussed in the text.

The aerosol optical depth (AOD) at three wavelengths has been retrieved from the radiance measured at the top of the atmosphere (TOA) by the ATSR‐2 (Along Track Scanning Radiometer) during the SAFARI‐2000 (Southern African Regional Science Initiative) dry season field campaign from 1 August to 30 September 2000. Two aerosol types were implemented in the ATSR‐2 retrieval algorithm: a highly absorbing aerosol that is mainly due to biomass burning and a less absorbing mixture of biomass burning, anthropogenic and biogenic aerosols. The mixing ratio of these two aerosol types was determined by comparison of the two modeled aerosol types with the ATSR‐2 measured signal. The accuracy of the AOD values determined from the ATSR‐2 data is 0.08 ± 0.06 for August and 0.14 ± 0.13 for September, as determined from comparison with various AERONET Sun photometers located in the area. In August 2000, the highly absorbing aerosol was the major aerosol component retrieved over the North‐Western part of the SAFARI‐2000 area. AOD values of up to 0.8 and Ångström coefficients of up to 2.1 were observed. Further to the South, the less absorbing type dominated with AOD values of up to 0.3 over the central SAFARI‐2000 area. During September the meteorological situation changed and the high absorbing aerosols were observed further South, due to advective transport of aerosol over a wider area. AOD values were up to 1 with Ångström coefficients similar to those in August. Low absorbing aerosols were observed over a relatively small area. Over the Namibian and Kalahari deserts dust emissions caused high AOD values of up to 0.75 during both months.

[1] Aerosol retrieval algorithms for ATSR-2 have been applied over land and water using data from the Indian Ocean Experiment (INDOEX) Intensive Field Phase (IFP) in February and March 1999. The goal was the extension of the ATSR-2 algorithms, developed for application over the U.S. east coast and Europe, to other areas with different types of aerosols and to explore the feasibility of deriving spatial variations in the aerosol composition. The ATSR-2 algorithm was extended with absorbing aerosols, and AERONET data were used to test the retrieved spectral aerosol optical depth (AOD). The resulting maps of AOD at 0.659 mm, Å ngström coefficient and urban/industrial aerosol contribution to the AOD over the ocean are evaluated by comparison with in situ data. AOD over land is in the range 0.18-0.45 with values up to 0.7 when biomass burning aerosol is present and decreases gradually over water with increasing fetch to 0.15 near the Intertropical Convergence Zone (ITCZ). Å ngström coefficients over land are in the range 1.5-2.0. Over water these values gradually decrease to almost zero. Over land urban/industrial aerosol dominates, and, as expected, over water the anthropogenic influence gradually decreases with fetch and the relative contribution of marine aerosol increases. South of the ITCZ the anthropogenic effect is negligible.Citation: Robles-Gonzalez, C., G. de Leeuw, R. Decae, J. Kusmierczyk-Michulec, and P. Stammes (2006), Aerosol properties over the Indian Ocean Experiment (INDOEX) campaign area retrieved from ATSR-2,