Mona Johnsrud

Intercomparison of Satellite Retrieved Aerosol Optical Depth over the Ocean

For an 8-month period aerosol optical depth (AOD) is compared, derived over global oceans with five different retrieval algorithms applied to four satellite instruments flown on board three satellite platforms. The Advanced Very High Resolution Radiometer (AVHRR) was flown on board NOAA-14, the Ocean Color and Temperature Scanner (OCTS) and the Polarization and Directionality of the Earth’s Reflectances (POLDER) on board the Advanced Earth Observing Satellite(ADEOS), and the Total Ozone Mapping Spectrometer (TOMS) on board the Earth Probe satellites. The aerosol data are presented on the same format and converted to the same wavelength in the comparison and can therefore be a useful tool in validation of global aerosol models, in particular models that can be driven with meteorological data for the November 1996 to June 1997 period studied here. Large uncertainties in the global mean AOD are found. There is at least a factor of 2 difference between the AOD from the retrievals. The largest uncertainties are found in the Southern Hemisphere, and the smallest differences mostly near the continents in the Northern Hemisphere. The largest relative differences are probably caused by differences in cloud screening.

Modeling the solar radiative impact of aerosols from biomass burning during the Southern African Regional Science Initiative (SAFARI-2000) experiment

[1] In this study, we model the radiative impact of biomass burning aerosols with meteorological data for the Southern African Regional Science Initiative (SAFARI-2000) experiment campaign period. Satellite, ground-based, and aircraft observations are used in the validation of the modeled aerosol optical depth (AOD), vertical profiles, and radiative impact of the aerosols. The modeled pattern and magnitude of the AOD is generally in good agreement with the observations. The meteorological conditions are found to be important in determining the distribution of the aerosols. The modeled radiative impact of the biomass aerosols compares well to measurements. During September 2000, the modeled radiative impact of biomass aerosols reaches 50 W m 2 locally. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; KEYWORDS: biomass burning, transport model, single scattering albedo, aerosol optical depth, aircraft measurements, radiative impact Citation: Myhre, G., T. K. Berntsen, J. M. Haywood, J. K. Sundet, B. N. Holben, M. Johnsrud, and F. Stordal, Modeling the solar radiative impact of aerosols from biomass burning during the Southern African Regional Science Initiative (SAFARI-2000) experiment, J. Geophys. Res., 108(D13), 8501, doi:10.1029/2002JD002313, 2003.

Comparison of the radiative properties and direct radiative effect of aerosols from a global aerosol model and remote sensing data over ocean

Measurements of C2–C8 non-methane hydrocarbons (NMHCs) have been made in situ at Halley Base, Antarctica (75◦35°S, 26◦19°W) from February 2004 to February 2005 as part of the Chemistry of the Antarctic Boundary Layer and the Interface with Snow (CHABLIS) experiment. The data show long- and short-term variabilities in NMHCs controlled by the seasonal and geographic dependence of emissions and variation in atmospheric removal rates and pathways. Ethane, propane, iso-butane, n-butane and acetylene abundances followed a general OH-dependent sinusoidal seasonal cycle. The yearly averages were 186, 31, 3.2, 4.9 and 19 pptV, respectively, lower than those which were reported in some previous studies. Superimposed on a seasonal cycle was shorter-term variability that could be attributed to both synoptic airmass variability and localized loss processes due to other radical species. Hydrocarbon variability during periods of hour-to-day-long surface O3 depletion in late winter/early spring indicated active halogen atom chemistry estimated to be in the range 1.7 × 103–3.4 × 104 atom cm−3 for Cl and 4.8 × 106–9.6 × 107 atom cm−3 for Br. Longer-term negative deviations from sinusoidal behaviour in the late August were indicative of NMHC reaction with a persistent [Cl] of 2.3×103 atom cm−3.Maximum ethene and propene of 157 and 179 pptV, respectively, were observed in the late February/early March, consistent with increased oceanic biogenic emissions; however, their presence was significant year-round (June–August concentrations of 17.1 ± 18.3 and 7.9 ± 20.0 pptV, respectively).