Southern African Regional Science Initiative Research Articles

Assessment of the EUMETSAT Multi Decadal Land Surface Albedo Data Record from Meteosat Observations

Surface albedo, defined as the ratio of the surface-reflected irradiance to the incident irradiance, is one of the parameters driving the Earth energy budget and it is for this reason an essential variable in climate studies. Instruments on geostationary satellites provide suitable observations allowing long-term monitoring of surface albedo from space. In 2012, EUMETSAT published Release 1 of the Meteosat Surface Albedo (MSA) data record. The main limitation effecting the quality of this release was non-removed clouds by the incorporated cloud screening procedure that caused too high albedo values, in particular for regions with permanent cloud coverage. For the generation of Release 2, the MSA algorithm has been replaced with the Geostationary Surface Albedo (GSA) one, able to process imagery from any geostationary imager. The GSA algorithm exploits a new, improved, cloud mask allowing better cloud screening, and thus fixing the major limitation of Release 1. Furthermore, the data record has an extended temporal and spatial coverage compared to the previous release. Both Black-Sky Albedo (BSA) and White-Sky Albedo (WSA) are estimated, together with their associated uncertainties. A direct comparison between Release 1 and Release 2 clearly shows that the quality of the retrieval improved significantly with the new cloud mask. For Release 2 the decadal trend is less than 1% over stable desert sites. The validation against Moderate Resolution Imaging Spectroradiometer (MODIS) and the Southern African Regional Science Initiative (SAFARI) surface albedo shows a good agreement for bright desert sites and a slightly worse agreement for urban and rain forest locations. In conclusion, compared with MSA Release 1, GSA Release 2 provides the users with a significantly more longer time range, reliable and robust surface albedo data record.

Simultaneous retrieval of aerosol and surface optical properties from combined airborne- and ground-based direct and diffuse radiometric measurements

Abstract. This paper presents a new method for simultaneously retrieving aerosol and surface reflectance properties from combined airborne and ground-based direct and diffuse radiometric measurements. The method is based on the standard Aerosol Robotic Network (AERONET) method for retrieving aerosol size distribution, complex index of refraction, and single scattering albedo, but modified to retrieve aerosol properties in two layers, below and above the aircraft, and parameters on surface optical properties from combined datasets (Cloud Absorption Radiometer (CAR) and AERONET data). A key advantage of this method is the inversion of all available spectral and angular data at the same time, while accounting for the influence of noise in the inversion procedure using statistical optimization. The wide spectral (0.34–2.30 μm) and angular range (180°) of the CAR instrument, combined with observations from an AERONET sunphotometer, provide sufficient measurement constraints for characterizing aerosol and surface properties with minimal assumptions. The robustness of the method was tested on observations made during four different field campaigns: (a) the Southern African Regional Science Initiative 2000 over Mongu, Zambia, (b) the Intercontinental Transport Experiment-Phase B over Mexico City, Mexico (c) Cloud and Land Surface Interaction Campaign over the Atmospheric Radiation Measurement (ARM) Central Facility, Oklahoma, USA, and (d) the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) over Elson Lagoon in Barrow, Alaska, USA. The four areas are dominated by different surface characteristics and aerosol types, and therefore provide good test cases for the new inversion method.

Using aircraft measurements to estimate the magnitude and uncertainty of the shortwave direct radiative forcing of southern African biomass burning aerosol

We estimate the shortwave, diurnally averaged direct radiative forcing (RF) in cloud‐free conditions of the biomass burning aerosol characterized by measurements made from the University of Washington (UW) research aircraft during the Southern African Regional Science Initiative in August and September 2000 (SAFARI‐2000). We describe the methodology used to arrive at the best estimates of the measurement‐based RF and discuss the confidence intervals of the estimates of RF that arise from uncertainties in measurements and assumptions necessary to describe the aerosol optical properties. We apply the methodology to the UW aircraft vertical profiles and estimate that the top of the atmosphere RF (RFtoa) ranges from −1.5 ± 3.2 to −14.4 ± 3.5 W m−2, while the surface RF (RFsfc) ranges from −10.5 ± 2.4 to −81.3 ± 7.5 W m−2. These estimates imply that the aerosol RF of the atmosphere (RFatm) ranges from 5.0 ± 2.3 to 73.3 ± 11.0 W m−2. We compare some of our estimates to RF estimated using Aerosol Robotic Network (AERONET) aerosol optical properties and show that the agreement is good for RFtoa, but poor for RFsfc. We also show that linear models accurately describe the relationship of RF with the aerosol optical depth at a wavelength of 550 nm (τ550). This relationship is known as the radiative forcing efficiency (RFE) and we find that RFtoa (unlike RFatm and RFsfc) depends not only on variations in τ550, but that the linear model itself is dependent on the magnitude of τ550. We then apply the models for RFE to daily τ550 derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite to estimate the RF over southern Africa from March 2000 to December 2006. Using the combination of UW and MODIS data, we find that the annual RFtoa, RFatm, and RFsfc over the region is −4.7 ± 2.7 W m−2, 11.4 ± 5.7 W m−2, and −18.3 ± 5.8 W m−2, respectively.

Aerosol properties over the SAFARI‐2000 area retrieved from ATSR‐2

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.

A methodology to retrieve self‐consistent aerosol optical properties using common aircraft measurements

Aerosol optical properties that include the extinction coefficient, single scattering albedo, and asymmetry factor are needed to calculate the radiative effects of aerosols. However, measurements of these properties are typically limited to a few wavelengths, and direct measurements of the asymmetry factor are not available. We describe and evaluate a retrieval methodology that uses commonly collected aircraft‐based measurements to derive self‐consistent aerosol optical properties for the majority of the solar spectrum. Measurements of aerosol scattering and absorption at three wavelengths are required to constrain this retrieval. We apply the retrieval to vertical profiles of biomass burning aerosol data collected by the University of Washington (UW) research aircraft during the Southern African Regional Science Initiative field campaign (SAFARI‐2000) and show that the retrieved (or “optically equivalent”) size distributions and wavelength‐dependent refractive indices reproduce available aerosol optical measurements within their respective uncertainties. The retrieved optically equivalent size distribution characteristics are consistent with past studies, but the wavelength‐dependent refractive indices retrieved using methods presented in this study are ∼14% (∼50%) greater than the real (imaginary) refractive indices retrieved from the Aerosol Robotic Network (AERONET) for three cases that were spatially and temporally colocated with the UW research aircraft. The retrieval presented in this study translates measured aerosol optical properties to parameters used directly as input to models and can be applied to any study that uses similar instrumentation. Provided that uncertainties are properly accounted for, self‐consistent aerosol optical properties derived from measurements strengthen the unique contribution of in situ data collection to the modeling community.

Case study of modeled aerosol optical properties during the SAFARI 2000 campaign

We present modeled aerosol optical properties (single scattering albedo, asymmetry parameter, and lidar ratio) in two layers with different aerosol loadings and particle sizes, observed during the Southern African Regional Science Initiative 2,000 (SAFARI 2,000) campaign. The optical properties were calculated from aerosol size distributions retrieved from aerosol layer optical thickness spectra, measured using the NASA Ames airborne tracking 14-channel sunphotometer (AATS-14) and the refractive index based on the available information on aerosol chemical composition. The study focuses on sensitivity of modeled optical properties in the 0.3-1.5 microm wavelength range to assumptions regarding the mixing scenario. We considered two models for the mixture of absorbing and nonabsorbing aerosol components commonly used to model optical properties of biomass burning aerosol: a layered sphere with absorbing core and nonabsorbing shell and the Maxwell-Garnett effective medium model. In addition, comparisons of modeled optical properties with the measurements are discussed. We also estimated the radiative effect of the difference in aerosol absorption implied by the large difference between the single scattering albedo values (approximately 0.1 at midvisible wavelengths) obtained from different measurement methods for the case with a high amount of biomass burning particles. For that purpose, the volume fraction of black carbon was varied to obtain a range of single scattering albedo values (0.81-0.91 at lambda=0.50 microm). The difference in absorption resulted in a significant difference in the instantaneous radiative forcing at the surface and the top of the atmosphere (TOA) and can result in a change of the sign of the aerosol forcing at TOA from negative to positive.

Modeling the transport and optical properties of smoke aerosols from African savanna fires during the Southern African Regional Science Initiative campaign (SAFARI 2000)

We investigate the transport and optical properties of smoke aerosols from southern Africa using an offline three‐dimensional aerosol transport model. We use Sun photometer retrieved particle size distributions and monthly mean satellite‐derived smoke emissions as input parameters. We find that using these observations in our model allows us to reproduce the measured optical properties collected during the Southern African Regional Science Initiative campaign (SAFARI 2000). In particular, we find day‐to‐day oscillations in the simulated aerosol optical thickness (AOT) similar to Aerosol Robotic Network (AERONET) retrievals, suggesting that variations in aerosol loading are controlled more by transport processes than fluctuations in smoke emissions. We also find that the simulated AOT, Ångström exponent, and single scattering albedo compare well to AERONET. The model and satellite observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multiangle Imaging Spectroradiometer (MISR) also show that the dominant transport of smoke plumes over Africa was westward during September 2000. However, the satellite observations show higher AOT values than our model over the Atlantic Ocean. These higher values observed by the satellites may be a result of poor single scattering assumptions and the contamination by subpixel clouds in the retrievals. However, the monthly mean smoke emissions may also be too low, resulting in low simulated AOT values. We also find discrepancies between MODIS and MISR, which limit our ability to use the satellite data to validate our model. Our work suggests strategies for improving the treatment of smoke aerosols from African biomass burning in climate and microphysical models.

Influence of aerosol particles from biomass burning on cloud microphysical properties and radiative forcing

Aerosol from biomass burning has been shown to strongly modify cloud microphysical properties and cloud lifetime through the so-called “indirect effect.” However, in the case of a lack of wet scavenging, it stays suspended for days to weeks and can be transported to considerable distances within an elevated layer above low-level cloud tops with minimal aerosol–cloud interactions. The observations carried out during the Southern African Regional Science Initiative (SAFARI) 2000 dry season field campaign often revealed the presence of an elevated biomass-burning aerosol layer above a semi-permanent stratiform cloud deck off the southern African coasts. MODerate-resolution Imaging Spectroradiometer (MODIS) cloud products were used to investigate the existence of an aerosol indirect effect on convective clouds. Results are presented documenting cloud effective radius and cloud radiative forcing variations due to the presence of the aerosol during the development of convective clouds. Radiative transfer simulations in the visible (0.8 μm, VIS) and near-infrared (1.6, 2.1 and 3.7 μm, NIR) wavelengths were instrumental in establishing the extent of the influence of a biomass-burning aerosol layer overlying a water cloud sheet on the MODIS satellite retrieval of cloud parameters, in particular the effective radius and the optical thickness. The radiative transfer simulations suggest that the presence of the aerosol induces a significant underestimation of the cloud optical thickness, whereas an underestimation of the retrieved effective radius is more pronounced in the retrieval that makes use of the 1.6 μm waveband than the 2.1 and 3.7 μm wavebands. The MODIS cloud products of 3 days of the SAFARI 2000 campaign were analyzed to determine whether the aerosol induced biases evidenced by the simulations also affect the operational cloud property retrieval. Cloud parameters, in particular the effective radius, are usually employed as indicators of the occurrence of aerosol–cloud interaction according to the “indirect effect.” However, these results highlight some of the difficulties associated with satellite retrievals of cloud properties and show the importance of an accurate sighting of the cloud and aerosol layer top and bottom heights in order to prevent erroneous detections of indirect effects.

Using the “blue spike” to characterize biomass‐burning sites during Southern African Regional Science Initiative (SAFARI) 2000

During several flights of the ER‐2 while participating in the Southern African Regional Science Initiative (SAFARI 2000), the University of Wisconsin–Madison's Scanning High Resolution Interferometer Sounder (S‐HIS) obtained spectra containing isolated fires within its field of view (FOV). These fire‐laden FOVs contain a spectral feature caused by rotational hot band transitions of CO2 near 2400 cm−1. Because of its location on the blue side of the 4.3 μm band of CO2, this feature is commonly referred to as the “blue spike.” Using this feature, we detected fires on four flights: 24 and 27 August and 6 and 7 September 2000. Fire locations are further verified by the ER‐2 pilot's flight logs and elevated brightness temperatures in the thermal detectors of the MODIS Airborne Simulator (MAS) also on board the ER‐2. Using line‐by‐line radiative transfer calculations (Genln2) with corrections for a fire's extreme high temperatures (HiTemp), we model S‐HIS spectra for various scenes: background (cool surface and cool atmosphere), smoldering (warm surface and cool atmosphere), hot gas layer (cool surface and warm atmosphere), and fire (hot surface and hot atmosphere) cases. Using the controlled burn in the Timbavati Game Reserve on 7 September 2000 as a test case, we spectrally modeled the blue spike feature seen in the spectra obtained by S‐HIS while the ER‐2 flew over the fire. For this case, we found that ∼4.12 ± 0.05% of the FOV contained the hot gas layer while ∼0.23 ± 0.05% was actively burning. Originally viewed as a straightforward task of using the blue spike to characterize the fire temperature and size (fraction of S‐HIS FOV), our analysis shows that numerous variables, including amount of carbon dioxide, amount of water vapor, and the temperature near the fire, play significant roles in the blue spike's shape and spectral position.

The effect of overlying absorbing aerosol layers on remote sensing retrievals of cloud effective radius and cloud optical depth

AbstractTwo types of partially absorbing aerosol are included in calculations that are based on intensive aircraft observations: biomass burning aerosol characterized during the Southern AFricAn Regional science Initiative (SAFARI 2000) and mineral dust aerosol characterized during the SaHAran Dust Experiment (SHADE). Measurements during SAFARI 2000 reveal that the biomass burning aerosol layer is advected over the South Atlantic ocean at elevated altitudes above the marine boundary layer which is capped by semi‐permanent stratocumulus cloud sheets. Similarly, the mineral dust is measured at elevated altitudes during SHADE resulting in transport above cloud for distances of several thousands of kilometres. We perform theoretical calculations of the effect of these partially absorbing aerosol layers on satellite retrievals of cloud effective radius and cloud optical depth, and show that, in these cases, retrievals of cloud optical depth or liquid water path are likely to be subject to systematic low biases. The theoretical calculations suggest that the cloud effective radius may be subject to a significant low bias for Moderate resolution Imaging Spectrometer (MODIS) retrievals that rely on the 0.86 and 1.63 µm radiance pair for an overlying aerosol layer of either biomass burning aerosol or mineral dust. Conversely, the cloud effective radius may be subject to a significant high bias for Advanced Very High Resolution Radiometer or MODIS retrievals that rely on the 0.63 and 3.7 µm radiance pair for an overlying aerosol layer of mineral dust. Analysis of 1 km resolution MODIS data for the SAFARI 2000 period suggests that the effective radius derived from the 0.86 and 1.63 µm radiance pair is, indeed, subject to a low bias in the presence of overlying biomass burning aerosol. These results show the difficulties associated with remote sensing retrievals, which must be kept in mind when attempting to assess any potential indirect effect. © Crown copyright 2004.

The SAFARI 2000 – Kalahari Transect Wet Season Campaign of year 2000

AbstractOver 50 scientists from eight different countries coordinated research efforts in the Kalahari sand mass in Zambia and Botswana during the 2000 wet season as a part of the Southern African Regional Science Initiative – Kalahari Transect Wet Season Campaign (S2K‐KT Wet Season Campaign). The work focused on change in ecological processes along the International Geosphere–Biosphere Programme‐designated Kalahari Transect (KT). Topics included ecosystem structure, function, biogeochemistry, and modeling at the patch, landscape and regional scale. The KT of southern and central Africa follows a sharp precipitation gradient within an otherwise climatically and geographically similar region that contains a widely distributed, physically uniform soil and relatively little variation in elevation. This paper outlines the focus of the SAFARI 2000 research campaign as it relates to this study area and provides references to archived data sets generated during the study. It also describes vegetation patterns, climate, and 2000 wet season meteorological conditions for the region.

Evolution of biomass burning aerosol properties from an agricultural fire in southern Africa

Measurements on the UK Met Office C‐130 within a distinct biomass burning plume during the Southern AFricAn Regional science Initiative (SAFARI 2000) show an increase in the single scattering albedo as the aerosol ages, from 0.84 at source to 0.90 in the aged regional haze in 5 hours. Condensation of scattering material from the gas phase appears to be the dominant mechanism; the change in black carbon morphology, from a chain to clump like structure, does not significantly affect the bulk aerosol single scattering albedo.

Africa burning: A thematic analysis of the Southern African Regional Science Initiative (SAFARI 2000)

The Southern African Regional Science Initiative (SAFARI 2000) was a major surface, airborne, and spaceborne field campaign carried out in southern Africa in 2000 and 2001 that addressed a broad range of phenomena related to land‐atmosphere interactions and the biogeochemical functioning of the southern African system. This paper presents a thematic analysis and integration of the Journal of Geophysical Research SAFARI 2000 Special Issue, presenting key findings of an intensive field campaign over southern Africa in August and September of 2000. The integrating themes deal with surface emissions characterization; airborne characterizations of aerosols and trace gases; regional haze and trace gas characterization; and radiant measurements by surface, aircraft, and remote sensing platforms. Enhanced regional fuel loads associated with the moist La Niña phase of the El Niño‐Southern Oscillation (ENSO) cycle produced above average biomass burning emissions, which consequently dominated all other aerosol and trace gas emissions during the dry season. Southward transport of a broad plume of smoke originating in equatorial Africa and exiting off the east coast toward the Indian Ocean (the river of smoke) is attributed to unusual synoptic airflows associated the ENSO phase. New and revised biogenic and pyrogenic emission factors are reported, including a number of previously unreported oxygenated organic compounds and inorganic compounds from biomass combustion. Emission factors are scaled up to regional emission surfaces for biogenic species utilizing species specific and light‐dependent emission factors. Fire scar estimates reveal contradictory information on the timing of the peak and extent of the biomass‐burning season. Integrated tall stack coordinated measurements (between ground, airborne and remotely sensing platforms) of upwelling and downwelling radiation in massive thick aerosol layers covering much of southern Africa yield consistent estimates of large negative forcing for both surface and top of atmosphere radiative forcing. Radiation calculations are supported by novel information on chemical speciation and internal aerosol particle structure. The overall conclusion is that SAFARI 2000, as an integrating theme, has been able to give significant new insights into the regional scale biogeochemical cycling of southern Africa and contributed in important ways to the validation of remote sensing instruments on board the NASA Terra spacecraft.

Exploring the potential of combining column‐integrated atmospheric polarization with airborne in situ size distribution measurements for the retrieval of an aerosol model: A case study of a biomass burning plume during SAFARI 2000

Ground‐based columnar and airborne in situ measurements of aerosol optical properties acquired during the Southern African Regional Science Initiative (SAFARI 2000) in August–September 2000 are analyzed to retrieve the aerosol model of a haze layer affected by long‐range transport of biomass burning emissions. One case study is considered. A columnar value of the aerosol polarized phase function Qmeasp(Θ) and of the aerosol single scattering albedo ω0, both at 870 nm, are retrieved from measurements acquired by a ground‐based Sun/sky photometer, assuming that the surface albedo is 0.3. The maximum value of the polarized phase function is 0.37 ± 0.02 at a scattering angle of 70°, ω0 is 0.80 ± 0.05. The in situ particle size distribution is measured in a vertical profile over the ground‐based site by an airborne optical particle counter. Because the size distribution integrated over the column is inconsistent with the polarized phase function, aerosol concentration of the 0.25 μm mode is reduced by a factor of 7.5. Taking into account that the estimation of particle size depends on particle refractive index, it is found that the radius of absorbing particles cannot be larger than 0.15 μm for reproducing Qmeasp(Θ), suggesting external mixture of absorbing particles smaller than 0.15 μm with nonabsorbing particles larger than 0.15 μm. The imaginary part of the effective refractive index is estimated to be (0.09 ± 0.03)i. Comparing Ångström exponent obtained from Sun/sky photometer extinction measurements and the Ångström exponent calculated for the in situ measured aerosol size distribution acquired in eleven vertical profiles allows us to conclude that in most considered cases, the mixture of absorbing with nonabsorbing particles is external with a radius limit at around 0.15 μm.

Haze layer characterization and associated meteorological controls along the eastern coastal region of southern Africa

Episodes of regionally extensive haze were observed over southern African during the dry season intensive of the Southern African Regional Science Initiative (SAFARI 2000). Several case studies of southern African haze layers were examined and characterized in terms of physical structure as they exited off of the eastern coastal region of southern Africa. In situ observations of aerosols and trace gases and their physical and chemical characteristics were collected on board South African Weather Service Aerocommander research aircraft. Haze structure, based on these measurements, is examined as it varies with synoptic type. Despite strong differences in the observed ENSO regime between SAFARI 2000 and that observed during the Southern African Fire‐Atmosphere Research Initiative (SAFARI‐92) and their respective aerosol accumulation mechanisms (col Rrgions/weak anticyclones versus strong anticyclones), a surprising degree of consistency in the observed vertical structure of the lower troposphere was found in southern Africa.

Spatial and temporal variations in biogenic volatile organic compound emissions for Africa south of the equator

Improved vegetation distribution and emission data for Africa south of the equator were developed for the Southern African Regional Science Initiative (SAFARI 2000) and were combined with biogenic volatile organic compound (BVOC) emission measurements to estimate BVOC emissions for the southern African region. The BVOCs are estimated to total 80 Tg C yr−1 for the region, with isoprene and monoterpenes contributing 56 and 7 Tg C yr−1, respectively. The large uncertainties, particularly in terms of basal emission capacity assignment, associated with these outputs are discussed. Woodlands are predicted to be the dominant vegetation type, covering 23% of southern Africa, and are the largest annual source of isoprene (20 Tg C), monoterpenes (3 Tg C), and other VOCs (4 Tg C). Mopane savannas and woodlands are predicted to contribute over 75% of all monoterpenes, primarily from light‐dependent emission processes. Rain forests cover only 3.5% of the total area but have high annual emission rates (9.8 g C m−2 yr−1). In the tropical regions with high rainfall, warm temperatures, and high plant productivity throughout the year, the seasonal variation in VOC emissions was small. In subtropical regions, dominated by highly seasonal savannas and grasslands, large variations were predicted, with emissions declining by up to 85% during dry winter periods (June–August) due to low leaf area index after leaf drop.

Characterization of sources for southern African aerosols through fatty acid and trajectory analyses

Biogeochemical cycles in southern Africa are affected by emissions from extensive biomass burning. Emitted trace gases and aerosols frequently accumulate and recirculate in the well‐defined synoptic pattern that persists for long time periods over southern Africa. The role of organic aerosols during atmospheric transport and the influence of neighboring air masses on biogeochemical dynamics in this nutrient‐limited region are insufficiently studied. The Southern African Regional Science Initiative (SAFARI 2000) was conducted in part to investigate the impacts of this large‐scale transport and deposition of increasingly anthropogenic emissions on southern African biogeochemical cycling. This study explores the understanding of regional atmospheric transport through the identification of chemical biomarkers to describe aerosols collected during the SAFARI 2000 dry season research campaign. Total suspended particulate aerosol samples were collected diurnally for a period of two weeks in Mongu, Zambia. Mongu is bordered by the Zambezi River on the west and the Miombo woodland savanna in all other directions. It also lies on the northern extent of the Kalahari Desert. This region is characterized by high biomass burning emissions of river floodplain grasses and woodland savanna during the dry season. Fatty acids were extracted from the collected aerosols and analyzed using gas chromatography. The resultant fatty acid compositions were examined for temporal patterns and trends. Furthermore, these results were compared to both synoptic meteorological patterns over the region, as well as to modeled air parcel trajectories, to gain insight into changes in aerosol composition resulting from changes in atmospheric transports from regions of different vegetation. The results of these analyses confirm that abundances of fatty acids are dependent on local and synoptic meteorology and can thus be used as an additional geochemical tracer to better describe aerosol sources and transport processes within the region.

Remote sensing of smoke, land, and clouds from the NASA ER‐2 during SAFARI 2000

The NASA ER‐2 aircraft was deployed to southern Africa between 13 August and 25 September 2000 as part of the Southern African Regional Science Initiative (SAFARI) 2000. This aircraft carried a sophisticated array of multispectral scanners, multiangle spectroradiometers, a monostatic lidar, a gas correlation radiometer, upward and downward spectral flux radiometers, and two metric mapping cameras. These observations were obtained over a 3200 × 2800 km region of savanna, woody savanna, open shrubland, and grassland ecosystems throughout southern Africa and were quite often coordinated with overflights by NASA's Terra and Landsat 7 satellites. The primary purpose of this high‐altitude observing platform was to obtain independent observations of smoke, clouds, and land surfaces that could be used to check the validity of various remote sensing measurements derived by Earth‐orbiting satellites. These include such things as the accuracy of the Moderate Resolution Imaging Spectroradiometer (MODIS) cloud mask for distinguishing clouds and heavy aerosol from land and ocean surfaces and Terra analyses of cloud optical and microphysical properties, aerosol properties, leaf area index, vegetation index, fire occurrence, carbon monoxide, and surface radiation budget. In addition to coordination with Terra and Landsat 7 satellites, numerous flights were conducted over surface AERONET sites, flux towers in South Africa, Botswana, and Zambia, and in situ aircraft from the University of Washington, South Africa, and the United Kingdom. As a result of this experiment, the MODIS cloud mask was shown to distinguish clouds, cloud shadows, and fires over land ecosystems of southern Africa with a high degree of accuracy. In addition, data acquired from the ER‐2 show the vertical distribution and stratification of aerosol layers over the subcontinent and make the first observations of a “blue spike” spectral emission signature associated with air heated by fire advecting over a cooler land surface.

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

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.

SAFARI-2000 characterization of fuels, fire behavior, combustion completeness, and emissions from experimental burns in infertile grass savannas in western Zambia

Fires in African savannas produce emissions contributing to changes in global biogeochemical processes. In the Southern African Regional Science Initiative (SAFARI-2000), fuels characteristics were measured before and after experimental burns in two different western Zambian grassland types (dambo and flood plain) situated on Kalahari Sands. The two land use types did not differ in terms of fuel characteristics, fire behavior or combustion completeness. As a consequence of a significantly wet year, fuel loads and moisture content were higher than those found during SAFARI-92. Use of moisture content and fire behavior component could increase the emission estimation through the fuel consumption calculation. Ranges of estimated emissions for CH 4 and NMHC were lower than previously stated.