J. S. Schafer

Variability of biomass burning aerosol optical characteristics in southern Africa during the SAFARI 2000 dry season campaign and a comparison of single scattering albedo estimates from radiometric measurements

A priority network utilizing a common bus coupled to a plurality of priority seeking peripheral devices wherein a processor or any number of processors is connected to the common bus. Each successive peripheral device is connected to the common bus in increasing priority order, such that each device will have a unique priority defined. Each peripheral device is provided with an associated peripheral control unit. Each of the peripheral control units is connected in serial fashion on an enabling line with the output of the higher priority control unit providing an enabling input to the next lowest priority peripheral control unit, such that the highest priority device requesting bus access prevents all lower priority devices from gaining access to the common bus until the higher priority device has completed its data transfer.

High aerosol optical depth biomass burning events: A comparison of optical properties for different source regions

Received 29 May 2003; revised 8 September 2003; accepted 17 September 2003; published 21 October 2003. [1] The optical properties of aerosols such as smoke from biomass burning vary due to aging processes and these particles reach larger sizes at high concentrations. We compare the spectra of aerosol optical depth (ta), columnintegrated volume size distributions, refractive indices, and single scattering albedo retrieved from AERONET observations for four selected events of very high smoke optical depth (ta � 2 at 500 nm). Two case studies are from tropical biomass burning regions (Brazil and Zambia) and two are cases of boreal forest and peat fire smoke transported long distances to sites in the US and Moldova. Smoke properties for these extreme events can be significantly different from those reported in more typical plumes. In particular, large differences in smoke fine mode particle radius (� 0.17 to 0.25 mm) and single scattering albedo (� 0.88 to 0.99 at 440 nm) were observed as a result of differences in fuels burned, combustion phase, and aging. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation. Citation: Eck, T. F., B. N. Holben, J. S. Reid, N. T. O’Neill, J. S. Schafer, O. Dubovik, A. Smirnov, M. A. Yamasoe, and P. Artaxo, High aerosol optical depth biomass burning events: A comparison of optical properties for different source regions, Geophys. Res. Lett., 30(20), 2035, doi:10.1029/ 2003GL017861, 2003.

The effects of biomass burning aerosols and clouds on the CO2 flux in Amazonia

Aerosol particles associated with biomass burning emissions affect the surface radiative budget and net ecosystem exchange (NEE) over large areas in Amazonia during the dry season. We analysed CO2 fluxes as a function of aerosol loading for two forest sites in Amazonia as part of the LBA experiment. Aerosol optical thickness (AOT) measurements were made with AERONET sun photometers, and CO2 flux measurements were determined by eddy-correlation. The enhancement of the NEE varied with different aerosol loading, as well as cloud cover, solar elevation angles and other parameters. The AOT value with the strongest effect on the NEE in the FLONA-Tapajós site was 1.7, with an enhancement of the NEE of 11% compared with clear-sky conditions. In the RBJ site, the strongest effect was for AOT of 1.6 with an enhancement of 18% in the NEE. For values of AOT lager than 2.7, strong reduction on the NEE was observed due to the reduction in the total solar radiation. The enhancement in the NEE is attributed to the increase of diffuse versus direct solar radiation. Due to the fact that aerosols from biomass burning are present in most tropical areas, its effects on the global carbon budget could also be significant.

Atmospheric aerosol and water vapor characteristics over north central Canada during BOREAS

A network of five automated and two handheld solar radiometers was operated during the 1994-1996 Boreal Ecosystem-Atmosphere Study (BOREAS) in northern Saskatchewan and Manitoba, Canada, in order to characterize the atmospheric aerosol properties. Direct solar measurements were used to measure atmospheric transmission and infer aerosol optical thickness and water vapor column abundance. Near-Sun sky radiance measurements (solar aureole) were used to estimate the aerosol size distribution. Aerosol conditions were heavily influenced by the presence or absence of forest fires. In 1996, when few fires occurred, conditions were uniform across the region with median aerosol optical thickness (AOT) at 500 nm of 0.12 and 90th percentlie values of 0.27 for the May-October period. During the 1994 and 1995 seasons, numerous fires occurred in the vicinity of the sites. The median AOT values were comparable with the 1996 values, though the 90th percentile values were larger, in general measuring 0.85 (southern 1994 season was 0.43). Median column water vapor measurements for the same 7 month period were in the range from 1.32 to 1.58 cm at both sites, with 1995 being the driest year of observation. Winter median values of AOT and water vapor were typically 0.09 and 0.34 cm, respectively. Size distributions derived from solar almucantar measurements show the predominance of small particles during smoke episodes when compared to that for background conditions. Spectral dependence of the AOT as characterized by the wavelength exponent, a, asymptotes at 1.8 for high optical depths for a 7 month season of cloud-screened data at the northern young jack pine site. This observed wavelength exponent for boreal biomass burning conditions is within the range of values found during the burning season in a study in Brazil.

Intercomparison of aerosol single‐scattering albedo derived from AERONET surface radiometers and LARGE in situ aircraft profiles during the 2011 DRAGON‐MD and DISCOVER‐AQ experiments

Single-scattering albedo (SSA) retrievals obtained with CIMEL Sun-sky radiometers from the Aerosol Robotic Network (AERONET) aerosol monitoring network were used to make comparisons with simultaneous in situ sampling from aircraft profiles carried out by the NASA Langley Aerosol Group Experiment (LARGE) team in the summer of 2011 during the coincident DRAGON-MD (Distributed Regional Aerosol Gridded Observational Network-Maryland) and DISCOVER-AQ (Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality) experiments. The single-scattering albedos (interpolated to 550 nm) derived from AERONET measurements for aerosol optical depth (AOD) at 440 nm ≥ 0.4 (mean SSA: 0.979) were on average 0.011 lower than the values derived from the LARGE profile measurements (mean SSA: 0.99). The maximum difference observed was 0.023 with all the observed differences within the combined uncertainty for the stated SSA accuracy (0.03 for AERONET; 0.02 for LARGE). Single-scattering albedo averages were also analyzed for lower aerosol loading conditions (AOD ≥ 0.2) and a dependence on aerosol optical depth was noted with significantly lower single-scattering albedos observed for lower AOD in both AERONET and LARGE data sets. Various explanations for the SSA trend were explored based on other retrieval products including volume median radius and imaginary refractive index as well as column water vapor measurements. Additionally, these SSA trends with AOD were evaluated for one of the DRAGON-MD study sites, Goddard Space Flight Center, and two other Mid-Atlantic AERONET sites over the long-term record dating to 1999.

The Boreal Climate

The boreal ecosystem encircles the Earth above about 48° N, covering Alaska, Canada, and Eurasia. It is second in areal extent only to the world’s tropical forests and occupies about 21% of the Earth’s forested land surface (Whittaker and Likins 1975). Nutrient cyding rates are relatively low in the cold wet boreal soils. Whittaker and Likins (1975) estimate the annual net primary productivity of the boreal forest at 800 g C m-2y-1 and its tundra at 140 g C m-2y-1, in contrast to tropical forests averaging 2200 g C m-2y-1 and temperate forests at 1250 g C m-2y-1. However, the relatively low nutrient cyding rates at high latitudes result in relatively high longterm boreal carbon storage rates averaging roughly 30 to 50 g C m-2y-1 (Harden et al. 1992), a result of relatively high root turnover from trees, shrubs and mosses with relatively low decomposition rates. Over the past few thousand years, these below-ground storage processes have created a large and potentially mobile reservoir of carbon in the peats and permafrost of the boreal ecosystem. Currently, the boreal ecosystem is estimated to contain approximately 13% of the Earth’s carbon, stored in the form of above-ground biomass and 43% of the Earth’s carbon stored below-ground in its soils (Schlesinger 1991). Meridional gradients in atmospheric CO2 concentrations suggest that forests above 40° N Sequester as much as 1 to 2 gigatons of carbon annually (Denning et al. 1995; Randerson et al. 1997), or nearly 15 to 30% of that injected into the atmosphere each year through fossil fuel combustion and deforestation. Given the enormous areal extent of the ecosystem, roughly 20 Mkm2 (Sellers et al. 1996b; >Fig. A.45), shifts in carbon flux of as little as 50 g C m-2y-1 can contribute or remove one gigaton of carbon annually from the atmosphere. The size of the boreal forest, its sensitivity to relatively small climatic variations, its influence on global climate and the global carbon cyde, therefore, make it critically important to better understand and represent boreal ecosystem processes correctly in global models.

Observations of the Interaction and Transport of Fine Mode Aerosols With Cloud and/or Fog in Northeast Asia From Aerosol Robotic Network and Satellite Remote Sensing

Analysis of sun photometer measured and satellite retrieved aerosol optical depth (AOD) data has shown that major aerosol pollution events with very high fine mode AOD (>1.0 in mid-visible) in the China/Korea/Japan region are often observed to be associated with significant cloud cover. This makes remote sensing of these events difficult even for high temporal resolution sun photometer measurements. Possible physical mechanisms for these events that have high AOD include a combination of aerosol humidification, cloud processing, and meteorological co-variation with atmospheric stability and convergence. The new development of Aerosol Robotic network (AERONET) Version 3 Level 2 AOD with improved cloud screening algorithms now allow for unprecedented ability to monitor these extreme fine mode pollution events. Further, the Spectral Deconvolution Algorithm (SDA) applied to Level 1 data (L1; no cloud screening) provides an even more comprehensive assessment of fine mode AOD than L2 in current and previous data versions. Studying the 2012 winter-summer period, comparisons of AERONET L1 SDA daily average fine mode AOD data showed that Moderate Resolution Imaging Spectroradiometer (MODIS) satellite remote sensing of AOD often did not retrieve and/or identify some of the highest fine mode AOD events in this region. Also, compared to models that include data assimilation of satellite retrieved AOD, the L1 SDA fine mode AOD was significantly higher in magnitude, particularly for the highest AOD events that were often associated with significant cloudiness.