Biomass‐burning plumes and haze layers were observed during the ABLE 2A flights in July/August 1985 over the central Amazon Basin. The haze layers occurred at altitudes between 1000 and 4000 m and were usually only some 100 to 300‐m thick but extended horizontally over several 100 km. They could be traced by satellite imaging and trajectory studies to biomass burning at the southern perimeter of the Amazon Basin, with transport times estimated to be 1–2 days. These layers strongly influenced the chemical and optical characteristics of the atmosphere over the eastern Amazon Basin. The concentrations of CO, CO2, O3, and NO were significantly elevated in the plumes and haze layers relative to the regional background. The NO/CO ratio in fresh plumes was much higher than in the aged haze layers, suggesting that more than 80% of the NOx in the haze layers had been converted to nitrate and organic nitrogen species subsequent to emission. The haze aerosol was composed predominantly of organic material, NH4+, K+, NO3−, SO4=, and anionic organic species (formate, acetate, and oxalate). While the concentrations of most aerosol ions were substantially higher in the haze layers than in the regional background aerosol, the ratios between the aerosol ions in the haze layer aerosols were very similar to those in the boundary layer aerosol over the central Amazon region. Simultaneous measurements of trace gas and aerosol species in the haze layers made it possible to derive emission ratios for CO, NOx, NH3, sulfur oxides, and aerosol constituents relative to CO2. Regional and global emission estimates based on these ratios indicate that biomass burning is an important contributor in the global and regional cycles of carbon, sulfur, and nitrogen species. Similar considerations suggest that photochemical ozone production in the biomass‐burning plumes contributes significantly to the regional ozone budget.

We interpret lidar observations by Browell et al. (1990) using single scattering calculations for nonspherical particles and aerosol microphysical calculations. Many of the lidar observations are consistent with particles containing 10 ppbv of condensed nitric acid vapor and an equivalent mass of water. The lidar observations of these Type 1 clouds identify two subtypes, whose properties we deduce. Type Ib particles arc spherical, or nearly spherical, and typically have radii near 0.5 (μm Type Ia particles are not spherical, and have a spherical volume equivalent radius exceeding 1.0 μm. Several factors may cause variations in the size of the particles. The UK) St significant factors are the cooling rate and the degree to which the air parcels cool below the condensation point. Specific examples in which cooling rate and cooling point nrny have led to variations in particle size are found in the Browell et al. (1990) data set. Condensation of 1 ppmm of water or less is quantitatively sufficient to account for the magnitude of the lidar backscatter observed from water ice clouds. The ice particles are not spherical in shape. The sizes of particles in water ice clouds cannot be determined because they are much larger than the wavelength of the lidar.

Abstract. We present analyses of lidar backscatter and depolarization ratios for polar stratospheric clouds (PSCs) observed during the 1989 Airborne Arctic Stratospheric Experiment. The backscatter and depolarization ratios are available at one visible and one infrared wavelength. Water ice PSCs were identified at low ambient temperatures based upon their relatively large backscattering and depolarization ratios. The remaining clouds fall into four major categories. First, we observe a class of clouds that are not depolarizing at either of the two wavelengths. These clouds are identified as Type 1 b PSCs, which are assumed to be composed of ternary solutions of H2SO4/HNO•/H20. Type 1 b clouds were never dominant, though on some dates they accounted for 25 to 40 % of the observations. We find from the wavelength dependence of the backscattering by these clouds that their size distributions must be very narrow. Other optical observations of these clouds should consider the possible impact of these narrow size distributions on their data analysis. These clouds have a relatively large total particulate mass that is comparable to the known gas phase reservoir of nitric acid. The number density of Type lb particles is similar to the concentrations of the ambient sulfate aerosols. The second category of clouds is highly depolarizing at both lidar wavelengths, but has relatively low backscattering ratios. We identify these clouds as Type 1 a PSCs (assumed to be nitric acid tri-or dihydrate) which form only on a small subset by number, approximately 1% or less, of the ambient sulfate aerosols. These clouds were the first to be observed, and were especially co•n•non on the first few flights. They accounted for more than 70% of the observations on three flights. Type l a particles are near 1 •m or larger in radius. The third type of cloud is depolarizing at visible wavelengths, but not at near infrared wavelengths. These clouds were seen during portions of nearly every flight and comprised 10 to 25% of all of the observations. These clouds, which we refer to as Type 1 c, are composed of small, solid particles. These clouds contain a relatively large mass of material, comparable to the gas phase reservoir of nitric acid. Type 1 c particles are a few tenths of a micrometer in radius and have a concentration that is similar to that of the ambient sulfate aerosols. The final class of clouds has no depolarization at the lidar's visible wavelength but has significant depolarization at the infrared wavelength. Such particles were seen on many of the flights and sometimes accounted for as much as 30% of all the observations. We interpret these clouds as being mixtures of Type 1 a and 1 b PSCs. Although some polar stratospheric clouds have fairly homogeneous properties over very large spatial scales, many have variable properties at relatively small scales. Thus the various types of particles are often observed within a single cloud. Homogeneous clouds composed only of solid particles seem inconsistent with a wave cloud origin. How...

No abstract

No abstract

Our knowledge about synoptic‐scale variations of atmospheric‐CO2 produced by interactions between midlatitude cyclones and regional‐scale surface fluxes remains limited due to the scarcity of observations. We synthesized observations of greenhouse gases (GHGs) with respect to frontal passages to understand how GHG distributions change vertically and horizontally during a synoptic event. We use the airborne in situ measurements of GHGs collected during the Atmospheric Carbon and Transport‐America summer 2016 field campaign. Using these measurements, we defined three metrics, (1) the differences in the GHG mole fractions across frontal boundaries in the atmospheric boundary layer (BL) and free troposphere (FT), (2) differences in the vertical contrasts in GHGs in warm and cold sectors, and (3) the size and magnitude of enhanced CO2 in the vicinity of frontal boundary. We found that frontal structures are clearly associated with spatially coherent and significant changes in GHG composition. Warm sector CO2 mole fractions [CO2] are higher than those in the cold sector. The cross‐frontal [CO2] contrasts are largest in the BL (5–30 ppm) with smaller differences in the FT (3–5 ppm). We found higher [CH4] in the BL in the warm sector than in the cold sector for 5 out of 11 cases. Analyses of vertical profiles revealed higher [CO2] in the FT than in the BL in the cold sector while opposite pattern in the warm sector. Average BL‐to‐FT [CO2] differences are 12 and −6 ppm in the warm and cold sectors, respectively. The observational analyses presented define new metrics involving horizontal and vertical GHG contrasts across fronts during summer which will be used to evaluate simulations of GHG transport.

The first remote measurements of O3 and aerosols across a tropopause fold are presented in this paper. An airborne differential absorption lidar (DIAL) system was used to obtain profiles of O3 and aerosols along a cross section of a fold on April 20, 1984, over southern Nevada and California. The DIAL measurements across the tropopause fold show a 2.0‐km‐deep layer, with high O3 concentrations and enhanced aerosol backscattering, that slopes downward from north of Las Vegas, Nevada, to the top of the planetary boundary layer (PBL) over Yuma, Arizona. This is the first continuous mapping of a tropopause fold from the upper troposphere to the PBL. Mixing ratios of O3 in excess of 200 parts per billion by volume (ppbv) were measured remotely in the fold, and these values were corroborated by in situ measurements of O3 through the fold at an aircraft altitude of 6.7 km. Enhanced aerosol back‐scattering was observed in the tropopause fold and attributed to stratospheric aerosols from the El Chichon eruption. An analysis of the potential vorticity distribution along the DIAL flight track was performed using radiosonde data. A high positive correlation was found between the DIAL O3 mixing ratios and the potential vorticity values in the fold. The average ratio between O3 and potential vorticity was found to be 50.2 ppbv/10−5 cm2 deg g−1 s−1 in the fold. The decrease in layer thickness, potential vorticity, ozone mixing ratio, and aerosol backscatter down the axis of the fold is consistent with a convergent entrainment of tropospheric air across both boundaries of the fold and subsequent irreversible mixing by small‐scale turbulent motions.

No abstract