scholarly journals Tropical South America–Atlantic Sector Convective Margins and Their Relationship to Low-Level Inflow

2010 ◽  
Vol 23 (10) ◽  
pp. 2671-2685 ◽  
Author(s):  
Benjamin R. Lintner ◽  
J. David Neelin
Keyword(s):  
South America ◽  
Convection Zone ◽  
Precipitable Water ◽  
Distribution Functions ◽  
Back Trajectory ◽  
Atlantic Sector ◽  
Air Masses ◽  
Northern Margin ◽  
Low Level ◽  
Tropical South America

Abstract The edges or margins of tropical convective zones are hypothesized to be sensitive to low-level inflow conditions. The present study evaluates where and to what extent convective margin variability is sensitive to low-level inflow variability using observed precipitation and reanalysis wind and total precipitable water data over the tropical South America–Atlantic sector in austral summer. Composite analysis based on an inflow measure defined by projecting low-level monthly-mean atmospheric boundary layer (ABL) or lower free troposphere (LFT) winds onto either mean horizontal precipitation or precipitable water gradients shows widespread contraction of the edges of convection zones in the direction of stronger convection for anomalously strong low-level inflow; such behavior is consistent with enhanced import of relatively dry air along the edges of convection zones. However, the distinction between ABL and LFT winds may be significant regionally, for example, along the Atlantic ITCZ’s northern margin. Back trajectory analysis is employed to estimate source regions of low-level air masses arriving at margin points over time scales (2–4 days) during which low-level air masses are expected to retain some memory of initial moisture conditions while also undergoing diabatic modification. Probability distribution functions of mean precipitation values encountered along trajectories facilitate objective quantification of the frequency with which trajectories approach the margin from drier areas outside the convection zone. While margin points in the ABL are strongly dominated by inflow (i.e., trajectories originating outside of the convection zone), points in the LFT may show inflow, outflow, or mixed inflow–outflow conditions. LFT locations dominated by inflow trajectories generally correspond to regions with composites exhibiting the clearest signatures of LFT wind variability on precipitation.

scholarly journals Transformation and aging of biomass burning carbonaceous aerosol over tropical South America from aircraft in-situ measurements during SAMBBA

2019 ◽  
Author(s):  
William T. Morgan ◽  
James D. Allan ◽  
Stéphane Bauguitte ◽  
Eoghan Darbyshire ◽  
Michael J. Flynn ◽  
...  
Keyword(s):  
South America ◽  
Biomass Burning ◽  
Chemical Properties ◽  
Carbonaceous Aerosol ◽  
Air Masses ◽  
Atmospheric Aging ◽  
Primary Driver ◽  
Tropical South America

Abstract. We present a range of airborne in-situ observations of biomass burning carbonaceous aerosol over tropical South America, including a case study of a large tropical forest wildfire and a series of regional survey flights across the Brazilian Amazon and Cerrado. The study forms part of the South American Biomass Burning Analysis (SAMBBA) Project, which was conducted during September and October 2012. We find limited evidence for net increases in aerosol mass through atmospheric aging combined with substantial changes in the chemical properties of organic aerosol (OA). Oxidation of the OA increases significantly and rapidly on the scale of 2.5–3 hours based on our case study analysis and is consistent with secondary organic aerosol production. The observations of limited net enhancement in OA coupled with such changes in chemical composition, imply that evaporation of OA is also occurring to balance these changes. We observe significant coatings on black carbon particles at source, but with limited changes with aging in both particle core size and coating thickness. We quantify variability in the ratio of OA to carbon monoxide across our study as a key parameter representing both initial fire conditions and an indicator of net aerosol production with atmospheric aging. We observe ratios of 0.075–0.13 μg sm−3 ppbv−1 in the west of our study region over the Amazon tropical forest in air masses less influenced by precipitation and a value of 0.095 μg sm−3 ppbv−1 over the Cerrado environment in the east. Such values are consistent with emission factors used by numerical models to represent biomass burning OA emissions. Black carbon particle core sizes typically range from 250–290 nm, while coating thicknesses range from 40–110 nm in air masses less influenced by precipitation. The primary driver of the variability we observe appears to be related to changes at the initial fire source. A key lesson from our study is that the complex nature of the regional aerosol and its drivers precludes aggregating our observations as a function of atmospheric aging due to the many conflating and competing factors present. Our study explores and quantifies key uncertainties in the evolution of biomass burning aerosol at both nearfield and regional scales. Our results suggest that the initial conditions of the fire are the primary driver of carbonaceous aerosol physical and chemical properties over tropical South America, aside from significant oxidation of OA during atmospheric aging. Such findings imply that uncertainties in the magnitude of the aerosol burden and its impact on weather, climate, health and natural ecosystems most likely lie in quantifying emission sources, alongside atmospheric dispersion, transport and removal rather than chemical enhancements in mass.

Recent changes in the atmospheric circulation patterns during the dry-to-wet transition season in south tropical South America (1979-2020): Impacts on precipitation and fire season

2021 ◽  
pp. 1-56
Author(s):  
Jhan-Carlo Espinoza ◽  
Paola A. Arias ◽  
Vincent Moron ◽  
Clementine Junquas ◽  
Hans Segura ◽  
...  
Keyword(s):  
South America ◽  
Atmospheric Circulation ◽  
Low Frequency ◽  
Fire Season ◽  
South American ◽  
Low Level ◽  
Atmospheric Circulation Patterns ◽  
Transition Season ◽  
Circulation Patterns ◽  
Tropical South America

AbstractWe analyze the characteristics of atmospheric variations over tropical South America using the pattern recognition framework of weather typing or atmospheric circulation patterns (CPs). During 1979-2020, nine CPs are defined in the region, using a k-means algorithm based on daily unfiltered 850 hPa winds over 0035°N-30°S, 90°W-30°W. CPs are primarily interpreted as stages of the annual cycle of the low-level circulation. We identified three “winter” CPs (CP7, CP8 and CP9), three “summer” CPs (CP3, CP4 and CP5) and three “transitional” CPs (CP1, CP2 and CP6). Significant long-term changes are detected during the dry-to-wet transition season (July-October) over south tropical South America (STSA). One of the wintertime patterns (CP9) increases from 20% in the 1980s to 35% in the last decade while the “transitional” CP2 decreases from 13% to 7%. CP9 is characterized by enhancement of the South American Low-Level Jet and increasing atmospheric subsidence over STSA. CP2 is characterized by southerly cold-air incursions and anomalous convective activity over STSA. The years characterized by high (low) frequency of CP9 (CP2) during the dry-to-wet transition season are associated with a delayed South American Monsoon onset and anomalous dry conditions over STSA. Consistently, a higher frequency of CP9 intensifies the fire season over STSA (1999-2020). Over the Brazilian states of Maranhão, Tocantins, Goiás and São Paulo, the seasonal frequency of CP9 explains around 35%-44% of the interannual variations of fire counts.

scholarly journals Transformation and ageing of biomass burning carbonaceous aerosol over tropical South America from aircraft in situ measurements during SAMBBA

2020 ◽  
Vol 20 (9) ◽  
pp. 5309-5326 ◽  
Author(s):  
William T. Morgan ◽  
James D. Allan ◽  
Stéphane Bauguitte ◽  
Eoghan Darbyshire ◽  
Michael J. Flynn ◽  
...  
Keyword(s):  
South America ◽  
Biomass Burning ◽  
Chemical Properties ◽  
Organic Aerosol ◽  
Carbonaceous Aerosol ◽  
Air Masses ◽  
Primary Driver ◽  
Tropical South America

Abstract. We present a range of airborne in situ observations of biomass burning carbonaceous aerosol over tropical South America, including a case study of a large tropical forest wildfire and a series of regional survey flights across the Brazilian Amazon and Cerrado. The study forms part of the South American Biomass Burning Analysis (SAMBBA) project, which was conducted during September and October 2012. We find limited evidence for net increases in aerosol mass through atmospheric ageing combined with substantial changes in the chemical properties of organic aerosol (OA). Oxidation of the OA increases significantly and rapidly on the scale of 2.5–3 h based on our case study analysis and is consistent with secondary organic aerosol production. The observations of limited net enhancement in OA coupled with such changes in chemical composition imply that evaporation of OA is also occurring to balance these changes. We observe significant coatings on black carbon particles at source, but with limited changes with ageing in both particle core size and coating thickness. We quantify variability in the ratio of OA to carbon monoxide across our study as a key parameter representing both initial fire conditions and an indicator of net aerosol production with atmospheric ageing. We observe ratios of 0.075–0.13 µgsm-3ppbv-1 in the west of our study region over the Amazon tropical forest in air masses less influenced by precipitation and a value of 0.095 µgsm-3ppbv-1 over the Cerrado environment in the east (where sm−3 refers to standard metre cubed). Such values are consistent with emission factors used by numerical models to represent biomass burning OA emissions. Black carbon particle core sizes typically range from mean mass diameters of 250 to 290 nm, while coating thicknesses range from 40 to 110 nm in air masses less influenced by precipitation. The primary driver of the variability we observe appears to be related to changes at the initial fire source. A key lesson from our study is that simply aggregating our observations as a function of atmospheric ageing would have been misleading due to the complex nature of the regional aerosol and its drivers, due to the many conflating and competing factors that are present. Our study explores and quantifies key uncertainties in the evolution of biomass burning aerosol at both near-field and regional scales. Our results suggest that the initial conditions of the fire are the primary driver of carbonaceous aerosol physical and chemical properties over tropical South America, aside from significant oxidation of OA during atmospheric ageing. Such findings imply that uncertainties in the magnitude of the aerosol burden and its impact on weather, climate, health and natural ecosystems most likely lie in quantifying emission sources, alongside atmospheric dispersion, transport and removal rather than chemical enhancements in mass.

IntCal, SHCal, or a Mixed Curve? Choosing a 14C Calibration Curve for Archaeological and Paleoenvironmental Records from Tropical South America

Radiocarbon ◽  
2018 ◽  
Vol 60 (3) ◽  
pp. 925-940 ◽  
Author(s):  
Erik J Marsh ◽  
Maria C Bruno ◽  
Sherilyn C Fritz ◽  
Paul Baker ◽  
José M Capriles ◽  
...  
Keyword(s):  
South America ◽  
Cultural Change ◽  
Calibration Curve ◽  
Substantial Part ◽  
South American ◽  
Lake Titicaca ◽  
Air Masses ◽  
Tree Ring Data ◽  
New Research ◽  
Tropical South America

AbstractBecause the 14C calibration curves IntCal and SHCal are based on data from temperate latitudes, it remains unclear which curve is more suitable for archaeological and paleoenvironmental records from tropical South America. A review of climate dynamics reveals a significant influx of Northern Hemisphere air masses and moisture over a substantial part of the continent during the South American Summer Monsoon (SASM). Areas affected by the SASM receive unknown amounts of input from both hemispheres, where an argument could be made for either curve. Until localized tree-ring data can resolve this, we suggest using a mixed calibration curve, which accounts for inputs from both hemispheres, as a third calibration option. We present a calibration example from a crucial period of environmental and cultural change in the southern Lake Titicaca. Given our current lack of data on past ∆14C variation in South America, our calibrations and chronologies will likely change in the future. We hope this paper spurs new research into this topic and encourages researchers to make an informed and explicit choice of which curve to use, which is particularly relevant in research on past human–environmental relationships.

Back-trajectory modelling and DNA-based species-specific detection methods allow tracking of fungal spore transport in air masses

2016 ◽  
Vol 571 ◽  
pp. 658-669 ◽  
Author(s):  
Agnieszka Grinn-Gofroń ◽  
Magdalena Sadyś ◽  
Joanna Kaczmarek ◽  
Aleksandra Bednarz ◽  
Sylwia Pawłowska ◽  
...  
Keyword(s):  
Fungal Spore ◽  
Detection Methods ◽  
Back Trajectory ◽  
Specific Detection ◽  
Air Masses ◽  
Species Specific ◽  
Trajectory Modelling

Avian Speciation in Tropical South America

Bird-Banding ◽  
1975 ◽  
Vol 46 (2) ◽  
pp. 191
Author(s):  
Burt L. Monroe, ◽  
J. Haffer
Keyword(s):  
South America ◽  
Tropical South America
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