Analysis of atmospheric conditions associated to <scp>CHACO</scp> events of the Low Level Jet East of the Andes and their implications for regional transport

Castañeda, María Elizabeth; Ulke, Ana Graciela

doi:10.1002/joc.4272

Cited by 6 publications

(5 citation statements)

References 21 publications

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“…The SALLJ is a southward flow of high-velocity winds originating in the Amazon basin (Fig. 3), following trajectories ranging from due south along the flank of the Andes to southeasterly toward Buenos Aires and eastern Argentina (60). Moisture delivered by the SALLJ is subsequently recycled during intense convective storms as warm air rises upward through colder westerly air masses flowing down off high Andean topography (59,61).…”

Section: Resultsmentioning

confidence: 99%

Mio-Pliocene aridity in the south-central Andes associated with Southern Hemisphere cold periods

Amidon

Fisher

Burbank

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Although Earth’s climate history is best known through marine records, the corresponding continental climatic conditions drive the evolution of terrestrial life. Continental conditions during the latest Miocene are of particular interest because global faunal turnover is roughly synchronous with a period of global glaciation from ∼6.2–5.5 Ma and with the Messinian Salinity Crisis from ∼6.0–5.3 Ma. Despite the climatic and ecological significance of this period, the continental climatic conditions associated with it remain unclear. We address this question using erosion rates of ancient watersheds to constrain Mio-Pliocene climatic conditions in the south-central Andes near 30° S. Our results show two slowdowns in erosion rate, one from ∼6.1–5.2 Ma and another from 3.6 to 3.3 Ma, which we attribute to periods of continental aridity. This view is supported by synchrony with other regional proxies for aridity and with the timing of glacial ‟cold” periods as recorded by marine proxies, such as the M2 isotope excursion. We thus conclude that aridity in the south-central Andes is associated with cold periods at high southern latitudes, perhaps due to a northward migration of the Southern Hemisphere westerlies, which disrupted the South American Low Level Jet that delivers moisture to southeastern South America. Colder glacial periods, and possibly associated reductions in atmospheric CO2, thus seem to be an important driver of Mio-Pliocene ecological transitions in the central Andes. Finally, this study demonstrates that paleo-erosion rates can be a powerful proxy for ancient continental climates that lie beyond the reach of most lacustrine and glacial archives.

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Section: Resultsmentioning

confidence: 99%

Mio-Pliocene aridity in the south-central Andes associated with Southern Hemisphere cold periods

Amidon

Fisher

Burbank

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…It is also interesting to note that a part of the LLJs does not generate precipitation in the subtropical La Plata Basin. In these cases, together with moisture, LLJ carries large amount of aerosols of fires from the Amazon (Castañeda and Ulke, ). High concentrations of aerosols in the atmosphere are known to hinder the formation of precipitation clouds (Costa and Pauliquevis, ).…”

Section: Continental Exchange Mechanismsmentioning

confidence: 99%

Hydrological processes interconnecting the two largest watersheds of South America from seasonal to intra‐monthly time scales: A critical review

Zanin

Satyamurty

2020

Intl Journal of Climatology

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Many articles on the subjects of moisture transport, precipitation and surface hydrology of the two largest watersheds of South America, the Amazon and the La Plata basins, are stitched together to obtain an overview of the aspects related to the hydrological processes interconnecting them on time scales ranging from seasonal to intra‐monthly. In the mean, moisture from the tropical Atlantic Ocean is transported by the trade winds into the Amazon Basin. A good part of it precipitates over the Amazon Basin and the other part reaches the La Plata Basin by northerly winds east of the Andes. Besides the moisture transported from the Atlantic, there is evapotranspiration in the Amazon and La Plata basins. A part of the evapotranspiration of the Amazon Basin precipitates over the same basin, contributing with about 1/3 of annual precipitation this basin, and a part joins the aerial stream into the La Plata Basin, contributing with about 1/4 of its annual precipitation. Semi‐permanent and transient meteorological systems such as Inter‐Tropical Convergence Zone, South Atlantic Convergence Zone, Low‐Level Jet (LLJ) east of the Andes, Madden–Julian Oscillation, cold fronts and cyclones play an important role in the seasonal and intra‐seasonal variations of precipitation, evapotranspiration and river discharge. The hydrological memory in Amazonian soils and the LLJ constitute an inter‐seasonal coupling between the water balances of the two basins. All these aspects are succinctly described and discussed in this review article. Hypotheses for future research are formulated.

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“…e occurrence of CJ1 events was diagnosed applying the modified Bonner criteria on GDAS (Global Data Assimilation System) data provided by NCEP (National Centers for Environmental Prediction) for the period 2001-2005 as detailed in [13].…”

Section: Methodsmentioning

confidence: 99%

“…at subset is known in the literature as CJ1 and is responsible for the regional transport of biomass-burning products from sources in central South America towards Buenos Aires. According to Castañeda and Ulke [13], CJ1 events, the most common SALLJ class, have the highest frequencies of occurrence in winter and spring, 16% and 10%, respectively, when all the days are considered. During August, the first month of the biomass-burning season, CJ1 occurrence increases sharply to 57% of the 16% occurrence in winter coinciding with the marked increase in the number of fire spots as seen in satellite imagery (see Figure 1, available at https://worldview.earthdata.nasa.gov).…”

Section: Introductionmentioning

confidence: 99%

Influence of Regional Transport Mechanisms on the Fingerprint of Biomass-Burning Aerosols in Buenos Aires

Ulke

2019

Advances in Meteorology

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e study focuses on the transport of aerosol particles resulting from biomass burning in central South America towards the megacity of Buenos Aires by the South American Low-Level Jet. In particular, the cases are studied in which the exit area of the Jet reaches the La Plata Basin with no precipitation associated, herein called Chaco Jet 1 (CJ1), which could remove aerosols from the atmosphere on their way towards the city. CJ1 events registered within the five-year period of 2001-2005 are examined along with changes in the optical properties of aerosols over the city from measurements from the Aerosol Robotic Network (AERONET) site. ree-dimensional backward trajectories of CJ1 were obtained to verify the connection between the receptor site and the biomass-burning source region. A cluster analysis of the trajectories allows further characterizing the features and impacts of regionally transported aerosols. A subsample of days on which impacts of the contribution of biomass burning could have occurred, showed a statistically significant increase in aerosol optical depth andÅngström exponent, reflected by an increase in the peak of the derived volume size distribution in the fine fraction size range, which also shifts slightly towards bigger radii. e days with AOD greater than 0.15 show overall behaviour like other urban sites with pollution of different origins. e evaluation of the selected data reveals that higher values of AOD and changes in theÅngström exponent are linked to the dispersion of biomassburning aerosols. Air mass trajectories coinciding with the CJ1 core present the strongest impact on aerosol characteristics, which can be seen in spectral measurements.

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Analysis of atmospheric conditions associated to CHACO events of the Low Level Jet East of the Andes and their implications for regional transport

Cited by 6 publications

References 21 publications

Mio-Pliocene aridity in the south-central Andes associated with Southern Hemisphere cold periods

Mio-Pliocene aridity in the south-central Andes associated with Southern Hemisphere cold periods

Hydrological processes interconnecting the two largest watersheds of South America from seasonal to intra‐monthly time scales: A critical review

Influence of Regional Transport Mechanisms on the Fingerprint of Biomass-Burning Aerosols in Buenos Aires

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