Side Of Andes Research Articles

Characteristics of cloud properties over South America and over Andes observed using CloudSat and reanalysis data

ABSTRACT CloudSat profile of attenuated corrected radar reflectivity (Ze) and cloud mask data are used to investigate the cloud properties over South America (SA) during Austral Summer monsoon seasons. Deep convective core (DCC), deep & intense convective systems (DCSs & ICSs), and cloud clusters (CCs) are defined based on the Ze and cloud mask values. The spatial distributions of DCCs show that land-dominated areas have higher frequency of DCCs and Atlantic Ocean has less DCCs. The Pacific Ocean does not consist of DCCs, whereas eastern flank of Andes has higher frequency of DCCs compared to western flank of the Andes. North La Plata basin (Sierra de Cordoba) has a higher fraction of deeper (shallower) DCCs. Deep convection over the Sierra de Cordoba and South La Plata Basin is characterized by precipitation-size particles compared to cloud-size particles, whereas deep convection over north La Plata Basin is dominated by mostly cloud-size particles. The horizontal span of DCSs and ICSs is higher over south La Plata Basin and Atlantic Oceans compared to other SA areas. Sierra de Cordoba (Atlantic Ocean) has the highest (lowest) frequency of small DCSs and vice versa. DCSs and ICSs show the opposite characteristic, as all the selected areas consist of a higher fraction of large (small) sized DCSs (ICSs). CCs develop more in horizontal than in vertical direction over the high latitude and vice versa over lower latitude. The CCs distribution reflects the orography and moisture flow pattern at the east and west side of Andes. The higher Ze, which is the proxy for rainfall, occurs at the eastern flank/slope of the Andes, and related to easterly moisture loaded synoptic flow, transported from Amazon and upslope flow along the slope.

The climatic association of population divergence and future extinction risk of Solanum pimpinellifolium.

Under intraspecific differentiation driven by differential climatic adaptation, it may be expected that intraspecific genetic groups occur at distinct environments. Populations occupying different niches may therefore differ in their ability to cope with climate change. Here, we addressed this hypothesis with a wild tomato, Solanum pimpinellifolium. This species is distributed from the west side of Andes to the coastal region in Peru and Ecuador and occupies a wide environmental diversity. This environmental diversity is related to the genetic structure of the species providing an ideal material to investigate the isolation by environment hypothesis. While previous hypothesis stated that S. pimpinellifolium originated from northern Peru and migrated northwards and southwards, our results support that S. pimpinellifolium originated from Ecuador and expanded to northern and southern Peru, and during this process, the niche space of S. pimpinellifolium became more associated with cold and drought. We further predicted its fate under anthropogenic climate change. According to our predictions, the northern group will maintain its current extent or even expand to the entire western region of Ecuador. In contrast, we predicted low habitat suitability for the southern group which could potentially lead to the shrinkage of its distribution. In conclusion, we revealed the distinct fates among the differentiated populations driven by environment under global warming conditions.

Analysis of Possible Triggering Mechanisms of Severe Thunderstorms in the Tropical Central Andes of Peru, Mantaro Valley

The aim of the present study is to analyze the triggering mechanisms of three thunderstorms (TSs) associated with severe rainfall, hail and lightening in the tropical central Andes of Peru, specifically above the Huancayo observatory (12.04 ∘ S, 75.32 ∘ W, 3313 m a.s.l.) located in the Mantaro valley during the spring-summer season (2015–2016). For this purpose, we used a set of in-situ pluviometric observations, satellite remote sensing data, the Compact Meteorological Ka-Band Cloud Radar (MIRA-35C), the Boundary Layer Tropospheric Radar and downscaling model simulations with the Weather Research and Forecasting (WRF) Model (resolutions: 18 km, 6 km and 2 km), and the Advance Regional Prediction System (ARPS) (resolution: 0.5 km) models in order to analyze the dynamic of the atmosphere in the synoptic, meso and local scales processes that control the occurrence of the three TS events. The results show that at synoptic scale, the TSs are characterized by the southern displacement of the South-east Pacific Subtropical Anticyclone up to latitudes higher than 35 ∘ S, by the weakening and south-eastern displacement of the Bolivian high–North east low system and by the intrusion of westerly winds along the west side of the central Andes at upper and medium levels of the atmosphere. At meso-scale, apparently, two important moisture fluxes from opposite directions are filtered through the passes along the Andes: one from the north-west and the other from the south-east directions converge and trigger the deep convection into the Mantaro valley. These moisture fluxes are generated by the intrusion of the sea-breeze from the Pacific ocean along the west of the Andes coupling with upper and middle westerly winds and by the thermally induced moisture fluxes coming from the South American low level jet at the east side of the Andes. At the local scale, there is a low-level conditional instability in the previous hours as well as during the occurrence of the TSs above the Huancayo observatory. In addition, the simulation results indicated the possibility of generation of inertial gravity waves in the Amazon basin, associated with geostrophic adjustment which transports energy and moisture into the central Andes plateau and consequently intensifies the thunderstorms above the Mantaro valley.

Differences in 10Be concentrations between river sand, gravel and pebbles along the western side of the central Andes

Cosmogenic nuclides in river sediment have been used to quantify catchment-mean erosion rates. Nevertheless, variable differences in 10Be concentrations according to grain size have been reported. We analyzed these differences in eleven catchments on the western side of the Andes, covering contrasting climates and slopes. The data include eight sand (0.5–1 mm) and gravel (1–3 cm) pairs and twelve sand (0.5–1 mm) and pebble (5–10 cm) pairs. The difference observed in three pairs can be explained by a difference in the provenance of the sand and coarser sediment. The other sand–pebble pairs show a lower 10Be concentration in the pebbles, except for one pair that shows similar concentrations. Two sand–gravel pairs show a lower 10Be concentration in the gravel and the other five pairs show a higher 10Be concentration in the gravel. Differences in climate do not reveal a particular influence on the 10Be concentration between pairs. The analysis supports a model where pebbles and gravel are mainly derived from catchment areas that are eroding at a faster rate. The five gravel samples with high 10Be concentrations probably contain gravel that were derived from the abrasion of cobbles exhumed at high elevations. In order to validate this model, further work should test if pebbles are preferentially exhumed from high erosion rate areas, and if the difference between pebbles with high 10Be concentrations and sand decreases when the erosion rate tends to be homogeneous within a catchment.

Spatial variability of atmospheric semivolatile organic compounds in Chile

Abstract In an effort to characterize the spatial variability of pesticides, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) in the Chilean atmosphere, XAD-based passive air samplers (PAS) were deployed for 12 months (2006–2007) along three elevational gradients in Northern, Central and Southern Chile, for a total of 20 sampling sites, ranging in elevation from 10 to 4400 m and ranging over 26 degrees of latitude. Hexachlorobenzene (HCB) had largely uniform air concentrations with latitude and altitude, and is therefore used to derive sampler specific sampling rates, that account for differences in uptake kinetics due to environmental factors such as altitude and temperature. Levels of pesticides in the atmosphere of Chile are very low and only α- and γ-hexachlorocyclohexane, α-endosulfan and chlorothalonil were present in all of the samples. The concentrations of these four pesticides in air decreased from North to South, with much steeper gradients for chlorothalonil and endosulfan. Chlorothalonil levels were greatly elevated in air samplers deployed in urban locations. Endosulfan concentrations in air tend to increase with elevation. Since endosulfan is particularly susceptible to mountain cold-trapping, such gradients may reflect the re-volatilization of endosulfan that had been preferentially deposited at higher altitudes. Alternatively, increasing endosulfan concentrations with elevation could be the result of transport to higher altitude sites from the other side of Andes. Airshed analysis indeed indicates that air masses originating outside of Chile have a higher influence on the higher elevation sites, especially along the Northern transect. Concentrations of four-ring PAHs ranged from 0.3 to 1300 pg m −3 , with higher levels in air samplers deployed in urban areas and close to roads. PCB concentrations were low (0.7–27 pg m −3 ), with slightly higher levels of volatile congeners in two urban sampling sites in Concepcion and Arica. PCB-52 is the only congener present in all samples, with levels that are remarkably uniform across the country.

Adiantum camptorachis (Pteridaceae), a New Species from South America with Notes on the Taxonomy of Related Species from the Southern Cone and Bolivia

Abstract We describe Adiantum camptorachis from the Tucumano-Boliviano forests of southern Bolivia and northwestern and central Argentina. This species was previously confused with A. glanduliferum, which is found on the Pacific side of Andes from southern Peru to central Chile. Adiantum camptorachis differs by having rhizome scales with distally ciliate margins, erose pinna margins, and by having a flexuous rachis. We also provide a detailed description for A. rufopunctatum, which had previously been treated as a synonym of A. raddianum by several authors. A key to similar South American species is presented. It includes all species with decompound non-conform laminae and orbicular to reniform or lunate sori in the Southern Cone, including Argentina Chile, Bolivia, Brazil, Paraguay, and Uruguay.

Influence of the Subtropical Andes on Baroclinic Disturbances: A Cold Front Case Study

Abstract The Andes Cordillera produces a significant disruption to the structure and evolution of the weather systems that cross South America. In particular, cold fronts tend to be “channeled” to the north immediately to the east of the Andes, fostering the advance of cold air incursions (cold surges) well into subtropical, and sometimes tropical, latitudes. In contrast, active cold fronts hardly reach subtropical latitudes along the western side of the Andes (Pacific sea border). Instead, as a cold front moves equatorward along the east side of the Andes, a marked low-level warming tends to appear along the west side of the subtropical Andes, leading to the formation of a mesoscale coastal low (or trough) in this region. To further understand the processes that lead to a contrasting evolution of the cold front at each side of the Andes, a typical frontal passage is studied in this work, using synoptic observations and a regional model [Eta–Centro de Previsão de Tempo e Estudos Climáticos (CPTEC)] simulation. The passage of the postfrontal anticyclone over southern South America produces a poleward-pointing pressure gradient and, hence, geostrophic easterly flow at low levels. The tall and steep mountains block the flow, leading to a very small zonal wind component close to the slopes. Convergence (divergence) of the zonal flow to the east (west) of the subtropical Andes is largely compensated for by upward (downward) motion, and the associated cooling (warming) over this region. The weak zonal wind component near the Andes also breaks down the geostrophic balance over this region, giving rise to an acceleration of the southerly winds (i.e., along-barrier flow) and the consequent increase in cold advection. Therefore, to the east of the subtropical Andes both horizontal and vertical advection cool the lower troposphere, fostering the equatorward propagation of the cold front. To the west of the Andes, horizontal advection is largely offset by the strong warming associated with the enhanced subsidence over that region hindering the advance of the cold front into subtropical latitudes.

Stable isotope composition of precipitation across the southern Patagonian Andes

A surface water and precipitation transect across the southern Patagonian Andes at 47°–48°S was conducted to assess how mountains affect the isotopic composition of precipitation. This westerly wind region derives its moisture that falls as precipitation from the Pacific. Orographic uplift of air over the Andes causes pseudoadiabatic cooling and orographic precipitation on the western side and a strong rain shadow on the eastern side of the mountains. These processes also produce a profound isotopic rain shadow, with δ18O values ∼4‰ lower in the east compared to the west. On the windward western side of the Andes, the isotope values of precipitation and surface waters show weak, although systematic, trends with elevation, but a pronounced correlation with distance from the main source of moisture (Pacific Ocean). A Rayleigh simulation of precipitation δ18O values as a function of condensation altitude matches our data well, suggesting that other processes, such as mixing of water sources and postcondensation evaporation, are negligible, and that topography is the dominant control on the isotope ratio of precipitation. In contrast, isotope ratios of waters on the leeward eastern side of the southern Patagonian Andes vary neither with elevation nor with distance from the mountains, consistent with much of the precipitation on the leeward side being derived from precipitation carried over the Andes by winds. Thus, paleoprecipitation isotopic composition on the leeward side of orogens in similar climatic settings (single moisture source and cool climate) yield useful estimates of the elevation of these orogens, but not local elevation.

Late Pleistocene palaeolakes in the Andean and Extra-Andean Patagonia at mid-latitudes of South America

Late Pleistocene palaeolakes on the eastern side of Andes (glacial lakes) and in the Patagonian Steppe (pluvial lakes) along 41°S latitude were studied. Natural dams (glaciers, moraines) that maintained a high water level in glacial palaeolakes were melted or cut by erosion during Late Pleistocene climate amelioration. With the retreat of the glaciers from the Andean valleys during prominent regional deglaciation, outflow from the eastern side of Andes to the Pacific Ocean was formed about 13.2 ka BP. As a result, the water level in glacial palaeolakes fell rapidly in stages. These changes were often preceded by volcanic-tectonic activity, which is suggested to be the “touch of butterfly” releasing mass balance adjustment in the changing landscape. The lacustrine tephra stratigraphic pattern from the Andes, comprising more than 50 horizons since the last glaciation, is presented. The correlation of palaeoenvironmental changes between the Andes and the Patagonian Steppe is suggested on the basis of two dacite marker horizons. The deglaciation event that led to development of the new hydrological system in the Andean palaeolakeland formed several large but short-lived palaeolakes in closed basins in the Patagonian Steppe probably due to melting of local ice and permafrost accumulated during glaciation on the surrounding mountains and elevated plains.