Munoz R.C.,University of Chile |
Quintana J.,Direccion Meteorologica de Chile |
Falvey M.J.,University of Chile |
Rutllant J.A.,University of Chile |
And 2 more authors.
Journal of Climate | Year: 2016
The climatology and recent trends of low-level coastal clouds at three sites along the northern Chilean coast (18.3°-23.4°S) are documented based upon up to 45 years of hourly observations of cloud type, coverage, and heights. Consistent with the subtropical location, cloud types are dominated by stratocumuli having greatest coverage (> 7 oktas) and smaller heights (600-750 m) during the nighttime of austral winter and spring. Meridionally, nighttime cloud fraction and cloud-base heights increase from south to north. Long-term trends in mean cloud cover are observed at all sites albeit with a seasonal modulation, with increasing (decreasing) coverage in the spring (fall). Consistent trend patterns are also observed in independent sunshine hour measurements at the same sites. Cloud heights show negative trends of about 100 m decade-1 (1995-2010), although the onset time of this tendency differs between sites. The positive cloud fraction trends during the cloudy season reported here disagree with previous studies, with discrepancies attributed to differences in datasets used or to methodological differences in data analysis. The cloud-base height tendency, together with a less rapid lowering of the subsidence inversion base height, suggests a deepening of the coastal cloud layer. While consistent with the tendency toward greater low-level cloud cover and the known cooling of the marine boundary layer in this region, these tendencies are at odds with a drying trend of the near-surface air documented here as well. Assessing whether this intriguing result is caused by physical factors or by limitations of the data demands more detailed observations, some of which are currently under way. © 2016 American Meteorological Society.
Flores-Aqueveque V.,University Paris Est Creteil |
Flores-Aqueveque V.,University of Chile |
Alfaro S.C.,University Paris Est Creteil |
Caquineau S.,French National Center for Scientific Research |
And 4 more authors.
Sedimentology | Year: 2012
The analysis of the aeolian content of marine cores collected off the coast of the Atacama Desert (Mejillones Bay, Chile) suggests that marine sediments can record inter-annual to inter-decadal variations in the regional southerly winds responsible for particle entrainment at the surface of the nearby desert. However, the establishment of a simple and direct correlation between the sediment and wind records is complicated by the difference of time scales between the erosion and accumulation processes. The aim of this work is to: (i) assess the inter-annual variability of the surface winds responsible for the sand movements; and (ii) determine whether the integration over periods of several months completely smoothes the rapid changes in characteristics of the transported and deposited aeolian material. To accomplish this aim, 14years of 10m hourly wind speed, measured at the Cerro Moreno (Antofagasta) Airport between 1991 and 2003 and at the Orica Station between 2000 and 2004, were analyzed. For each year, the wind speed statistical distribution can be represented by a combination of two to three Weibull functions. Winds of the lowest Weibull mode are too weak to move the sand grains at the surface of the pampa; this is not the case for the intermediate mode and especially for the highest speed mode which are able to erode the arid surface and transport particles to the bay. In each individual year of the period of study, the highest speed mode only accounted for a limited number of strong erosion events. Quantitative analysis of the distribution of the friction velocities and of their impact on erosion using a saltation model suggests that, although all wind speeds above threshold produce erosion events, values around 0·45msec -1 contribute less to the erosion flux. This gap allows separation of the erosion events into low and high saltation modes. The correlation (r=0·997) between the importance of the third Weibull mode and the extent of higher rate saltation indicates that the inter-annual variability of the erosion at the surface of the pampa, as well as the transport of coarse particles (>100μm), are directly related to inter-annual variations in the prevalence of the strongest winds. Finally, a transport and deposition model is used to assess the possible impact of the wind inter-annual variability on the deposition flux of mineral particles in the bay. The results suggest that inter-annual differences in the wind speed distributions have a quantifiable effect on the intensity and size-distribution of this deposition flux. This observation suggests that a detailed analysis of the sediment cores collected from the bay could be used for reconstructing the inter-annual variability of past winds. © 2011 The Authors. Journal compilation © 2011 International Association of Sedimentologists.
Vasquez J.A.,Catolica del Norte University |
Vasquez J.A.,Center for Advanced Studies in Arid Zones |
Piaget N.,Catolica del Norte University |
Vega J.M.A.,Catolica del Norte University
Journal of Applied Phycology | Year: 2012
In Chile, management of natural resources usually starts right before its imminent collapse or after evident declination. In the northern area of the country, the fishery of brown seaweeds has an enormous social, ecological, and economical importance. More than 11,000 people depend directly or indirectly on the collection and harvesting of this resource. Ecologically, kelps constitute areas for food, reproduction, and refuge for hundreds of invertebrates and fish species. Economically, landings up to 300,000 dry tons per year represent close to US $60 million for the industry. Until 2002, the Chilean brown seaweed fishery was mainly sustained by natural mortality, where plants cast ashore were collected by artisanal fishermen. Since then, three brown seaweed species of economic importance (Lessonia nigrescens, Lessonia trabeculata, and Macrocystis pyrifera) have been intensively harvested in coastal areas between 18° and 32° S. To manage kelp populations along the northern Chilean coast, regulations have been based on the principle "how you harvest is more important than how much you harvest". This exploitation strategy has been adopted in consensus between fishermen, industries, governmental entities, and scientists. Since L. nigrescens represents more than 70% of total brown seaweed landings, this study tests the effects of L. nigrescens harvesting on the following population variables: (1) abundance, (2) distribution, (3) juvenile recruitment, (4) plant morphology, (5) frequency of reproductive plants, and (6) biodiversity of the macroinvertebrate community associated to kelp holdfasts. Our results show that, despite the enormous harvesting pressure on Lessonia density and biomass, the associated macroinvertebrate richness has been maintained, due to normal plant growth and high recruitment all year round. © 2012 Springer Science+Business Media B.V.
Lapazaran J.,Technical University of Madrid |
Petlicki M.,Center for Advanced Studies in Arid Zones |
Navarro F.,Technical University of Madrid |
Machio F.,Pontifical University of Salamanca |
And 3 more authors.
Polar Research | Year: 2013
Ariebreen is a small (0.37 km2)-valley glacier located in southern Spitsbergen Our ground-penetrating radar surveys of the glacier show that it is less than 30 m thick on average, with a maximum thickness of 82 m, and it appears to be entirely cold. By analysing digital terrain models of the ice surface from different dates, we determine the area and volume changes during two periods, 1936-1990 and 1990-2007. The total ice volume of the glacier has decreased by 73% during the entire period 1936-2007, which is equivalent to a mean mass balance rate of -0.61±0.17 m y-1 w.eq. The glacier thinning rate has increased markedly between the first and second periods, from -0.50±0.22 to -0.95±0.17 m y-1 w.eq.Polar Research 2013. © 2013 J. Lapazaran et al.
Nunez J.,University of Concepcion |
Nunez J.,Water Center for Arid |
Rivera D.,University of Concepcion |
Oyarzun R.,Center for Advanced Studies in Arid Zones |
Arumi J.L.,University of Concepcion
Journal of Hydrology | Year: 2013
This paper addresses the relationship between multitemporal variability and regime shifts in the Pacific Decadal Oscillation and El Niño Southern Oscillation, with precipitation and streamflows in Andean watersheds of the north-central region of Chile. In addition, an analysis of the effect of a regime shift displayed by annual streamflow records on their distributional properties is performed. By applying empirical fluctuation processes to monthly standardized PDO, Niño 3.4, precipitation and streamflow time series, the occurrence of a regime shift in the streamflow series, consistent with that for PDO, but highly dependent on the latitude of particular watersheds, is shown. No regime shift is detected for the precipitation time series. Using the ensemble Empirical Mode Decomposition procedure on all series, a relationship between climatic indices and hydrological variables in two main modes is determined: the former associated with a mean period of quasi 1.5-3. years related to interannual variability, and the latter with a mean period of quasi 30-35. years, related to decadal low frequency variability. Using the regional frequency analysis based on the L-moments procedure, it is found that the distributional properties of streamflow records are influenced by the phases of the PDO, with changes that affect the mean, L-CV, L-skewness and L-kurtosis in three identified homogeneous regions. The importance of incorporating low-frequency climate variability for distributional analysis and the implications of these results for water resources management and planning in north-central Chile and similar areas is discussed. © 2013 Elsevier B.V.