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Mena-Carrasco M.,Ministerio del Medio Ambiente | Mena-Carrasco M.,Centro FONDAP CIGIDEN | Saide P.,University of Iowa | Delgado R.,Direccion Meteorologica de Chile | And 5 more authors.
Urban Climate | Year: 2014

Santiago, an emerging megacity of 7 million plus inhabitants has shown great improvement in its air quality reducing PM2.5 concentrations from 69μg/m3 in 1989 to 24μg/m3 in 2013 with a comprehensive air quality management strategy. An operational air quality forecasting model that has shown great potential in predicting air quality episodes is used to establish how the climate A1B scenario can impact the frequency of bad air days. In comparison to 2011, in 2050 extreme air quality episodes will be reduced in 20%. WRF-Chem is used to evaluate the effect of anthropogenic emissions on the regional climate including aerosol radiative feedbacks for October-November 2008. Anthropogenic emissions of sulfur and black carbon show different geographical patterns which result in local cooling (0.2-1°C) in coastal Chile, due to large sources of SO2. Central Chile, where most of the population of the country lives, shows transportation of black carbon emissions into the Andes mountain range, resulting in local warming of 0.4°C. While global forcings may cause regional heating for 2050, reducing current black carbon emissions in Central Chile can reduce anthropogenic warming with immediate benefits to the regional climate, and simultaneously reducing local air pollution. © 2014 Elsevier B.V.

Cordero R.R.,University of Santiago de Chile | Seckmeyer G.,Leibniz University of Hanover | Damiani A.,University of Santiago de Chile | Jorquera J.,University of Santiago de Chile | And 5 more authors.
Atmospheric Research | Year: 2014

Santiago de Chile (33°27' S-70°41' W) is a mid-latitude city of 6 million inhabitants with a complicated surrounding topography. Aerosol extinction in Santiago is determined by the semi-arid local climate, the urban pollution, a regional subsidence thermal inversion layer, and the boundary-layer wind airflow. In this paper we report on spectral measurements of the surface irradiance (at 290-600. nm wavelength range) carried out during 2013 in the heart of the city by using a double monochromator-based spectroradiometer system. These measurements were used to assess the effect of local aerosols, paying particular attention to the ultraviolet (UV) range. We found that the aerosol optical depth (AOD) exhibited variations likely related to changes in the subsidence thermal inversion and in the boundary-layer winds. Although the AOD at 350. nm typically ranged from 0.2 to 0.3, peak values of about 0.7 were measured. The AOD diminished with the wavelength and typically ranged from 0.1 to 0.2 at 550. nm. Our AOD data were found to be consistent with measurements of the particulate matter (PM) mass concentration. © 2014 Elsevier B.V.

Quintana J.M.,Direccion Meteorologica de Chile | Aceituno P.,University of Chile
Atmosfera | Year: 2011

The evolution of annual rainfall along the west coast of South America from 30 to 43° S (central Chile) is analyzed for the period 1900-2007. A prevailing negative trend in annual rainfall has been documented for this region in several previous studies. Here we focus on the significant changes and fluctuations occurring at the decadal time scale, exploring the links with regional atmospheric circulation anomalies associated with large-scale oscillatory modes of the ocean-atmospheric system. In particular, the relatively dry condition that prevailed from the 1950s to the early 1970s in the northern part of central Chile (30-35° S) is consistent with an intensified subtropical anticyclone in the southeast Pacific during a period characterized by a prevailing positive phase of the Southern Oscillation (SO) and the cold phase of the Pacific Decadal Oscillation (PDO). The shift of the PDO toward the warm phase by the mid-1970s was followed by an increased frequency of the negative phase of the SO and associated El Niño episodes. Concurrent weakening of the subtropical anticyclone favored an increased frequency of wet years in this region. Further south the negative trend in annual rainfall that prevailed since the 1950s in the region from 37 to 43° S intensified by the end of the 20th century. Changes in the meridional sea level pressure gradient at mid-latitudes and high-latitudes in the southeast Pacific, which are partially connected to the Antarctic Oscillation (AAO), play a significant role in modulating the interannual rainfall variability in all central Chile, especially during the austral winter semester (April-September). Thus, an intensified (reduced) meridional pressure gradient in that region favors a southward (northward) displacement of the latitudinal band of migratory extratropical low pressure systems and associated fronts. The significant positive trend that both the AAO index and its regional counterpart in the southeast Pacific exhibit since the 1950s may partially explain the observed downward trend in annual precipitation in the southern portion of central Chile, resulting from a reduction in both the frequency of wet days and the intensity of precipitation. Most of the global and regional climate models used to assess future climate scenarios associated with an enhanced planetary greenhouse effect, also call for a reduction of rainfall in this region which is consistent with the positive trend in the AAO predicted by those models.

Fan X.,Shanxi University | Wang Q.,Shanxi University | Wang M.,Shanxi University | Jimenez C.V.,Direccion Meteorologica de Chile
PLoS ONE | Year: 2015

An analysis of the annual mean temperature (TMEAN) (1961-2010) has revealed that warming amplification (altitudinal amplification and regional amplification) is a common feature of major high-elevation regions across the globe against the background of global warming since the mid-20th century. In this study, the authors further examine whether this holds for annual mean minimum temperature (TMIN) and annual mean maximum temperature (TMAX) (1961-2010) on a global scale. The extraction method of warming component of altitude, and the paired region comparison method were used in this study. Results show that a significant altitudinal amplification trend in TMIN (TMAX) is detected in all (four) of the six highelevation regions tested, and the average magnitude of altitudinal amplification trend for TMIN (TMAX) [0.306±0.086 °C km-1(0.154±0.213 °C km-1)] is substantially larger (smaller) than TMEAN (0.230±0.073 °C km-1) during the period 1961-2010. For the five paired highand low-elevation regions available, regional amplification is detected in the four high-elevation regions for TMIN and TMAX (respectively or as a whole). Qualitatively, highly (largely) consistent results are observed for TMIN (TMAX) compared with those for TMEAN. Copyright: © 2015 Fan et al.This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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.

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