Abstract
Crucial aspects of a strong thermally-driven wind system in the Atacama Desert in northern Chile during the extended austral winter season (May–September) are studied using 2 years of measurement data from the Sierra Gorda 80-m meteorological mast (SGO, 22° 56′ 24″ S; 69° 7′ 58″ W, 2,069 m above sea level (a.s.l.)). Daily cycles of atmospheric variables reveal a diurnal (nocturnal) regime, with northwesterly (easterly) flow and maximum mean wind speed of 8 m/s (13 m/s) on average. These distinct regimes are caused by pronounced topographic conditions and the diurnal cycle of the local radiative balance. Wind speed extreme events of each regime are negatively correlated at the inter-daily time scale: High diurnal wind speed values are usually observed together with low nocturnal wind speed values and vice versa. The associated synoptic conditions indicate that upper-level troughs at the coastline of southwestern South America reinforce the diurnal northwesterly wind, whereas mean undisturbed upper-level conditions favor the development of the nocturnal easterly flow. We analyze the skill of the numerical weather model Global Forecast System (GFS) in predicting wind speed at SGO. Although forecasted wind speeds at 800 hPa do show the diurnal and nocturnal phases, observations at 80 m are strongly underestimated by the model. This causes a pronounced daily cycle of root-mean-squared error (RMSE) and bias in the forecasts. After applying a simple Model Output Statistics (MOS) post-processing, we achieve a good representation of the wind speed intra-daily and inter-daily variability, a first step toward reducing the uncertainties related to potential wind energy projects in the region.
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Acknowledgments
Funding for this research was provided by a cooperation agreement between the University of Chile and the Chilean Ministry of Energy under Exempt Decree 249 of 2013. The measurement campaign in northern Chile was carried out by programs of the Chilean Ministry of Energy, with partial support from the German GIZ Agency (Deutsche Gesellschaft für Internationale Zusammenarbeit GmbH). NCEP Reanalysis data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site (http://www.esrl.noaa.gov/psd/). GFS data was obtained from the USA NOAA National Climatic Data Center (http://www.ncdc.noaa.gov/). MJC acknowledges ForWind (Universität Oldenburg, Germany), in particular Dr. Thomas I. Petroliagis, for the experience gained during a research internship financed by “Programa en Energías” (CONICYT-Chile). This paper was greatly improved by the comments and suggestions of two anonymous reviewers.
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Jacques-Coper, M., Falvey, M. & Muñoz, R.C. Inter-daily variability of a strong thermally-driven wind system over the Atacama Desert of South America: synoptic forcing and short-term predictability using the GFS global model. Theor Appl Climatol 121, 211–223 (2015). https://doi.org/10.1007/s00704-014-1231-y
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DOI: https://doi.org/10.1007/s00704-014-1231-y