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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

Jacques-Coper, Martín ; Falvey, Mark ; Muñoz, Ricardo

In: Theoretical and Applied Climatology, 2015, vol. 121, no. 1-2, p. 211-223

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    Titel
    • 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
    Autor
    • Jacques-Coper, Martín. Oeschger Centre for Climate Change Research and Institute of Geography, University of Bern, Hallerstrasse 12, 3012, Bern, Switzerland
    • Falvey, Mark. Departamento de Geofísica, Universidad de Chile, Av. Blanco Encalada, 2002, Santiago, Chile
    • Muñoz, Ricardo. Departamento de Geofísica, Universidad de Chile, Av. Blanco Encalada, 2002, Santiago, Chile
    Dokumententyp
    • Postprint
    Sprache
    • Englisch
    Veröffentlicht in
    • Theoretical and Applied Climatology, 2015, vol. 121, no. 1-2, p. 211-223. Springer Vienna
    Andere elektronische Ausgabe
    Klassifikation
    • Erdwissenschaften
    OAI-PMH-ID
    • oai:doc.rero.ch:332261
    Summary
    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 2years of measurement data from the Sierra Gorda 80-m meteorological mast (SGO, 22° 56′ 24″ S; 69° 7′ 58″ W, 2,069m 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 8m/s (13m/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 800hPa do show the diurnal and nocturnal phases, observations at 80m 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.