Dry season circulation‐type classification applied to precipitation and temperature in the Peruvian Andes

• Published in: International journal of climatology 2020-12, Vol.40 (15), p.6473-6491
• Main Authors: Bonshoms, Martí, Álvarez‐Garcia, Francisco J., Ubeda, Jose, Cabos, William, Quispe, Kelita, Liguori, Giovanni
• Format: Article
• Language: English
• Subjects: Andes; Anomalies; Circulation types; Classification; Cloud cover; Cloudiness; Clustering; Daily; Dry season; Dynamic height; El Nino; El Nino phenomena; Geopotential; Geopotential height; k‐means; La Nina; Low temperature; Mean daily temperatures; Mean temperatures; Minimum temperatures; Precipitation; Rain; Rainfall; Rainy season; Seasons; Southern Oscillation; Temperature; Temperature effects; Tropical circulation; Tropical climate; tropics; Wet season
• ISSN: 0899-8418; 1097-0088
• DOI: 10.1002/joc.6593

We present the first systematic classification of circulation regimes that characterize the Tropical Andes during the dry season (May–August). We apply the hierarchical k‐means clustering method to ERA‐Interim reanalysis data of daily mean geopotential height at 500‐ and 200‐hPa levels for the period 1981–2015. Specifically, by combining the variability in intensity and location of geopotential anomalies we identify 12 circulation types (CTs). We then establish the relationship between the CTs and surface conditions in the Peruvian Andes (PA) analysing high‐resolution gridded datasets of daily mean temperature and rainfall. Our results indicate that intense precipitations and low minimum temperatures are often associated with an Upper Tropospheric Trough (UTT) centred at subtropical latitudes (~30°S) and between 80° and 70°W of longitude. Moreover, drier and warmer conditions across the entire PA region are largely associated with three anticyclonic CTs. Strong negative anomalies in daily maximum (minimum) temperatures can be related to the effect of day (night) cloudiness in the radiative balance, but also to subtropical cold air advections favoured by the UTT. While CTs featuring warmer (colder) conditions have become more (less) frequent in the last decades of the record, there is no systematic link between positive or negative trends in occurrence and the wetter and drier character of the CTs. The annual frequencies of 10 CTs are significantly correlated with El Niño‐Southern Oscillation, with warmer and drier (cooler and wetter) CTs generally preceded by an El Niño (La Niña) in the previous wet season. This study presents the first circulation‐type classification focussed on the Tropical Andes during the dry season for the 1981–2015. An objective technique has been applied to Z500 and Z200 ERA‐Interim daily geopotential height data, identifying 12 circulation types (CTs). Relevant impacts on daily precipitation and extreme temperature over the Peruvian Andes have been found. A significant correlation between El Niño‐Southern Oscillation and upper‐level CTs, confirm their potential impacts on tropical Andes climatic conditions, also in the dry season.