Summer heat waves in southeastern Patagonia: an analysis of the intraseasonal timescale

Abstract

We explore the occurrence of intraseasonal summer heat waves in southeastern Patagonia (SEPG, 46∘ –52∘S; 65∘ –70∘W) since the late 19th century by means of the Twentieth Century Reanalysis version 2 (20CRv2). In total, we identify 201 cases for 1872–2010 using criteria of intensity and persistence. In SEPG, the corresponding intraseasonal temperature signals are centred around the first day of each cluster of days fulfilling those conditions (named day 0). The mean warm deviation lasts for approximately 2 weeks and exhibits a mean temperature peak of 4.3 ∘C on day 0 (the warmest day in the mean signal). In a regional context, the mean temperature perturbation associated with these heat waves affects a broad area on both sides of the Andes. The warming in SEPG is caused by temperature advection and enhanced radiative heating, following a high pressure system over southern South America (SSA). This atmospheric perturbation is embedded in a wave-train-like pattern along the South Pacific. As part of this pattern, a cyclonic anomaly progresses eastward over the Tasman Sea in Oceania, moving from southeastern Australia (day −6, causing a dry anomaly there) over New Zealand (day −3, inducing a wet anomaly on its Southern Island). The anomalous circulation triggered by the wave train leads thus to a teleconnection between SSA and Oceania, documented in a previous work for the interannual scale. Two thirds of the heat wave events are linked to enhanced ascent in the South Atlantic Convergence Zone (SACZ) and around one third of the events within 1957–2010 are associated with extreme absolute maximum temperatures observed at a station-based record from SEPG. Finally, possible spatial modulations of the wave train pattern at the interannual and interdecadal timescales are discussed.