IANIGLA   20881
INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Contrasting precipitation and temperature patterns in the Southern Andes related to the recent shift in the Antarctic Oscillation Index
Autor/es:
RIVERA, J.; MASIOKAS, M.H.; VILLALBA, R.; SRUR, A.M.
Reunión:
Conferencia; Climate Impacts on Glaciers and Biosphere in Fuego-Patagonia; 2017
Resumen:
The Southern Annular Mode (SAM), also known as the Antarctic Oscillation (AAO), describes the north?south movement of the westerly wind belt that circles Antarctica, dominating the middle to higher latitudes of the Southern Hemisphere. The changing position of the westerly wind belt influences the strength and position of cold fronts and mid-latitude storm systems, and is an important driver of temperature and precipitation variability in southern South America. In a positive SAM event, the belt of strong westerly winds contracts towards Antarctica. This results in weaker than normal westerly winds and higher pressures over southern South America, restricting the penetration of cold fronts inland. Conversely, a negative SAM event reflects an expansion of the belt of strong westerly winds towards the equator. This shift in the westerly winds results in more frequent storms and low pressure systems over southern South America. Although the influence of SAM on American climate is well accepted by the scientific community, the temporal and spatial patterns of temperature and precipitation associated with SAM in the southern tip of South America have not been clearly defined. This lack of precision is due to numerous factors including the lack of extensive and homogeneous climate records in Patagonia and the seasonal nature of SAM-climate relations in the southernmost region of South America. Marked changes in the Antarctic Oscillation Index (SAM) have recently been recorded. Following persistent positive trends since early 2014, an abrupt shift to negative SAM values occurred in October-November 2016 and persisted to early February 2017. Based on the SAM-Marshal Index, January values varied from +3.13 in 2016 to -1.12 in 2017. This contrasting shift provides a good opportunity to determine the temperature and precipitation variations across southern Patagonia associated with SAM phases. We recorded substantial changes in January temperatures between 2016 (warm) and 2017 (cool) over the Andes between 45° and 49°S. At Cochrane, a difference of 3.9°C was recorded between mean January temperatures in 2016 and 2017. Differences were lower to the south (0.6° and 0.2°C at Punta Arenas and Ushuaia, respectively) and in eastern directions, where opposite trends between January 2016 (cool) and 2017 (warm) were recorded at San Julian (-0.4°C) and C. Rivadavia (-0.3°C) on the Atlantic coast. Recorded changes in precipitation were also larger across the southern Andes. Extremely drier conditions in January 2016 contrast with abundant rainfalls during January 2017. On the eastern side of the Southern Patagonian Icefield, rainfall in January 2017 was ten times greater than in January 2016. At C. Masilla and Villa O?Higgins, January rainfalls varied from 5.6 to 110.1mm and 7.9 to 108.3 mm, for January 2016 and 2017, respectively. This rainfall pattern extended north at least to 46°S, where total January precipitations at Balmaceda of 0.2mm in 2016 contrast with 57 mm in 2017. These changes in precipitation decreased comparatively to the south. At Puerto Natales, January precipitation in 2017 (38.2 mm) was approximately three times larger than during the same month in 2016 (12.5 mm) and less than double farther south at Puerto Williams in Tierra del Fuego (51.6 and 90.6 in January 2016 and 2017, respectively). We emphasize the need to precisely document the temperature and precipitation changes related to SAM across southern South America to properly identify the spatial patterns of climate variability associated with this major mode of climate variability at high latitudes in the Southern Hemisphere.