Evidence for a modulation by the Madden-Julian Oscillation of the intraseasonal summer temperature in Eastern Patagonia.

JACQUES-COPER M.; BRONNIMANN, S.; MARTIUS, C.; VERA, C. ; CERNE, S. BIBIANA

JOURNAL OF GEOPHYSICAL RESEARCH

AMER GEOPHYSICAL UNION

Lugar: Washington; Año: 2015 vol. 120 p. 7340 - 7357

0148-0227

We describe the relationship between the intraseasonal component of surface air temperature(SAT) variability in Eastern Patagonia and the Madden-Julian Oscillation (MJO) during austral summer basedon ~50 years of daily instrumental records, the Twentieth Century Reanalysis, and a century-long MJOindex reconstruction. Our results show that the summer SAT variability in Patagonia is highly driven by theintraseasonal activity (~80%), especially by that associated with the MJO. The active MJO phases modulatethe spatial mean intraseasonal temperature signal in Eastern Patagonia with ~1.5°C of amplitude. In most ofthe region, the warmest (coldest) conditions are found during active phase 8 (4). These opposite states of thetemperature perturbations are related to almost inverse midlevel circulation anomalies over southern SouthAmerica and the southwest Atlantic, which are part of a large-scale Rossby-like wave train of alternatingcirculation anomalies extended along the South Pacific. The corresponding outgoing longwave radiationanomalies suggest that these structuresmay be triggered by anomalous convection in the tropics. Furthermore,we show that intraseasonal heat waves in southeastern Patagonia tend to occur during active MJO phase 8.These events are also induced by a wave train pattern over the South Pacific, associated with other intraseasonalvariability sources. Hence, as shown in a case study, circulation anomalies over the South Pacific triggered, ingeneral, by tropical convection variability and, in particular, by theMJO activitymay constructively interact withcirculation patterns resulting fromthe extratropical dynamics, eventually leading to intraseasonal heat waves insoutheastern Patagonia.