IANIGLA   20881
INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
A seven-year synoptic climatology of heavy winter orographic precipitation events over the subtropical central Andes (30¨¬-37¨¬S).
Autor/es:
MAXIMILIANO VIALE; FEDERICO AUGUSTO NORTE; MARIO NESTOR NUÑEZ
Lugar:
Centro de Ingeniería de la Innovación y Facultad de Ciencias Forestales y Recursos Naturales, Universidad Austral de Chile, Valdivia, Chile.
Reunión:
Simposio; II Internacional Symposium ¡°Reconstructing Climate Variation in South America and the Antartic Peninsula over the last 2000 years¡±; 2010
Institución organizadora:
PAGES 2010
Resumen:
ABSTRACT
This study investigates the synoptic conditions during the 46 heaviest winter (Apr-Sep)
orographic precipitation events from 1970 to 1976 over the Central Andes (30¨¬-37¨¬S). Four to
five heavy winter events account for most (~70%) of the winter total precipitation, which in
turn represents more than 90% of the total annual precipitation. Consequently, heavy
orographic precipitation events play a crucial role in the regional water cycle on central Chile
and central-western Argentina, supplying water and generating in some cases floods,
avalanches and road blocking. Based on the ERA-40 reanalysis and rawinsonde data, the
dominant and key pattern for these events was a long (>2000km) and narrow (<1000km)
plume of large Integrated Water Vapor (IWV) with strong low-level northwesterly winds, along
the cold-front surface in the warm sector of extratropical cyclones moving eastward over the
Pacific Ocean. These IWV plumes, called ¡°atmospheric river¡± in previous studies on the
western coast of North America, made landfall on south-western South America discharging
large water vapor amounts as precipitation over the Andes by orographic lifting mechanisms.
Moisture flux and IWV fields of two sub-groups of 46 heavy precipitation events revealed that
extreme (i.e., daily precipitation into the 95%-100% percentile) and intense events (i.e., into
the 75%-95% percentile) were associated with atmospheric rivers in 91% and 75% of the
cases, respectively. Consistently, anomalous low-level northwesterly winds predominated in
heavy events, exceeding 2¥ò from winter climatology in 70% of 46 cases. Deeper cyclones
and stronger atmospheric rivers against the Andes occurred with extreme than intense
events, suggesting more accentuated upslope moisture flux raining out over the mountains.
The results of this study indicate that atmospheric rivers greatly modulate winter
precipitations over the subtropical central Andes.