No abstract

The physical processes driving the wind intensification in a coastal band of ~100 km off Peru during the intense 1997-1998 El Niño (EN) event were studied using a regional atmospheric model. A simulation performed for the period 1994-2000 reproduced the coastal wind response to local sea surface temperature (SST) forcing and large scale atmospheric conditions. The model, evaluated with satellite data, represented well the intensity, seasonal and interannual variability of alongshore (i.e. NW-SE) winds. An alongshore momentum budget showed that the pressure gradient was the dominant force driving the surface wind acceleration. The pressure gradient tended to accelerate the coastal wind, while turbulent vertical mixing decelerated it. A quasilinear relation between surface wind and pressure gradient anomalies was found. Alongshore pressure gradient anomalies were caused by a greater increase in near-surface air temperature off the northern coast than off the southern coast, associated with the inhomogeneous SST warming. Vertical profiles of wind, mixing coefficient, and momentum trends showed that the surface wind intensification was not caused by the increase of turbulence in the planetary boundary layer. Moreover, the temperature inversion in the vertical mitigated the development of pressure gradient due to air convection during part of the event. Sensitivity experiments allowed to isolate the respective impacts of the local SST forcing and large scale condition on the coastal wind intensification. It was primarily driven by the local SST forcing whereas large scale variability associated with the South Pacific Anticyclone modulated its effects. Examination of other EN events using reanalysis data confirmed that intensifications of alongshore wind off Peru were associated with SST alongshore gradient anomalies, as during the 1997-1998 event.

A Peruvian Coastal Thermal Index (PCTI) was developed from 1982 to 2014 for the detection and forecasting of warm and cold periods off Peru. It showed differences in thermal conditions between the Peruvian Upwelling Ecosystem (PUE) and the Equatorial Pacific Ocean usually monitored by the Oceanic Niño Index (ONI). This index represented 87.7% of the total variation of the sea surface temperature anomalies on the PUE.

El Ecosistema de Afloramiento Peruano (EAP) es frecuentemente perturbado por el arribo de las Ondas Kelvin de hundimiento en el Pacifico Ecuatorial Oriental, ocasionando efectos en el ecosistema marino y la hidrología frente al Perú. Este trabajo tiene como objetivo comparar las propagaciones de las Ondas Kelvin Ecuatoriales (OKE) durante El Niño 2015-2016 y El Niño Costero 2017 (ENC 2017) frente a Perú, usando modelos de simulación y datos observacionales. Los resultados muestran que durante El Niño 2015-2016, se propagaron siete OKEs de hundimiento (modo 1), de las cuales seis de ellas se propagaron como ondas atrapadas a la costa de hundimiento, mientras que durante la ocurrencia de ENC 2017 frente al Perú, se propagó una OKE de hundimiento (modo 1). Así, mientras que las OKEs de hundimiento jugaron un papel clave en el inicio y desarrollo del calentamiento asociado al evento EN 2015-2016 frente al Perú, para ENC 2017 su rol fue secundario, contribuyendo a extender el calentamiento, ya iniciado por otros procesos.