Seasonal to interannual variations of wind forcing in the Peruvian upwelling system

The Humboldt (Peruvian) Upwelling System (HUS) is the most productive among the main Eastern Boundary Upwelling Systems (EBUS), namely California, North West Africa, Benguela and itself. In spite of comparable upwelling intensity its fisheries production exceeds that of the other upwelling systems considerably (Chavez and Messie 2009). Wind is the major driving force of the coastal and curl driven upwelling, that controlls the nutrient supply from the deep water pool to the euphotic surface layer. Strength, spatial and temporal variability of the wind forcing are subjected to seasonal and interannual changes. The core of this study is describe the wind driven upwelling cells in the Peruvian coastal area in detail using long-term data which is not well understood. A better understanding of the state and dynamics of HUS seems essential for fututre regional climate predictions. ASCAT wind stress data for the period of 11 years (2008-2018) is analyzed to assess the spatio-temporal variations of the wind stress field, coastal upwelling and Ekman pumping along the Peruvian coast. The meridional component of wind stress off the peruvian coast, which is the main driver of offshore transport, has been marginally inensified over the entire priod. However, a high level of interannual variability is evident. The El-Niño years show anomalously high wind stress and associated Ekman transoprt. Our results indicate that the southern sector is more influenced by ENSO cycle than the northern sector. Additionally, a strong seasonality in the wind stress is observed. During the austral summer (December-February) the wind stress show the minimum value while the high values are observed in July-September.