title: Salinity anomaly as a trigger for ENSO events.
abstract: According to the classical theories of ENSO, subsurface anomalies in ocean thermal structure are precursors for ENSO events and their initial specification is essential for skillful ENSO forecast. Although ocean salinity in the tropical Pacific (particularly in the western Pacific warm pool) can vary in response to El Niño events, its effect on ENSO evolution and forecasts of ENSO has been less explored. Here we present evidence that, in addition to the passive response, salinity variability may also play an active role in ENSO evolution, and thus important in forecasting El Niño events. By comparing two forecast experiments in which the interannually variability of salinity in the ocean initial states is either included or excluded, the salinity variability is shown to be essential to correctly forecast the 2007/08 La Niña starting from April 2007. With realistic salinity initial states, the tendency to decay of the subsurface cold condition during the spring and early summer 2007 was interrupted by positive salinity anomalies in the upper central Pacific, which working together with the Bjerknes positive feedback, contributed to the development of the La Niña event. Our study suggests that ENSO forecasts will benefit from more accurate salinity observations with large-scale spatial coverage.
authors.affiliation: Center for Ocean-Land-Atmosphere Studies, George Mason University, Fairfax, Virginia, USA.
authors.forename: Jieshun
authors.initials: J
authors.lastname: Zhu
authors.affiliation: 1] Center for Ocean-Land-Atmosphere Studies, George Mason University, Fairfax, Virginia, USA [2] Department of Atmospheric, Oceanic, and Earth Sciences, College of Science, George Mason University, Fairfax, Virginia, USA.
authors.forename: Bohua
authors.initials: B
authors.lastname: Huang
authors.affiliation: Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.
authors.forename: Rong-Hua
authors.initials: RH
authors.lastname: Zhang
authors.affiliation: Climate Prediction Center, National Centers for Environmental Prediction/NOAA, College Park, Maryland, USA.
authors.forename: Zeng-Zhen
authors.initials: ZZ
authors.lastname: Hu
authors.affiliation: Climate Prediction Center, National Centers for Environmental Prediction/NOAA, College Park, Maryland, USA.
authors.forename: Arun
authors.initials: A
authors.lastname: Kumar
authors.affiliation: European Centre for Medium-Range Weather Forecasts, Reading, United Kingdom.
authors.forename: Magdalena A
authors.initials: MA
authors.lastname: Balmaseda
authors.affiliation: Center for Ocean-Land-Atmosphere Studies, George Mason University, Fairfax, Virginia, USA.
authors.forename: Lawrence
authors.initials: L
authors.lastname: Marx
authors.affiliation: 1] Center for Ocean-Land-Atmosphere Studies, George Mason University, Fairfax, Virginia, USA [2] Department of Atmospheric, Oceanic, and Earth Sciences, College of Science, George Mason University, Fairfax, Virginia, USA.
authors.forename: James L
authors.initials: JL
authors.lastname: Kinter