Seasonal Changes in Satellite-Derived Coastal Ocean Fields - Variability in the Timing of the Transitions (Phenology)
Strub, P. Ted; James, Corinne
Oregon State University, UNITED STATES
Satellite fields allow us to look at seasonal changes in wind-forcing and response in coastal ocean regions. In particular, we characterize the annual cycles along the U.S. west coast of wind stress, wind stress curl, sea surface height (SSH), sea surface temperature (SST) and surface chlorophyll-a concentrations (CHL). Annual cycles are traditionally defined by averages of the calendar months if the time series are long enough or by harmonic analysis for shorter records. These methods determine ''stationary'' seasonal cycles, whereas the timing of seasonal transitions vary from year to year. Here we explore methods that define seasonal cycles but allow variability in the transition dates of each year, comparing simple approaches such as band pass filters to more complex methods such as cyclostationary EOFs. In strongly wind-driven coastal ocean systems, many studies have used wind forcing from meteorological buoys and SSH from tide gauges to examine the timing of upwelling and downwelling. Changes in buoy SST and the appearance of chlorophyll blooms also serve to indicate seasonal transitions. Where there are no instruments to collect field data, satellite data must be used. Advances in bringing satellite data closer to the coast (especially altimeter SSH and scatterometer wind fields) will be evaluated within the context of methods used to define seasonal cycles with variable transition dates.