The Influence of ENSO on the North Pacific Ocean through Daily Weather Changes

During El Niño-Southern Oscillation (ENSO) events, enhanced convection in the equatorial Pacific creates a wave pattern over the Pacific-North America (PNA) region. The associated changes in winds, temperatures, and moisture foster atmospheric forcing on the North Pacific Ocean, which induce sea surface temperature (SST) anomalies, especially during winter. This atmospheric connection between two ocean basins, termed the “atmospheric bridge”, has been well documented on seasonal and monthly time scales, so this research investigated the North Pacific Ocean’s response to the atmospheric bridge on daily time scales during two strong ENSO winters.

November through March of 1997-98 and 2015-16 were analyzed using daily Climate Forecast System Reanalysis (CFSR) anomaly data for sea level pressure, SSTs, surface wind, latent and sensible heat flux, sea level pressure, and 500mb geopotential height. The daily SST tendency was calculated throughout both seasons, since forcings affect the SST tendency directly.

Using a threshold of one standard deviation below the average daily SST tendency over both seasons, composites of the above variables were analyzed for days meeting this criterion. SST tendency had a particularly high dependency on latent heat flux. The days included in the composites accounted for 125.17% of the cooling that occurred over the 1997-98 season, whereas 69.82% of the cooling over the 2015-16 season occurred during days included in the composite, highlighting differences between ENSO events.