Intraseasonal Variability of the Gulf Stream Current: Physical Mechanisms and Connections to Atmospheric Forcing

Intraseasonal variability of ocean currents is a relatively new area of study. One major internal mode of atmospheric intraseasonal variability, the Madden-Julian Oscillation (MJO), modulates global tropospheric circulation on intraseasonal (30–45-day) time scales. Via its modulation of upper-troposphere Rossby Waves, the MJO has direct and indirect influences on many atmospheric features, including surface winds. Because the MJO is known to modulate surface wind speed and direction, the hypothesis tested in this study was that MJO would also modulate surface ocean currents in the Gulf Stream system off the U.S. southeast coast. To test this hypothesis, time-lagged composite anomalies of sea surface temperature (SST) and sea surface height (SSH) were created for each active phase of the MJO for the winter season. The SST anomalies were derived from the NASA Multi-scale Ultra-high Resolution Sea Surface Temperature (MUR SST) data product. The SSH anomalies were derived from the EU Copernicus Marine Environment Monitoring Service. Our analyses indicate that the position of the west and north walls of the Gulf Steam varies by phase of the MJO. To better understand physical mechanisms for these observed anomalies, atmospheric composite anomalies of upper-troposphere height, lower-troposphere height and wind, mean sea level pressure, and surface winds from the NASA MERRA reanalysis were also calculated for each active MJO phase for the winter season. Preliminary results indicate a link between wind forcing and the position of the Gulf Stream. To our knowledge, this is among the first studies attempting to connect surface ocean current variability in this region to the MJO. Thus, our study improves our understanding of atmosphere and upper-ocean processes on the intraseasonal time scale.