Gulf Stream warm surges: Thermal anomalies resulting from cold core ring interactions

Abstract

Observations from thermal satellite imagery reveal a thermal anomaly pattern in the sea surface temperature (SST) field of the Gulf Stream downstream of Cape Hatteras which is a direct result of Gulf Stream‐eddy interactions upstream of Cape Hatteras. The general sequence of events observed in the images is as follows: (1) Detrainment of Gulf Stream surface water occurs as a result of an interaction with a cold core ring; (2) downstream of the interaction the Gulf Stream's SST decreases several degrees over a few days owing to the loss of the upstream surface flow; (3) a visible “jet” of warm surface water is advected down the major axis of the Gulf Stream after the stream‐ring interaction subsides and the detrainment diminishes. The jet maintains a 1–3°C temperature difference with the surrounding Gulf Stream water as it propagates downstream. This paired cooling/warming process is labeled a “warm surge event” because the sharp leading edge of the warm jet (i.e., the surge) is easily detectable in the satellite images, while the anomalous surface cooling preceding the passage of the warm jet is difficult to observe. Vertical profiles of temperature, downstream velocity, and cross‐stream velocity all indicate that the upper 100–150 m of the Gulf Stream are significantly altered during an event. Satellite and in situ data also indicate that just downstream of the interaction there is enhanced entrainment of Sargasso Sea surface waters into the Gulf Stream to replenish the detrained Gulf Stream water.