Sea surface temperature

Sea surface temperature (SST) is the water temperature at or near the ocean surface (typically the upper 1-10 m). It is one of the most important boundary conditions for the atmosphere, governing energy and moisture exchange at the air-sea interface.

Role in climate

SST controls several fundamental atmospheric processes:

1. Surface energy fluxes: Warmer SSTs increase latent and sensible heat flux to the atmosphere, providing energy and moisture for convective systems. The Clausius-Clapeyron relation dictates that saturation vapor pressure increases approximately 7% per degree of warming.

2. Atmospheric stability: The temperature contrast between the ocean surface and the overlying air determines the stability of the marine boundary layer. Cool SSTs (as in the Galapagos Cold Pool) promote a stable, well-mixed boundary layer capped by a temperature inversion, favoring stratocumulus clouds. Warm SSTs destabilize the column and promote deep convection.

3. Precipitation: SST is a primary control on Precipitation patterns in the tropics. Schneider et al. (2025, Geophys. Res. Lett.) showed that local SST variability directly modulates the occurrence of heavy rainfall events in the Galapagos.

4. Large-scale circulation: Spatial gradients in SST drive atmospheric pressure gradients that shape the Walker and Hadley circulations. ENSO is fundamentally an oscillation in equatorial Pacific SST patterns.

Measurement

SST is measured through:

• In situ: Ship intake thermometers, moored and drifting buoys (e.g., the TAO/TRITON array in the tropical Pacific)
• Satellite: Infrared and microwave radiometers provide global SST fields. Infrared sensors have higher spatial resolution but are obscured by clouds; microwave sensors penetrate clouds but at coarser resolution.
• Reanalysis: Products like ERA5 assimilate both in situ and satellite observations to produce gridded SST fields.

SST and the Galapagos

In the Galapagos, SST is the primary driver of the seasonal and interannual climate cycle:

• During the Garua season, cold upwelling from the Pacific Equatorial Undercurrent reduces SSTs, stabilizing the atmosphere and producing fog and stratocumulus
• During the hot season, SSTs rise and promote convective Precipitation
• El Nino events can substantially elevate SSTs relative to background conditions, shifting the precipitation regime
• Local SST anomalies summarized by GReNI are especially informative for rainfall extremes in the archipelago

The DARWIN project climate analysis used dynamically downscaled ERA5 data to capture the SST-driven atmospheric response at meso-scale resolution over the archipelago.

See also: El Nino-Southern Oscillation, Galapagos Cold Pool, Precipitation, Temperature inversion, Thermocline