The Role of Buoy and Argo Observations in Two SST Analyses in the Global and Tropical Pacific Oceans

The monthly Extended Reconstructed Sea Surface Temperature version 5 (ERSSTv5) and Daily Optimum Interpolation Sea Surface Temperature version 2 (DOISST) are frequently used for El Nino, La Nina, and Southern Oscillation (ENSO) monitoring and assessment. ERSSTv5 uses in situ observations from ships, buoys, and Argo floats. DOISST uses observations from ships, buoys, and satellites, while biases of satellite observations are corrected according to in situ observations. Therefore, in situ observations (both number and area coverage) are critical to these sea surface temperature (SST) analyses.

Relative roles of buoy and Argo observations on two sea surface temperature (SST) analyses are studied in the global and tropical Pacific oceans over 2000–16 using monthly Extended Reconstructed SST version 5 (ERSSTv5) and Daily Optimum Interpolation SST version 2 (DOISST). Experiments show an overall higher impact by buoys than Argo floats over the global oceans and an increasing impact by Argo floats in recent years. Impact by Argo floats is generally larger on the Southern Hemisphere than on the Northern Hemisphere. Impact on trends and anomalies of globally averaged SST by either one, when the other is used, is small in recent years. The warming trend over 2000–16 remains significant by including either buoys or Argo floats or both.

In the tropical Pacific, impact by buoys is large over 2000–2005 when the number of Argo floats was low, and becomes smaller over 2010–2016 when the number and area coverage of Argo floats increased. Magnitude of El Niño and La Niña decreases when observations from buoys, Argo floats, or both are excluded. Impact by the Tropical Atmosphere Ocean (TAO) and Triangle Trans-Ocean Buoy Network (TRITON) is small in normal years and during El Niño events. Impact by TAO/TRITON buoys on La Niña events is small when Argo floats are included in the analysis systems, and large when Argo floats are not included. The reason for the different impact on El Niño and La Niña events is that the drifting buoys are more dispersed from the Equatorial Pacific region by stronger trade winds during La Niña events.