El Niño-Southern Oscillation (ENSO) is a periodic climate pattern in the Pacific Ocean that can have consequences on fisheries in South America and bring cooler, wetter conditions to the U.S. Southwest and drought to countries in Indonesia and Australia. However, not all El Niño events are equal in strength, and their impacts on the globe can vary largely.

In the last 30 years, there have been 2 extreme El Niño events: in 1997/98 and 2015/16. Earlier this year, bursts of high sea level, called Kelvin waves, traveled along the equator towards South America. These waves typically precede an El Niño event, signaling this year’s event. The impact of this year's El Niño on sea levels is notably milder compared to the two previous significant events. Although there is a level of uncertainty, it is essential to monitor the ongoing developments in the coming months, especially given the abnormal high global sea surface temperatures this year. Observing how the situation unfolds will be crucial in understanding the long-term effects.

Sea surface height (SSH) data from satellite missions such as the Sentinel-6 Michael Freilich mission helps us study and understand the complex interactions between the ocean and the atmosphere that affect global weather and climate such as El Niño. SSH data can help to monitor El Niño events because when the water warms up (which is the case during El Niño), it expands, causing sea level to rise.

Figure 1 shows sea level anomalies (SLA) measurements from the TOPEX/Poseidon, Jason-3, and Sentinel-6 Michael Freilich missions in the beginning of October 1997, 2015, and 2023, respectively. During these three events, warm water (and higher sea levels) build up along the west coast of South America (orange, red and white). Sea levels in October 1997 and 2015 were much higher (15-20 cm) and spread over a much larger area than in 2023. Also, cold waters (lower sea levels; blue and purple) in the western equatorial Pacific Ocean are not as deep in 2023 as in the 1997 or 2015 events.

Figure 2 shows the El Niño sea level-based index developed by Hamlington et al. (2019). It confirms that this year’s event’s effect on sea level is much more modest than in 1997 or 2015 as of October. This year, El Niño’s global impact may not be as far reaching or long lasting as in 1997 or 2015. Instruments and satellites such as Sentinel-6 Michael Freilich will help to continue monitoring ocean conditions in the Pacific in the next months.

Each year, the NASA Ocean Surface Topography Science Team Meeting gathers scientists and engineers from both Europe and the United States who are engaged in altimetry missions like Sentinel-6 Michael Freilich. This year’s meeting will be in San Juan, Puerto Rico from November 7 to November 11, 2023. Over the course of the week, scientists will present findings enabled by altimetry, covering topics such as El Niño, sea level rise, hurricane intensification, ocean circulation, and more. Additionally, engineers will engage in discussion regarding the calibration, validation, performances of the instruments aboard the satellites such as the Sentinel-6 Michael Freilich.