Summary

NASA and European partners are using the Sentinel-6 Michael Freilich and Sentinel-6B satellites to measure sea level, waves and atmospheric conditions during El Niño. The observations are being prepared for hurricane forecasting models that estimate how quickly storms may intensify.

NASA and its European partners are using two Sentinel-6 satellites to observe the ocean during an El Niño that oceanographers expect to be unusually significant. The spacecraft are measuring sea-surface height, waves, marine wind speed and atmospheric conditions—data that can improve estimates of how quickly hurricanes will strengthen.

Sentinel-6B was launched last November and now flies about 30 seconds behind Sentinel-6 Michael Freilich. Together, they form the Copernicus Sentinel-6/Jason-CS mission, an international programme designed to maintain highly precise measurements of Earth's changing seas.

Contents

What the satellites measure

Each Sentinel-6 spacecraft carries a radar altimeter. It sends thousands of radar pulses per second toward the ocean and measures their reflections from wave crests and troughs. This provides measurements of ocean height, wave size and marine wind speed.

Sea-surface height is particularly useful for estimating ocean heat. Warm water expands, so areas with greater sea height can indicate where more heat is stored in the upper ocean. That heat can supply energy to tropical storms and influence how rapidly they intensify.

The satellites also carry a Global Navigation Satellite System–Radio Occultation instrument, or GNSS-RO. It measures atmospheric properties including humidity, pressure and temperature. These observations complement the ocean measurements by describing conditions in the atmosphere through which storms develop.

The satellites are collecting these measurements during an El Niño, a naturally occurring climate pattern in which warmer-than-usual Pacific waters shift global weather patterns. During the event, weakened westward winds allow heat to spread eastward toward South America. The resulting redistribution of ocean heat can alter rainfall, storms and the balance of hurricane activity between the Atlantic and Pacific.

How ocean measurements support hurricane forecasts

Sentinel-6B began delivering low-latency data to scientists on July 15. The data must first be incorporated into the research and forecasting models used by meteorologists and climate scientists. Deirdre Byrne, an oceanographer and altimetry expert at NOAA, plans to begin adding the satellite ocean-height observations to NOAA's Satellite Ocean Heat Content Suite algorithm by the end of the year.

That algorithm has operated since 2012 and is used in hurricane tracking. Better information about heat stored in the ocean can help forecasters estimate both the amount and the rate of storm intensification. This is important because a tropical storm can take a week or more to reach hurricane strength and a coastline, while a hurricane can intensify rapidly during the 48 hours before landfall.

Forecast outputs can support decisions such as placing sandbags, mobilising emergency organisations and issuing evacuation orders. The satellite observations are therefore an upstream input to those decisions rather than a replacement for the forecasting models and agencies that interpret them.

A continuous record of changing seas

The Sentinel-6 mission also extends a precise record of global sea-level observations that began with the TOPEX/Poseidon mission in 1992. The record has continued through Sentinel-6 Michael Freilich, allowing scientists to compare measurements collected over more than three decades using consistent methods.

Sentinel-6B is scheduled to take over as the reference satellite for global sea-level measurements later this year. Maintaining that continuity matters because long-term changes are easier to detect when measurements are collected in the same way over time.

The mission was jointly developed by ESA, EUMETSAT, NASA and NOAA, with funding support from the European Commission and technical performance support from France's CNES. EUMETSAT handles spacecraft monitoring, control and processing of the altimeter science data on behalf of the European Union's Copernicus programme.

Sources