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A Climate Story NASA SATELLITES SHED LIGHT ON the delicate balance between OUR PLANET'S OCEAN & ATMOSPHERE

Time Will Tell

Climate is the prevailing condition that you plan for. Weather is what you get. The difference between the two is simply time. For decades, weather satellites have helped us plan our days' activities. Collecting and analyzing these data over time has resulted in more accurate weather forecasts. Similarly, predicting climate involves long-term studies of Earth's interconnected ocean and atmosphere system.

Pioneer Days

NASA launches in 1978 set the stage for future ocean research. SeaSat (left) only operated for 110 days but served as a proof of concept for several types of ocean sensors, including those that monitor winds, currents, and sea level. Nimbus-7 (right) included the Coastal Zone Color Scanner, which proved that ocean color could be measured from space.
In 1982, Landsat-4 (left) carried the first Thematic Mapper (TM). Scientists used TM data to derive the characteristics of tiny particles suspended in our atmosphere, known as "aerosols." The first Advanced Very High-Resolution Radiometer (AVHRR) capable of studying aerosols and clouds was launched around this time. Since then, AVHRR has been included on a long series of polar-orbiting satellites (right) operated by the National Oceanic and Atmospheric Administration (NOAA).

These research-and-development (R&D) satellites paved the way for today's – and tomorrow's – observations of our ocean, aerosols, and clouds.

From R&D to Climate Studies

Over two decades later, in 2005, NASA's Earth-observing fleet had grown in size and scope. Dedicated ocean satellites observed color (SeaWiFS), sea level (TOPEX, Jason-1) and winds (QuikSCAT). Continuing measurements that began with Nimbus-7, atmospheric ozone was being monitored by Aura and the Total Ozone Mapping Spectrometer - Earth Probe (TOMS-EP) satellite. Aerosol and cloud research was fueled by imager data from the Moderate-resolution Imaging Spectroradiometer (MODIS) on the Earth Observing System Aqua and Terra satellites, along with Terra's Multi-angle Imaging SpectroRadiometer (MISR).

Climate Data Continuity

Comparing NASA's 2005 and current fleet of Earth satellites tells the story of persistence and change. Veteran sensors have been joined by newer active-sensor orbiters such as CloudSat and CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations), which are used to study the effects of clouds and aerosols on climate and weather. The MODIS imager was the pathfinder sensor for the new Visible/Infrared Imager and Radiometer Suite (VIIRS) on Suomi-NPP that will also fly on future NOAA operational polar orbiting satellites.

Significant to understanding climate, MODIS instruments on Terra and Aqua have provided over 15 years of data on aerosol and cloud properties while extending ocean color records beyond 2 decades. Efforts have begun to extend NASA records into the VIIRS era.

Ocean-Aerosols-Clouds

What's the connection?

Let's begin to answer this complicated question with one example of a sequence of events...

Stronger winds...

... stir larger ocean waves...

... releasing more aerosols such as sea salt from the ocean into the air...

... creating "cloud condensation nuclei," which produce more droplets that, in turn, can change cloud properties.

Some aerosols in the atmosphere have a chemical composition that can trigger water droplet formation that eventually creates clouds. In fact, without such aerosols, clouds would not form.

Sea salt is not the only type of aerosol emitted from the ocean surface. Microscopic ocean plants and algae, known as phytoplankton, can also produce organic compounds that seed cloud formation.

Aerosols both leave and enter our seas, adding complexity to another example ocean-cloud story...

Stronger winds...

... blow more dust over the ocean...

... supplying nutrients such as iron for phytoplankton growth...

... fueling larger phytoplankton blooms...

... potentially creating aerosols that produce more cloud droplets.

These ocean-based scenarios involve atmospheric aerosols and cloud formation, two variables that create the most uncertainty about how future climate change will unfold.

Why?

Low clouds predominantly reflect the sun’s rays to cool Earth's surface...

... while high thin clouds predominantly trap outgoing heat that would otherwise be emitted to space.

Likewise, some aerosols scatter light and cause a cooling effect...

... while others absorb light and cause a heating effect.

The connections between aerosols and clouds are more complicated still. For example, interactions in which cloud drops form on aerosols - and aerosols are themselves washed out of the air by rain - are not well understood and indeed may depend on the types of clouds and aerosols involved.

Aerosols and clouds are complex but critical pieces of the climate puzzle, so researchers are working to understand their interactions with each other and Earth's ocean, as well.

To predict climate, we need to continue monitoring Earth's ocean-aerosols-cloud system with ever-improving technologies that address:

  • What are the long-term changes in aerosol and cloud properties that can continue to be revealed by satellites? How are these changing properties interconnected with variations in climate?
  • How do aerosols influence ocean ecosystems and cycling of matter in our ocean? Conversely, how do ocean processes affect our atmosphere?

These questions will be tackled by the PACE satellite, scheduled to join NASA's Earth Observation Fleet in 2022.

References

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