In anticipation of another CERES instrument launched onboard JPSS-1 (now scheduled for 4:47 am EST on November 15), I thought I’d share a little about CERES and why it’s so important to understanding our Earth – and how GLOBE observations fit into this science.
NASA’s CERES instrument, which stands for Cloud and the Earth’s Radiant Energy System, measures reflected sunlight and thermal infrared radiation emitted by the Earth. It measures the amount of energy leaving the Earth so we can compare this to the amount of energy entering the Earth. You may have seen a diagram like this before, which illustrates the Earth’s Energy Budget.
The basic idea is this - if our energy budget was balanced, the amount of energy leaving the Earth would be the same as the amount of energy entering the Earth. If we have more energy entering than leaving, then we would be unbalanced, leading to heating of our planet. If we have more energy leaving than entering, then we’d have a cooling planet. You can watch this video to learn more about how CERES monitors Earth’s energy: https://nasaeclips.arc.nasa.gov/video/ourworld/our-world-monitoring-the-earths-climate-with-ceres
It’s important to keep track of Earth’s energy budget over long periods of time so we accurately know if and how Earth’s energy budget is changing. Gaps in data lead to uncertainty and limits our ability to understand and predict global temperature changes. Luckily, NASA has been studying the energy budget of Earth since the 1980s with the launch of an instrument called ERBE, or Earth Radiation Budget Experiment.
That first ERBE instrument collected data from space for 15 years! A newer instrument design is CERES. We have multiple CERES instruments in space, one on board the Aqua, Terra, and Suomi NPP satellites. We also had one on the TRMM satellite (retired in 2015). Having multiple copies of the same instrument helps us validate, so have confidence in the data collected. After all, two pairs of eyes are better than one. The CERES family of instruments is the only instrument group in the world directly providing a global top-of-atmospheric energy budget data set!
So, I did call this Clouds and the Earth’s Radiant Energy System, so where do clouds come into play? As you can see in the Earth’s Energy Budget picture above, clouds reflect solar radiation (sunlight) entering Earth, and block thermal infrared radiation leaving Earth. In other words, clouds affect the Earth’s Energy Budget. To see what I mean take a look at the picture below which shows a global map of solar insolation on Earth (note the faint outline of the continents). Insolation is the amount of incoming solar radiation reaching the surface. There’s only a handful of things that impacts how much solar energy reaches our surface. The major variable is the angle of incident, which is the angle of the Sun’s rays. There also can be some variability given the amount of air above that location, and the amount of dust and smoke in the air. And then there are clouds. There’s not much else that blocks the Sun’s energy from reaching us here on the ground. The solar incidence angle is controlled by astronomy, but clouds and everything else are products of weather and climate.
In this image, bright whites and yellows represent areas receiving more solar energy. Dark reds represent areas receiving less energy. The image depicts solar insolation for the month of January 2017 and you can see that the Northern Hemisphere is dark red, while the Southern Hemisphere is orange and yellow. This is because during January, the tilt of the Earth makes the North Pole face away from the Sun, and the South Pole face towards the Sun so the Southern Hemisphere receives more sunlight. However, in this image you can also see patches and swirls of red and orange mixed in with yellow in the Southern Hemisphere. Without clouds, these maps would show variations that look uniform from west to east, but instead we see a map that looks more interesting. For example, you can see deep red by the Amazon where there are lots of clouds blocking sunlight from reaching the surface. Around the equator you can see long thin bands of red in the area referred to as the Inter Tropical Convergence Zone or ITCZ. This is the area where the trade winds from the Northern and Southern hemispheres converge and cause large convective clouds, like cumulonimbus clouds. You can notice that desert areas are lighter colors because they don't have as many clouds.
Clouds are certainly fun to watch, but can be tricky to understand. After reading this, you might think all clouds block sunlight and help cool the Earth, but scientists have learned that not all clouds act the same. High, thin clouds (like cirrus) let most of the Sun’s energy pass right through them, heating the Earth. Then, when Earth emits energy back to space, those high clouds trap some of the heat. Low puffy clouds have the opposite impact. Low clouds block most sunlight from reaching Earth, but let most of the energy from Earth’s surface escape into space. The image below describes how different clouds affect energy entering and exiting Earth. The image shows that high, thin clouds like cirrus clouds warm Earth, and low think clouds like cumulus clouds cool Earth.
This is why it’s so important in GLOBE that we identify cloud type and also consider the opacity of the cloud – how much light/energy passes through the cloud. Your ground observation are helpful to scientists since it’s difficult to “see” thin clouds from space. Learn more about opacity with this hands-on activity is: Cloud Clues.
Now that you understand more about clouds and Earth’s energy budget, I hope you will help GLOBE collect data about the clouds you see! If you want more information or a summary video about why clouds are so important to track and understand, visit our GLOBE Clouds page online: https://www.globe.gov/web/s-cool/home.
Oh – and don’t forget to watch the JPSS Launch: http://www.jpss.noaa.gov/!
Authors: Jessica Taylor, Brant Dodson and Cayley DeFontes