We’re launching a new mission to the International Space Station to continue measurements of the Sun’s energy reaching Earth.
The Total and Spectral solar Irradiance Sensor (TSIS-1) will precisely measure the total amount of sunlight that falls on Earth and how that light is distributed among different wavelengths, including the ultraviolet, visible and infrared. This will give us a better understanding of Earth’s primary energy supply and help improve models simulating Earth’s climate.
1. You are my sunshine, my only sunshine. You make me happy when skies are blue.
The Sun is Earth’s sunshine and it does more than make us happy; it gives us life. Our Sun’s energy drives our planet’s ocean currents, seasons, weather and climate. Changes in the Sun also alter our climate in at least two ways.
First, solar radiation has a direct effect where it heats regions of Earth, like our oceans, land, and atmosphere. Second, the solar radiation can cause indirect effects, such as when sunlight interacts with molecules in the upper atmosphere to produce ozone which can affect human health.
Earth’s energy system is in a constant dance to maintain a balance between incoming energy from the Sun and outgoing energy from Earth to space, which scientists call Earth’s energy budget. If you have more energy absorbed by the Earth than leaving it, its temperature increases and vice versa. Because the Sun is Earth’s fundamental energy source and only sunshine, we need a quantitative record of the Sun’s solar energy output. TSIS-1 will provide the most accurate measurements ever made of sunlight as seen from above Earth’s atmosphere.
2. You’re hot then you’re cold…You’re in then you’re out. You’re up then you’re down.
The energy flow between the Earth and Sun’s connection is not a constant thing. The Sun can be fickle, sometimes it puts out slightly more energy and some years less. Earth is no better. The Earth absorbs different amounts of the Sun’s energy depending on many factors, such as the presence of clouds and tiny particles in the atmosphere called aerosols.
What we do know is that the Sun’s cycle is about 11 years rolling through periods of quiet to times of intense activity. When the Sun is super-intense it releases explosions of light and solar material. This time is a solar maximum.
When the Sun is in a quiet state this period is called the solar minimum.
Over the course of one solar cycle (one 11-year period), the Sun’s total emitted energy varies on average at about 0.1 percent. That may not sound like a lot, but the Sun emits a large amount of energy – 1,361 watts per square meter. Even fluctuations at just a tenth of a percent can affect Earth. That’s why TSIS-1 is launching: to help scientists understand and anticipate how changes in the Sun will affect us on Earth.
3. You’re so vain. You probably think this climate model is about you.
Scientists use computer models to interpret changes in the Sun’s energy input. If less solar energy is available, scientists can gauge how that affects Earth’s atmosphere, oceans, weather and seasons by using computer simulations. But the Sun is just one of many factors scientists use to model Earth’s climate. A lot of other factors come into play in addition to the energy from the Sun. Factors like greenhouse gases, clouds scattering light and small particles in the atmosphere called aerosols all can affect Earth’s climate so they all need to be included in climate models. So, while we need to measure the total amount of energy from the Sun, we also need to understand how these other factors alter the amount of energy reaching Earth’s surface and affect our climate.
4. Someday we’ll find it, the rainbow connection. The lovers, the dreamers and me.
We receive the Sun’s energy in many different wavelengths, including visible light (rainbows!) as well as light we can’t see like infrared and ultraviolet wavelengths. Each color or wavelength of light from the Sun affects Earth’s atmosphere differently.
For instance, ultraviolet light from the Sun can affect Earth’s ozone. High in the atmosphere is a layer of protective ozone gas. Ozone is Earth’s natural sunscreen, absorbing the Sun’s most harmful ultraviolet radiation and protecting living things below. But ozone is vulnerable to certain gases made by humans that reach the upper atmosphere. Once there, they react in the presence of sunlight to destroy ozone molecules. Currently, several satellites from us and the National Oceanic and Atmospheric Administration (NOAA) track the ozone in the upper atmosphere and the solar energy that drives the photochemistry that creates and destroys ozone. Our new instrument, TSIS-1, will join that fleet with even better accuracy.
TSIS-1 will see different types of ultraviolet (UV) light, including UV-B and UV-C. Each plays a different role in the ozone layer. UV-C rays are essential in creating ozone. UV-B rays and some naturally occurring chemicals regulate the abundance of ozone in the upper atmosphere. The amount of ozone is a balance between these natural production and loss processes.
TSIS-1 data of the Sun’s UV energy will help improve computer models of the atmosphere that need accurate measurements of sunlight across the ultraviolet spectrum to model the ozone layer correctly. While UV light represents a tiny fraction of the total sunlight that reaches the top of Earth’s atmosphere, it fluctuates from 3 to 10 percent, a change that, in turn causes small changes in the chemical composition and thermal structure of the upper atmosphere.
This is just one of the important applications of TSIS-1 measurements. TSIS-1 will measure how the Sun’s energy is distributed over 1,000 different wavelengths.
5. Every move you make…every step you take, I’ll be watching you.
TSIS-1 will continue our nearly 40 years of closely studying the total amount of energy the Sun sends to Earth from space. We’ve previously studied this ‘total solar irradiance’ with nine previous satellites, currently with Solar Radiation and Climate Experiment, (SORCE).
NASA’s SORCE collected this data on the total amount of the Sun’s radiant energy throughout Sept. 2017. The satellite actually detected a dip in total irradiance – or the total amount of energy from the Sun- during the month’s intense solar activity.
But there’s still very much we don’t know about total solar irradiance. We do not know how it varies over longer timescales. Longer term observations are especially important because scientists have observed unusually quiet magnetic activity from the Sun for the past two decades with previous satellites. During the last prolonged solar minimum in 2008-2009, our Sun was the quietest it has ever been since we started observations in 1978. Scientists expect the Sun to enter a solar minimum within the next three years, and TSIS-1 will be primed to take measurements of the next minimum and see if this is part of a larger trend.
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