NASA - Kasha Patel
For nearly 40 years, NASA has been measuring how much sunshine powers
our home planet. This December, NASA is launching an instrument to the
International Space Station to continue monitoring the Sun’s energy
input to the Earth system. The Total and Spectral solar Irradiance
Sensor (TSIS-1) will precisely measure what scientists call “total solar
irradiance.” These data will give us a better understanding of Earth’s
primary energy supply and help improve models simulating Earth’s
climate.
But it’s not so simple: the Sun’s output energy is not constant. Over
the course of about 11 years, our Sun cycles from a relatively quiet
state to a peak in intense solar activity — like explosions of light and
solar material — called a solar maximum. In subsequent years the Sun
returns to a quiet state and the cycle starts over again. The Sun has
fewer sunspots — dark areas that are often the source of increased solar
activity — and stops producing so many explosions, going through a
period called the solar minimum. Over the course of one solar cycle (one
11-year period), the Sun’s 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.
In addition to those 11-year changes, entire solar cycles can vary
from decade to decade. 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 as quiet it has been observed since 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.
In terms of climate change research, scientists need to understand the
balance between energy coming in from the Sun and energy radiating out
from Earth, as modulated by Earth's surface and atmosphere. Measurements
from TSIS, the Total and Spectral Solar Irradiance Sensor, will help
our understanding of the Earth-Sun connection and improve climate
models. Credit: NASA/Michael Starobin.Download this video from the Scientific Visualization Studio.
“We don’t know what the next solar cycle is going to bring, but we’ve
had a couple of solar cycles that have been weaker than we’ve had in
quite a while so who knows. It’s a pretty exciting time to be studying
the Sun,” said Dong Wu, the TSIS-1 project scientist at NASA’s Goddard
Space Flight Center in Greenbelt, Maryland. Goddard is responsible for
the overall development and operation of TSIS-1 on the International
Space Station.
TSIS-1 data are particularly important for helping scientists
understand the causes of total solar irradiance fluctuations and how
they are connected with the Sun’s behavior over decades or centuries.
Today, scientists have neither enough data nor the forecasting skill to
predict whether total solar irradiance has any long-term trend, said
Doug Rabin, deputy project scientist at Goddard. TSIS-1 will continue a
data sequence that is vital to answering that question.
These data are also important for understanding Earth's climate
through models. Scientists use computer models to interpret changes in
the Sun’s energy input. If less solar energy is available, scientists
can gauge how that will affect Earth’s atmosphere, oceans, weather and
seasons by using computer simulations. The input from the Sun is just
one of many factors scientists used to model Earth’s climate. Earth’s
climate is also affected by other factors such as greenhouse gases,
clouds scattering light and small particles in the atmosphere called
aerosols — all of which are taken into account in comprehensive climate
models.
TSIS-1 will study the total amount of solar radiation emitted by the
Sun using the Total Irradiance Monitor, one of two sensors on the
instrument. The second sensor, called the Spectral Irradiance Monitor,
will measure how the Sun’s energy is distributed over the ultraviolet,
visible and infrared regions of light. TSIS-1 spectral irradiance
measurements of the Sun's ultraviolet radiation are critical to understanding the ozone layer — Earth's natural sunscreen that protects life from harmful radiation.
“Knowing the Sun’s behavior and knowing how Earth’s atmosphere
responds to the Sun is even more important now because of all the
different factors that affect climate change. We need to understand how
all of these interact on Earth’s system,” said Pilewskie.
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