With an exponential rise in satellite-based services used for navigation and communications, obtaining forecasts and data on the health of Space weather is of supreme importance.
But what factors drive Space weather? National Aeronautics and Space Administration (NASA) is set to launch the Atmospheric Waves Experiment (AWE) to study one of the important drivers of Space weather – the Earth’s weather.
First, what exactly is Space weather and why is it important?
Just like there is weather on the Earth, the environment around the Earth and the other planets remains constantly under the influence of the Sun and its behaviours – solar flares and emissions, along with the kinds of prevailing matter in the Space surroundings.
During certain days, when the weather over Earth turns rough or extreme, Space weather, too, can suffer extreme events. These have a direct impact on vital installations on Earth, like satellite-based communication, radio communication, and Space-based aircraft orbits or stations – affecting the smooth operations of the navigation and Global Positioning Systems (GPS) and power grids.
Apart from influences from the Sun-bound emissions, Space weather also comes under the impact of terrestrial weather.
What is a gravity wave?
The simplest way to explain a gravity wave is by considering the example of ripples formed when a pebble is thrown into the calm waters of a pond. Close to where the pebble touches the water surface, the waves are concentric and tightly packed whereas they become less defined at a far point from the pebble.
Similarly, in the atmosphere, there are a wide variety of waves, travelling both horizontally and vertically. Atmospheric Gravity Waves (AWS) are one such kind of vertical wave. They are mostly generated when there is an extreme weather event or a sudden disturbance leading to a vertical displacement of stable air.
Natural phenomena like thunderstorms, hurricanes, tornadoes, regional orography and others have the potential to send out a variety of periodic waves, including AGWs, in the lower levels of the atmosphere.
“There is limited data about these waves provided by satellites. But we need a better understanding of the vertical motion of waves, the altitude and causes for their development – all of which are vital to better our understanding of these waves and their impacts on the overall weather, climate along with Space weather,” said Thara Prabhakaran, senior meteorologist at the Indian Institute of Tropical Meteorology (IITM), Pune.
A stable atmosphere plays an important role in the generation of gravity waves, that is, when the atmosphere is stable, the temperature difference between the rising air and the atmosphere produces a force that pushes this air to its original position. The air will continuously rise and sink, thus creating a wave-like pattern.
AGW is a wave that moves through a stable layer of the atmosphere, wherein the upward-moving region is the most favourable for the formation of cloud patterns or streaks. AGWs continue all the way to Space, where they contribute to the Space weather.
As a meteorologist, Prabhakaran stressed the need for data obtained by vertically profiling the atmosphere. “This data can be used as weather model inputs and thereby, help improve the weather forecasts,” she said.
What is the Atmospheric Waves Experiment (AWE)?
AWE is a first-of-its-kind NASA experimental attempt aimed at studying the interactions between terrestrial and Space weather.
Planned under NASA’s Heliophysics Explorers Program, the $42 million mission will study the links between how waves in the lower layers of the atmosphere impact the upper atmosphere, and thus, Space weather.
AWE will be launched and mounted on the exterior of the Earth-orbiting International Space Station (ISS). From the vantage point, it will look down at the Earth and record the colourful light bands, commonly known as airglow.
The new NASA mission will try to understand the combination of forces that drive the Space weather in the upper atmosphere.
“AWE could open a new window of study, wherein scientists are attempting to understand if Space weather is affected by terrestrial and bottom-up forces,” said Dibyendu Nandi, solar physicist and head, Center of Excellence in Space Sciences India, IISER, Kolkata.
AWE will measure the airglow at mesopause (about 85 to 87 km above the Earth’s surface), where the atmospheric temperatures dip to minus 100 degrees Celsius. At this altitude, it is possible to capture the faint airglow in the infrared bandwidth, which appears the brightest enabling easy detection.
AWE will be able to resolve waves at finer horizontal scales than what satellites can usually see at those altitudes, which is part of what makes the mission unique, said Ruth Lieberman, AWE mission scientist, Goddard Space Flight Center in Greenbelt, in a NASA article.
The health of the ionosphere, whose lower layers sit at the edge of Space, is important for maintaining seamless communication. It is still not fully understood if the ionosphere is affected by the transient events or intense perturbations resulting from hurricanes or tornadoes.
From its original scheduled launch in August 2022, the fresh launch is planned sometime this month.
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What will NASA’s AWE do?
AWE will perform focused mapping of the colourful airglows in the Earth’s atmosphere.
Onboard AWE is an Advanced Mesospheric Temperature Mapper (ATMT), an instrument that will scan or map the mesopause (a region between the mesosphere and thermosphere). Using the four identical telescopes comprising an imaging radiometer, scientists hope to obtain the brightness of light at specific wavelengths.
This information can then be converted into a temperature map, which could reveal the airglow movement and ultimately, give clues on their role in the upper atmosphere and Space weather.
Anjali Marar works at the Raman Research Institute, Bengaluru.