Space weather

 Chaotic and hard to predict

 Space weather

If we calculate, nearly seven decades into the space age, scientists' understanding of space weather is still very crude. Unlike terrestrial weather, which is now forecasted by powerful supercomputers with great accuracy and timeliness, space weather predictions are more hit-and-miss. Generally, an inaccurate space weather forecast just means that someone's elevated aurora-viewing expectations are not met. To overcome this problem, scientists are building a "beyond state-of-the-art" digital model of space around Earth to improve forecasting of solar storms and their effects on infrastructure.

Humanity is increasingly dependent on technologies which are vulnerable to the whims of space weather. From brief radio blackouts to GPS disruptions and lasting power outages, space weather can throw our daily lives off — perhaps not as frequently as torrential rains and windstorms, but with similar ferocity. A new model, developed by a team of researchers led by the Johns Hopkins University Applied Physics Laboratory (APL), is a step toward closing the gap between space and Earth weather predictions. Scientists, however, admit that it might take decades for space weather forecasting to fully catch up.

"We cannot predict space weather without first deeply understanding the physics of it," Slava Merkin, a space physicist at APL and director of its Centre for Geospace Storms (CGS), said . "We're building the model and doing science with the model and, through that, we're discovering the physics of geospace storms."  With the new model introduced, called Multiscale Atmosphere-Geospace Environment (MAGE), the researchers want to capture processes taking place in the geospace up to the distance of 1.2 million miles (2 million kilometers) from Earth. It's is a vast region, extending four times farther away from the planet than the distance of the moon. But Earth's influence over the cosmos extends even farther. The very outer edge of Earth's magnetosphere, its magnetotail, can be traced nearly 4 million miles (6.5 million km) from Earth in the direction away from the sun. 

Geospace is a term that scientists use to describe the region around our planet that includes Earth's upper atmosphere and the surrounding space. Generated by the motion of molten metals inside Earth's core, the magnetosphere interacts with bursts of solar wind — the streams of charged particles that constantly emanate from the sun. This interaction produces the space weather events that we experience on Earth. The process is extremely complex, said Merkin. "Our challenge number one is to treat this system holistically," said Merkin. "But the problem is that each of these domains is governed by different physics. They are populated by different plasma populations, different gas particles, and they all engage in very complex interactions, particularly during geomagnetic storms."

It involves little-understood physical interactions that take place in the thermosphere (the second-highest level of Earth's atmosphere) and the ionosphere (an overlapping region containing high concentrations of charged particles created in interactions with ultraviolet light from the sun). The team celebrated a breakthrough success in 2020 when their nascent model provided unprecedented insights into the formation of bead-like structures in aurora that sometimes appear above Earth's polar regions ahead of major geomagnetic storms. The MAGE model revealed that these pearls of polar light arise when magnetic lines in the distant magnetotail stretch farther away from the planet before geomagnetic storms and then slingshot bubbles of light plasma toward Earth.

But the discovery also aptly demonstrated the difficulty with forecasting space weather. Like the proverbial wave of a butterfly's wing, a physical process in a distant region of geospace can produce visible and measurable effects near Earth's surface. "The computer model that we are developing needs to be able to capture processes that take place on very large scales but also those on very small scales," said Merkin. "At the same time, it needs to capture all of the different physics problems and understand how the various domains — the lower and middle atmosphere, the ionosphere and the magnetosphere — influence each other."

"At any given moment in time, we actually have fairly few spacecraft out there in this enormous region," said Merkin. "The point-to-point measurements may be very accurate, particularly with recent spacecraft, but we don't have the coverage to really know what's going on at the system level. "Unlike terrestrial weather-forecasting models, which digest millions of measurements taken daily all over the world by hundreds of thousands of weather stations, airliners and high-altitude balloons, MAGE has to make do with far fewer data points.

Merkin and his colleagues have access to data accumulated since the beginning of the space age. Still, major gaps exist. For example, the lower layer of the thermosphere, situated at altitudes between 60 and 120 miles (100 to 200 km) and sometimes dubbed the "ignorosphere," is little understood. Too high for stratospheric balloons to reach but too low for satellites to explore, the ignorosphere is where auroras occur. "As we go, the model becomes more and more complex," said Merkin. "We're adding more and more physics to it. The ultimate product will represent the geospace in its ultimate complexity."

MAGE might be able to fill some of those gaps by taking advantage of powerful supercomputing and detailed measurements taken by satellites higher up in the atmosphere, along with information from radars and other sensors on the ground. It might take decades before researchers get there. Modeling space weather is a hugely complicated endeavor. The MAGE collaboration involves dozens of software engineers, computer scientists, physicists and other experts working at research labs across the US.