From Science Node: “1 millionº and breezy: Your solar forecast”

Science Node bloc
Science Node

24 May, 2017
Alisa Alering

Space is a big place, so modeling activities out there calls for supercomputers that match. PRACE provided scientists the resources to run the Vlasiator code and simulate the solar wind around the earth.

Courtesy Minna Palmroth; Finnish Meteorological Institute.

Outer space is a tough place to be a lonely blue planet.

With only a thin atmosphere standing between a punishing solar wind and the 1.5 million species living on its surface, any indication of the solar mood is appreciated.

The sun emits a continuous flow of plasma traveling at speeds up to 900 km/s and temperatures as high as 1 millionº Celsius. The earth’s magnetosphere blocks this wind and allows it to flow harmlessly around the planet like water around a stone in the middle of a stream.

Magnetosphere of Earth, original bitmap from NASA. SVG rendering by Aaron Kaase

But under the force of the solar bombardment, the earth’s magnetic field responds dramatically, changing size and shape. The highly dynamic conditions this creates in near-Earth space is known as space weather.

Vlasiator, a new simulation developed by Minna Palmroth, professor in computational space physics at the University of Helsinki, models the entire magnetosphere. It helps scientists to better understand interesting and hard-to-predict phenomena that occur in near-Earth space weather.

Unlike previous models that could only simulate a small segment of the magnetosphere, Vlasiator allows scientists to study causal relationships between plasma phenomena for the first time and to consider smaller scale phenomena in a larger context.

“With Vlasiator, we are simulating near-Earth space with better accuracy than has even been possible before,” says Palmroth.

Navigating near-Earth

Over 1,000 satellites and other near-Earth spacecraft are currently in operation around the earth, including the International Space Station and the Hubble Telescope.

Nearly all communications on Earth — including television and radio, telephone, internet, and military — rely on links to these spacecraft.

Still other satellites support navigation and global positioning and meteorological observation.

New spacecraft are launched every day, and the future promises even greater dependence on their signals. But we are launching these craft into a sea of plasma that we barely understand.

“Consider a shipping company that would send its vessel into an ocean without knowing what the environment was,” says Palmroth. “That wouldn’t be very smart.”

Space weather has an enormous impact on spacecraft, capable of deteriorating signals to the navigation map on your phone and disrupting aviation. Solar storms even have the potential to overwhelm transformers and black out the power grid.

Through better comprehension and prediction of space weather, Vlasiator’s comprehensive model will help scientists protect vital communications and other satellite functions.

Three-level parallelization

The Vlasiator’s simulations are so detailed that it can model the most important physical phenomena in the near-Earth space at the ion-kinetic scale. This amounts to a volume of 1 million km3 — a massive computational challenge that has not previously been possible.

After being awarded several highly competitive grants from the European Research Council, Palmroth secured computation time on HPC resources managed by the Partnership for Advanced Computing in Europe (PRACE).

Hazel Hen

She began with the Hornet supercomputer and then its successor Hazel Hen, both at the High-Performance Computing Center Stuttgart. Most recently she has been using the Marconi supercomputer at CINECA in Italy.

Marconi supercomputer at CINECA in Italy

Palmroth’s success is due to three-level parallelization of the simulation code. Her team uses domain decomposition to split the near-Earth space into grid cells within each area they wish to simulate.

They use load-balancing to divide the simulations and then parallelize using OpenMP. Finally, they vectorize the code to parallelize through the supercomputer’s cores.

Even so, simulation datasets range from 1 to 100 terabytes, depending on how often they save the simulations, and require anywhere between 500 – 100,000 cores, possibly beyond, on Hazel Hen.

“We are continuously making algorithmic improvements in the code, making new optimizations, and utilizing the latest advances in HPC to improve the efficiency of the calculations all the time,” says Palmroth.

Taking off into the future

In addition to advancing our knowledge of space weather, Vlasiator also helps scientists to better understand plasma physics. Until now, most fundamental plasma physical phenomena have been discovered from space because it’s the best available laboratory.

But the universe is comprised of 99.9 percent plasma, the fourth state of matter. In order to understand the universe, you need to understand plasma physics. For scientists undertaking any kind of matter research, Vlasiator’s capacity to simulate the near-Earth space is significant.

“As a scientist, I’m curious about what happens in the world,” says Palmroth. “I can’t really draw a line beyond which I don’t want to know what happens.”

Significantly, Vlasiator has recently helped to explain some features of ultra-low frequency waves in the earth’s foreshock that have perplexed scientists for decades.

A collaboration with NASA in the US helped validate those results with the THEMIS spacecraft, a constellation of five identical probes designed to gather information about large-scale space physics.

Exchanging information with her colleagues at NASA allows Palmroth to get input from THEMIS’s direct observation of space phenomena and to exchange modeling results with the observational community.

“The work we are doing now is important for the next generation,” says Palmroth. “We’re learning all the time. If future generations build upon our advances, their understanding of the universe will be on much more certain ground.”

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