NASA CINDI Mission: Monitoring the Ionosphere

When high frequency radio waves, such as those used for the Global Positioning System (GPS), travel through a disturbed layer of Earth’s electrically charged atmosphere, the ionosphere, they can be disrupted. 

Credit: U.S. Air Force Research Laboratory (AFRL)

On April 16, 2008, a suite of NASA instruments was launched into space to study a unique region of Earth’s upper atmosphere: the electrically charged region called the ionosphere.

The instruments, known collectively as CINDI (Coupled Ion-Neutral Dynamics Investigation), fly aboard an Air Force Research Laboratory satellite called C/NOFS (Communications/Navigation Outage Forecasting System) to study this region that hovers some 60 to 400 miles above Earth.

The ionosphere is crucial for modern communications. Low-frequency radio waves bounce off it to travel from one part of Earth to another.

Various satellites, including the global positioning system (GPS), send high-frequency radio waves through the ionosphere down to receivers on Earth. In this region the right conditions exist to allow incoming energy from the sun to knock electrons off the atoms.

So the area seethes with charged particles moving under forces of both conventional winds and of electric fields that drive the particles perpendicular to the magnetic field lines surrounding Earth.

The ionosphere changes constantly: between night and day, with the seasons, between the equator and the poles, and with every incoming burst of radiation from the sun.

These simulations of the nighttime, low latitude ionosphere – representing altitudes of about 120 to 750 miles above Earth -- show how "chimneys" of lower density form at the base of the ionosphere and then rise up, creating branches at ever smaller scales. 

These perturbations can disturb radio waves moving through the region. 

Each colour shows a different density of material. 

The colour green corresponds to low-density regions. 

Red represents the densest region of the ionosphere, over 100 times more dense. 

Credit: John Retterer

Small changes in the ionosphere, at night, for example, can simply garble the radio waves – a phenomenon known as scintillation. But at worst, an event such as a giant solar flare can black out radio transmissions completely.

Rob Pfaff

“All the space assets we have come to rely on, in one way or another propagate radio waves through this region of Earth’s atmosphere so we need to understand it better,” says Rob Pfaff, project scientist for CINDI at NASA’s Goddard Space Flight Center in Greenbelt, Md.

“Our goals with CINDI are to determine why the region becomes irregular, and, ultimately, to be able to forecast when and where it will be irregular.”

Studying the ionosphere is like trying to understand a very complicated lava lamp, in which blobs of different materials move up and down in response to changes in temperature.

In the case of the ionosphere, scientists want to understand the kinds of heat and energy affecting particle movement and how these motions interact and rely on each other.

Every piece of data, such as where certain particles appear and what causes areas of lower and higher density, represents a significant advance toward predicting change in the region.

Over the last five years, CINDI has gleaned information about the distribution in height of different kinds of particles, about how winds sweep through the atmosphere in response to events on the sun, and what causes density changes in both the charged and neutral particles in the ionosphere.

One of the early observations by CINDI was of the top of the ionosphere layer, which is dominated by hydrogen ions near dawn.

The middle layer of the area is dominated by oxygen ions. In 2008, CINDI found that the transition region, where there is an equal number of both particles, was located about 370 miles up, much closer to Earth than expected.

Since CINDI launched at a time of low solar activity -- a period of the sun’s approximate 11-year cycle known as solar minimum – the mission has had the chance to observe how the ionosphere changes as the sun’s activity ramps up to solar maximum, currently expected in late 2013.

Over five years of watching, this oxygen/hydrogen transition region has now moved up in space to over 430 miles in altitude, providing an indicator of how Earth’s atmosphere swells and expands in response to increased energy coming in from the sun.