NASA's Use of Tracers in the Upper Atmosphere
Colorful “Tracers” Reveal the Motions of the Earth’s Upper Atmosphere and Ionosphere
The Earth’s atmosphere extends far into space, more than 620 miles (1000 kilometers) above the surface. Just as there are winds in the atmosphere near the surface of the Earth, the upper atmosphere is also constantly in motion, resulting in very high altitude winds in space that change with altitude, local time, latitude, and season.
Global computer model of the upper atmosphere winds at 218 miles (350 kilometers) altitude. Graphic Courtesy of A. Maute
Above about 62 miles (100 kilometers) altitude, a tiny fraction of the upper atmosphere is ionized by EUV radiation from the sun. This ionized component, called the ionosphere, co-exists in the same volume as the upper atmosphere, and also extends far into space. The ionized gases are also in motion, but their movements are guided by the Earth's magnetic and electric fields in space.
Since the earliest days of the space age, scientists have been studying the motions of both the upper atmosphere winds and the ion drifts in the ionosphere. In particular, scientists seek to understand how the winds and ion drifts are coupled to each other. This area of research is especially interesting, since the winds are driven, in part, by heating and energy sources from below whereas the ion drifts are driven, in part, by energy sources from above. In particular, the largest ion drifts are driven by electric fields that are generated by solar wind interactions with the Earth’s magnetic field at very far distances in the magnetosphere. Ultimately, the source of energy of both the upper atmosphere winds and the ion drifts, is the sun.
Just as there are familiar weather patterns for atmospheric conditions near the ground, the upper atmosphere winds and ion drifts are also organized into patterns that change with latitude, local time, season, and altitude. Computer models show how the upper atmosphere winds and ion drifts are believed to change across the globe, and show in particular how the winds and ion drifts become much stronger at high latitudes. Computer models also show how the winds are believed to change with altitude.
Although computer models are exceedingly useful and important, scientists seek to measure the actual motions of the upper atmosphere and ionosphere to discover the real behavior of their motions and to learn if the models are correct. Measuring these motions is not easy. In order to learn what are the actual winds in the upper atmosphere, scientists typically use probes on satellites and rockets, as well as ground-based instruments, such as powerful radars, lidars, and optical imagers.
A graphic showing where vapor trails from sounding rockets are used to reveal the winds of the upper atmosphere as a function of altitude.Credit: NASA
Another particularly useful technique that provides very accurate information involves the release of a very small, artificial vapor that creates a trail or “cloud” in the region of space being studied. After releasing this material in space, researchers then visually observe the subsequent movement of the vapor as it traces the motions of background environment. This technique is analogous to that of injecting a small, harmless dye into a river or stream, to study its currents, eddies, and other motions.
NASA and other space agencies around the world use vapor tracers released from sounding rockets to track the motions of upper atmospheric winds and ion drifts. Below, we provide information regarding how NASA carries out sounding rocket missions to reveal the upper atmospheric winds and ion drifts using vapor tracers, or trails, released along the near-vertical trajectories of sounding rockets in space.
Want to know more about vapor tracers, the metals used, and the upcoming tracer missions?