Deng leading NASA project to examine effect of wind shears on upper atmosphere

Thursday, Jun 02, 2022 • Greg Pederson :

A space physicist at The University of Texas at Arlington is leading a NASA project which will utilize satellite data to gain new understanding of neutral wind shear in the upper atmosphere, which plays a key role in space weather and can disrupt satellite and Earth-based communications.

Yue Deng, UTA distinguished professor of physics, is principal investigator of a three-year, $447,507 grant from NASA for the project, titled “Neutral wind shear and its impact on electrodynamics and meso-scale plasma structures”. 

Co-investigators include Cheng Sheng, UTA research scientist in physics; Brian Harding, assistant research physicist at the University of California Berkeley Space Sciences Laboratory; Gang Lu, a senior scientist at the National Center for Atmospheric Research (NCAR); and Qingyu Zhu, an Advance Study Program postdoctoral fellow at NCAR who earned his Ph.D. from UTA in 2020 with Deng as his faculty advisor. Joseph Huba, a senior research scientist at Syntek Technologies, is collaborating on the project.

The team will use information gathered by NASA’s Ionospheric Connection Explorer (ICON), a satellite launched in 2019 with the goal of helping scientists understand how solar wind and other space weather phenomena interact with the layer of Earth’s atmosphere called the ionosphere. Deng and her team will conduct data-model comparisons to improve scientists’ physical understanding of neutral wind shears, which are a major contributor to plasma irregularity in the ionosphere.

“The ionosphere and thermosphere system near the equator is a very complex system due to the ion-neutral coupling and electrodynamic processes,” Sheng said. “The ICON satellite aims to help us understand this complex system through simultaneous measurements of ion and neutral properties.”

The ionosphere overlaps the top of Earth’s atmosphere and the very beginning of space. It stretches roughly 50 to 400 miles above Earth's surface and is comprised of charged particles, which makes it highly reactive to changing magnetic and electric conditions in space. Because it is formed when particles are ionized by the Sun’s energy, the ionosphere changes from Earth’s day side to night side.

Changes to this region of space can have practical repercussions, given our reliance on technology. Many low-Earth orbit (LEO) satellites are located in the ionosphere, and they can be adversely affected by the constantly changing conditions. In addition, radio and GPS signals travel through this region, and changes in the ionosphere’s density and composition can result in distortions or even complete disruption of these signals. Scientists constantly measure and simulate the ionosphere so that disruptions in radio communications can be anticipated.

Other influences on the ionosphere include regular weather events in the lower atmosphere and space weather — changing magnetic and electric conditions in space, as well as bursts of charged particles, all of which are usually connected to solar activity.

The ionosphere has three main regions, called the D region, the E region, and the F region. The regions’ boundaries vary during the course of each day and from season to season. The E region of the ionosphere is strongly coupled with the thermosphere, which is a layer of Earth’s atmosphere that extends above the mesosphere and below the exosphere.

“Numerical models often significantly underestimate the E-region neutral wind shears as measured by rockets and satellites,” Deng said. “There is currently no comprehensive study of the climatology of neutral wind shears in response to season and local time. The main goal of this proposal is to fill this critical gap in the E-region ionosphere-thermosphere (I-T) coupling.”

The project will address three main questions:

   1. What is the climatology of E-region neutral wind shears, such as their dependence on latitude, longitude, season, and local time on the dayside?

   2. What is the correlation between the E-region neutral wind shears and the conjugate F-region plasma irregularities?

   3. How do neutral wind shears affect the morphology of dayside plasma irregularities and what is the relative significance of neutral wind shears compared to other triggering mechanisms?

One of the most striking features of the new dataset available from the ICON mission is the large wind shear in the thermosphere, Harding said. He noted that it is not uncommon to see the atmosphere moving 200 mph in one direction, and then several miles higher up, the movement can be 200 mph in the other direction. Although this has been observed and theoretically predicted previously, ICON provides a global view of this phenomenon, he said.

“The goal of this project is to characterize the occurrence of wind shears and determine how they are organized in space and time,” Harding said. “This might give some clues into what is producing the largest shears, for example, tides and atmospheric gravity waves. These shears are interesting by themselves, but they are also important because of the effect they have on the ionosphere — they can concentrate plasma to form thin layers which the radio community calls ‘sporadic E’. This can have a degrading effect on radio propagation, such as for communication and radar systems.”

The neutral wind contributes to space weather through its effect on many of the processes of the ionosphere. The E-region winds exhibit strong vertical shears, which have been attributed as the leading cause of mesoscale plasma structures, such as sporadic E layers and medium-scale traveling ionospheric disturbances (MSTIDs), Deng said.

“Our project aims to provide for the first time a climatology of E-region neutral wind shears and to uncover the important connections between the E-region neutral dynamics and F-region plasma structures at mesoscales,” Deng said. “It will fill a key science gap in the ion-neutral coupling and advance the specification of the energy and momentum inputs and understanding of the disturbances in the I-T system. While we will focus our studies on the dayside low-latitude region, the understanding of physical processes is applicable to other domains and the impact to the field can be broad.”

It is hoped that knowledge gained from the project will help improve the predictability of how radio waves are propagated in the ionosphere. The study will also use ICON measurements of plasma densities to try to better understand the relationship between wind shears and plasma irregularities.

“The outcome of this project will advance our understanding of the F-region plasma irregularities, which may cause scintillations of radio signals and then affect satellite communication and navigation,” Sheng said.

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