• On April 5, 2019, the NASA sounding rocket missions AZURE finally launched from Andøya Space Center in Norway. It was a most beautiful display of chemiluminescent tracers released between 100 and 300 km and dispersed by the thermospheric wind and electric fields (big image above). The name of the experiment AZURE stands for Auroral Zone Upwelling Release Experiment. The principal investigator is Dr. Miguel Larsen, also from our department. As co-investigator, I contributed two ionization gauges, a cold-cathode and a hot-cathode type gauge, that measured neutral densities and temperatures between 90 and 150 km on the descent of each parabolic suborbital flight. Preliminary results show distinctly different densities and temperatures between 110 and 130 km, where auroral heating is expected. The payload also included photometers built by the The Aerospace Corporation that observed auroral optical emissions.

    A new paper (Lehmacher et al., 2020) used 12 years of high-resolution Jicamarca data to propose a new idea what causes the striking gaps in the 150-km echoes necklace. The data were collected in a collaborative effort with University of Illinois (Erhan Kudeki, Pablo Reyes) and the Jicamarca Radio Observatory. I presented the results at the recent 2019 AGU Fall Meeting in San Francisco, and was amazed that theoretical calculations by William Longley (Rice University) closely reproduced the observed gaps. His results will be published soon.

    In 2019, two new NASA projects started for me. The Vorticity Experiment (VortEx) will look at mesoscale dynamics between 90 and 120 km, where gravity wave amplitudes maximize and extreme winds and wind shears form. Radars, lidars, and imagers will support the launches, which are scheduled for January 2022 from Andøya Space Center as part of the new Grand Challenge Initiative: Mesosphere Lower Thermosphere. For more details see Research.

    The second NASA project is led by my colleague, Dr. Stephen Kaeppler, and is called INCAA: An Investigation of Ion-Neutral Coupling During Active Auroral Conditions. I will contribute two ionization gauges to measure neutral densities and temperatures which will help determine collision frequencies and E region conductivities. The missons are to be launched in April 2021 from Poker Flat Research Range, Alaska.

    Research opportunities for interested undergraduate and graduate students in physics are available. Please contact glehmac (at) clemson (dot) edu.


  • Assembly of the AZURE payloads at NASA Wallops Flight Facility. Photo: G. Lehmacher.

  • Gaps in 150-km echoes (yellow, red, and cyan lines in row above) represent specific electron densities (or plasma frequencies, in row below) and they shift in altitude depending on local electron density. Left: Near solar minimum. Right: Near solar maximum. Lehmacher et al., 2020.