Radar Observations
Simulation and theory are the core of our group’s work, but they do not stand alone. Throughout our research on the ionosphere and on meteors, we collaborate closely with high-power radar observatories — and occasionally lead observing campaigns of our own — to obtain the measurements that our simulations are designed to explain. Observations tell us what the plasma actually does; our codes and theory tell us why. Keeping the two in close contact is what turns a simulation into science.
Two facilities appear again and again in this work: the 50 MHz Jicamarca Radio Observatory (JRO) in Peru, sitting almost directly beneath the magnetic equator, and the 440 MHz Millstone Hill incoherent scatter radar at MIT’s Haystack Observatory in Massachusetts. Between them they let us study equatorial and mid-latitude plasma physics, meteors, and the enigmatic 150 km echoes.
Meteor Observations: Head and Trail Echoes
When a meteoroid ablates in the upper atmosphere it produces two distinct radar targets: a compact head echo that travels downward with the meteoroid at tens of km/s, and a longer-lived trail echo from the column of plasma left behind. High-power radars record thousands of these events, and their range–time, Doppler, and interferometric-phase signatures encode the meteoroid’s speed and the plasma physics of the trail. We work with the Jicamarca, Millstone Hill, and other radars to catalog and interpret head and trail echoes (Akharman et al. 2025), and use the Jicamarca radar’s interferometry to resolve the trails in both amplitude and phase.
Non-Specular Meteor Trail Echoes Give High-Precision Winds
Meteor trails drift with the neutral wind, such that tracking these echoes turns each meteor into a wind sensor in the mesosphere and lower thermosphere (80–105 km), an altitude region nearly inaccessible to any other technique. Using high-resolution non-specular echoes at Jicamarca, we developed a method for measuring wind profiles with high-precision temporal and spatial resolution, revealing intense winds and sharp vertical shears (Oppenheim et al. 2009; Oppenheim et al. 2014).
Equatorial Electrojet Observations at Jicamarca
The equatorial electrojet is a strong current that flows along the Earth’s magnetic equator. Frequently, this current is strong enough to drive the Farley–Buneman and gradient-drift instabilities that fill the overhead sky with plasma turbulence. Because JRO looks straight up the magnetic field, it images this turbulence directly, mapping the coherent echoes in altitude and angle as they evolve through the day. These observations are the direct real-world counterpart of the 3D electrojet turbulence we simulate on supercomputers, and comparing the two is central to our ionospheric program.
▶ Play the electrojet imaging movie
Auroral Precipitation and E-Region Turbulence
The same Farley–Buneman turbulence that fills the equatorial electrojet also erupts at high latitudes, wrapped around the shifting arcs of the aurora. Combining the ICEBEAR coherent-scatter radar in Saskatchewan with co-located optical auroral imaging, this work — led by Magnus Ivarsen, with our group among the collaborators — found that the small-scale E-region turbulence tends to appear just outside the bright optical arcs, driven by the strong electric fields that flank regions of auroral precipitation. It ties the microphysics of E-region instabilities directly to the large-scale structure of the aurora (Ivarsen et al. 2024).
The 150 km Echoes
For decades, radars near the magnetic equator have recorded mysterious coherent echoes from around 150 km altitude — well above the E region, where standard instability theory predicts no turbulence. Our group proposed and simulated a mechanism for them (photoelectron-driven upper-hybrid waves), and continued observations at Jicamarca and elsewhere keep refining the picture. The echoes appear in characteristic altitude bands that drift through the day, and comparing their morphology across radar frequencies is a key observational test of the theory (see the Ionosphere page for the underlying physics).
Observations, Theory, and Simulation Together
Observations are a complementary strand of the group’s work, woven through its research on the ionosphere and meteors. The measurements shown here motivate the questions our simulations address and provide the data that test them — theory, computation, and observation advancing the same science from three directions.
Research in the group runs through the BU Astronomy PhD program: bu.edu/astronomy/graduate.