Cross-Altitude Coupling of Electrojet Farley-Buneman Waves

The Farley-Buneman instability (FBI) can create plasma density irregularities and anomalous electron heating in the E-region ionosphere which are regularly seen by radars and rockets during geomagnetic storms. Linear theory predicts that the FBI grows only at certain altitudes, ~98-120 km for the high-latitude ionosphere, and simulations at those altitudes confirm the linear theory. Both the linear theory and the simulations, however, do not include the effects of wave coupling across different altitudes which may affect the behavior of the waves in the nonlinear stages. A recent large-scale 3D electrostatic particle-in-cell (PIC) plasma simulation captures the effects of cross-altitude wave coupling by including multiple altitudes within a single simulation box. This large-scale “global” run is compared with 8 smaller “local” runs where each run corresponds to only a single altitude. Results from both sets of simulations at most altitudes show similar profiles with matching large anomalous conductivities and electron heating where the FBI occurs. Above 120 km, however, the two sets of simulations show different results. The “local” runs do not show instability above 120 km, agreeing with the linear theory, but the “global” run shows clear wave growth as high as 126 km. Spectral analysis shows that these topside waves have similar characteristics to the waves immediately below them, suggesting that they may have been produced through cross-altitude coupling. The study shows that the FBI may grow at higher altitudes than once thought, further affecting the conductivities and electron temperatures in the high-latitude E-region ionosphere.