Abstract:
We report F-region airglow imaging of fossil
plasma depletions around midnight that revived afresh un der persisting thermospheric gravity wave (GW) activity. An
all-sky imager recorded these events in OI 630 nm imag ing over Ranchi (23.3° N, 85.3° E; mlat. ∼ 19° N), India,
on 16 April 2012. Northward-propagating and east–west aligned GWs (λ ∼ 210 km, v ∼ 64 m s−1
, and τ ∼ 0.91 h)
were seen around midnight. Persisting for ∼ 2 h, this GW
activity revived two co-existing and eastward-drifting fos sil depletions, DP1 and DP2. GW-driven revival was promi nently seen in depletion DP1, wherein its apex height grew
from ∼ 600 to > 800 km, and the level of intensity deple tion increased from ∼ 17% to 50 %. The present study is
novel in the sense that simultaneous observations of thermo spheric GW activity and the associated evolution of deple tion in OI 630 nm airglow imaging, as well as that around
local midnight, have not been reported earlier. The current
understanding is that GW phase fronts aligned parallel to the
geomagnetic field lines and eastward-propagating are more
effective in seeding Rayleigh–Taylor (RT) instability. Here,
GW fronts were east–west-aligned (i.e., perpendicular to the
geomagnetic field lines) and propagated northward, yet they
revived fossil depletions.
