Vertical Wave Coupling in the Low-Latitude Ionosphere-Thermosphere as
revealed by Concurrent ICON and COSMIC-2 Observations
Abstract
It is now well established that waves generated in the lower atmosphere
can propagate upward and significantly impact the dynamics and mean
state of the ionosphere-thermosphere (IT, 100-600 km) system. Given the
geometry of magnetic field lines near the equator, a significant
fraction of this IT coupling occurs at low latitudes and is driven by
global-scale waves of tropical tropospheric origin, such as the diurnal
eastward-propagating tide with zonal wavenumber 3 (DE3) and the
ultra-fast Kelvin wave (UFKW). Despite recent progress, lack of
coincident global observations has thus far precluded full
characterization of the sources of day-today variability of these waves,
including nonlinear interactions, and impacts on the low-latitude IT. In
this work, in-situ ion densities from Ionospheric Connection Explorer
(ICON) and Constellation Observing System for Meteorology, Ionosphere
and Climate 2 (COSMIC-2) Ion Velocity Meter (IVM) along with
remotely-sensed zonal winds from ICON Michelson Interferometer for
Global High-resolution Thermospheric Imaging (MIGHTI) are used to reveal
a rich spectrum of waves coupling the lower (∼90-105 km) and middle
(∼200-270 km) thermosphere with the upper F-region (∼540 and ∼590 km)
ionosphere. Spectral analyses for a 40-day period of similar local time
demonstrate prominent IT coupling via DE3, a 3-day UFKW, and the two
∼1.43-day and ∼0.77-day secondary waves from their nonlinear
interactions. While all these waves are found to dominate the F-region
spectra, only the UFKW and the 1.43-day secondary wave can propagate to
∼270 km suggesting E-region wind dynamo processes as major contributors
to their observed ionospheric signatures.