On the modernization of the falling spheres technique to measure neutral
winds in the thermosphere
Abstract
This paper introduces a modernized application of the falling spheres
technique for measurement of neutral winds and densities in the
mesosphere and lower thermosphere (MLT) region regardless of time of day
or tropospheric conditions, using an Observing System Simulation
Experiment (OSSE) of falling spheres equipped with
commercial-off-the-shelf (COTS) Global Navigation Satellite Systems
(GNSS) receivers. The modernization of this technique is crucial since
current techniques to measure the neutral winds in the MLT are often
tied to the location of a certain instrument or heavily dependent on
clear nighttime skies. We show how state-of-the-art COTS inertial
measurement units (IMUs) and GNSS receivers enable precise retrieval of
neutral wind and density profiles under various atmospheric conditions
represented both by wind profiles measured during the Super Soaker and
Auroral Jets sounding rocket missions and by wind profiles simulated via
the Whole Atmosphere Community Climate Model with thermosphere and
ionosphere extension (WACCM-X). Even under highly conservative
conditions (e.g., relatively extreme position uncertainty of
$\sigma =\sim$100 m, a low sampling rate
of 100~Hz, and strong vertical winds of 25 m/s) the
estimated neutral densities exhibit errors of less than
1\%, while estimated neutral wind errors typically do
not exceed 2 m/s. The latter errors are largest where the shears
maximize in the lower thermosphere. The significance of this work lies
in its potential to enhance our understanding of the dynamics within the
MLT region, including in situ processes and the interaction with the
lower atmosphere.