On the modernization of the falling spheres technique to measure neutral winds in the thermosphere

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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.

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