Importance of the semidiurnal tide, and future measurements needed to improve its characterization

Interactions between lower atmosphere and space is an exciting new frontier in geospacer science. We recommend that the community should emphasize understanding of semidiurnal tidal variations and their impact on the ionosphere-thermosphere-mesosphere (ITM) system as a major component of lower/upper atmosphere coupling studies. Many factors about tidal influence on the ITM system remain unknown, primarily due to the lack of observations in the critical altitude region between 90-200 km, where waves reach their peak amplitudes and are damped. We propose multi-pronged solution that consists of several components: 1) investment in advanced ground-based observational capabilities, including networks of instrumentation; 2) further investments in incoherent scatter radars capabilities for understanding tidal dynamics above ~105km altitude; 3) implementation of DYNAMIC-like mission to obtain global, day and night wind and temperature observations, with further expansion to a more comprehensive DYNAMIC+ mission; implementation of GDC mission to understand global ionospheric response; 4) strengthening of inter-division (within single agency), inter-agency, and international collaboration to maximize return on investment in research infrastructure