The non-storm time corrugated upper thermosphere: What is beyond MSIS?

<p>Observations in the recent decade have revealed many thermospheric density corrugations/perturbations under nonstorm conditions (<em>K</em><em>p</em> \&lt; 2). They are generally not captured by empirical models like Mass Spectrometer Incoherent Scatter (MSIS) but are operationally important for long-term orbital evolution of Low Earth Orbiting satellites and theoretically for coupling processes in the atmosphere-ionosphere system. We review these density corrugations by classifying them into three types which are driven respectively by the lower atmosphere, ionosphere, and solar wind/magnetosphere. Model capabilities in capturing these features are discussed. A summary table of these corrugations is included to provide a quick guide on their magnitudes, occurring latitude, local time, and season.</p>