Abstract: As geomagnetic storm energy dissipates in the upper atmosphere heating expands the thermosphere and neutral density typically increases at a fixed altitude. This atmospheric expansion influences the dynamics of low Earth orbiting satellites and has been the subject of considerable forecasting effort in terms of satellite drag.  I will show that some solar wind density enhancements and pressure pulses can lead to intense low-energy particle precipitation and an associated, but unexpected, damping of thermospheric density response. The key element of the unexpected damping is enhanced production of thermospheric Nitric Oxide (NO) by precipitating particles and subsequent storm heating.  In turn the NO over-cools the thermosphere via infrared emissions.  One path to the unusual NO emissions is likely a result of coronal mass ejection-driven sheath-enhanced storms that alter magnetosphere-ionosphere coupling via particles and Poynting flux. Superposed epoch comparisons reveal that low energy (< 10 keV) particle precipitation is markedly different between storms with typical upheaval behavior and storms with thermospheric damping.   I will discuss the roles of solar wind pre-conditioning and solar cycle dependency in the problem storms. These problem neutral-density storms reveal an element of “geo-effectiveness” that highlights competition between hydrodynamic aspects of the solar wind and other interplanetary drivers.