Investigation of the Relationship Between Horizontal Wind Divergence and Vertical Winds

Thermospheric vertical winds in high-latitude regions play a key role in ionosphere–thermosphere coupling, yet their primary drivers remain debated between horizontal wind divergence and localized heating. We analyzed 17 tristatic Scanning Doppler Imager (SDI) observations over Alaska during geomagnetically disturbed periods to investigate the relationship among vertical winds, horizontal divergent winds, and energy deposition. All events show weak-to-moderate correlations (r > 0.2) between vertical winds and horizontal wind divergence, indicating that horizontal divergence is associated with vertical wind motions. In 5 of the 17 events, scale heights estimated from divergence-based calculations are approximately twice as large as those derived from SDI neutral temperatures and the MSIS model, whereas the remaining 12 events show comparable scale heights between the two approaches. These enhanced scale heights suggest additional heating-related contributions to the observed vertical winds. During these 5 events, vertical winds in the lower and upper thermosphere are positively correlated with each other. In addition, the auroral emission intensity ratio (I630/I558) shows the strongest relationship with F-region vertical wind variations, while Joule heating rates are only weakly correlated. These results suggest that soft electron precipitation plays a more important role than E-region Joule heating in enhancing vertical winds when heating effects are active. Furthermore, intermittent heating signatures within the auroral oval imply the presence of mesoscale spatial variability in thermospheric heating and energy deposition.