Response of the Upper/Middle Atmosphere to Coronal Holes and Powerful High-Speed Solar Wind Streams in 2003

High-speed solar wind streams originating from large coronal holes reached a maximum in 2003 during the descending phase of solar cycle 23. At the same time, magnetic activity (as indicated by the aa index) reached the highest levels of the last four solar cycles. The rotation of active regions behind the limb and the appearance of coronal holes contribute to a decrease in EUV radiation at Earth prior to the arrival of a high-speed stream. This leads to a cooling of the upper atmosphere and a decrease in the total electron content (TEC). Changes in ∑O/N₂ are also expected but contributions from local time and seasonal changes as the satellite orbit precesses during a solar rotation will require additional simulations to unravel. These systematic changes are intriguing because auroral disturbances expand further equatorward in latitude and deeper in altitude as F10.7 decreases. Disturbances in nitric oxide (NO), the dominant cooling agent in the upper atmosphere, continue for the duration of the high-speed stream activity and may not fully recover before the next stream hits. These disturbed conditions might actually represent the most common state of the upper atmosphere in years of strong recurrent high-speed streams. Finally, the persistent source of thermospheric NO in the auroral region during high-speed streams, when combined with favorable meteorological conditions in the dark polar middle atmosphere, results in significant enhancements in stratospheric NO_x. These correspond to increases in stratospheric ozone loss, establishing a previously unexplored link between high-speed streams and stratospheric variability.