Solar atmospheric coupling by electrons (SOLACE): 1. Effects of the May 12, 1997 solar event on the middle atmosphere

Abstract

An analysis is carried out of the effects on middle atmospheric NO_y and O₃ of a coronal mass ejection (CME) event which occurred on May 12, 1997, and which is coupled with observed solar wind fluctuations. Observations of electron fluxes by instruments aboard the SAMPEX and NOAA 12 satellites indicate large enhancements of magnetospheric electron fluxes occurring with the arrival of the high-speed solar wind. Calculations suggest that significant formation rates of NO_y should occur in the mesosphere and the lower thermosphere at mid to high latitudes. Halogen Occultation Experiment (HALOE) NO observations reveal increases of more than an order of magnitude between 85 and 120 km in both hemispheres within 1–2 days after the electron flux increases. Two dimensional chemical transport simulations were carried out to assess the fate of the NO_y increases. Northern hemispheric increases were lost to photochemical destruction shortly after the event ended. Southern hemispheric increases were transported in part into the stratosphere by advective descent. By October 1997, high-latitude NO_y increases of 20–40% were calculated near 25 km leading to O₃ reductions of up to ≈ 20% when compared to a simulation with no electron precipitation. A solar atmospheric coupling by electrons precipitating from the outer trapping and auroral regions of the magnetosphere, and which affects middle atmospheric NO, is clearly demonstrated by the observations alone.