Solar flare soft X-ray irradiance and its impact on the Earth's upper atmosphere

Solar flares dramatically enhance the soft X-ray region of the solar spectrum. The enhancement is more significant than previously thought, and the solar soft X-ray instruments aboard the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) and Solar Radiation and Climate Experiment (SORCE) satellites have observed more flares than expected. This dissertation presents a state-of-the-art analysis used to determine flare spectra from TIMED and SORCE solar observations. A relationship is established between Geostationary Operational Environmental Satellite (GOES) flare 0.1-0.8 nm irradiances and XPS flare 0.1-2 and 0.1-7 nm irradiances. Solar flares primarily enhance the soft X-ray irradiance in the 0.1-2 nm range, and rapidly modify the energy input to the lower thermosphere. Most of the excess flare 0.1-2 nm irradiance comes from 1-2 nm. Thus, flares deposit a large amount of their energy between 100-110 km. One of the key effects of this energy deposition is to modify nitric oxide (NO), which plays an important role in the energy balance of the thermosphere as it is a source of radiative cooling through infrared emissions. The density of NO is highly variable as a function of time and latitude, and reaches a maximum in the same altitude region where the flare irradiance is absorbed. This dissertation also presents valid comparisons between Student Nitric Oxide Explorer (SNOE) satellite NO observations and those predicted by a photochemical thermospheric model to provide a better understanding of low latitude flare enhanced NO column density. Large flares can deposit the same amount of 0.1-2 and 0.1-7 nm energy to the thermosphere during a relatively short time as the Sun normally deposits in one day. The NO column density doubles as the daily integrated energy to the thermosphere doubles.