CEDAR: Exploration of Trends in Thermospheric+Exospheric Hydrogen Using H-Alpha Emission Intensities and Hydrogen Column Abundances Retrieved from the Wisconsin Long Term Record

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Upward fluxes of hydrogen containing molecules such as methane, water vapor, and molecular hydrogen are the primary source of hydrogen-containing chemical species in the middle and upper atmosphere. Understanding the sensitivity of the thermosphere and exosphere to hydrogenous species distributions below, to sources of natural variability, and to possible long-term climatic changes are central questions for geocoronal research. Observations of thermospheric and exospheric hydrogen-alpha column emissions by the Wisconsin H-alpha Mapper Fabry-Perot (WHAM) over the 1997-2001 rise in the solar cycle are the first Wisconsin-based observations to show a statistically significant solar cyclical variation in the geocoronal H-alpha emission, with higher emissions during solar maximum periods. These observations are scheduled to continue over the decline in the solar cycle, through at least 2005. The WHAM observations corroborate suggestions of such a trend seen in past mid latitude Wisconsin-based H observations. Collectively, this long term, consistently calibrated data record now spans two solar cycles. The research focuses on: analysis of and examination of trends in Fabry-Perot observations of thermospheric and exospheric H intensities; forward modeling retrieval of the thermospheric and exospheric hydrogen column abundance using a global resonance radiative transport code; and comparison of hydrogen column densities retrieved from H observations with those generated using output from a global mean model and the Thermosphere-Ionosphere-Mesosphere Electrodynamics General Circulation Model (TIME-GCM) as input to the radiative transfer code. A primary component to understanding the earth's climate and climate change due to human activities is knowledge of natural variability in the atmosphere. This study contributes to this effort by investigating the influence on upper atmospheric hydrogen of changes in the sun's ultraviolet output over the solar cycle. Upper atmospheric hydrogen is a byproduct of hydrogenous species chemistry in the middle atmosphere, involving molecules such as methane and water vapor, two primary atmospheric greenhouse gases. It is anticipated that characterization of upper atmospheric hydrogen, together with observational diagnostics lower in the atmosphere, will contribute to studies of vertical patterns in hydrogen containing species and their influence upon one another. The WHAM data add to a long-term body of hydrogen emission data now spanning a 20 year period. Their high precision and signal-to-noise facilitate comparisons with past and future data sets. This work will continue current educational and public outreach efforts focused on enhancing scientific literacy concerning climate change and other atmospheric topics, and on promoting diversity in the study of science.