Solar Irradiance of the Earth’s Atmosphere

The sun is the primary driver of terrestrial atmospheric phenomena and energy source for the earth. It emits radiation over a large energy band and ejects highly energetic plasma fluxes of charged particles into space. The sun is an active star that (i) goes through a 12-year maximum-minimum emission cycle, (ii) has huge, non-periodic eruptions in solar flares and coronal mass ejections, and (iii) has nearly equipartition of energy between particle and radiation fluxes. Variations in these emissions interact with all atmospheric layers down to the earth surface. The precise nature of these interactions can be examined through microscopic physics at atomic and molecular levels for illustration of physical and chemical processes, and their impact on macroscopic problems such as global climate change, and more localized manifestations such as the atmospheric brown cloud (ABC) prominent in Asia. I will describe some of these calculations for atomic and molecular species such as carbon, nitrogen, oxygen, sulfur and their compounds. While the visible and nearinfrared solar radiation penetrates through, more energetic components in the ultraviolet (UV) and the X-ray are absorbed by the upper layers of the atmosphere and thus provide protecting shields for life on earth. The atmosphere has been maintaining a fine energy balance of solar radiation entering the earth by radiating the same amount into space. Certain atmospheric gases trap radiation energy and reflect back near earth’ surface to heat it up in an energy cycle. This phenomenon is known as the Greenhouse effect and has maintained the average earth surface temperature at 14C. However, for over a hundred years the balance is being perturbed due to changes in atmospheric compositions of greenhouse gases. More energy is being trapped than released, leading to global warming and climate change. Depletion of atmospheric ozone molecules has created holes for harmful radiation to reach earth’s surface. The basic scientific data in current atmospheric models lack accurate parameters for fundamental atomic and molecular processes, and hence provide predictions which have large uncertainties. We aim to explore the sensitivity of numerical simulations to accurately predict the response of the earth’s atmosphere to changes in elemental and molecular composition. To wit, what is the effect of including new highaccuracy photoionization and radiative transition rates in C, N, O, H2O, etc. in climate models? How do temporal-spatial and temperature-density dependencies of fundamental physical and chemical parameters and rates affect the absorption of solar radiation by the ABC? Such studies should lead to an improved understanding of global warming and climate change processes, and help in the future steps. Acknowledgements: Partially supported by a NASA grant.