A CODE TO COMPUTE HIGH ENERGY COSMIC RAY EFFECTS ON TERRESTRIAL ATMOSPHERIC CHEMISTRY Alex J. Krejci 1 , Adrian L. Melott 1 , Brian C. Thomas 2 ABSTRACT A variety of events such as gamma-ray bursts may expose the Earth to an increased flux of high-energy cosmic rays, with potentially important effects on the biosphere. An atmospheric code, the NASA-Goddard Space Flight Center two-dimensional (latitude, altitude) time-dependent atmospheric model (NGSFC), can be used to study atmospheric chemistry changes. The effect on atmospheric chemistry from astrophysically created high energy cosmic rays can now be studied using the NGSFC code. A table has been created that, with the use of the NGSFC code can be used to simulate the effects of high energy cosmic rays (10 GeV – 1 PeV) ionizing the atmosphere. We discuss the table, its use, weaknesses, and strengths. Keywords: High Energy Cosmic Rays (HECRs), Atmospheric Chemistry, CORSIKA, Ionization, Astrobiology, Cosmic Ray Spectrum 1 University of Kansas, Department of Physics and Astronomy, 1251 Wescoe Dr. # 1082, Lawrence, KS 66045-7582, United States of America; xelo11@ku.edu, melott@ku.edu 2 Washburn University, Department of Physics and Astronomy, Topeka, KS 66621, United States of America; brian.thomas@washburn.edu