Earth global reference atmospheric model (GRAM-99) and trace constituents Original Research Article

Global reference atmospheric model (GRAM-99) is an engineering-level model of the Earthʹs atmosphere. It provides both mean values and perturbations for density, temperature, pressure, and winds, as well as monthly- and geographically-varying trace constituent concentrations. From 0 to 27 km altitude, thermodynamics and winds are based on National Oceanic and Atmospheric Administration Global Upper Air Climatic Atlas (GUACA) climatology. Above 120 km altitude, GRAM is based on the NASA Marshall Engineering Thermosphere (MET) model. In the intervening altitude region, GRAM is based on Middle Atmosphere Program (MAP) climatology that also forms the basis of the 1986 COSPAR International Reference Atmosphere (CIRA). MAP data in GRAM are augmented by specially derived longitude variation climatology. Atmospheric composition is represented in GRAM by concentrations of both major and minor species. Above 120 km, MET provides concentration values for N2, O2, Ar, O, He, and H. Below 120 km, species represented also include H2O, O3, N2O, CO, CH4, and CO2. Water vapor in GRAM is based on a combination of GUACA, Air Force Geophysics Laboratory (AFGL), and NASA Langley Research Center climatologies. Other constituents below 120 km are based on a combination of AFGL and MAP/CIRA climatologies. This report presents results of comparisons between GRAM constituent concentrations and those provided by Naval Research Laboratory (NRL) climatology. GRAM and NRL concentrations were compared for seven species (CH4, CO, CO2, H2O, N2O, O2, and OH3) for months January, April, July, and October, over height range 0–115 km, and latitudes −90° to + 90° at 10° increments. Average GRAM-NRL correlations range from 0.878 (for CO) to 0.975 (for OH3), with an average over all seven species of 0.936 (SD 0.049).