Earth Global Reference Atmospheric Model (Earth-GRAM) 2026: User Guide

Reference or standard atmospheric models have long been used for design and mission planning of various aerospace systems. The NASA Global Reference Atmospheric Model (GRAM) was originally developed in response to the need for a design reference atmosphere that provides complete global geographical variability, altitude coverage (surface to orbital altitudes), and seasonal and monthly variability of the thermodynamic variables and wind components. A unique feature of GRAM is that, in addition to providing the geographical, height, and monthly variation of the mean atmospheric state, it includes the ability to simulate spatial and temporal perturbations in these atmospheric parameters (e.g. fluctuations due to turbulence and other atmospheric perturbation phenomena). A summary comparing GRAM features to the characteristics and features of other reference or standard atmospheric models, can be found in the Guide to Reference and Standard Atmosphere Models1. The original GRAM2 has undergone a series of improvements over the years with recent additions and changes.3-10, 54, 58, 59 This software program is now called Earth-GRAM to distinguish it from similar programs for other bodies (e.g. Mars, Venus, Neptune, Titan, Jupiter, and Uranus). An overview of the basic features of Earth-GRAM, including recent additions, are found in section 1. Section 2 provides a more detailed description of Earth-GRAM and how the model output is generated. Section 3 presents sample results and section 4 gives specific user information. Appendix A describes the headers for Earth-GRAM output file. Appendix B provides an example NAMELIST format input file. Appendix C gives a description of the sample output LIST file. Appendix D provides a summary of the files provided with Earth-GRAM. Appendix E provides instructions for building Earth-GRAM. Finally, appendix F provides a history of Earth-GRAM version revisions.