An Analysis of NASA's MERRA Meteorological Data to Supplement Observational Data for Calculation of Climatic Design Conditions

ASHRAE Technical Committee 4.2, Climatic Information, publishes a quadrennial update of climatic design information in Chapter 14 of the ASHRAE Handbook-Fundamentals (ASHRAE 2009a). The design information for 5564 locations around the world is based upon hourly values of dry-bulb temperature, wet-bulb temperature, dew-point temperature, wind speed and direction, surface pressure, and solar radiation. The 2009 design conditions provided a significant enhancement over the 2005 design conditions with respect to the global coverage-5564 locations in 2009 versus 4422 locations in 2005. The ASHRAE design conditions, based on meteorological data, are calculated using hourly surface data from stations having a minimum of 8 years of observations, but more stations typically span 25 years of observations; although frequently the time series are discontinuous. The ASHRAE solar-related design conditions are based on model-derived solar radiation. A potential source for both global and time contiguous meteorological and solar data is NASA's POWER (Prediction of Worldwide Energy Resource) web portal (NASA 2013a). This includes the recently available meteorological data based on an improved reanalysis model-Modern Era Retrospective-analysis for Research and Applications (MERRA). MERRA yields global, hourly surface meteorological parameters for the years 1981 to present. An initial evaluation of the MERRA daily maximum, minimum, and averaged temperatures indicates accuracies sufficient to warrant their use to supplement existing surface observations. In this paper, we present an evaluation of the accuracy of the MERRA daily temperatures, followed by an assessment of the applicability of the MERRA hourly temperatures in the development of annual dry-bulb climate design criteria and annual heating and cooling degree-days over the continental United States.