MERRA Data

MERRA U-WIND in June 1979
(Credit: Image from NASA)

MERRA is an abbreviation for Modern Era Retrospective-Analysis for Research and Applications. The datasetsoriginates from the Global Modeling and Assimilation Office of NASA / Goddard Space Flight Center.The MERRA analysis are being conducted with the GEOS-5 Atmospheric Data Assimilation System(ADAS).

Resolution and Coverage

The model grid is 0.5 degree latitude and 2/3 degree longitude.
It holds 1 hourly values in a period from 1979 until present.
Coverage is global for land-areas and coastal regions. Offshore coverage is only to be expected up to approximately 50 km from the coast line.

Data Availability

MERRA data is commonly available within WindPRO with a time-tag of 1-2 months. This is due to the processing time of the data at NASA and the subset-processing at EMD. When the data has been processed at EMD, then the following parameters are available from within the online-dataservices WindPRO. Please note that the displacement height is the height at which the log wind profile projects the wind to be zero. See more at the MERRA-FAQ.

Table: Overview of MERRA Dataset Parameters.

Parameter	Description
time	UTC time stamp
pressure	Sea level pressure
temperature	Temperature at 2 m above the displacement height
wDir	Wind direction at 50 m above surface
wSpeed	Wind speed at 50 m above surface
dispHeight	Displacement height

Data Experiences

Generally, the MERRA data is always considered when seeking for candidate reference wind datasets for a particular site. Correlation between local measurements and MERRA data is often high, see the figure below. For his particular study made in 2010, MERRA data was compared against NCEP/NCAR, 3Tier (commercial data) and SYNOP data.

Comparing Tall Mast data (Risø) to NCEP/NCAR, 3Tier, MERRA and SYNOP data

External Links

• The full MERRA data-set is available at http://gmao.gsfc.nasa.gov/research/merra/
• The MERRA-FAQ is available at: http://gmao.gsfc.nasa.gov/research/merra/faq.php

Acknowledgement

Credits: The Global Modeling and Assimilation Office (GMAO) for the MERRA-analysis and the GES DISC for the dissemination of MERRA.