MERRA-2 Data

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Example of MERRA-2 mean wind speeds at 50 m. Screen shot from http://www.windprospecting.com/
Observations assimilated in MERRA2 (top) and MERRA (bottom) datasets for the period 01.1980 until 12.2014. Units are millions per 6 hours. From Bosilovich et al.

Introduction

MERRA-2 is the most recent version of the popular MERRA dataset modelled and distributed by the Global Modeling and Assimilation Office of NASA / Goddard Space Flight Center. The original MERRA dataset is discontinued in early 2016. After this point MERRA-2 is the most recent and updated MERRA dataset. MERRA-2 uses a newer version of the modelling system and also incorporates newer data sources and observations (see the lower-figure to the right).

At EMD, we have done a comprehensive evaluation of the performance of the MERRA2 dataset for wind-energy applications. Please consult the paper by Thøgersen et al, "Is MERRA2 Able to Replace MERRA as a Trusted Reference Wind Dataset?". The paper is available from the windPRO knowledgebase, here.

Dataset Overview

  • Content:: Renewable energy focused data subset of MERRA2 data.
  • Spatial Resolution:
    • 0.5 degree latitude
    • 0.625 degree longitude
  • Temporal Resolution: Hourly values.
  • Coverage:
    • Coverage is global for land-areas and coastal regions.
    • In windPRO, offshore coverage is at a distance of approximately 300 km from any known coastlines.
  • Period: 25+ years. The EMD databases will hold data back to 1992.
  • Update schedule:
    • EMD updates the dataset once a month - with data being available with a 1-2 month delay from real-time due to NASA/MERRA data availability.

Usage Notes and User Notifications

2020-11-05: NASA has released a revised MERRA-2 dataset covering the month of September 2020. This revised data is released with windPRO on November 6th 2020. It is confirmed that the 50m wind-speeds are affected, see our map that visualizes the difference between the two batches of data - here. We have also a plot that visualizes the time-series differences in 50m wind speed for a single node at location N56.0 E9.4, here. If you have downloaded the September 2020 data in the period from October 24th to November 3rd, we recommend that you: 1) Delete the month of September 2020. 2) Download the most recent data. 3) Re-do your calculations. Read the final newsletter about this issue here
2020-11-03: NASA has notified us about an issue with the September 2020 data (released from NASA on October 20th 2020). The MERRA-2 science team at NASA do not recommend using the data - and are currently reprocessing the data. In the windPRO online-data services, September 2020 data has now been removed as of November 3rd. If you have downloaded the MERRA-2 data in the period between October 24th to November 3rd, we recommend that you disable or remove the MERRA2-data for the month of September 2020. The actual nature of the issue is unknown to the windPRO online-data team. We will send out a notification when new data has been released from NASA. Read the original statement from NASA here. Read the windPRO newsletter about this issue, here.

Data Availability

MERRA-2 data is commonly available within windPRO with a time-lag 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 have been processed at EMD, then the following parameters are available from within the online-data services within windPRO. Please note that the displacement height is the height at which the log wind profile projects the wind to be zero.

Table: Overview of MERRA-2 Dataset Parameters.
Parameter Description
time UTC time stamp
psfc Surface pressure
msl Mean Sea Level pressure
wSpeed.50 Wind speed at 50 m above surface
wDir.50 Wind direction at 50 m above surface
wSpeed.850hpa Wind speed at 850 hpa
wDir.850hpa Wind direction at 850hpa
temperature.10 Temperature at 10 m above surface
temperature.50 Temperature at 50 m above surface
dispHeight Displacement height
precIceWater Total precipitable ice water
precLiqWater Total precipitable liquid water
precWaterVapor Total precipitable water vapor
specHumidity.10 Specific humidity at 10 m

External Links and References

  • The MERRA-2 project page - HERE
  • Bosilovich et al "MERRA-2: Initial Evaluation of the Climate" - HERE
  • Thøgersen et al, "Is MERRA2 Able to Replace MERRA as a Trusted Reference Wind Dataset?" - HERE.

Acknowledgement

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