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To clarify, I meant the northward direction is positive, i.e., positive value when the wind blows from south to north.

Yes. Positive is north wind.

Please check this FAQ: MERRA-2 FAQ: MERRA-2 has multiple processing streams, what are the transition dates? (https://forum.earthdata.nasa.gov/viewtopic.php?t=6467) Our MERRA-2 Project page (https://disc.gsfc.nasa.gov/information/mission-project?keywords=MERRA-2&title=MERRA-2#section+3) also has ...

Dear user, We are glad to assist you. To better help you, we need additional information as below: - A screenshot of your error messages - When the errors occurred - The URL of the dataset you accessed to - The collection name you have had an issue with - Time range (e.g., Jan 1, 2000 to Jan 1, 2020...

Have you overcome this issue? The OPeNDAP URL works for me now. The MERRA-2 data is popular thus the data system was likely overcrowded with many requests. When you got the 500 error next time, please try it later. If you used a command like wget to get the data, we suggest restricting the concurren...

PBLH in MERRA-2 is the height about ground level, not sea level.

Which data do you refer to, MERRA-2 or any observations? The PBLH might be defined differently in different data. Please refer to this paper: Ding, F., Iredell, L., Theobald, M., Wei,J., & Meyer, D. (2021). PBL height from AIRS, GPS RO, and MERRA-2 products in NASA GES DISC and their 10-year sea...

Hi Lisa,
I am glad to hear from you!
Thank you so much for your reply to my first question.
I will email you regarding the second question. It is complicated to explain through the forum.
Xiaohua

This is Xiaohua from NASA GES DISC. I'd like to know who I should contact regarding the AQ data at SEDAC. 1. I found some similar collections, as below. I wonder if some collections are similar but in different versions, e.g., V1.10 and v1. Which one is the current version? https://www.earthdata.nas...

Yes, the coordinates in MERRA-2 correspond to the center of the 0.625° x 0.5°grid. For additional information on MERRA-2's grid structure , please read MERRA-2 File Specification Document (Chapter 4) (https://gmao.gsfc.nasa.gov/pubs/docs/Bosilovich785.pdf), and refer to the MERRA-2 project page: htt...