You may want to take a look at the official NCEP/NCAR Reanalysis documentation.
I am not familiar enough with the Reanalysis dataset to answer your question and will
have to refer you to the Reanalysis project and their documentation.
I found the following explanation on the FAQ page
You may want to look at the following reference:
My understanding from the Reanalysis documentation is that the soil moisture represents
the fraction of the soil column (between 10 and 200 cm) composed of water, by volume.
The online documentation for the DASILVA dataset refers to the original distribution
of the surface marine atlas (1945-1989).
In the calculation of the SST anomalies in this dataset, the following climatology
was subtracted from the SST dataset:
While you are welcome to acknowlege the LDEO/IRI Data Library, it is not required.
The appropriate reference for the GCPS dataset can be found on the documentation page
for the dataset in the IRI Data Library.
Weather Bureau/Army/Navy ID
We do not have documentation that details how the monthly averages of vapor pressure
deficit were calculated.
Unfortunately, there is no straight-forward answer.
You can find more information about the model here
Once you have selected the data that you would like to download, look for the "Data
Files" link in the table at the top of the page
When you are looking at the figure, make sure that you can see a table at the bottom
of the page that includes the phrases "Just the Figure Formats" and "Just the Scale
Formats"
If you are using Internet Explorer, then try downloading your file with Netscape.
The 'Load to Local Disk ... ' message refers to an option to be set on your browser.
The grid values represent the center of each grid cell.
That information does not appear to be in the IRI Data Library.
Maps of climatological wind speed, geopotential, surface height, surface pressure,
specific humidity, 2-meter temperature,and zonal and meridional wind are publicly
available within the Data Library.
To save these images, simply click on them with the right button of your mouse.
The convention is that negative meridional values indicate wind blowing from north
to south (north wind) and positive meridional values indicate wind blowing from south
to north (south wind).
I would suggest that you look at the following overview of the GHCN: