Both of these data are available in rda.ucar.edu website., i.e. https://rda.ucar.edu/datasets/ds628.0/

You must register in this website to have access to the mentioned data sets.

JRA-25 is the older version of Japanese reanalysis. It has lower spatial resolution and some deficiencies (https://www.jstage.jst.go.jp/article/jmsj/93/1/93_2015-001/_article). JRA-55 is much more reliable except you want to do a comparison/sensitivity study. 

I usually download JRA product from its main page in http://jra.kishou.go.jp/JRA-55/index_en.html. 

Kindly check..

https://rda.ucar.edu/datasets/ds628.0/

Also..see here

https://rda.ucar.edu/datasets/ds628.0/

See please..

http://jra.kishou.go.jp/JRA-55/index_en.html

Please explore..

https://gcmd.nasa.gov/KeywordSearch/Metadata.do?Portal=idn_ceos&KeywordPath=Parameters%7CTERRESTRIAL+HYDROSPHERE%7CSNOW%2FICE%7CSNOW+WATER+EQUIVALENT&OrigMetadataNode=GCMD&EntryId=NCAR_DS628.0&MetadataView=Full&MetadataType=0&lbnode=mdlb3

More info, please..

https://s-rip.ees.hokudai.ac.jp/resources/links.html

I recommend this site:

https://s-rip.ees.hokudai.ac.jp/resources/links.html

So have you desovled your problem?

I have registered in this website,but I am not eligible to the JRA55. How to deal with it? Thank you a lot.

Hello, this video shows how to download data from JRA 55: https://www.youtube.com/watch?v=sxDtOXecyoc

What about JRA55-do?

You can check this link: https://rda.ucar.edu/datasets/ds628.0/#!access