Table 2.

Key characteristics of water vapor treatment in reanalyses

Reanalysis	Assimilation of satellite humidity radiances?	Highest level of assimilated WV observations	Highest level of analyzed WV1	Stratospheric WV used in radiative transfer	Stratospheric WV treatment	Stratospheric methane oxidation parameterization?
NCEP R1	No	300 hPa	300 hPa	Climatology	None	No
NCEP R2	No	300 hPa	10 hPa (RH only)	Climatology	None	No
CFSR	Yes	250 hPa	None	Analyzed; negative values set to 0.1 ppmv	Prognostic	No
ERA-40	Yes	Diagnosed tropopause. Radiosonde humidity generally used to 300 hPa	Diagnosed tropopause	Analyzed	Prognostic	Yes. Relaxation to 6 ppmv WV at stratopause
ERA-I	Yes	Same as ERA-40	Diagnosed tropopause	Analyzed	Prognostic	Yes. Relaxation to 6.8 ppmv WV at stratopause
JRA-25	Yes	100 hPa	50 hPa	Constant 2.5 ppmv	Prognostic2	No
JRA-55	Yes	100 hPa	5 hPa	Climatological annual mean from HALOE and UARS MLS during 1991–1997	Prognostic2	No
MERRA	Yes	300 hPa	None	Analyzed	3-day relaxation to zonal-mean monthly-mean satellite-based climatology	No
MERRA-2	Yes	300 hPa	None	Same as MERRA	Same as MERRA	No

¹Level above which assimilation-related increments are not allowed.

²Water vapor not provided above 100 hPa in pressure level analysis products.