In the current operational system, a data thinning is applied to IMS by using "bufr_filter" to pick up part of IMS (select 1 every 36 IMS raw observations). However, it looks inhomogeneous especially in some areas. The new data thinning has been tested by using "bufr_grid_screen_parallel" as same as satellite observations. The following configuration have been used:
The impacts are as below.
- The new thinning leads to more homogeneous spatial distribution at the horizontal resolution of 25 km.
- The number of IMS observations used in 2D-OI is reduced from 251926 to 169726.
- The spatial distributions can be more consistent between IMS and ESA CCI Snow.
