## 4 Results
### Comparison of LEO IR and MW Sounder Data Assimilated
For the latency_20m run, about 92% of the IR sounder measurements are assimilated into the global model. In the case of the latency_5m run, the data usage further increases by 6%, reaching up to about 98% for all IR sounders. Similar to the results of the IR sounders, a 20-min latency (5-min latency) also enhances the data usage ratio of the ATMS MW sounders up to about 90% (95%) (Figure 4). For the operational GFS (control run), the data usage ratio of ATMS onboard S-NPP satellite is lower than that of ATMS  
Figure 4: Time series of assimilated data ratio of Advanced Technology Microwave Sounder (ATMS) MW sounders onboard (**a**) Suomi National Polar-orbiting Partnership (S-NPP) and (**b**) National Oceanic and Atmospheric Administration (NOAA-20) satellites for the period from 7 July to 22 August 2018. Black, red, and blue lines indicate the control, latency_20m, and latency_5m runs, respectively. Figure 3: Time series of assimilated data ratio of (**a,b**) CrIS, (**c,d**) IASI, and (**e**) AIRS IR sounders for the period from 7 July to 22 August 2018. Black, red, and blue lines indicate the control, latency_20m, and latency_5m runs, respectively. onboard NOAA-20 satellite due to the same reason as the CrIS instrument. As the data usage of other MW temperature and moisture sounders, i.e., Advanced Microwave Sounding Unit-A (AMSU-A) and Microwave Humidity Sounder (MHS), shows quite similar patterns to the results of IR sounders and ATMS sensor (Figures 3 and 4), the time series of AMSU-A and MHS sounders are not shown. In addition to the total data usage, it is also of interest to examine the data usage depending on the IR and MW sounding channels. For the hyperspectral IR sounders, a subset of channels has been selected for each instrument to represent information contained in the full spectrum. NWP centers have only received the observations of a subset of IR sounder channels. CrIS subset is different depending on the operation model, i.e., the normal spectral resolution (NSR) and the full spectral resolution (FSR). In NSR mode, CrIS subset contains 399 channels that are from CrIS 1305 channels with different spectral resolution for all three bands (0.625, 1.25, 2.5 cm\({}^{-1}\) for long-wave IR, mid-wave IR, and short-wave IR, respectively). In FSR mode, CrIS subset consists of 431 channels pre-selected from all CrIS 2211 channels with spectral resolution of 0.625 cm\({}^{-1}\). IASI and AIRS instrument has 616 and 281 channels, respectively. This is done to reduce data transfer and computation cost. Each NWP center further pre-selects the channels from these subsets for assimilation. For example, 164 of 616 IASI channels, are assimilated in the GFS. For CrIS instrument onboard NOAA-20 satellite in FSR mode, 93 of 431 CrIS subset are assimilated. For CrIS instrument onboard S-NPP satellite in NSR mode, 82 of 399 CrIS subset are used. Figures 5 and 6 show the mean data number of the assimilated CrIS and ATMS channels for three trial runs, respectively. Similar to what is shown in Figure 3a,b, a maximum data number is presented for the latency_5m run and the number of CrIS data onboard NOAA-20 satellite is larger than that of S-NPP satellite for the control run (Figure 5). However, the number of observations assimilated per channel significantly differs due to the spectral characteristics of CrIS channels being distributed on different absorption bands. For the GFS, there are two major quality-control processes that determine if the observations are to be assimilated into the GFS. First, if the cloud is detected in the CrIS field of view (FOV), the cloud-affected CrIS channels are discarded if their peaks of the weighting function of channels are below the top height of the cloud detected from the satellite measurements. Second, under the clear-sky condition, the surface-sensitive channels are rejected if the departures between the observed radiances and model-simulated radiances exceed certain thresholds due to the uncertainty of used surface information (i.e., surface temperature and surface emissivity).