The gradient descending curve of the AMSU-A test achieves a stable value after the third iteration, that of the AMSU-A_GRD test has a large fluctuation in the 10th iteration and afterwards is stable, and that of the AMSU-A_GRD_C test is also nearly stable after the 10th iteration.
In this paper, the ideal experiment of AMSU-A data is performed with the CRTM model to verify the feasibility of gradient information assimilation.
Cheng, "Reconstruct the Mesoscale Information of Typhoon with BDA Method Combined with AMSU-A Data Assimilation Method," Advances in Meteorology, vol.
Test Whether to assimilate the Whether to use gradient grouping gradient information information as a constraint AMSU-A No No AMSU- Yes No A_GRD AMSU- Yes Yes A_GRD_C Table 2: Schemes of numerical test.
We speculate that this additional resilience of the OPS observing system (Andersson and Sato 2012), by having more AMSU-A instruments in orbit relative to the future 20-4S configuration, has the potential to increase skill marginally in the time mean, but more importantly it may reduce the possibility of an episodic low-score forecast.
Comparing the OSE CNTL with NCEP's OPS, it appears that adding three AMSU-A MW sounders increases the mean Z500AC score incrementally, but not significantly, in both hemispheres.
These numbers suggest that the three additional AMSU-A instruments add resilience to the COS, consistent with Andersson and Sato (2012).
(1) For the MW instrument, we used NOAA-19 AMSU-A and MHS instead of ATMS because it was originally planned to run an additional experiment to substitute ATMS for the NOAA-19 MW instruments.