Status June 28

Since the last post, work has progressed on setting up the validation experiments. Initial conditions are being created and assorted other tasks to make sure the system is configured. The jobs should be close to starting. However, there are some ongoing experiments that may affect the setup. First, the data group has applied some corrections to the sonde data for known biases (e.g. radiation). I don't have the citations handy but I'll try to get them posted before long. With the corrections applied to the data, the quality control code needs to be modified to reflect that. The experiment is just a sanity check to make sure that the data and code are implemented properly.

While investigating the "sawtooth" problem discussed in earlier posts, the analysis group looked more closely at some of the statistics for the temperature assimilation. A feature in the lowest atmospheric layers of the statistics may partly contribute to the sawtooth, so they are testing a correction to the statistics. Preliminary results seem positive, and a full resolution was being started. This correction would be much more broad than the target correction already applied to fix the sawtooth. So, we will need to look closely at the experiment before it is implemented for validation.

In parallel, the code is being engineered to work on a newer supercomputer at GSFC called Discover. This will be where MERRA production is carried out. The system is running well there. However, occasional random crashes are being investigated. A likely cause is a memory leak. These things happen, and the folks working on the problem should have it fixed without impact on production.

The SSMI 2 degree experiment is nearly complete (Jan 1984 - Dec 1989). The main purpose was to checkout the potential impact of the introduction of SSMI (radiances and surface ocean winds) to the data stream. Several people are still looking at it. The preliminary results show that the SSMI does not seem to have considerable impact on atmospheric moisture and precipitation. However, it is plainly apparent in the global time series of surface wind, moisture and evaporation (all increasing). There is a slight upward trend in global precipitation after the introduction of SSMI, but it does not exhibit a a shock or step (to the eye, statistical analysis would probably reflect the introduction).

One feature that this experiment has demonstrated is that the operational NOAA satellites, and their variations do seem to be influencing the precipitation time series. Firstly, the global mean precipitation (averaged for Jan 1984 - Dec1987) is lower than any experiment we have run to this point, 2.2 mm/day compared to 2.6 mm/day for GPCP and ~3mm/day for JRA25 and ERA40. Resolution might be part of the deficit. In some recent tests, we have not seen a large change in precipitation going from 1/2 to 2 degrees. However, some previous experiments did show ~0.2mm/day global deficit in the 2 degree system compared to 1/2. So, we are putting a new experiment into the validation experiments, July 1986. This will run at 1/2 degree with the latest system, and be included in the validation experiments.

Another issue from the SSMI experiment is that the precipitation bias is not uniform across the period of analysis. In 1984, precipitation is quite close to GPCP at2.4 mm/day, but it has a downward drift over the next few years, from early 1985 (NOAA 9 starts in Dec 1984) until Jan 1987 when NOAA 10 begins. The analysis increments are negative (removing water vapor) and getting more in time. There are jumps in the time series of moisture increments when the NOAA satellites change. We still have a bit of work to do on this, as well as check the 1/2 degree experiment. A more detailed evaluation is being prepared, and we have much more to investigate.

The primary validation experiments will be Jan and Jul 2004 (expected to run for six months each to make a full annual cycle). The Jul 1986 is also being put on a fast track. They should start soon, and more info will be posted then. The secondary runs, Jan/Jul 2001 and Jan 2006 will begin when CPUs become available.