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.

Sawtooth Update June 15

The experiment testing the impact of not using AMSUA for land snow conditions progressed several more days overnight. The results show that a weaker version of the Sawtooth shows up as we get deeper into winter, even without AMSUA. AIRS radiances are still being assimilated. Further analysis shows that in Siberia (where the Sawtooth is worst) the synoptic conditions change, decreasing clouds, and the Sawtooth simultaneously appears. The figure below shows the original Sawtooth (b5_b10p9), the latest experiment restricting AMSUA (exp06g) and NCEP Operational analysis for Jan 1-11, 2006. It is important to note that the weakened Sawtooth in exp06g somewhat compares to a semi-diurnal cycle in the NCEP operational analysis (between Jan 9-11, should have been still using the SSI analysis).

The working hypothesis for why the weakened sawtooth appears is that AIRS is still prevalent in this region. Some are looking into the radiative transfer model. Also, we are not using the latest NCEP CRTM. There was some discussion on updating the CRTM to the latest, however, it quickly determined that this would require a complete update of the GSI in the GEOS5 system. Of course, that would incur significant delays.

For now, we are going to continue to monitor the experiment. But the major portion of the problem seems to be under control. Since theGEOS5 is in range of NCEP operational analyses, plans for validation will go forward. In validation we will examine further whether this feature adversely affects the science quality of the data set. The good news would be that the problem has finite bounds in, only over land snow, and only occur then when AIRS is available (starting 2002).

Just a quick note and reminder of the positive aspects of this system we have previously reported (we tend to hammer at the problems). The precipitation from the configuration for MERRA seems to be well in line with GPCP, and a good contribution compared to other reanalyses. TPW looks reasonable compared to NVAP data (though those obs may have bias). There will be data supporting the stratosphere community that should be very unique. At one-hourly intervals, the surface diagnostics should be very useful for diurnal cycle studies. These and a few other aspects should help make MERRA a reasonable contribution.

Status June 14

Just a brief update, as our regular meeting was relatively brief and focused.

Progress has been made on the sawtooth problem. The results presented today show that rejecting all AMSUA radiance over land snow conditions eliminates the sawtooth. There are some experiments ongoing to test which channels (surface peak and high peak) might be included without the instigating a sawtooth. Also, there is an experiment with all AMSUA, but with much stricter quality control. We should have the results from those experiments in a couple working days. However, the fallback position would be to not use AMSUA over snow.

During these tests, some other minor bugs and updates to the system have been found and fixed. An experiment pulling the system all together is being configured and run over the weekend. That should be evaluated next week along with the AMSUA quality checks. If all goes as expected there, validation experiments will begin soon thereafter.

The 2 degree SSMI experiment is ongoing, and producing a month every 14 hours or so. Presently it is at 16 February 1988. While we're monitoring some of the data as it progresses, some analysis of SSMI impact will be done when we have 1 year after SSMI starts (probably try to get 2 years after, eventually).

Land Fractions

One feature in the GEOS5 GCM that is different previous reanalyses is fractional surface tiles, as opposed to a land/sea mask. Each grid box contains a fraction of land, water, lake or land ice. The fractions are based on the 1km Global Land Cover Characteristics (GLCC) database. Along coast lines, the land processes are blended with sea surface processes. Inland, lakes and rivers are also included. This will require some attention of users calculating precise budgets. For example, the grid box average evaporation that would be appropriate for an atmospheric budget, may not be appropriate for in-situ data comparisons and land surface budget studies, if the lake fraction is substantial. Figures showing some examples of land and lake fractions are shown below.

To support the analysis of land water and energy budgets, a land only output data collection will be produced (tavg1_2d_lnd_Nx in the MERRA File Specification Document). These grids would be for the land only fraction of the surface. Users will be able to differentiate land evaporation from total evaporation in grid boxes near the coast and near inland water bodies. Soil water (GWET variables) will show up in grid boxes that appear to be oceanic. The model does provide an integer land/ocean mask (variable name LWI). However, this is simply a 50% cutoff between land/land ice and ocean fractions. For some specific purposes, this may not be appropriate, and users should use the land fraction to develop their own mask.

Additionally, the land fraction is subset into tiles based on the Catchment hydrology. The land collection includes data from the catchments. For more information, the interested reader should review Koster et al. (2001, J. Geophys. Res. Vol. 105 , No. D20 , p. 24,809, 2000JD900327).

Status June 5

We've had some good news and bad news. The good news is that efforts by the analysis group to revise the error statistics have had the expected positive impact on a systematic zonal wind bias in the tropics at upper levels. Further, the adjustments in the convective parameterizations by the model group have held up through this testing, and precipitation looks be reasonable compared to other reanalyses and observation data sets at the monthly time scales.

The bad news is that the "saw tooth" problem persists, but progress is being made in understanding it. In one of the data sweeper runs, we find that the analysis is reasonable, through Dec 2000, then the sawtooth begins in January 2001. This is at the same time NOAA 16 data begins to be used in the input data stream. Presently, the satellite bias corrections used in the system are being reexamined. The current thinking is that, if an inappropriate bias is included, the analysis rejects the radiance observations (near the surface), then the bias is never properly adjusted. To test this, an experiment started with zero bias is being started, this should spin up a new bias correction. Most of the system testing has simply carried bias corrections along from older systems.

So, while the system is getting closer and we are certainly learning more on the system with every experiment, the important validation experiments have not yet begun. Some minor corrections have also been identified. For example, it was found that snow was reaching the surface in regions too warm and equatorward. The snow production algorithm was not including surface temperatures, so now a check has been added.

The 2 degree experiment to test SSMI in the late eighties has progressed into 1987, and is closing on the onset of SSMI in July. However, the experiment is being removed from the priority queues. The GMAO is gearing up for operational support for TC4, which needs high priority, and also the experimentation on the sawtooth problem takes priority.

To emphasize the critical nature of the sawtooth problem, the figure below shows an example of how it looks at the worst. The time series is 850 mb temperature at a point every 6 hour analysis time. The points closest to the NCEP operational analysis are the when sondes are present (00Z and 12Z) and the very warm temperatures are when only satellite data are available. At this point, the GEOS5 surface temperature is much colder than NCEP and the surface channel radiances are being rejected by the quality controls.

June 11 Follow up: Recent experiments have shown that the AMSU channels over ice may be the root of the sawtooth problem. Further work is aimed at identifying specific channels. Result should be posted in the next status report, probably Friday June 15.