Status Apr 11 - Long

There has been much going on, and a lot keeping me from these updates, unfortunately. There are several items I'll include here.

First, our late 90's "scout run" (2 degree resolution, same system as MERRA) was running well ahead of the reanalysis, but encountered a problem in a single file of MSU data. There was a corruption in the input file. it has been found and corrected. That's the benefit of these coars scout runs, they should find the problems that would otherwise slow down the processing.

The system had been running at just over 10 days per calendar day for some time. However, we have been only getting ~7 days per day lately. It's a technical problem that the computer folks are working. It basically comes down to increased usage on the machine, affecting the MERRA jobs. People are looking at it, to try to get the performance back up.

We have a monitoring routine established. Some climate maps are being inspected each month of reanalysis. (Some examples posted below) Soon we hope to make those available on the internet. The monitoring code also includes range checking on each and every variable and layer produced by the system. We have some hits in the range checking from variables SHLAND (land only sensible heat flux) and TSTAR (surface layer temperature scale). TSTAR seems to be spiking sporadically, but in conditions with low wind speed and near the change from night to day (stable to unstable) conditions. It does not appear to be a severe problem, there is no plan to stop or back up MERRA for these flags. SHLAND is showing range check errors at a few, very repeatable points. Those are where the fraction of land is much smaller than that for ocean. So, it appears that ocean is driving a surface atmosphere that is causing convergence problems in the land parameterization where the fraction of land is small. For example dry soil with a dominantly tropical ocean point. So far, the grid average sensible heat seems reasonable, so there is no immediate plans to correct this, or stop and rewind MERRA.

Range checking has also found occasional occurrences of shortwave radiation diagnostics are reporting negative numbers. The magnitude is very very small, and the result of roundoff in the interpolation, and not protecting against such negative values. The net effect of these should be extremely small, but may trip code that expects perfectly zero values of shortwave radiation components. Users will be advised to clear such negative values.

A systematic difference from other reanalyses has been occurring monthly and in each season. Below the zonal specific humidity and 850mb map of specific humidity compared to ERA40 in JJA 1979 is attached. These biases were noted in validation. The contour interval is small and the range close. The MERRA data is dry in the tropics at 85omb and wet above 700mb. This is an interesting result, considering that the total column water and precipitation have been very well reproduced.

There's more to come, including online access to figures that the GMAO is using for monitoring.

Zonal mean specific humidity for JJA 1979 compared to ERA40.
850 mb Specific Humidity for July 1979 compared to ERA40.
Global Precipitation difference of existing long reanalyses compared to GPCP (CMAP differences included for reference) for July 1979.