Friday, January 29, 2010

Arctic System Reanalysis

Recognizing the importance of the Arctic region, as well as the tremendous amount of field work and supporting data sets, the Arctic System Reanalysis will perform a high resolution limited domain reanalysis for the Arctic. Recently, there was a Call for Community Involvement (unfortunately AGU member can only download this), printed in EOS (v 91, #2, 12 Jan 2010) looking for supplemental data and science interest in the project.

There has been quite a bit of recent evaluations of MERRA polar energy and water cycles. Some will be posted here shortly.

Wednesday, January 27, 2010

Pressure levels greater than surface pressure

Some questions have come in regarding differences between MERRA and other reanalysis at pressure 1000mb and 850mb pressure levels. It is very important to note that MERRA does not extrapolate pressure level data vertically greater than the surface pressure. The result is that there is undefined data points in much of the 1000mb fields. This will affect the representativeness of both time and area averages of MERRA data compared with reanalyses or other data that extrapolates gridpoints to pressure levels greater than the surface pressure. The GMAO provides a summary of the impact that this has on averaging. In addition, the FAQ will be updated to call out this difference with other data sets. The main GMAO www page also has other pages with useful practical information about the data and assimilation system.

Friday, January 15, 2010

CFSRR

Some News which may interest those who read these pages:

On 1/14/2010 6:16 PM, Suranjana.Saha@noaa.gov wrote:
> Dear Colleagues
>
> I am happy to inform you that the CFS Reanalysis is now complete for 31
> years (1979-2009) and the paper has just been submitted to BAMS.
>
> You can download it at the CFS website at:
>
> http://cfs.ncep.noaa.gov
>
> The first set of CFSR data will be made available to the public at NCDC
> and NCAR on Feb 1, 2010. The complete high resolution datasets will be
> distributed in the next 6 months or so.
>
> Thanks
> Suru Saha

Wednesday, January 13, 2010

MERRA Turns 30

31DEC2008 has just been produced by the reanalysis system. This extends the MERRA Mainstream to 30 Years. 2008 is still being checked for quality, but should be posted online at the MDISC within a week or so.

At approximately 1 year per six weeks, 2009 should be produced by the end of February. MERRA production will make a transition then, where we expect data to be released monthly. The production is delayed from real time to allow ingest of the most complete observations, but also to quality check the data files.

Friday, January 8, 2010

1993 Flood

Hydrologic anomalies can be persistent leading to extreme regional conditions. Much has been written on the 1993 flood in the central United States. The soil was saturated at the start of the summer becasue of above normal spring precipitation. During June, several strong synoptic scale events brought continued wet conditions. During July at the center of the flooding rains, convective events occurred almost every day. This post is just a quick look at the MERRA anomalies. It is interesting to note that the magnitude of the heavy precipitation anomaly is weaker than what was observed by gage measurement (figure below). Likewise, the precipitation anomaly for 1988 (severe persistent drought) is also a smaller magnitude than observed (not shown).


The following figure shows the time series of MERRA and gage July-Aug (JJA) precipitation area averaged for the sub-basins of the Mississippi. The curious feature in this comparison is that the various sub-basins in MERRA tend to track similar to each other, or perhaps, more than the gage observations. This is apparent from the mid 1990s through the early 2000s. It seems that the spatial scale of precipitation anomalies in MERRA is larger than observed.

These features still need to be more thoroughly studied.