NCAR Research Data Archive Blog
1938 atmospheric river that caused the Los Angeles flood of 1938
At least one person asked why I used a reanalysis that does not assimilate satellite water vapor data to study an atmospheric river (AR) event.
That’s a good question because the NOAA/CIRES Twentieth Century Global Reanalysis Version 2c (20thCR V2c) only ingests three things: surface pressure, sea ice coverage and sea surface temperature. The rest of the analysis is generated by the physical models of NOAA’s Global Forecast System (GFS).
I find this disturbing.
The short answer is that 20thCR V2c extends all the way back to 1851, which means you can compare storm intensity between storms, including events that occurred before the modern satellite era.
What was it, one land thermometer in the southern hemisphere during 1850? Seen the SST data source maps, even today these are very sparse.
Total counts of grid cells data points for decades can be accessed some way down a blog post from last year here.
Worrying. I’d like to see the results of validation checks done independently by unfriendly outsiders, auditors from hell.
Dig a bit deeper
What is the 20th Century Reanalysis Project?
The goal of this project is to use a Kalman filter-based technique to produce a global tropospheric circulation dataset at four-times-daily resolution back to 1851. The only dataset available for the early 20th century consists of error-ridden hand-drawn analyses of the mean sea level pressure field over the Northern Hemisphere. Modern data assimilation systems have the potential to improve upon these maps, but prior to 1948, few digitized upper-air sounding observations are available for such a reanalysis. The global tropospheric circulation dataset will provide an important validation check on the climate models used to make 21st century climate projections in the upcoming Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).
Validation check on a model?
Umm… from top “The rest of the analysis is generated by the physical models of NOAA’s Global Forecast System (GFS).”
Oh I see, a physical model, wassat then, made of wood?
So what do the British establishment have to say?
Centre for Environmental Data Archival
Science and Technoloy Facilities Council
National Environment Research Council (NERC)
The 20th Century Reanalysis (Version 2) Dataset was produced by the National Oceanic and Atmospheric Administration (NOAA) and University of Colorado’s Cooperative Institute for Research in Environmental Sciences (CIRES), members of the international Twentieth Century Reanalysis (20CR) project. The data were produced through international cooperation under the auspices of the international Atmospheric Circulation Reconstructions over the Earth (ACRE) initiative, and working groups of the Global Climate Observing System (GCOS) and the World Climate Research Program (WCRP). The 20CR project produced comprehensive global atmospheric circulation data spanning from late 19th century to the early 21st century, having only assimilated surface synoptic pressure observations and using observed monthly sea-surface temperature and sea-ice distributions from the HadISST dataset, courtesy of the Met Office Hadley Centre, as boundary conditions. Analyses every 6 hours on a 2 degree grid were produced to give the most likely state of the atmosphere based on a 56 ensemble member runs. Means, spreads and all ensemble members for each time step are available in the dataset archived at the BADC. The current 20CR output produced spans from 1871 to present with the BADC copy being updated when possible.
And provides data it seems no-one can read if the “tearing my hair out” from programmer space is correct. I couldn’t find the file format documentation either. Life is too short.
New blog… and from there Dame Julia “The science is well ahead of our ability to implement it.”
Post by Tim