[Rda-users] CISL Research Data Archive News

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The following news article has been posted by the CISL Research Data Archive at NCAR:

"Exploring the NOAA/CIRES Twentieth Century Global Reanalysis Version 2c"

Each reanalyses has its strengths and weaknesses. To better select the optimal
dataset for your research, it's helpful to take several datasets out for a test
spin. I put our newest reanalysis dataset, the NOAA/CIRES Twentieth Century
Global Reanalysis Version 2c
[http://rda.ucar.edu/datasets/ds131.2/index.html#!description], and a timely
topic, Atmospheric Rivers (ARs), together into a data exploration exercise by
visualizing a strong AR event from Dec 2004 to Jan 2005.*

Atmospheric rivers [http://www.esrl.noaa.gov/psd/atmrivers/] are narrow regions
that transport water from the tropics to higher latitudes. They are defined as
areas of high precipitable water content (greater than 20 kg m-2) that are
longer than 2000 km but narrower than 1000 km. ARs have been in the news
recently because of the severe drought in California and their historical role
in breaking droughts; they break about half the droughts of the arid American
West [http://journals.ametsoc.org/doi/abs/10.1175/JHM-D-13-02.1].

First, I made a global animation of Dec 26, 2004 to January 11, 2005 to show
atmospheric rivers peeling off from the moisture belt of the tropics. In the
global animation, ARs are light cyan to red in color. Click to view the global
animation
[https://drive.google.com/open?id=0B4uEllQBkwzDV2RwbnNEN0JiMDQ&authuser=1].

Then I zoomed in to the regional-scale and changed the color range of the
precipitable water scale from [0.1, 70] to [0.1, 40] to better show the
structure in mid-latitudes like California. In this animation, ARs are yellow to
red. Click to view the regional animation
[https://drive.google.com/open?id=0B4uEllQBkwzDbEQ4VGFKcE1QVkk&authuser=1].

Notice a first pulse of moisture in late December that came in through the Gulf
of California. It was responsible for the record-setting heavy rains in Death
Valley and the inland deserts of California. The rains formed a lake in Death
Valley that persisted for several months and was 30 miles long, 5 miles wide and
4 feet deep at its fullest. People kayaked and wind-surfed on the lake.

Then an atmospheric river hit the coast of California with multiple pulses of
heavy moisture. According to NOAA's California Nevada River Forecast Center
[http://www.cnrfc.noaa.gov/]'s Heavy Precipitation Report for this event
[http://www.cnrfc.noaa.gov/storm_summaries/jan2005storms.php], these two storms
dropped an impressive amount of rain in southern California, including a
whopping 51.77 inches at Opids Camp.

I made the visualizations with the help of NASA's free Panoply data viewer
[http://www.giss.nasa.gov/tools/panoply/] and GIFMaker [http://gifmaker.me/].
Panoply can handle many common atmospheric science data formats, including
various flavors of GRIB. Panoply can read and display both the 2x2 degree
Lat/Lon and the Gaussian T-62 grids of NOAA/CIRES Twentieth Century Global
Reanalysis Version 2c
[http://rda.ucar.edu/datasets/ds131.2/index.html#!description].

For further guidance selecting from among the RDAs many reanalyses
[http://rda.ucar.edu/#!lfd?nb=y&b=plat&v=REANALYSIS MODELS], please
contact the data specialist for each particular reanalysis.

* While there are better reanalyses for studying recent events, 20thC R2c
extends back to 1851, making it ideal for studies that require very long time
series.