30 March 2015

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, 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 are narrow regions that transport water from the tropics to higher latitudes.  They are defined as areas of high precipitable water content (> 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.

First, I made a global animation of Dec 26, 2004 through January 12, 2005 to show atmospheric rivers peeling off from the moisture belt of the tropics.   In this global animation, ARs are light cyan to red in color.
Animation of PWV from NOAA/CIRES Twentieth Century Global Reanalysis Version 2c for 2004-12-26-00 to 2005-01-12-00 UTC.
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.
Animation of PWV from NOAA/CIRES Twentieth Century Global Reanalysis Version 2c for 2004-12-26-00 to 2005-01-12-00 UTC.
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.
PWV for 2004-12-29-00 UTC, the first pulse of moisture.

Then an atmospheric river hit the coast of California with multiple pulses of heavy moisture. According to NOAA's California Nevada River Forecast Center's Heavy Precipitation Report for this event, these two storms dropped an impressive amount of rain in southern California, including a whopping 51.77 inches at Opids Camp.
PWV for 2005-01-09-18 UTC.
I suspected that this would be a once-in-a-lifetime event; I dragged my family to the shores of Lake Manly, which had grown from a small pond to a lake 30 miles long, 5 miles wide and 4 feet deep.
My then 4 yo daughter on the shore of Lake Manly (usually dry) in March 2005.  She was watching the kayakers and windsurfers until I took the camera out.  Then she refused to pose.
See the National Park Service's images of Badwater,  the lowest point in North America.  What a difference an atmospheric river (or two) makes!
Salt formations at Badwater.  Public domain image from NPS DV image gallery.
I made the visualizations with the help of NASA's free Panoply data viewer and GIFMaker.   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.

For further guidance selecting from among the RDAs many reanalyses, please contact the data specialist for each particular reanalysis.


  1. The weather machine is a steam engine. The boiler is along the equator. The condensers are the poles. The jet stream is the turbine. Condensation sucks.

  2. The long term interannual climatological impact of atmospheric rivers (AR) on the hydrology of California is also discussed in UC Berkeley professor B. Lynn Ingram's book "The West Without Water" in which she uses as a case study the Great Flood of 1862 (December 1861 - January 1862) when most of the Central Valley was completely inundated. Such events have prompted studies such as the U.S. Geological Survey's Multi Hazards Demonstration Project (MHDP) ARkStorm Scenario. Ingram also goes to great lengths to help the reader understand that the relatively "wet" conditions of the American west over the last 125 - 150 years are an anomaly (unfortunately encouraging westward expansion and rapid development) and that the long term interannual variability (100's to 1000's of years) is dominated by extensive droughts lasting decades to centuries. Perhaps the first person to realize this was John Wesley Powell, who strongly warned against rapid development of the west, especially for agricultural purposes dependent on abundant supplies of water.


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