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Marine Data Literacy 2.0

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Home > 9. Operational/Synoptic > 9.29 Recent Precip

9.29 Visualizing Cumulative Recent TRMM Precipitation in IDV: Giovanni

  • Exercise Title:  Visualizing Cumulative Recent TRMM Precipitation in IDV: Giovanni

  • Abstract:  Although precipitation is widely understood and frequently presented in climatologies, synoptic views of precipitation are often restricted only to weather nowcasts/forecasts.  In such cases, due to the very small space scales (O(km)) and time scales (O(hr)), the general presentation is usually quite spotty and difficult to interpret in relation to natural events or human activities.  A better way would be to view cumulative very recent precipitation, where the user objectively defines "recent" and "cumulative" on the basis of regional/local characteristics and relevant temporal factors (e.g. algae blooms, cruise sampling).  In this exercise you'll learn how to obtain such data for areas and over times you select, for easy display in IDV.

  • Preliminary Reading (in OceanTeacher, unless otherwise indicated):

  • Required Software:

  • Other Resources: 

    • Giovanni - NASA data server that "provides a simple and intuitive way to visualize, analyze, and access vast amounts of Earth science remote sensing data without having to download the data." [from the website]
    • Tropical Rainfall Measuring Mission (TRMM) - "During its mission and broad sampling footprint between 35N and 35S, is providing some of the first detailed and comprehensive dataset on the four dimensional distribution of rainfall and latent heating over vastly undersampled oceanic and tropical continental regimes." [NASA website]

    Author:  Murray Brown

  • Version:  July 2013

1.  Open the Giovanni website and take a few minute to read through the explanatory materials.

Then examine the 5-part "Giovanni Portals" to see what they contain.

2.  Open the Meteorological Portals section.  Then click on the TRMM ONLINE VISUALIZATION AND ANALYSIS SYSTEM (TOVAS) control.
3.  Read over this page, which contains warnings and other data product information.
3.  Very near the bottom of the page you'll find the NRT products list, consisting of these 4 items.

Click on the TMPA-RT item (the first one).

4.  A complex, multi-part interface opens, with this location map at the top.
5.  Enter the coordinates for Liberia, and lick on UPDATE MAP.

This regional map will open to replace the global map.

6.  In the PARAMETERS section, select the second item for current data.  [The first item denotes a dataset that goes only to mid_2012.]
7.  In the TEMPORAL section, select the most recent single day.  [In this case it was July 12-13, 2013]
9.  Click GENERATE VISUALIZATION to create the analysis image.  Watch the top row of your browser for warnings while it is working, and always click ALLOW to continue the processing.
10.  After a few seconds or minutes, this image appears.  Notice that in a period of around a day, the rainfall has been rather spotty, and the maximum value was just over 110 mm.
11.  Along the top of the map, select DOWNLOAD DATA.  This list of datasets appears.
  • The first group of titles refers to 3-hour products within the total time period.
  • The "Two-Dimensional" product is the one you want
12.  Find the NCD control directly to the right of the "Two-Dimensional" product, and check it.


13.  Navigate to DATA > OCEAN > TRMM (or perhaps GIOVANNI) and save the file as precip_cumul_20130712_20130713_liberia_trmm_giovanni.gz.  Unzip the contents (1 file) and rename it (i.e. just a change of the extension).
14.  Now just for your understanding of the data accumulation process, we'll also download some data for long periods.
15.  Here is the image for the 2-week period preceding July 13, 2013.
16. Download and unzip this product as
17.  Here is the image for the 4-week period preceding July 13, 2013.
18.  Download and unzip this product as
19.  Run IDV.
  • Navigate to the folder where the new NC files were saved
  • Select all 3 NC files
  • Click ADD SOURCE
20.  In the object list on the left, select the July 12-13 product.  Then make these settings, and click CREATE DISPLAY.
21.  This IDV map appears.  It looks fine, but the value range on the color palette doesn't match the top value seen in Panel 10.
22.  To fix the palette, open the dashboard and select COLOR TABLE > PRECIP > CHANGE RANGE.
23.  Select USE PREDEFINED > FROM ALL DATA.  Then click OK
24.  Click OK.
25.  Now you have a better value range for the palette.  This is the final figure for July 12-13, 2013.
26.  Using the same steps, including the adjustment of the color palette, here is the final figure for the 2-week period prior to July 13, 2013.
27.  And here is the 4 week period prior to July 13, 2013.
28.  The point above is to show you that as you move to longer accumulation times, the analyses appears to "smooth" out.  This is the very nature of climatological analyses.  We're looking at synoptic data here, but by adding more time we're approaching the process you would actually use to make, for example, a climatology for July rainfall.  Of course you'd take many different July's, made as you see above, and add them together, etc. etc.
29.  You can save these products separate or together with the FILE > SAVE AS function in IDV.