Details and instructions on the 6-Hourly Compositing Page


Variables are from the NCEP/NCAR Reanalysis. All NCEP variables start Jan 1 1948. Most continue through a few days before the present. Some are updated only through the last month.

bulletEnter Level

Levels are analysis levels. Geopotential Height and specific humidity are not available at the surface. For pressure or SLP, specify surface.

bulletEnter date(s)

Individual Dates
Enter yyyy, mm, dd, hh for the date you desire.
Date File

Create a text file in the following format


You can now use your own anonymous ftp file name or your own http address! By doing that, you don't have to ftp your file to PSL everytime you want to change something. Either put your (text) file in an http: accessible directory and specify it's name as in
Make sure there is no miscellaneous text at the top of the file like headers. Choose custom and enter the address.
Alternatively, you can put the file in an anonymous ftp directory. Make sure no passwords are needed to read the file. Type
Or, you can still ftp to PSL. Type ftp Use anonymous ftp and type in your email for the password. Put your file in /Public/incoming/dates/. Files are deleted after 2 days (not my idea) so you may need to reftp a file. Then, type in the filename /Public/incoming/dates/yourfilename and type in a plot label. If the plot label is blank, all the days will be written which may not fit.

This feature is in test mode now. I think it works but I may beed to clarify things further or make a few small changes. Email me w/problems. Date range

Enter the starting and ending day of the year. Also enter the year of the data. The year corresponds to the year of the last day of the range. For the days to be used, a year must be entered. If a year is entered, it overides anything in the individual date entry boxes.

bulletEnter Color

Color or Black and White. Color ranges are chosen arbitrarily by me (and may be subject to change).

bulletEnter Shading

Shaded or contour levels are available.

bulletEnter Type


Average of the days specified.

bullet(Optionally) Enter Contour range/interval option

A desired contour interval and range can be input instead of the default being used. Different plots can be easily compared (and the resulting gifs could be animated). For this option to work, the interval AND the range must be input. There must be at least 2 and less than 33 contours. The contour interval must be positive and the range must go from low to high.

bulletPlotting Regions

To plot over the dateline, use values from 0 to 720. For example, to plot 180W eastward to 180W, use 180 to 540. Be sure that the western most longitude is less than the eastern., For example, to plot 100W to 70W, use -100 to -70 or 260 to 290 and NOT 100 to 70.
There are 6 custom projections:
Northern Hemisphere: 0-90N, 0-360W in using a polar stereographic projection
Globe: 90S-90N 0E-360W
United States: 20N-65N; 235-285 polar stereographic projection
Tropics: 60S-60N
Tropical Pacific: 35N-35S 100E to 60W
4-corner States of the Western US:31-42.5N, 244.5-258.5W CO,UT,AZ,NM
Indio-Pacific (20S-20N,60E-160W)
To rotate polar stereographic plots

To rotate map, choose "custom" map projection and then choose either northern or southern polar stereographic projection. For lat range, enter 0 to 90 (for northern hemisphere) or -90 to 0 for southern. For longitude, the center of the longitude range input will be at the bottom of the plot. To center along 0E, choose -180 to 180, for example. To center at 90E, choose -90 to 270. You can plot sectors as well. The longitudes -90 to 90 in the NH will plot the half hemisphere from the US across the Atlantic to Europe.

bulletHow this page was created

The main interface for this page is an html form. The data that are input into this form are processed by a Perl script. The script reads the inputs, tests for bad inputs and then executes a FORTRAN code that produces a composite file (in netCDF). This file is what is processed by a GrADS script. The GrADS script is run as a batch job with the plot created in a virtual frame buffer (to increase the quality of the gif output). Plot options are input into the GrADS script at this time. The plot in the frame buffer is converted to gif and this gif is displayed as part of a html document. The netCDF file and the gif file are kept in a directory where the files are periodically deleted.


Please let me know if find the page useful. Likewise, let me know if you think any instructions are unclear, if you think there are bugs or if you have any suggestions for improvements of any type. I would particularly like to know if you use these pages for teaching purposes and if so, how. I can be reached by email at

bulletHow to reference

Find out how to reference plots and datasets in publications