Details and instructions on the monthly mean 20th Century Reanalysis Google Earth Compositing Page

Year entry boxes | Year Range | List of years | Climate time series | Variables | Type of Plot (Mean, Climatology and Anomaly) | Composite Calculation
Plotting Regions | Lagged Composites | Contour interval option | Crossections | Page Creation | Feedback

Page will plot maps of selected variables. Select desired options and hit "create plot". Most options have a default setting so a selection is not required. Default for year is last year and month available for dataset. You can select one or more years to composite, the season, the type of statistic plotted (mean, anomaly, climatology), variable, level, map color, and contour interval/range. If you have problems, please email with ALL the options you chose.

Please read ALL the instructions. Failure to do so may lead to misinterpretation of results.

  • Variable, years and levels available
    Data is available from Jan 1908 to Dec 1958. Vector winds: magnitude of winds are contoured. Arrows show direction.
  • Enter Years
  • Enter each year in a separate box. The year should correspond to the last month of a season. Years should be w/i the range of the dataset you select. You can subtract one set of years from another by entering a negative year.
  • Enter Range of Years
  • Enter a range of years within the range of the data. You can also enter a range of years or use a time series or list of years (see next entry).
  • Use a list of years
    You can use a file containing the years you would like. The format is
    # of years

    Ftp to as anonymous. Please deposit your time series in /Public/timeseries using a unique name. Type in full pathname (/Public/timeseries/yourfilename where requested.
  • Compositing off a time series
    You may select a time series or enter one yourself. Details on the supplied ones are at Climate Index Web Page for a complete reference for the included time series. Credit, proper references and definitions are provided. Please read before using a particular time series or you may misinterpret what you are seeing. You can use the webpage to create your own from monthly mean datasets. For ENSO years, see the PSL's ENSO FAQ.

    To use you own or one obtained from the /gcos_wgsp/Timeseries/ webpage, ftp to as anonymous. Place time series in /Public/incoming/timeseries using a unique name. Check the "list of years" box and those years will be used. To use a time series, ftp a file to the same directory as above. However, the format is

     yearstart yearend
    year1 val1 val2 val3 val4 val5 val6 val7 val8 val9 val10 val11 val12
    year2 val1 val2 val3 val4 val5 val6 val7 val8 val9 val10 val11 val12
    yearend  val1 val2 val3 val4 val5 val6 val7 val8 val9 val10 val11 val12
    missing value

    The missing value is mandatory and cannot be in the range of the data (-9999 is a good one). Select "custom" time series.

    For either a supplied time series or your own, you can composite off the actual values, anomalies (mean is based on the complete range of years of the time series you submit or use, standardized anomalies (anomalies divided by the standard deviation), or the percentile (0 to 100). Years used for composites are the subset of those years which match the criteria AND are in the dataset. For example, if you choose a Nino3.4 time series that has values greater than 1.0 sigma and the dataset you are looking at goes to 1995, you will NOT get 1998 even if the Nino3.4 value is greater than 1.5 sigma.

    For a concrete example, let's composite 850mb zonal wind for winter seasons (Dec-Jan-Feb) where the NAO index exceeds 1.0 sigma.

    1. Choose zonal wind.
    2. Choose 850mb level
    3. Select timeseries "NAO.
    4. Select "monthly time series"
    5. Select "standardized anomaly"
    6. Select "greater than or equal to"
    7. Select "anomaly"
    8. Select "create plot"
    9. Choose default (make no selection) for other options.
    Note that there are 9 years returned. Years: Value used in composites 1910,1913,1920,1922,1923,1925,1937,1949,1957. The typical dipole patternover over North America clear is visible. Now, try years less than or equal to -1.0 sigma. Less years are returned: 1955,1956,1965 and the plot is somewhat opposite in pattern but with more amplitude over the Northern Atlantic .
  • Lagged composites
    Selecting a nonzero value for this will allow you to do a lagged composite. The years are determined from one of the year entry methods above. Then, a composite is made N months before the dates you selected (-N) or after the dates you selected (N). If lagging results in a date that is not in the range of the dataset, that date is not used. As an example, select January 500 geopotential height for the PNA values greater than 1.25sigma. If you choose lag =-1, you will get 5 years: 1977,1981,1985,1992. A negative lag of one month will composite geopotential height for Dec 1976,1980,1984,1991. A positive lag of 3 months will composite for April of 1976,1980,1984,1991. All lags are specified in months!. Please do lags only on positive years.
  • How the composite is calculated
    The composite represents the average of the variable for all months and years entered. Composites can be created for one set of years minus another. The years are normalized as in the following example: a set of 5 years minus a set of 2...
    will be calculated as
    Where each year represents a monthly/seasonal value. There is currently no data before 1948 for reanalysis so, for example, the season DJF 1948 contains Dec 1947 and therefore will not be calculated. Likewise, seasons that would have years after the end of a dataset will not be calculated. Missing values will not be used for data outside the time range of the dataset.
  • Type of Plot
    Plots are averages of all months and years that are input.
    Plots are based on 1921-1950 climatologies. Choose season; years are not needed. If years are entered, they are ignored.
    Plots are of mean-climatology for each season/month. Climatology time period is generally on 1921-1950.
  • To reverse colorbar
    By typing in negative years (e.g. -1983 and not 1983), the color bar will be reversed since you will be getting -1 times the value (either mean or anomaly).
  • 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.
  • Black and White Option
    You can select black and white contours and shading for printing on noncolor printers or monitors..
  • How 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. Plot options are input into the GrADS script. The plot in the frame buffer is converted to gif and this gif is displayed as part of a html document. The image is manipulated and then placed into a file containing appropriate KML metadata. The KML file is zipped with the image and can be downloaded as KMZ. For those with an appropriate browser extension installed, the image can be viewed in a version of google earth that run in a web browser. The netCDF file and the gif file are kept in a directory where the files are periodically deleted.
  • Feedback
    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 or by phone at (303) 497-6263.