Help and Directions for the Gridded SLP page

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, map location or bounds for vertical composites 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 available

  Different historic SLP datasets are available for plotting. Time coverage and gridsize differ for each dataset. Data generally starts in the 1800's until near the present. Data will be updated when possible and more datasets may be added as we get them.

• 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
  year1
  year2
  year3
  ...
  lastyear
  

  
  Ftp to ftp.cdc.noaa.gov as anonymous. Please time series in /Public/incoming/timeseries using a unique name. Type in full pathname (/Public/incoming/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 http://www.esrl.noaa.gov/data/timeseries/ 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 /data/timeseries/ webpage, ftp to ftp.cdc.noaa.gov as anonymous. Place time series in /Public/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
  etc
  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 you choose. For example, if you choose a Nino3.4 time series that has values greater than 1.5 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 500mb geopotential height for winter seasons (Dec-Jan-Feb) where the PNA index exceeds 1.25 sigma.

  1. Choose geopotential height.
  2. Choose 500mb level
  3. Select timeseries "PNA".
  4. Select "monthly time series"
  5. Select "standardized anomaly"
  6. Select "greater than or equal to"
  7. Select "anomaly"
  8. Select "all" for map
  9. Select "create plot"
  10. Choose default (make no selection) for other options.

  Note that there are 8 years returned. Years: Value used in composites 1961, 1978, 1981, 1983, 1986, 1987, 1992, 1998. The typical 3 center pattern over North America clear is visible. Now, try years less than or equal to -1.25 sigma. Only 3 years are returned: 1955,1956,1965 and the plot is somewhat opposite in pattern but with more amplitude over the Northern Atlantic .

• Subtitle for plot

  If the time label is too long or you would like something that is more clear (15 strongest El Ninos) the time label will be replaced with this label.

• 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...

  (1980+1981+1982+1983+1984)-(1985+1986)

  will be calculated as

  (1980+1981+1982+1983+1984)/5.-(1985+1986)/2.

  Where each year represents a monthly/seasonal value. Only full seasons are created.

• 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.

• Type of Plot

• Mean

  Plots are averages of all months and years that are input.

  Climatology

  Plots are based on different climatological time periods depending on the dataset. Choose season; years are not needed. If years are entered, they are ignored.

  Anomaly

  Plots are of mean-climatology for each season/month. Climatology time periods differ for each dataset.

• 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 non-color printers or monitors..

• Plotting Regions

  Maps
  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: 35S-35N (changed from 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)

• 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 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 cathy.smith@noaa.gov or by phone at (303) 497-6263.

This page hosted by: NOAA Physical Sciences Laboratory (webmaster.psl@noaa.gov) http://psl.noaa.gov/gcos_wgsp/Gridded/Plot/Help/index.html