- Selecting a geographic location.
- Confirming the location.
- Reviewing the data availability.
- Buying data for more than one area.
- Purchasing the area using WorldPay.
- The WorldPay Confirmation of Purchase.
- Choosing an analysis.
- Wind speed probability.
- Wave height and period scatter tables.
- Extreme wave heights.
- Persistence of storms and calms.
- The data, and the NMIMET analysis used to create it
- European Database
- Neil Hogben
Wave Scatter Table
The wave scatter table gives the joint probability of significant wave height and wave zero crossing period. The rows give the different wave height classes, and the columns the zero crossing period classes. The probability is shown as parts per thousand, so that a value of 78 represents a probability of 0.078, or 7.8%.
In order to convey a visual impression of the wave scatter, the cells are colour coded, as follows:
- Red - Height period combinations with a joint probability of 9.95% or more.
- Yellow - Combinations with a joint probability between 0.95% and 9.95%.
- Green - Joint probabilities between 0.05% and 0.95%.
- White - Probabilities of less than 0.05%.
The right hand column of the table gives the marginal probability of height (probability of wave height irrespective of period). Likewise, the top row of the table gives the marginal probability of wave period (probability of wave period irrespective of wave height). These marginal probabilities are colour coded in a similar fashion to the joint probabilities.
It should be noted that the probabilities displayed have been rounded to the nearest part per thousand. As a result, the tabulated values may not always total exactly 1000.
By popular request, a higher resolution version of the scatter table has now been provided. Clicking on the table resolution button at the top-right of the table displays a version of the scatter table with values in parts per million, rather than parts per thousand. Clicking on the button again reverts to the parts per thousand display.
Please note that each of the data sets presented for a sea area are the result of applying a statistical fitting and smoothing process to the raw data for that season and directional sector. Each set was processed independently to produce the best fit to the data available. As a result, the sum of each of the different directional sectors is not always exactly the same as the "All Directions" data. Likewise the sum of the results for each season is not always identical to that for "All Year".
Also, the accuracy of the fit may not be good enough to justify all of the significant figures displayed, particularly in the parts per million display.
Wave Probability Plots
The page can also show a plot of the wave probability data. Three classes of plot may be generated:
- Wave Contours of the joint height / period probability.
- Wave Height marginal probability plots.
- Wave Period marginal probability plots.
The class of plot is selected using the first of two pull down menus.
For the marginal probability plots, one of three forms of presentation of the data may be selected using the second menu:
Histogram - This is a plot of the tabulated probability values in a histogram format.
Linear - This is a plot of the non-exceedance probability, on a linear scale.
Weibull - This is a plot of the non-exceedance probability on special scales such that a two parameter Weibull distribution would appear as a straight line.
This option has no effect if contour plots have been selected.
Clicking the "Plot Wave Statistics" button then refreshes the page in order to show the requested plot.
The "Return to Analysis Selection" button at the bottom of the page will take you back to the page for selecting a new season or directional sector.
The tabs in the menu bar can be used to move through the various levels.