Explanation of the NTS Lightning Strikes Displays

Updated October 18, 2000

Overview

The NTS Lightning Strikes Displays shows cloud-to-ground lightning strikes sensed by the equipment at ARL/SORD. The focus of this lightning system is the Nevada Test Site. Strikes are sensed at quite a distance from the Site, but the accuracy of the strike placement deteriorates with distance.

The strikes are shown on the displays as dots or plus signs. If a strike is shown as a dot, it is a "negative" strike. If a strike is shown as a plus sign, then it is a "positive" strike.

Displays are provided showing strikes for the prior two hours or for the prior 28 minutes ("recent strikes"). Overview and zoom views are available. The overviews start with the Southwest and progressively zero-in on the NTS. The zoom displays zero-in on a particular center point, with views showing strikes within a forty, thirty, twenty or ten mile radius of the selected point.

There is a red line drawn on the overview displays approximately twenty miles outside the NTS border. The enclosed area is considered the Lightning Alert Area. Strikes inside this area trigger the issuance of a Lightning Alert at the NTS.

Color-Coded Strike Age

During lightning activity, each view is updated every minute. As the strikes age, they change color to indicate the age of the strike. The chart below gives the age range of each color.

Color Name

2 Hour Age (in Minutes)

Recent Age (in Minutes)
    At least Not more than At least Not more than
Red   5   4
Light Green 5 20 5 8
Blue 20 40 9 12
Cyan 40 60 13 16
Black 60 80 17 20
Yellow 80 100 21 24
Beige 100 120 25 28

This information is shown on the left edge of the display when there is at least one strike on the display.

Summary Counts

If there are strikes, a summary of the strike counts is shown. The total number of strikes on the display is shown as "Total". (This covers a two hour period or a 28 minutes period, depending on selection.)

On two hour displays, the number of strikes in the five minutes prior to the display generation is shown as "Recent". On 28 minute displays, the number of strikes in the prior four minutes is shown as "Recent".

The number of positive strikes is shown as "Pos (+)". If there are no positive strikes, this count is suppressed. (If a strike is not a positive strike, it is a negative strike.)

The outermost two overview displays may sometimes show a "Test:" field. This is used for testing the lightning system and is of no particular interest to the user.

Screen Updating Frequency

During periods of lighting activity, each view is regenerated every minute. During periods of inactivity (no strikes for the prior two hours), each view is regenerated every ten minutes. The web page through which you view the display auto-refreshes every minute. There is a brief flicker as the web page refreshes. You can tell that the display data changed by watching the times shown in the upper left corner. The times are shown in Pacific Daylight Time (April - October) or Pacific Standard Time (October - April).)

These pages do not auto-refresh properly with Netscape Navigator 4.02 or later. It is recommended that Internet Explorer 4.0 or later be used when working with these displays.

Strike-o-meter

On the two-hour displays is shown the distribution of the strikes for the prior two hours. Labelled "Strikes/Min", this small chart shows how many strikes occurred in each of the prior 120 minutes. The rightmost column shows the most recent minute. The leftmost represents the oldest minute. The height of a column shows how many strikes occurred in that minute. This variably-scaled chart shows the current scale factor in parentheses under the chart. For example, (6) means that the most strikes in one minute for the last two hours is six and that lines in the chart that go all the way to the top represent minutes that had six strikes each. Minutes with fewer strikes are shown by lines of proportionally shorter length. The small tick mark under the base line shows where the one hour point is.

Acknowledgements

The design and programming of this system was done by Rick Holmes, SCI Consulting, Inc. The SUN Solaris FORTRAN77 and C++ compilers were used. The GIF subroutines were based on the gd display package from Tom Boutell and the Quest Center at Cold Spring Harbor Labs.

The map backgrounds were devised by Ray Livsey, Air Resources Laboratory/Special Operations and Research Division (ARL/SORD) using Precision Mapping 2.0 software.

The web pages providing access to the graphics were generated by Jim Sanders, ARL/SORD, using the Front Page Editor.

The javascript software used in the animations is based on jsImagePlayer 1.0, 9/96, copyrighted by BASTaRT of Praha, Czech Republic, Europe.

Please direct comments or suggestions on these displays to SORD Webmaster.