• After witnessing the continued decrease of involvement in the SpotterNetwork staff in serving SN members with troubleshooting issues recently, I have unilaterally decided to terminate the relationship between SpotterNetwork's support and Stormtrack. I have witnessed multiple users unable to receive support weeks after initiating help threads on the forum. I find this lack of response from SpotterNetwork officials disappointing and a failure to hold up their end of the agreement that was made years ago, before I took over management of this site. In my opinion, having Stormtrack users sit and wait for so long to receive help on SpotterNetwork issues on the Stormtrack forums reflects poorly not only on SpotterNetwork, but on Stormtrack and (by association) me as well. Since the issue has not been satisfactorily addressed, I no longer wish for the Stormtrack forum to be associated with SpotterNetwork.

    I apologize to those who continue to have issues with the service and continue to see their issues left unaddressed. Please understand that the connection between ST and SN was put in place long before I had any say over it. But now that I am the "captain of this ship," it is within my right (nay, duty) to make adjustments as I see necessary. Ending this relationship is such an adjustment.

    For those who continue to need help, I recommend navigating a web browswer to SpotterNetwork's About page, and seeking the individuals listed on that page for all further inquiries about SpotterNetwork.

    From this moment forward, the SpotterNetwork sub-forum has been hidden/deleted and there will be no assurance that any SpotterNetwork issues brought up in any of Stormtrack's other sub-forums will be addressed. Do not rely on Stormtrack for help with SpotterNetwork issues.

    Sincerely, Jeff D.

CGs and tall structures

  • Thread starter Thread starter Dan Robinson
  • Start date Start date

Dan Robinson

I found yet another example of a cloud-to-ground lightning strike not hitting the 'highest point'. This CG to the Sears Tower on October 2, 2006 hits in the cluster of secondary antennas well below the main two antenna masts.

http://youtube.com/watch?v=1LIQv0CeXRk

I saw a still frame of this from another angle on the CBS 2 Chicago web site, but I can't locate it now.

Cloud-to-ground strikes to tall structures are more rare and behave differently than the more common upward-moving ground-to-cloud discharges that most of us have seen time and time again to tall towers. While a upward discharge starts (by leader initiation) from the top of the structure, a CG stepped leader starts in the cloud and moves downward - only jumping over and hitting a tall structure if it happens to descend near it or directly above it. In other words, unlike upward moving lightning, the skyscraper or tower doesn't play a role in the initiation of the CG, only in its final few steps before earth connection.

From photographic evidence, it appears that 25% to 40% of cloud-to-ground strikes to tall buildings and structures do not hit the highest point on the structure.

It is known that the stepped leader is 'blind' to objects on the ground until it gets very close to the ground or a grounded structure. In these cases, it appears that a horizontal propagation is made only after the stepped leader has already descended to an altitude lower than the top of the structure.

I have to bring up this excellent photo by Kevin Ambrose again as it illustrates this perfectly:

http://epod.usra.edu/archive/epodviewer.php3?oid=255040

In the Sears Tower shot above, if the building did not exist, the CG would have still likely decended in the same spot - in other words, the building was inconsequential until the stepped leader got close enough to it. In the Washington Monument shot, that strike was clearly not 'aware' of the monument nor influenced by it until the final steps toward earth.

Pretty fascinating stuff.
 
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