The probability of a chance association with background sferics
is found by applying the procedure at control times offset from the TGF time.
The simplest sferic
detector in the cockpit is the old fashioned twitching ADF needle, but more common are Stormscope and Strike Finder instruments.
The limitations on sferics
are severalfold, but the biggest for our purposes is that the distance to a strike is essentially estimated based on the strength of the signal; the weaker the energy, the further away it's assumed to be.
That's an important observation when it comes to using the tools we have available, especially since both airborne weather radar and sferics
like a Stormscope or Strikefinder are real-time devices.
By tracking strike rate, sferics
give instantaneous information on a storm's maturity level and of all the detectors we've tried, Avidyne's TWX670 has the best overall featureset for the price.
Very Low Frequency (VLF) sferics
are electromagnetic impulses with frequencies between 1 kHz and 100 kHz, which are generated by lightning discharges.
If there's a developing line of convective activity on the Datalink NEXRAD image, it's neither safe nor smart to assume that the area you plan to penetrating is free of activity, unless you can see with your eyes, onboard radar or sferics
no cells have popped up or moved into since the last datalink update, or aren't heavy enough to show on NEXRAD.
Avidyne's two-piece (three with a display) tactical weather avoidance TWX670 system is the most modern sferics
device to be had.
As always, those images should be considered only for advance planning: We've never recommended using them to navigate actual weather--even when backed up by a sferics
To decide if sferics
is worth the expense for your mission, you need to understand how datalink differs from sferics
and the lighting products you're might be receiving via datalink.
if and only if you have weather radar, a sferics
device like a Storm-scope and/or datalinked Nexrad in the cockpit, plus weather flying experience and a solid-gold Plan B.
Traffic alerting, XM weather and sferics
display cost extra but are available.