Q: At what elevation is the location/strength determined?
A: The cloud-to-ground flash and stroke locations are where the channel strikes the ground. In fact, about the lowest 50 meters of the channel are being measured by low-frequency lightning detection systems, since that part of the channel is essentially vertical, as shown by photography close to lightning.
Q: From the elevation at which the location is determined, what horizontal distance can still be traveled by a strike before actual ground strike?
How large area can a lightning cover?
A: An in-cloud flash can spread horizontally for several tens of kilometers. Sometimes they are up to 50 or 100 km in length, and the longest we have observed is 190 km in one continuous mapped cloud flash that lasted about two seconds in the Dallas-Fort Worth area. A cloud-to-ground flash can extend outward from the rain area falling on the ground up to 15 to 20 km in the most extreme case.
Q: Surely precipitation amount and intensity is related to lightning intensity or density. Is there a clear and significant relationship?
A: There have been quite a few studies of the relationship between lightning and radar or raingage-measured rainfall. There is an excellent summary in the following paper: Kempf, N.M., and E.P. Krider, 2003: Cloud-to-ground lightning and surface rainfall during the Great Flood of 1993. Monthly Weather Review, 131, 1140-1149.
Additional research since that study is summarized in Pessi, A., and S. Businger, 2009: Relationships among lightning, precipitation, and hydrometeor characteristics over the North Pacific Ocean. Journal of Applied Meteorology and Climatology, 48, 833–848.
While the relationships are generally good, they vary among different meteorological, seasonal, and climatological regimes. Also, some heavy rainfall occurs without lightning, so the lightning relationships are only useful in convective regimes.
Q: How long in advance can Vaisala system forecast a lightning? I mean CG lightning mainly.
A: There are many tools available to aid in forecasting lightning. Sensors are a primary method used to detect cloud-to-ground (CG) and cloud (IC) lightning directly at significant distances. It has been shown that IC lightning generally precedes CG lightning by minutes to tens of minues and therefore the monitoring of IC lightning can be a good predicator that CG lightning may be expected. Electric field mills can be used locally to indicate the development of overhead lightning threats based on changes in the local atmospheric electric field.
Software additionally provides some capabilities for providing lightning forecasts and warnings. Range rings can be established around locations of concern and alarms/warnings can be sent based on lightning parameters occuring in given rings (for example, if there are 3 CG events in a 2 minute period in a ring 30km away from a building, a warning is issued to customers located in a ring that within 5km of the building).
Q: How many stations are required at least to monitor the lightning system? What is the lowest distance required?
A: Gross lightning detection can be obtained with as few as a single (1) sensor, such as with Vaisala's TSS928 product. The TSS928 detects lightning within 50km., and directionally classifies it into one of 8 directional octants. Precision networks provide additional data over larger areas, and generally require 3 or more sensors. Precision networks can cover large areas and provide exact details of timing, location (latitude/longitude), signal strength & polarity, multiplicity, confidence ellipses, etc.
Q: Is it possible to predict lightning using temperature, humidity, and wind velocity?
A: That’s a difficult idea for a short response. It is not possible to predict lightning using only surface temperature, humidity, and winds. Lightning detection systems do not predict lightning, they locate the flashes and strokes.
Predicting is another matter. One method is to attach the lightning data to a radar cell-tracking method; many radar tracking methods exist. Another way is to track only lightning and come up with the statistical probability that lightning will occur at some later time or place, typically within a few tens of minutes. There are also methods that use existing numerical weather prediction models to identify lightning at future time and space scales based on model output that originated with temperature and other variables. Finally, a few mathematical-dynamical models have been developed that explicitly forecast the existence, timing, and location of lightning within a cloud, but those are in the early stages of development.
Q: For purposes associated with the insurance claims process; we secure lightning reports to determine coverage and/or to support a potential theory of liability involving lightning and (for example) CSST pipe igniting as an origin and the cause being lightning. Is there a distance between the lightning strike and the risk location that can confirm the lightning as its only cause of loss?
A: The distance to confirm lightning as the only cause of loss would have to be extremely small, approaching zero, to have absolute 100% confidence.
With lightning strike reports, 99% confidence ellipse are provided that indicate the locational area of lightning strikes within the bounds of that ellipse, which combined with the time of strike can be used to aid insurance companies in determining the probability that lightning may be the only cause.
Q: What polarisation do you expect the elmag. wave from lightning will have (cloud-to-ground, cloud-to-cloud)?
A: Cloud-to-ground flashes usually lower negative charge to ground, about 90 to 95 percent of the time, and those are called negative cloud-to-ground flashes. The rest of the time, cloud-to-ground flashes lower positive charge to ground, and those are called positive cloud-to-ground flashes.
Q: Is there any delay in the real time feed of GLD360?
A: The current data latency for the GLD360 is 88 seconds, with Vaisala continually working on improving this.
Q: Are lightning data enough to start talking about a global lightning climatology?
A: The Vaisala Global Lightning Dataset GLD360 is being filled out in terms of using an improved location algorithm, more uniform and higher detection efficiency, and still better up time.
It is uncertain when we will be ready to make long-term large-scale climatologies, since performance evaluations are in progress, but it's going to be interesting!
Q: Does the GLD360 have the same detection efficiency throughout the world?
A: The detection efficiency is not the same throughout the world; currently, although DE is 70% for the majority of the northern hemisphere with multiple validation studies being completed.
More questions? Please send your question to
sales@vaisala.com or your local representative. You are also welcome to present questions in our upcoming webinars. The dates for any future lightning related webinars will be available on this page.