Lightnings are phenomena of electrical discharge that happen whenever a great potential difference occurs between clouds, parts of a cloud, or between a cloud and the earth. If the discharge occurs between a cloud and the earth’s surface, the cloud possesses a negative charge, the soil underneath positive.

What mechanism gives rise to such big potential difference, and what other phenomenon is produced by it besides lightnings?

During storms, strong currents of warm and humid air ascend with velocities that can reach one hundred kilometers per hour (a few months ago in Australia a paraglider was unwillingly pulled about 10,000 meters above sea level by such a current)…

More at The Origins of Lightnings.

This is a summary and review of the paper by Christian et al. titled Global Frequency and Distribution of Lightning as Observed from Space by the Optical Transient Detector. Because the actual abstract is so long, I’ve cherry-picked the parts that I think are most important. See the entire thing at the link above.

Parital Abstract: The Optical Transient Detector (OTD) is a space-based instrument specifically designed to detect and locate lightning discharges as it orbits the Earth. Given the orbital trajectory of the satellite, most regions of the Earth are observed by the OTD instrument more than 400 times during a 1 year period, and the average duration of each observation is 2 min. The OTD instrument optically detects lightning flashes that occur within its 1300 × 1300 km² field of view during both day and night conditions. A statistical examination of OTD lightning data reveals that nearly 1.4 billion flashes occur annually over the entire Earth. This annual flash count translates to an average of 44 ± 5 lightning flashes (intracloud and cloud-to-ground combined) occurring around the globe every second, which is well below the traditional estimate of 100 fl s^−1 that was derived in 1925 from world thunder day records.

This paper is obviously one of the first papers published about the Optical Transient Detector, as most of the paper is on the methodology of the instrument rather than on science gathered from its data. The introduction to the paper motivates the need for a lightning detector that can view a large percentage of the globe, and also be able to distinguish diurnal, and seasonal cycles. According to the paper, much of the previous lightning detection from space was an unintended bonus. Previous methods were unable to accurately quantify the frequency and distribution of the lightning flashes.
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