Boyden Index

The Boyden Index (often also abbreviated to BI ) is used to estimate the probability of a thunderstorm . The BI was introduced in 1963 by the British meteorologist C. J. Boyden in order to be able to more easily estimate the probability of a thunderstorm emanating from frontal systems moving across the British Isles . The greater the value of the BI , the greater the probability.

The calculation requires the altitude difference ( Z ) between the altitude with an air pressure of 700  hPa and the altitude with 1000 hPa and the temperature ( T ) at the altitude with 700 hPa. From a BI of 94, a thunderstorm is considered likely.

Calculation: BI = 0.1 Z - T - 200 or: BI = 0.1 (Z ₇₀₀ - Z ₁₀₀₀ ) - T ₇₀₀ - 200

Despite the lack of inclusion of humidity in the calculation, the Boyden index is considered reliable.

In addition to the Boyden Index, there are other indices such as the CAPE or the Bradbury Index , introduced in 1977 , which also take humidity into account.