2
$\begingroup$

Coming from the aviation site: What is the westerly index?

The westerly index is:

... the Trenberth Z1 index (Trenberth 1976), which is the departure of the monthly mean pressure difference between Auckland and Christchurch (near 44°S) from its mean over the 1961–90 period.

journals.ametsoc.org

Those two places are ~750 km apart (not a small distance), and judging by the METAR reports, the QNH difference in the past 72 hours varies from 4 to 7 millibars or so. Is that unusual? What's the significance of that index?

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.