The Meandering Index (M) measures the waviness of troposperic planetary waves.
The hemispheric meandering index ‘M’, based upon the most strongly meandering isohypse in each individual day. This index accounts for the full path of the isohypse, without modifying or simplifying its shape, such that also shapes during wave breaking events (with multiple latitudinal positions of the isohypse at one longitude) are correctly considered.
Reference
Di Capua G and Coumou D 2016 Changes in meandering of the Northern Hemisphere circulation Environ. Res. Lett. http://iopscience.iop.org/article/10.1088/1748-9326/11/9/094028