Sudden Stratospheric Warmings
A simple NCL's code to calculate the central dates of the SSWs following Charlton and Polvani (2007) and the stratospheric final warming (SFW) following Black et al., (2002)
SSWs Criteria:
- The central date or event date of a SSW occurs when the daily-mean zonal-mean zonal winds at 10 hPa and 60N first change from westerly to easterly between November and March.
- The winds must return to westerly for 20 consecutive days between events (to avoid counting the same event twice, roughly equivalent to the thermal damping timescale at 10 hPa).
- If the winds do not return to westerly for at least 10 consecutive days before 30 April, the warming is a final warming and is not included.
SFWs Criteria:
- SFW events are identified as the final time that the zonal-mean zonal wind at 70°N (the core latitude of the stratospheric polar vortex) drops below zero without returning to a specified positive threshold value until the subsequent autumn.
- We apply this criterion to running 5-day averages at 10 hPa (with a threshold of 10 m/s).
