The Northern Polar Vortex and its Breakings: Relations to Particle Precipitation, EUV Irradiance, QBO Phase, ENSO and Volcanic Activity
Abstract
Polar vortex (PV) is a jet of strong westerly winds in the stratosphere that develops each winter around the winter pole. The northern PV experiences considerable inter-annual variability, which is reflected on tropospheric weather as the NAO/NAM weather pattern. The positive phase of the NAO/NAM pattern is favored during the declining phase of the solar cycle, which gives evidence for PV being enhanced by solar wind-accelerated energetic particle precipitation (EPP) into the upper atmosphere. Solar EUV irradiance, ENSO and volcanic aerosols can also indirectly affect the polar vortex by modifying conditions in the equatorial stratosphere. It is also known for long that the easterly phase of Quasi-Biennial Oscillation (QBO) favors the occurrence of sudden stratospheric warmings (SSW), the momentary disruption of the PV. These external and internal effects are partly interrelated. E.g., EPP-related variations to the PV in late winter are predominantly observed in the easterly QBO phase. Here we study the effects of two solar-related drivers (EPP and EUV) and three internal factors (QBO, ENSO and volcanic aerosols) to the northern PV in 1957-2017 using multiple linear regression analysis. We find that EPP is the most significant factor affecting the northern PV variability. We also examine SSW occurrence in the same winters, confirming the well-known result that SSWs occur more often in the easterly than westerly QBO phase. We also show that the difference in SSW occurrence between easterly and westerly QBO winters strengthens (weakens, resp.) if geomagnetic activity or solar activity is low (high), or if the ENSO is in a cold (warm) phase. In easterly QBO phase significantly more SSWs occur during low geomagnetic activity than high activity.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.728M