Synoptic Analysis of Siberian Pulse Events

Past research has shown a connection between Siberian Pulse Events (SPEs) that occur as surface high pressure anomalies and simultaneous vertical Wave Activity Fluxes (WAFz) that can reach into the lower stratosphere during the boreal cold season. On average, the stratospheric polar vortex weakens notably in the three-week period following SPEs. Here we conduct lead-lag analysis relative to the onset of the pulses, considering the spatial structure of daily standardized anomalies of sea level pressure, geopotential heights at 500 hPa, 200 hPa, and 100 hPa, and WAFz. Pulses are additionally divided up into active versus inactive years, and pulses that last less than 5 days ("short") versus more than 5 days ("sustained"). Finally, a multi-variate Self-Organizing Map (SOM) analysis is applied to the daily height fields, as an additional perspective on circulation patterns.

The spatial structure of the SPEs, as expected, have a westward tilt with height, and are very similar to the structure of local blocking events. Results show that higher correlation coefficients between tropospheric levels as well as with stratospheric occur during active SPE years. In addition, the time lag between lower and upper troposphere is almost negligible, as the highest correlated lag times were 0 and 1 day, while the lag between lower troposphere and stratosphere as well as between upper troposphere and stratosphere was about 5-7 days, with higher amounts during active SPE years. Both the tropospheric development and the stratospheric response are much stronger during sustained pulses. In the mid-troposphere, a wide-spread tropical response develops in the 5-day period following the onset of sustained SPEs. In the SOM analysis, of the 9 robust maps for all fall days, the SPEs are reliably associated with only 2, one for SPE onset days and another for the subsequent SPE days.