CONTEST STATUS - Updated: SUN...20-JUL-14 @ 7:35 PM EDT

Winter '14 / '15 - Snowfall Forecast Contests

---
16th Annual 'Regular Season'

---
14th Annual 'Season-total'

Friday, December 30, 2011

Winter '11 / '12 - Arctic Oscillation - Day 30

500 mb height anomalies
associated with
three states of the
Arctic Oscillation
Thirty days into the season...the Arctic Oscillation (AO) remains well above zero despite a weakening polar vortex (PV) and hi-latitude easterly winds.
The 500 mb height anomalies (below right) have looked more like the top chart which has kept arctic cold away from the mid-latitudes.  The ECMWF continues to depict a weak anti-cyclone building over the Pole; however the on-set is always at least seven days away. 

Today/s 500 mb height anomalies
The minor stratospheric warming event @10 mb has contributed to a weakened PV but is occurring well away from the pole INVOF northeast Asia and has not propagated below 30 mb.

Minor warmings do not cause the PV to break down or cause a wind reversal from west to east so it's debatable how much influence this event will have on establishing hi-latitude blocking.  Best guess:  very little.

---
Below is a time-series of the AO on 30-DEC throughout the 60+ year period of record (1950 - 2011).  The blue line is a trace of the daily AO index on 30-DEC.  The dark red line is a a trace of the same data after applying a nine-point binomial filter.  The filter removes low frequency noise and highlights decadal trends.


Not sure what this says about the AO at the end of December other than there is a decernable cycle every seven years or so.

2 comments:

jmarqui said...

Excelent my friend, very interesting, as always. Let's see how vortex evolve this january and february. Decembers with strong AO+ has been followed by January with AO+, with one exception perhaps, 1979-80.

TQ said...

The PV has weakened but has been reluctant to split in two...so I don't look for it to contribute much...if anything...to a sign-reversal of the AO.

You are right about DEC +AOs. When +AO in DEC...the odds favor +AO in JAN. Only a 1-in-3 chance for a -AO JAN.