PDO Influence Aloft

Tuesday's post on the persistent warmth aloft above Fairbanks (despite recent chill at the surface) sparked the question of how the PDO affects temperatures at different elevations.  This is a question that deserves more detailed investigation that I can give it now, but a simple chart tells the tale for early winter: see below.  The colored lines on the chart show the mean temperature for the November-December period at 500, 700, and 850 mb, for each year since 1948, and the black columns show the November-December mean PDO index.

The high correlation between temperatures at various levels in the lower half of the atmosphere is clearly evident, and it's also plain that the PDO has a strong connection to temperatures even up at 500 mb (~18000 feet).  Here are the Pearson correlation coefficients between the November-December PDO index and temperature:

Surface: +0.65
850 mb: +0.72
700 mb: +0.67
500 mb: +0.50

Interestingly the correlations are slightly higher at 850 and 700 mb than at the surface, and the correlation remains a fairly robust +0.50 at 500 mb.

The deep and coherent nature of the warm air over Fairbanks since the start of winter is illustrated by a time-height cross-section of temperature anomalies for the lowest 3000 m (see below).  It's clear that the recent cold spell at the surface was a very shallow phenomenon; warmth continues unabated aloft.  In fact, temperatures have warmed dramatically again in the past 24 hours, and this afternoon's balloon sounding reported a temperature of +7.6 °C at 850 mb, which is 19.2 °C above normal.  This is just about the greatest warm anomaly seen so far this winter at 850 mb (+19.8 °C was seen in November).