A Dynamic Analysis of a Record Breaking Winter Season Blocking Event

Abstract

The objective of this work is to study in detail a strong North Pacific, large amplitude, and long-lived blocking event that occurred during January 23–February 16, 2014. Indeed, it was the 11th strongest Northern Hemisphere event lasting longer than 20 days since 1968. This event formed out of the strong ridge that was associated with the devastating drought in the Western United States during the winter season of 2013-2014. This blocking event had many outstanding dynamical characteristics, the chief of which was that it survived an abrupt change in the planetary-scale flow when the Pacific North American pattern index changed from positive to negative in early February. The block then reintensified and persisted into mid-February. Several diagnostic techniques are employed to investigate the change in the planetary-scale flow during early February 2014 that have been applied to blocking before but aren’t as well known in the blocking literature.

The Nonequilbrium Thermodynamics of Atmospheric Blocking

“…As noted in the Introduction, these anomalies were a response in part to the strong ridging in the region prior to the blocking event. As described in (Jensen, 2015;Bond et al, 2015a), anomalous sea surface temperatures changed during the early part of February coinciding nearly with the reintensification of the blocking event after a precipitous decline in the BI, Jensen (2015). This suggests that the sea surface temperature anomalies and the blocking event were coupled, as can be seen in the surface entropy flux calculations below.…”

“…As seen in Tables 1 and 2 regime, as discussed in detail in Jensen (2015). This change in the large-scale flow also likely had an influence on the change in the entropy variables from January to February 2014.…”

“…from Jan 23 -Feb 16, 2014 and was centered at 130 • W, while at the same time the anomalously warm sea surface temperatures in the NE Pacific, known as the Blob, were intensifying, (Bond et al, 2015a, b;Jensen, 2015). This association adds another dimension to the present work beyond just the dynamics of blocking since the Blob contributed in a dramatic way to the surface heat fluxes that made up part of the entropy balance.…”

“…The blocking events were identified using the methodology found in (Lupo and Smith, 1995;Wiedenmann et al, 2002) and used in various other references, (see e.g., Mokhov et al, 2014;Jensen, 2015).…”

“…The strong blocking event that formed out of the ridge in early 2014, Jensen (2015), was influenced by diabatic heating (see 25 figure 12 and discussion in Jensen (2015)) as can be seen through the surface entropy supply and entropy production, as will be shown below. The event in early 2015 was also influenced by diabatic heating, as can be seen in the entropy production and surface entropy supply calculations provided below.…”