Monday 29 August 2011

Playing Around with PIOMAS.

The daily PIOMAS volume anomaly series shows the difference for each day's volume from the volume for an average period. In this post I've used the 20 year period 1979 to 1998 to calculate the daily average.

To melt a given volume of ice requires a certain amount of energy, this is the enthalpy of fusion, 334kj/kg. So the volume anomaly can be transformed into an energy anomaly, in this post I call this the implied energy anomaly: it's the energy anomaly implied by the volume anomaly.

Sunday 21 August 2011

Arctic Dipole: Sea-Ice Loss.

In what I consider a very important paper, Wang et al 2009 ask: "Is the Dipole Anomaly a major driver to record lows in Arctic summer sea ice extent?"

They start by noting that since 2002 the Arctic Oscillation (AO) has become neutral to negative, yet there has been rapid sea-ice retreat over that period. Since the 1970s there has been a correlation between the AO and sea ice loss through the Fram Strait, with the positive AO of the 1990s leading to a significant increase in sea ice loss. So it seems that the AO has not played a role in the ice loss since 2002. As previously discussed, Zhang found that in the period 2002 to 2007 the Arctic Dipole (AD) has become the dominant mode of variability in the Arctic, taking over from the AO.

Monday 15 August 2011

Home straight.

It's now coming up to a month until this year's minimum. I normally don't provide a running commentary of ice conditions as that's done more comprehensively elsewhere than my time will allow. Furthermore in my opinion earlier in the season short term events have less of an impact on the final minimum figure. However as we near the end of this season the game is still afoot.

Thursday 11 August 2011

Arctic Dipole: A dominant role.

Zhang et al (2008) identify a recently emerging Dipole Anomaly in the Arctic, they call this the Arctic Rapid Change Pattern, or ARP, throughout this post I will however use the commonly accepted term; Arctic Dipole (AD). They use a running window EOF technique to examine small time periods over which the AD has changed. This means that instead of Wu et al's approach of applying the EOF to a long period, Zhang et al apply the EOF to short (5 year) runs over the period 1886 to 2006, this allows them to analyse the spatial changes with time. They don't refer to the previously discussed Wu et al paper.

Tuesday 9 August 2011

28 Weeks Days Hours Later.

Here in the UK the vermin are rioting. I guess I can't let this go without blogging, it is pretty amazing.

Monday 8 August 2011

Arctic Dipole: In the 20th Century.

The classic mode of variability in the Arctic atmosphere is the Arctic Oscillation. This is annular (circular) in form so moves air around the Arctic Basin. The AO is identified using a technique called Empirical Orthogonal Functions (EOFs), which is a technique used to identify patterns in data. Recently a pattern called the Arctic Dipole has been found, this has a key role in the recent atmospheric changes in the Arctic.

Monday 1 August 2011

Sea-ice drift speeds in the Arctic.

Hakkinen et al, 2008, use observations of sea-ice drift to examine possible trends in Arctic sea ice drift. Their aim is to examine whether sea-ice drift reveals anything about possible increase in storms in the Arctic, previous research has suggested that mid-lattitude storm systems are more frequently moving into the Arctic. As the authors note because sea-ice movement responds within hours to changes in wind this is a reasonable approach to the problem.

The mechanisms of sea-ice loss: A clarification.

I'm cramming a load of papers about the Arctic Atmosphere, changes in Arctic atmospheric circulation will be my theme for the next few posts. In the process of re-reading papers and reading new ones it's occurred to me that I haven't been as prescise as I should have been in some of my previous statements.

In an earlier post I've claimed that thermodynamics best explain the loss of Arctic sea-ice, I still think that this is the case. however think some clarification may be appropriate as I don't discount atmospheric and oceanic factors and may have given the impression that I do.