It was only June when there were expectations of an El Nino coming. But the sea has cooled rapidly since then — much faster than usual — and now NOAA thinks a La Nina is slightly more likely. If so, global temperatures will decline.

Cold water is upwelling across the Eastern Pacific. Sea Surface Temp Anomaly.  | Image Sept 6, 2017

I notice that there is also unusually cold water on the surface of the eastern Indian Ocean near West Australia (see below). One spot is 2.5C cooler than normal. I don’t know the significance…

Cooling ocean in the east Indian Ocean too.  Sea Surface Temp Anomaly.  | Image Sept 6, 2017

It may be a milder wetter summer downunder (our grid managers will be happy about that.) In the US, drying conditions in the south, but more snow or rain in the midwest, Northern California. A cooler snowier winter in Canada. It means more Atlantic Hurricanes.

The best explanation I’ve heard on how El Nino works is from Bill Kininmonth: The deep oceans drive the atmosphere.

h/t GWPF

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September 6, 2017 at 10:56AM

aer Atmospheric and Environmental Research

September 5, 2017 Dr. Judah Cohen of AER posted his monthly forecast for the Arctic and NH based on the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO).  Excerpts below.

The AO is currently slightly negative (Figure 1), reflective of mostly positive geopotential height anomalies across the Arctic and mixed geopotential height anomalies across the mid-latitudes of the NH (Figure 2). Geopotential height anomalies are mostly negative across Greenland and Iceland (Figure 2), and therefore the NAO is slightly positive.
Figure 1. (a) The predicted daily-mean near-surface AO from the 00Z 5 September 2017 GFS ensemble. Gray lines indicate the AO index from each individual ensemble member, with the ensemble-mean AO index given by the red line with squares.

The AO is predicted to straddle neutral next week as geopotential height anomalies remain mixed across the Arctic. Similarly, with mixed geopotential height anomalies stretching across Greenland and Iceland, the NAO will likely be near neutral as well.  

(Note: AO and NAO are signed differently than one might expect; the reference point is outside the Arctic itself.  Thus negative phases of these indexes mean higher pressures in the Arctic and lower outside, while positive phases indicate lower pressures in the Arctic.  Now that the Arctic sun is setting, the main issue for ice extent is storminess which requires low Arctic pressures.)

Impacts

It is the first week of fall, a season of transition from summer to winter. One important sign IMO of this seasonal transition is the return of the polar vortex in the stratosphere. The models predict the possible formation of the polar vortex sometime next week. Starting in October, I will be watching variability in the polar vortex for signs of pattern changes in the weather across the NH.

Another sign of the seasonal transition is the minimum in Arctic sea ice extent, which will be achieved in the coming days and/or weeks. The trajectory of sea ice melt has slowed since early August. In my last blog I suggested the possibility that the sea ice minimum could be similar to the years 2008 and 2010 and that is looking more likely but is difficult to predict. Over the coming months, I will be following Arctic sea ice variability for signs of the severity of the upcoming winter. Our understanding for how anomalies in sea ice extent influence the weather in the mid-latitudes is still immature IMO but I do think that important progress has been made recently.

Another sign of the transition from summer to winter is the return of snowfall to the NH. Snowfall over the sea ice in August probably helped retard the melt of sea ice and snowfall is now even occurring over Siberia and Alaska but is still very regionalized. Again I will be monitoring the advance of snow cover extent across the continents for signs of the strength of the polar vortex and the possible resultant weather.

Finally I find it interesting that while the atmospheric circulation has transitioned from the dominant summer pattern across Eurasia it has not across North America. The dominant summer pattern across Eurasia was ridging across Europe (with the exception of Northern Europe) and East Asia but with troughing in Western Asia. The forecast for the coming weeks is the opposite with troughs across Europe and East Asia but ridging in Western Asia. This is an overall cooler pattern than the dominant summer pattern. However across North America there are no similar signs of transition. The dominant summer pattern was strong ridging across western North America and troughing in eastern North America and at least for now that pattern looks to continue for much of the month of September. I don’t know the reason behind the persistent western ridge/eastern trough pattern across North America but how long this pattern can persist will obviously have important implications for the weather across North America in the coming months.

Summary

Bottom line, looks like September weather will be ordinary in the Arctic with seasonal cooling in the NH.  Dr. Cohen also thinks the annual ice extent minimum will be near average for the decade.

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September 6, 2017 at 10:30AM

Northern Hemisphere Spatial Coverage

As noted in the September Outlook Arctic Ice, NOAA’s Sea Ice Index (SII) typically shows less ice than MASIE from National Ice Center (NIC). SII is a satellite product processed from passive microwave sensors. MASIE (Multisensor Analyzed Sea Ice Extent) adds other sources such as satellite imagery and field observations to produce high resolution ice charts for navigational purposes.

A post in 2016 NOAA Is Losing Arctic Ice showed how discrepancies between the two datasets vary considerably throughout the year, usually lower in SII except for October. Walt Meier directs the SII production and published a study in October 2015 comparing SII and MASIE, also discussed in that post.

In 2016 NOAA upgraded from SII version 1 to version 2, and later to version 2.1. The latest documentation says few datapoints were changed in v2.1, and that anomalies were unchanged. My cursory look seemed to confirm that. However, on closer inspection, there are significant differences between v1 and v2 (which carry over to v2.1). This post describes those differences.

I prepared two spreadsheet arrays for SIIv1 and SIIv2.1 and then a third array to calculate the differences. The graph below shows the results for 2006 to 2015 inclusive, being the years for which datapoints can be compared with MASIE.

It is clear that V2.1 is systematically lower than V1, on average -200k km2. The differences are less than 100k km2 the first four months, then increase May, June, July, before shrinking again in August and September. The big changes come in the last months, especially October. The October correction is not surprising. The comparison by Meier and in my post discussed large SII surpluses over MASIE in October that did not appear credible.

The graph is limited to one decade since that is the period to be compared with MASIE. The spreadsheet shows that the differences are typical of the whole dataset going back to 1979, albeit with considerable variety through the years. The graph below shows the month by month differences for all years through 2015.

As stated before, the average all years difference in green is comparable to the last decade. Differences were calculated by subtracting v1 from v2, since v2 is mostly lower. However, as the Min Diff line shows, v2 was higher for some datapoints, notably in July. The Max Diff shows that some Octobers were changed by as much as 1M km2. The dotted lines show the standard deviation for the average differences, which averaged  +/- 90k km2.

Summary

It is challenging to estimate Arctic ice extents. NOAA is to be commended for recognizing the erroneous October values, and correcting them. Clearly some of that overall diminishing of extents by 200k km2 derives from removing the bogus surpluses.

Those claiming that SII is for certain and MASIE is dubious need to reconsider. MASIE has its own challenges but is reasonably consistent in recent years. Meanwhile SII had to improve its product, resulting in changes to past values in the dataset. While error ranges are not available for these statistics, the standard deviation gives some indication of the variability in the estimates.

Fortunately, it appears that the critical months of March and September have not changed much in the new SII version.  However, it is not encouraging to see SII averages for the last two months -500k km2 below MASIE.  See September Outlook Arctic Ice

It is a good thing that several agencies and methods are involved in the effort to measure and understand Arctic ice dynamics. It is not good to claim certainty for a single record or to ignore the errors that are found along the way. It is wise to remember that measuring anything in the Arctic is difficult.

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September 6, 2017 at 10:30AM

As the Talkshop reaches the milestone of 5 million visits, do we hear echoes of Scotty of Star Trek fame: ‘Ye cannae change the laws of physics’? Does fundamental mean universal – or could some ‘laws’ depend on where you look in the universe? Meanwhile Tallbloke is boldly going…somewhere…

A study that will ‘test our understanding of how the Universe works, particularly outside the relatively narrow confines of our planet’ is being undertaken by an international team of researchers led by the University of Leicester, reports Phys.org.

The research probes whether the fundamental laws of physics are the same everywhere in the universe.

In their new study, the Leicester-led team assesses whether these laws are the same within the hot, dense conditions in the atmosphere of a dying white dwarf star as here on Earth.

These stars have masses around half that of the Sun compressed into a radius similar to that of the Earth, leading to extreme gravity within the atmosphere of the star.

The preliminary analysis, led by the research group of Professor Martin Barstow, Pro-Vice-Chancellor; Strategic Science Projects Director, Leicester Institute of Space & Earth Observation; Professor of Astrophysics & Space Science, Department of Physics & Astronomy, features on the cover of the online journal Universe.

Postdoctoral researcher Matthew Bainbridge is the lead author of the early-stage study titled “Probing the Gravitational Dependence of the Fine-Structure Constant from Observations of White Dwarf Stars.” The study involved Matthew Bainbridge, Martin Barstow and Nicole Reindl from Leicester along with colleagues from the U.S., France, The Netherlands, Australia and collaborators in the U.K.

The researchers use the light of white dwarf stars observed with the Hubble Space Telescope. Dr Nicole Reindl, leading the observations, says: “These particular stars contain metals, such as Iron and Nickel, floating within the surface layers of their atmospheres. The light generated within the depths of the star passes through the heavy metals, leaving behind a “fingerprint” in the stars’ light that we can study.”

Continued here.

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September 6, 2017 at 09:24AM