Support the Arctic Sea Ice Forum and Blog

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Topics - Niall Dollard

Pages: [1]
1
Arctic sea ice / Cold Pool in the Bering Strait
« on: August 21, 2019, 11:13:00 PM »
I noticed this cold pool in the Bering Strait recently on various SST charts for the Bering region. SST of sub 4 C surrounded by areas 8 C and higher on all sides. (Although I note these low temps are not showing currently on Nullschool).

If we accept it is true, I wonder what dynamics are involved?  Cooler currents sliding along Russian Arctic coast and then surfacing for some reason in the Bering Strait ?

 

2
Permafrost / Intensity of Insolation
« on: July 24, 2019, 01:29:00 AM »
Earlier in the melting thread I aroused a certain amount of debate on the role of the sun and insolation at high lattitudes.

And following proper ASIF protocol, hopefully anyone who wishes to make any further comment will do so here and not derail the melting thread.

As the big dipole approaches I spent a lot more time than I normally would teasing through the many timelapse charts at the ESRL website.

https://www.esrl.noaa.gov/psd/forecasts/seaice/

What I was particularly interested in was watching the dynamic of the melting as the dipole unfolded. Top melt, bottom melt, precipitation, wind direction, melt ponding, albedo changes. These are all available at ESRL.

They are only forecasts and cannot at all be assumed to be highly accurate.

The ESRL charts showed the melting evolving over time, peaking about 5 days from now (on that forecast time period). As expected the weak edges of the ice took a battering where winds were onshore (to ice edge) but there was bands of higher melt rate up the middle of between the two dipole centres.

Underneath the HP centre, though it didnt show much melt. This got me thinking what will melt conditions be like under the anticyclonic conditions at 85N between the pole and CAA. The albedo charts indicate that the ice quality is a bit better there, once you move away from the edge.

In four to five days time the dipole will be well established. At the same time we will be 38 days past the solstice (sun angle equivalent to approximately May 16th). 

This page has a slider that shows intensity of direct radiation in kW/m² throughout the day. Day 1 on the left is the solstice.

https://www.pveducation.org/pvcdrom/properties-of-sunlight/calculation-of-solar-insolation

It is the amount of power that would be received by a tracking concentrator in the absence of cloud. It does not take into account such things as atmospheric effects, cloud and albedo quality.

Is there a threshold intensity above which good quality ice snow will more readily melt.? If the albedo/ice quality is good enough, there will come a level which the clear sky solar intensity is not sufficient to melt.

Think of any practical experiences you may have observed. Given temperatures near zero, when sun angle is near 20 degrees, typically I dont see much melt on snow/ice on flat ground.  By the time you get to sun angle of 30 degrees, it's radically changed.

Binntho showed the graph of daily insolation at different lattltudes but that's the level that's spread out over a full day.The heat will not build up if it is radiated back. Intensity is different and there will always be a point where the albedo of the ice surface is not sufficient to prevent solar melting from occuring.

We will be shortly approaching the time when intensity of insolation will not be enough to melt good quality ice above 85 N. That's the way the planet moves - but of course this year even above 85N there is a dearth of quality ice. And any holes/melt ponds will lower the albedo and allow melting to continue.

I had nt intended either to address the other atmospheric issues, clouds, smoke, aerosols, black soot which will also encourage melting but the purpose of this post was to address the intensity of insolation and its effect on good quality snow/ice.

This is not meant to be a comment on the current state of the ice (hence moving it away from the melt season thread) but more a theoretical look at interplay between albedo and intensity of insolation.

3
Science / Sentinel 3B - Successful Launch by the ESA 25/04/18
« on: April 25, 2018, 09:43:34 PM »
Not sure how long this video will be available but launch was at circa 01:28 into the video at this link.

https://livestream.com/accounts/362/events/8163264/player?width=640&height=360&enableInfoAndActivity=true&autoPlay=true&mute=false

4
Developers Corner / NSIDC Gridded SI Extent and Conc. 1850 onwards
« on: January 04, 2018, 05:58:23 PM »
In their January 2018 news release the NSIDC announced that using a compilation of maps, ship reports, and other records, NOAA has published monthly estimates of Arctic sea ice extent spanning 1850 to 2013.

The historical observations come in many forms: ship observations, compilations by naval oceanographers, analyses by national ice services, and others.

Details can be had here:

https://nsidc.org/the-drift/data-update/gridded-monthly-arctic-sea-ice-back-to-1850-for-analysis-or-browsing/

The monthly charts are centred on the 15th of the month. In the user guide NSIDC recommend which colour palettes to use and map projection to use.

Using panoply and following the NSIDC guide, I produced this animated GIF on Sea Ice Concs for 1933.

5
Developers Corner / Creating an Arctic Temperature Inversion plot
« on: November 27, 2017, 11:35:58 PM »
Recent discussion about the measure of the Arctic temperature inversions in the freezing thread got me thinking about creating a plot of the difference between 850 hPa temperatures and the 2m temperatures.

Are such plots already available anywhere ? ESRL gives separate plots of both 850hPa temps and 2m temps for both RASM-ESRL and GFS data.

Perhaps A-Team or anyone else could have a look at this?. I have only got as far as downloading panoply, but am eager to learn! 

If 2m temps means 2m ASL (and not 2m above surface of the ground) a simple subtraction of 850 temps minus 2m temps would show the measure of the inversion. A preferred colour palate would be blues for negative results/no inversion (ie 850 temps < 2m temps) changing to green at zero and yellows/reds for positive/high positive results. 

6
Arctic sea ice / Null School Sea Surface Temperature Anomalies
« on: November 11, 2017, 06:57:36 PM »
I could not find a thread already open specifically for null school output. I have seen this discussed before though but I am wondering can anyone shed some light on why there is always very high SSTs displayed west of Svalbard and also to the SE of Svalbard.

I know the West Spitzbergen Current is a renowned warm,salty current but the temps shown by null school are well out of line. Today for example it shows SSTs of 16 C. There are also SSTs of 13 C to the south east of Svalbard and it is also picking up very warm lake temps from Finland.

Any thoughts why it (Null School) is picking up these high values at these locations. It is very persistent also?

In contrast SSTs from the Norwegian met here

7
Arctic background / Distribution of sea ice around Iceland from 1877
« on: March 30, 2017, 01:16:53 AM »
In the past 150 years or so the south coast of Iceland is the nearest that the Arctic sea ice has advanced to those of us in NW Europe.

I remember back in the pre-internet 1980s, when access to meteorological data was very limited, always being intrigued by the BBC Shipping forecast especially in winter or early springtime when you would occasionally hear mention of "light icing" or even moderate or severe icing warnings. Different times.  :o 

I came across this article of maps showing ice extent around the coasts of Iceland covering period of 1877 to 1968 (cropped image attached) :

http://www.vedur.is/media/hafis/frodleikur/is_koch_hlynur_1877-1968.pdf



The maps are largely the work of Lauge Koch (covering period pre 1940) and Hylner Sigtryggsson (post 1940) which probably explains why the maps are not listed in chronological order but begin with 1939 back to 1877 and then progressing from 1941 to 1967. While maps give a fairly good overview of the position of the ice this season can not take them too literally.  Usually a maximum spread of the month rather than a typical spread. Koch used maps and other information to create a measurement number of ice spread from year to year. The so called Koch Index.

1881 is regarded as the severest ice year in the past 200 years. As early as January the whole northwest, north and east coasts were blocked by ice. In April the ice began to spread to the south coast and in May a very broad belt of ice extended along the east coast with a broad belt also along the south coast as far as Reykjanes peninsula. 

Here is my chronology of sea ice around Iceland :

1878 : Ice Mar-Jun along north coast

1881 : Severest ice year

1882 : Not much better. Ice along parts of north coast even in September.

1887 : Ice along all of the north coast through August and September. That was some export through the Fram !!  This year also corresponded with a remarkably dry anticyclonic dominated year over NW Europe.

1892 : Another severe year but after this conditions improved.

1911 : Next severe year.

1918 : Another severe year

1926 & 1927 : Two low ice years in a row.

1931 : Ice hardly visible on any monthly map. Akin to most recent years.

1934-1936 : Three low ice years in a row.

1944 : Ice back on north coast Mar-Apr

1965 : Conditions something like the late 19th century. This was the beginning of the so called Icelandic "Ice Years". 1965-1971.

1972-1978 : Some warming again

1979-1986 : Cold period

1987 : Warming again with one cold year in 1995.

2010 : Ice comes close to the north coast in January and later in December. On January 27 a polar bear was shot in the NE of the country. According to this report the bear’s arrival in Iceland is highly unusual. Two polar bears were shot and killed in Iceland in the summer of 2008 and no others had been spotted for around 20 years before.

(Since 2010 there has been another report of a polar bear shooting in the NW of the country in summer 2016. Unlikely to be ice related. The head of the Icelandic Institute of Natural History believed it most likely that the bear swam a huge distance from the coast of Greenland.)

 

8
Arctic sea ice / DMI 80N+ graph, large increase at start of year 2000
« on: February 07, 2017, 01:12:28 AM »
Recent posts in the 2016/2017 freezing thread about centring the DMI 80N+ temp graph at winter time (rather than summer) prompted me to look back over the previous years.

Assuming the graphs display the full 365/366 days (and no days have been truncated) I noticed a large jump in the order of +16 K when you compare the last day of 1999 (~246 K) with the first day on the 2000 year graph (~262 K). Graph attached.

http://ocean.dmi.dk/arctic/meant80n.uk.php

I wonder is it possible to have such a large increase in one day ? By my eye the daily increases are never more than about 5 K.

So is this some sort of bug in the data ? The infamous Y2K bug?   

9
The link below has an interactive chart on maximum extent of ice cover in the Baltic Sea from 1720.

http://www.eea.europa.eu/data-and-maps/daviz/maximum-extent-of-ice-cover-1#tab-chart_1

The Baltic Sea covers an area of circa 420,000 km2. Complete ice coverage has been achieved 16 times since 1720. The last time being 1947. Since then 1987 has come closest (407k coverage).

The first time there was complete coverage was 1740 (no real surprise there!). Followed by 1754, 1789, 1799.

In the 19th century it happened 9 times, with a particular cluster in the last half of the century (6 times in less than 30 years). 1809,1830,1838,1867,1871,1877,1881,1888,1894

In the 20th century there were only 3 occasions (all in the 1940s) : 1940,1942,1947

Of note is the huge variability from year to year. Even just 3 years after the cold year of 1740 there was a very low max extent of only 90k.

The 15 year average line shows a significant downward trend (especially since 1981).

The lowest max extent was in 2008 (49k). 2015 was close to this (51k) and by the looks of things this year will be very low too.

10
I find it remarkable now (given the current state of the Arctic sea ice) that the ice was so thick back in the summer of 1975. Regarded as the worst years for many decades from an Arctic navigation point of view. I can't believe this has changed so much in my lifetime.

I came across this account of the navigation difficulties encountered by the Foss tugs endeavouring to make it to Prudhoe Bay.

http://www.mxak.org/community/jeffrey_foss/Pages%20from%20TowBitts_April2013.pdf

The ice at Point Barrow did not yield as 'normal' in early August. It wasn't until Sept 2nd before the first lead opened to allow tugs navigate through the pack ice. It took 2 days to work through the 165 miles of ice clogged waters and make it to Prudhoe.

But all through September the ice never relented and by Sept 28, 6 inches of new ice had formed. They needed the assistance form the coast guard ice breaker to make it through.

11
Greenland and Arctic Circle / Piteraq - The Greenland katabatic wind
« on: November 15, 2016, 11:54:52 PM »
The Piteraq originates on the Greenlandic icecap and sweeps down the east coast. The word "piteraq" means "that which attacks you".

Currently one running down the east coast today.

At 18Z today the station at Ikermit had gusts to almost 193 km/hr (coupled with an air temp of -6.4  :o )

http://www.ogimet.com/cgi-bin/gsynres?lang=en&ind=04373&decoded=yes&ndays=2&ano=2016&mes=11&day=15&hora=18

Pages: [1]