Thursday, February 2, 2012 4:30:18 PM
Climate change effects the extent of Arctic sea ice, which again effects the climate. In my cartoon below I have shown two ways in which the ice cover effects the temperature.
The albedo effect
: Albedo is the fraction of solar energy (shortwave radiation) reflected from the Earth back into space. It is a measure of the reflectivity of the earth's surface. Ice, especially with snow on top of it, has a high albedo: most sunlight hitting the surface bounces back towards space. Water is much more absorbent and less reflective. So, if there is a lot of water, more solar radiation is absorbed by the ocean than when snow or ice dominates.
The lid effect
: Ice cover prevents release into the atmosphere of heat stored in the ocean.
Such effects make Arctic sea ice an important component in the global climate system.
A study recently published in the scientific journal Tellus A
shows that the probability of cold winters with much snow in Central Europe rises when the Arctic is covered by less sea ice in summer. A shrinking summertime sea ice cover changes the air pressure zones in the Arctic atmosphere and impacts the European winter weather.
Retreat of the light ice surface reveals the darker ocean, causing it to warm up more in summer from the solar radiation (ice-albedo feedback). The diminished ice cover can no longer prevent the heat stored in the ocean being released into the atmosphere (lid effect). As a result of the decreased sea ice cover the air is warmed more greatly than it used to be particularly in autumn and winter because during this period the ocean is warmer than the atmosphere. The warming of the air near to the ground leads to rising movements and the atmosphere becomes less stable. Winds are driven by air pressure difference between the Arctic and mid-latitudes: the so-called Arctic oscillation with the Azores highs and Iceland lows. If this difference is high, a strong westerly wind will result which in winter carries warm and humid Atlantic air masses right down to Europe (cf. the severe January storms we had in North Western Europe last month (January 2012) - January on average in fact being the most stormy in this region). If the wind does not come, cold Arctic air can penetrate down through to Europe, as was the case in the winters of 2009/2010 and 2010/2011. Model calculations show that the air pressure difference with decreased sea ice cover in the Arctic summer is weakened in the following winter, enabling Arctic cold to push down to mid-latitudes.
It must be pointed out that other factors of course also play a role. The sea ice-atmosphere relationship suggests however a potential for use in operational Northern Hemisphere seasonal forecasts.Reference
Jaiser et al.Impact of sea ice cover changes on the Northern Hemisphere atmospheric winter circulation
Tellus A 2012, 64, 11595
(NB: published under the terms of the Creative Commons Attribution-Noncommercial 3.0 Unported License -- and thus not behind a pay-wall).
Tuesday, January 31, 2012 7:22:03 PM
Have you seen the doctor lately. Here is one that helps keep South African Cape Town healthy - "die Kaapse dokter"
in English known as "The Cape Doctor“
. The Cape Doctor is the local name for a strong south-eastern wind – also known as South-Easter - that blows around Cape Town. It is said to clear all pollution (dispersing brown haze, allergens, pollutants and irritants) in the city and across the Cape Flats, offering an amazing clear sky and view of the City and its Table Mountain. Last week it also helped extinguish a fire
in the Tygerberg Nature Reserve in Plattekloof. Some winds seem to have a better reputation than e.g. the Californian Santa Ana winds
- that by the way aggravate fire danger.
The wind was named "die Kaapse dokter"
by early settlers. it occurs regularly between October and March (the South African summer) and is not always benign. Cape winds have been responsible for 484 shipwrecks and thousands of deaths in Table bay and on the shore of the Cape peninsula over the last 500 years.
The South-Easter/”Cape Doctor“
originates from the South Atlantic High pressure system, which moves further southwards in summer as the westerlies retreat polewards. The South Atlantic High then ridges south of the country and joins up with the South Indian High pressure system often forming a band of high pressure to the south of the country during summer. Air flows anti-clockwise around a high pressure and clockwise around a low pressure in the southern hemisphere, so the resultant wind over the Western Cape in summer is mainly from the south east.
Thursday, January 26, 2012 8:07:38 PM
A few days ago I visited a special exhibition in the natural history museum of Berlin called “Feathered Flight - 150 Years of Archaeopteryx”
. The name Archaeopteryx
derives from the Ancient Greek ἀρχαῖος (archaīos) meaning "ancient", and πτέρυξ (ptéryx), meaning "feather". It got its name from the first find of this rare bird/dinosaur, which was actually only a single feather found in 1860 near Solnhofen and described by Meyer in 1861.
Later fossil skeletons of the whole creature were found, and the original of the best preserved of these is on exhibition in the same natural museum of Berlin - the real thing - my picture here below is only of a mould exhibited in a museum at Solnhofen.
What the plumage looked like has been an item of discussion. Here is a a model of Archaeopteryx lithographica
on display at the Oxford University Museum.
Recently it has been discovered that many feathers are preserved as melanosomes (containing light-absorbing pigments), and that the distribution of these structures in fossil feathers can preserve the colour pattern in the original feather. The discovery of preserved melanosomes opens up the possibility of interpreting the colour of extinct birds and other dinosaurs. An international team of scientists now finds that the well-preserved feather on Archaeopteryx's wing was black. The group located patches of hundreds of melanosomes encased within the fossil. The sausage-shape melanosomes were about 1 millionth of a meter long and 250 billionths of a meter wide — that is, about one-hundredth the diameter of a human hair in length and less than a wavelength of visible light in width. To determine the color of these melanosomes, researchers compared the fossilized structures with those found in 87 species of living birds that represented four classes of feathers — black, gray, brown and ones found in penguins, which have unusually large melanosomes compared with other birds. According to Ryan Carne the feather was predicted to be black with 95 percent certainty.
This all means that the Archaeopteryx lithographica
might have looked a bit like this (with black feathers):
The findings were published online on 24 January 2012 in the journal Nature Communications. (The first colour study ever on an Archaeopteryx
See also my posts:
Wednesday, January 25, 2012 3:04:54 PM
are found in permafrost regions. Permafrost is the easy word - it means of course perma
or in particular perma
en ground, or should I say frozen groundwater. Talik
is not that easy to understand for non-russian speakers - it is derived from таять which means melt or thaw. So permafrost is permanently frozen ground, and talik is a (Russian) term for permanently unfrozen ground in regions of permafrost.
Most permafrost areas have an upper active layer that is between 1 to 3 meters thick. This layer thaws up in the summer and freezes back again in the winter. It is thus not permanently frozen. Taliks often occur underneath lakes and rivers, where the deeper water does not freeze in winter, and thus the soil underneath will not freeze either. Please bear in mind that (fresh) water has a maximum density at around 4°C, and this leads to bodies of water maintaining this temperature at their lower depths during extended periods of freezing weather (preventing the ground under the water from freezing). It is also worth to mention that salinity alters the density and freezing point of water, which may influence the formation of taliks in coastal areas. Saline water in soil freezes below 0°C, so that talik occurs below parts of the shores of the Arctic Ocean and in cold brine pockets in the ground. If the talik continuous from the surface to the area below the permafrost it is called a “through talik
“. An ”open talik
“ on the other hand is a pocket of unfrozen ground that is open to the ground surface but otherwise surrounded by permafrost. Unfrozen ground totally surrounded by permafrost is known as a ”closed talik
“. A closed talik may for instance exist under a depression where a lake used to exist or dried out to become a bog. Closed taliks can also form where groundwater flow prevents the soil from freezing.
If the heat to prevent the soil from freezing is supplied by groundwater flowing through the talik, we have a hydrothermal talik
If freezing is prevented by mineralised groundwater flowing through the talik, we have a hydrochemical talik
Here are a few other more or less well defined talik terms, you may explore: ”isolated talik
“, ”lateral talik
“,” thermal talik
“, and ”transient talik
Why bother? With the increasing degrading of permafrost due to global warming the formation and development of taliks have received increased interest, and taliks need to be included in models of the evolution of permafrost systems.
Monday, January 23, 2012 8:05:40 PM
ESA satellites show that a large dome of fresh water has been building up in the Arctic Ocean over the last 15 years. The sea surface in the centre of the Beaufort Gyre has risen by about 15 cm, and the volume of fresh water accumulating in this are has increased by some 8000 km3 – around 10% of all the fresh water in the Arctic Ocean. That is about 10 % of the more than 70,000 km3 of freshwater that are stored in the upper layer of the Arctic Ocean, leading to low salinities in upper-layer Arctic sea water, separated by a strong halocline from warm, saline water beneath.
The findings were published on 22 January 2012 in the online version of the scientific journal, Nature Geoscience
. The dome could be a result of strong Arctic winds accelerating in the Beaufort Gyre, causing the sea surface to bulge. The freshwater itself is a result of melting ice and river runoff, and to some extent of course precipitation.
The Beaufort Gyre is an ocean and ice circulation pattern in the Beaufort Sea, north of Alaska. I have marked it with a B on the map above. This gyre moves in a clockwise direction (looking from above the North Pole). This circulation results from an average high-pressure system that spawns winds over the region. Ice that forms in or drifts into the Beaufort Gyre has historically remained in the Arctic ice system for years, accumulating snow and thickening each winter. Beginning in the late 1990s, the ice began melting away while in the southern parts of the gyre, before completing the circulation, counting for some of the increase in freshwater.
is a vertical zone in the water column in which salinity changes rapidly with depth.
Tuesday, January 17, 2012 10:05:07 AM
is a dreaded cold fall wind that originates on the ice cap and thunders down the East Coast of Greenland. Pitaracks are hurricane-force winds with speeds that can reach 80 m/s (288km/h). Similar winds are seen in Antarctica, where they give rise to the polar deserts known as the “Dry Valleys”
Pitaracks often occur when there are no clouds over Greenland. The air closest to Greenland’s icecap (an icecap that rises to something like 3000 m) cools off rapidly by contact with the ice so that even in summer the air temperature might be between -20 and -30ºC, while the layer of air above it stays warm, so the temperature actually increases with height. Near the coast, air in the valleys is warmed by the sea. Gravity pulls the cooler air down into the valleys, which suddenly within minutes sets up a strong wind blowing from the west-northwest. Pitaraqs are most intense whenever a low pressure area approaches the coast. Down-slope winds flowing from high elevations of mountains, plateaus, and hills down their slopes to the valleys, planes or sea below are called katabatic winds. Katabatic is derived from the Greek, namely from καταβαινω (katabaino) - to go down. An upslope wind is called anabatic. Kata means down and ana means up.
Pitaraq weather situations are characterised by a deep blue sky, very clear and dry atmosphere and intense sunlight. Cigar-shaped clouds perpendicular to the wind direction can usually be seen towards the inland ice. Such winds show up well on satellite images in the infra-red bands, due to their higher temperature relative to the surrounding air masses. Their occurrence appears to be related to the passage of depressions, up the Denmark Strait. As the katabatic winds in Antarctica, the Pitaraq is a very dry wind.
Here is a an image
captured by NASA’s Terra satellite on 20 September 2003. What looks like a streamer of snow is probably the surface of the sea reacting to the strong winds, because snow evaporates quickly in the dry arctic air. Further evidence that the streamer is on or close to the surface comes from the shadows that the clouds at sea cast on it. The threadlike structures near the coast are likely made by blowing snow or sea foam.
Saturday, January 14, 2012 10:59:11 AM
Waves can form at any interface between two different fluids, when one of the fluids is moving faster than the other.
This is well known from water waves at the interface between sea water and the atmosphere, but can also take place at the interface of waters with different density (e.g. cold water and warm water (stratified) layers in the ocean), or in the atmosphere between different layers of air.
Here is an example of waves at the interface between thick clouds and fast-moving air higher in the sky.
The clouds are examples of "Kelvin-Helmholtz waves". This type of turbulence forms when a fast-moving layer of fluid slides on top of a slower, thicker layer, dragging its surface. When the difference between the air and cloud speed increases to a certain point, the waves "break" — their crests lurch forward — and they take on the telltale Kelvin-Helmholtz shape. The clouds were moving from left to right (i.e. from west to east). I saw these clouds above the Eyjafjallajökul on 11 January 2012.
Fascinating isn’t it? — my best guess is that you have never seen such rare cloud waves, for most of us they are only for “once in a lifetime”.
And here is a nice collection of photos better than mine (but I suppose I'll never get a second chance):http://www.mentalfloss.com/blogs/archives/111522
Friday, January 6, 2012 10:36:08 AM
Poyang Lake is (was) the largest freshwater lake in China. It has/had a surface area of 3,585 km², a volume of 25 km³ and an average depth of 8 m.
The surface area has shrunk to 183 km². Persistent droughts for more than a decade caused by lack of rainfall in the upper reaches of the 5 feeding rivers have been blamed for the lake’s shrinkage. Human activity is, however, also partially to blame for the shrinking lake. Multiple construction projects have sprung up around the lake, including an international resort and commercial buildings. Some areas of the lake have been filled in to create more room for construction. A park near the village of Hedong was built by filling in part of the lake and building on top of it. People who live near Poyang Lake have become accustomed to seeing the lakebed partially exposed and fishing boats stranded in the past 10 years. The annual per capita income of fishermen in Poyang Lake fell to 1/4 of previous years. Water supplies in nearby cities are under pressure due to the shrinking lake.
Sunday, January 1, 2012 2:09:22 PM
If everything goes to plan I’ll be in Iceland next week to attend the Nordic Geological Winter Meeting
. After the meeting I expect to join a short field trip to the Eyjafjallajökull. I hope to tell you more about that in about two weeks time. In the meantime just a bit about the names.
I suppose you all remember the volcanic eruptions last year at Eyjafjallajökull. As I mentioned in my post on Katla Next Icelandic Volcano to Blow?
the eruption end March 2010 actually started at the Fimmvörduháls Pass between the Eyjafjallajökull ice field to the west (left) and the Mýrdalsjökull ice field to the east (right).
To my mind it would therefore have been more appropriate to talk about the Fimmvörðuháls eruption instead of Eyjafjallajökull. It has also been proposed to rename the new volcano to “Kreppa”, an Icelandic girl’s name, “Katla” the name of the nearby Katla volcano also being a girl’s name.
The name Fimmvörðuháls means five cairns pass
(fimm = five, varða, in plural vörður = cairn (pile of stone to mark a summit), háls = pass (literally neck or throat)). For the meaning of Eyjafjallajökull and Mýrdalsjökull see my Katla post
Wednesday, December 28, 2011 10:20:41 AM
Since last week I have been trying to figure out just where a mysterious new volcano eruption in the red Sea had taken place. A satellite image has now stilled my curiosity.
Last week fishermen reported that they had seen lava fountains rising 20-30 meter near the Zubair islands about 50 km west of Salif, in Yemen. The exact location was however unclear. The eruption apparently lead to the birth of a new island, which can be seen on this satellite image fro NASA Earth Observatory.
The activity in the Red Sea included more than one eruption. By 23 December 2011, what looked like a new island appeared in the region. The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured this high-resolution, natural-color images on 23 December 2011. The image shows an apparent island where there had previously been an unbroken water surface. A thick plume rises from the island, dark near the bottom and light near the top, perhaps a mixture of volcanic ash and water vapor. The volcanic activity occurred along the Zubair Group, a collection of small islands off the west coast of Yemen. Running in a roughly northwest-southeast line, the islands poke above the sea surface, rising from a shield volcano. This region is part of the Red Sea Rift where the African and Arabian tectonic plates pull apart and new ocean crust regularly forms.
Four years ago there was a similar eruption at the Yemeni Jabal al-Tair island.
These volcanoes are situated at the Red Sea Rift, a spreading ridge between two tectonic plates, the African (or Nubian) Plate and the Arabian Plate. It extends down the length of the Red Sea, stretching from the southern end of the Dead Sea Transform to a triple junction with the Aden Ridge and the East African Rift (the Afar Triple Junction) in the Afar Depression of eastern Africa. The rift zone indeed includes the island of Jabal al-Tair, formed by the basaltic stratovolcano of the same name, located northwest of the Bab al-Mandab passage at the mouth of the Red Sea, about half way between Yemen and Eritrea, a volcano that erupted on 30 September 2007 after 124 years of dormancy.
See also my 2007 post