In the wake of wicked storm Henry which produced 100 mph winds on the exposed but low lying Tay Road Bridge and 149 mph over Cairngorm Summit Monday, northerly winds on the depression’s rear has helped force exceptionally cold air within the lower stratosphere (50,000+ feet) with the southern extension of the polar vortex dropping down over the UK. Clear, cold and most importantly dry air in the mid to upper atmosphere presented us with a stunning display of rare nacreous cloud over Ireland and UK.
Strong stratospheric warming from Asia across the pole into North America is responsible for bringing an arctic phenomenon to our part of the world.
10mb temperature profile over the arctic
Credit: Tropical Tidbits
50mb temperature profile over arctic
In the wake of Henry, we have a nice vertically stacked cold atmosphere from lower atmosphere (5,000ft) all the way to lower stratosphere, allowing the sightings of polar stratospheric clouds more typical of the polar atmosphere.
Look at where the polar vortex core is positioned above and now look at where the winds on the backside of Henry (positioned over the Norwegian Sea) are blowing from.
Credit: Tropical Tidbits
Credit: Met Office
Storm Henry is technically below the level of the polar stratosphere but there’s not just simply strong warming at 10 down to 50mb within the polar stratosphere causing the displacement towards Europe but there’s tremendous forcing and downward energy transfer which is essentially pushing the lower stratospheric conditions down to lower altitude and winds at 500 to 200mb winds associated with Storm Henry’s rear is pulling down extremely cold air over the UK at roughly 50-60,000ft allowing these rare cloud sightings throughout UK and Ireland skies this morning. This clouds are typical within the polar regions.
This morning’s capture.
Newbridge, West Lothian
CREDIT: Paul Utterson @utterson81
East Lothian
CREDIT: Maple23 @map1e23
CREDIT: Maple23 @map1e23
Co Kildare
CREDIT: Kel @GinghamSkyPhoto
CREDIT: Kel @GinghamSkyPhoto
CREDIT: Kel @GinghamSkyPhoto
Bangor, Northern Ireland
CREDIT: Noel Blaney @LividLFC
From Wikipedia
Polar stratospheric cloud
| Polar Stratospheric Cloud | |
|---|---|
Antarctic stratospheric cloud (nacreous clouds)
|
|
| Abbreviation | PSC |
| Altitude | 15,000–25,000 m (49,000–82,000 ft) |
| Classification | Other |
| Appearance | Glowing brightly with vivid iridescent colors |
| Precipitation cloud? | no |
Polar stratospheric clouds or PSCs, also known as nacreous clouds (/ˈneɪkriː.əs/, from nacre, or mother of pearl, due to its iridescence), are clouds in the winter polar stratosphere at altitudes of 15,000–25,000 meters (49,000–82,000 ft). They are best observed during civil twilight when the sun is between 1 and 6 degrees below the horizon.[1] They are implicated in the formation of ozone holes.[2] The effects on ozone depletion arise because they support chemical reactions that produce active chlorine which catalyzes ozone destruction, and also because they remove gaseous nitric acid, perturbing nitrogen and chlorine cycles in a way which increases ozone destruction.[3]
Formation[edit]
The stratosphere is very dry; unlike the troposphere, it rarely allows clouds to form. In the extreme cold of the polar winter, however, stratospheric clouds of different types may form, which are classified according to their physical state and chemical composition.
Due to their high altitude and the curvature of the surface of the Earth, these clouds will receive sunlight from below the horizon and reflect it to the ground, shining brightly well before dawn or after dusk.
PSCs form at very low temperatures, below −78 °C (−108 °F). These temperatures can occur in the lower stratosphere in polar winter. In the Antarctic, temperatures below −88 °C (−126 °F) frequently cause type II PSCs. Such low temperatures are rarer in the Arctic. In the Northern hemisphere, the generation of lee waves by mountains may locally cool the lower stratosphere and lead to the formation of PSCs.
Forward-scattering of sunlight within the clouds produces a pearly-white appearance. Particles within the optically thin clouds cause colored Interference fringes by diffraction. The visibility of the colors may be enhanced with a polarising filter.
Types[edit]
A type II (water) PSC showing iridescence
PSCs are classified into three types Ia, Ib and II according to their chemical composition which can be measured using LIDAR. The technique also determines the height and ambient temperature of the cloud.[4]
- Type I clouds contain water, nitric acid and/or sulfuric acid and they are a source of polar ozone depletion.[5]
- Type Ia clouds consist of large, aspherical particles, consisting of nitric acid trihydrate (NAT).[4]
- Type Ib clouds contain small, spherical particles (non-depolarising), of a liquid supercooled ternary solution (STS) of sulfuric acid, nitric acid and water.[4]
- Type Ic clouds consist of metastable water-rich nitric acid in a solid phase.[6]
- Type II clouds, which are very rarely observed in the Arctic, consist of water ice only.[4]
Only Type II clouds are necessarily nacreous[1] whereas Type I clouds can be iridescent under certain conditions, just as any other cloud.
-
Isobaric Height Approx. Height ASL
-
1000 hPa 500′
-
975 hPa 1,000′
-
950 hPa 1,500′
-
925 hPa 2,500′
-
900 hPa 3,000′
-
850 hPa 5,000′
-
800 hPa 6,000′
-
750 hPa 8,000′
-
700 hPa 10,000′
-
650 hPa 12,000′
-
600 hPa 14,000′
-
550 hPa 16,000′
-
500 hPa 18,000′
-
450 hPa 20,500′
-
400 hPa 24,000′
-
350 hPa 27,000′
-
300 hPa 30,000′
-
250 hPa 34,000′
-
200 hPa 39,000′
-
150 hPa 45,000′
-
100 hPa 53,000′
-
70 hPa 60,000′
-
50 hPa 67,000′
-
20 hPa 87,000′
-
10 hPa 102,000′All this made possible with on going stratospheric warming episode.
This could well lead to a much colder pattern for Western Europe mid February onwards.
See today’s video for a look at the medium/long range prospects.
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