Nacreous clouds form in the lower stratosphere over polar regions when the Sun is just below the horizon. The clouds are illuminated from below and often glow in vivid colours.
Height of base: 68,500 - 100,000 ft
Shape: large thin discs, often reflecting vivid colours
Latin: no direct Latin translation, but the old English word “Nacre” means “mother of Pearl”
What are Nacreous clouds?
Nacreous clouds are rare and very high clouds, known mainly for the coloured light they reflect after sunset and before sunrise. The colours are reminiscent of the colours which reflect from a thin layer of oil on top of water, an effect known as iridescence.
How do Nacreous clouds form?
Nacreous clouds form in the lower stratosphere over polar regions when the Sun is just below the horizon. The ice particles that form nacreous clouds are much smaller than those that form more common clouds. These smaller particles scatter light in a different way, which is what creates the distinctive luminescent appearance.
Due to their high altitude and the curvature of the Earth’s surface, these clouds are lit up by sunlight from below the horizon and reflect it to the ground, shining brightly well before dawn and after dusk. They are most likely to be viewed when the Sun is between 1º and 6º below the horizon and in places with higher latitudes, such as Scandinavia and northern Canada. For this reason, they are sometimes known as polar stratospheric clouds. Nacreous clouds only form below -78 °C so are most likely to occur during the polar winter.
Because of the very low temperatures required, nacreous clouds are usually only visible from the UK when the cold air which circulates around polar regions in the stratosphere (known as the stratospheric polar vortex) is displaced and hovers temporarily over the UK.
What weather is associated with Nacreous clouds?
Because they form in a polar vortex, they are associated mostly with very cold and dry weather.
How do we categorise Nacreous clouds?
Nacreous clouds are classified into three types, Ia, Ib and II, according to their chemical composition, height and ambient temperature.
Mawingu yenye rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi. Mawingu huangazwa kutoka chini na mara nyingi huangaza kwa rangi nyangavu. "Kutoka kwa lugha ya Kiingereza, ""Nacre"" ni neno la Kiingereza la zamani linalomaanisha ""mama wa lulu.""" Mawingu ya Nacreous ni mawingu ya nadra na ya juu sana, inayojulikana hasa kwa nuru ya rangi inayorudisha baada ya machweo na kabla ya jua kuchomoza. Rangi ni reminiscent ya rangi ambayo kutafakari kutoka safu nyembamba ya mafuta juu ya maji, athari inayojulikana kama iridescence. Mawingu ya Nacreous hufanyizwaje? Mawingu yenye rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi ya rangi. Chembe za barafu zinazofanyiza mawingu ya nacreous ni ndogo sana kuliko zile zinazofanyiza mawingu ya kawaida zaidi. Chembe hizo ndogo-ndogo hutawanya nuru kwa njia tofauti, na hiyo ndiyo inayosababisha mwangaza huo wa kipekee. Kwa sababu ya urefu wao na mwinuko wa uso wa Dunia, mawingu haya huangazwa na mwangaza wa jua kutoka chini ya upeo wa macho na kuutazama chini, akitoa mwangaza mzuri kabla ya mapambazuko na baada ya mapambazuko. Inaonekana wakati jua liko kati ya 1 ° na 6 ° chini ya upeo wa macho na katika maeneo yenye latitudi za juu kama vile Scandinavia na Canada ya Kaskazini. Kwa sababu hiyo, nyakati nyingine huitwa mawingu ya stratospheric ya mviringo. Mawingu ya Nacreous hufanyizwa tu chini ya -78 ° C, kwa hivyo ni uwezekano mkubwa kutokea wakati wa majira ya baridi kali. Kwa sababu ya joto la chini sana linalohitajika, mawingu ya nacreous kwa kawaida huonekana tu kutoka Uingereza wakati hewa baridi ambayo inazunguka maeneo ya polar katika stratosphere ( inayojulikana kama vortex ya polar ya stratosphere) inahama na kuelea kwa muda juu ya Uingereza. Ni hali gani ya hewa inayohusiana na mawingu ya Nacreous? Kwa sababu hufanyizwa katika mzunguko wa barafu, zinahusianishwa hasa na hali ya hewa baridi sana na kavu. Tunawekaje wingu la Nacreous katika makundi? Mawingu ya Nacreous yamegawanywa katika aina tatu, Ia, Ib na II, kulingana na muundo wao wa kemikali, urefu na joto la mazingira.