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The common phrase "red sky at morning" is a line from an ancient rhyme often repeated with variants by mariners [1] and others: Red sky at night, sailors' delight. Red sky at morning, sailors take warning.
Noctilucent clouds (NLCs), or night shining clouds, [1] are tenuous cloud-like phenomena in the upper atmosphere of Earth. When viewed from space, they are called polar mesospheric clouds (PMCs) , detectable as a diffuse scattering layer of water ice crystals near the summer polar mesopause .
This effect is further enhanced when there are at least some high level clouds to reflect this light back to the ground. [10] When weather systems predominantly move from west to east, a red sky at night indicates that the high pressure air (and better weather) is westwards. In the morning the light is eastwards, and so a red sky then indicates ...
The clouds do not become that color; they are reflecting long and unscattered rays of sunlight, which are predominant at those hours. The effect is much like if a person were to shine a red spotlight on a white sheet. In combination with large, mature thunderheads this can produce blood-red clouds.
Particles in the air scatter short-wavelength light (blue and green) through Rayleigh scattering much more strongly than longer-wavelength yellow and red light. Loosely, the term crepuscular rays is sometimes extended to the general phenomenon of rays of sunlight that appear to converge at a point in the sky, irrespective of time of day. [3] [4]
The clouds, which are formed by the marine layer, move in at night, usually after midnight, and typically dissipate in the late morning, giving way to clear, sunny skies. During a heavy June Gloom season, the condition may persist into the afternoon, or even all day during an exceptionally strong event.
At night, high thin cirrostratus clouds can lead to halos around the Moon, which indicate the approach of a warm front and its associated rain. [20] Morning fog portends fair conditions and can be associated with a marine layer, an indication of a stable atmosphere. [21] Rainy conditions are preceded by wind or clouds which prevent fog formation.
The Rayleigh sky causes a clearly defined polarization pattern under many different circumstances. The degree of polarization however, does not always remain consistent and may in fact decrease in different situations. The Rayleigh sky may undergo depolarization due to nearby objects such as clouds and large reflecting surfaces such as the ocean.