In the Open Air

Painters of the 19th century, seeking a certain atmospheric quality of light, were drawn to paint realistic and impressionistic landscapes en plein air. En plein air is a French phrase meaning in the open air.

Claude Monet Painting by the Edge of a Wood
by John Singer Sargent (1885).

The popularity of plein air painting grew in part because the technological advance of premixed and  transportable oil pigments made it possible for artists to take to the field. But the popularity of painting in the open air also grew from a new-found appreciation of the natural world.

Europeans and Americans were in the throes of unprecedented change and undergoing a technological point of inflection (industrial revolution). The primary draw to painting in the open air was perhaps a recognition of the need to engage with ― and reconnect to ― the natural environment.

"For me, a landscape does not exist in its own right, since its appearance changes at every moment; but the surrounding atmosphere brings it to life, the air and the light, which vary continually for me, it is only the surrounding atmosphere that gives subjects their true value."
― Claude Monet

Clouds in paintings by John Constable paintings were declared remarkably true to life. Scientists believed they could derive the season, or even the hour of the day from the skies depicted in Constable's paintings.

Cloud Study by John Constable (1821)

Claude Monet's Haystacks, painted between the summer 1890 and the winter 1891, exemplify the study of ―  if not near obsession with ― qualities of light and temporal atmospheric conditions. Monet painted a series of 25 canvases depicting haystacks in a field at Giverny. During that time Monet wrote to a critic,

"I am working very hard, struggling with a series of different effects (haystacks), but at this season the sun sets so fast I cannot follow it. . . . The more I continue, the more I see that a great deal of work is necessary in order to succeed in rendering what I seek."

Haystacks (1890-1891) by Claude Monet

A glimmer of light cannot truly be seen without much that is dark, and darkness cannot truly be felt without shadowy forms rising from the blackness.
― Anonymous

REFERENCES

• En Plein Air, Wikipedia.
• Environmental Art, Wikipedia.
• Haystacks (Monet), Wikipedia.
• Heilbrunn Timeline of Art History, The Metropolitan Museum of Art.
• Plein Air: Painting the American Landscape, PBS.
• The 10 best... skies in art, by Laura Cumming, The Observer, 10 March 2012.

Rain from Clouds

Water is continually evaporating and condensing in the sky. Clouds contain water vapor and small drops of condensed water (cloud droplets). Most of the condensed water in clouds does not fall as precipitation

Potential rain forms when water droplets condense on dust, salt, or smoke particles, which act as a cloud seeding nucleus.

When the water droplets become large enough that their fall speed exceeds the updraft speed in the cloud, they fall toward the ground. If the water drops do not evaporate as they travel earthward, they reach the ground as rain.

Virga, oil on canvas by Crystal Foreman Brown

Virga is the term for visible streaks or shafts of water that fall from clouds but evaporate before reaching the ground.

After the last of the rain had fallen from the sky and come to earth — leaving the sky clear and the earth damp and gleaming — the world below grew joyful in the cool left by the rain, and the greater clarity of life that returned with the blue of the heavens furnished each soul with its own sky.
~ Fernando Pessoa (1888-1935) from The Book of Disquiet.

Rain Drop Size

Size, fall velocity, and particle density (drops per square foot of air) vary for different types of rain (shown below).

Rain Type	Intensity inches/hour	Median diameter millimeters	Fall Velocity ft./sec.	Drops per sec. per sq. ft.
Fog	0.005	0.01	0.01	6,264,000
Mist	.002	.1	.7	2,510
Drizzle	.01	.96	13.5	14
Light rain	.04	1.24	15.7	26
Moderate rain	.15	1.60	18.7	46
Heavy rain	.60	2.05	22.0	46
Excessive rain	1.60	2.40	24.0	76
Cloudburst	4.00	2.85	25.9	113
Source: Lull, H.W., 1959, Soil Compaction on Forest and Range Lands, U.S. Dept. of Agriculture, Forestry Service, Misc. Publication No.768

Rain is grace; rain is the sky descending to the earth; without rain, there would be no life.
~ John Updike (1932-2009)

References

• USGS, The Water Cycle: Precipitation