Glossary Terms

vernalization
vernalization

Exposure of seed or plants to low temperature to induce or accelerate the development of the ability to form flowers.

rime
rime

A white or milky and opaque granular deposit of ice formed by the rapid freezing of supercooled water drops as they impinge upon an exposed object.

Frazil
Frazil

Ice crystals that form in supercooled water that is too turbulent to permit coagulation into sheet ice. This is most common in swiftly flowing streams, but is also found in a turbulent sea (where it is called lolly ice). It may accumulate as anchor ice on submerged objects obstructing the water flow.

Pingo
Pingo

A large frost mound of more than one year's duration.

Polar Stratospheric Clouds
Polar Stratospheric Clouds

(Abbreviated PSC; also called nacreous clouds, mother-of-pearl clouds; rarely, luminous clouds.) Clouds are cirrus or altocumulus lenticularis, and show very strong irisation similar to that of mother-of-pearl, especially when the sun is several degrees below the horizon.

Sun Pillar
Sun Pillar

A halo in the form of a pillar of light extending above or below the sun and usually seen when the sun is low in the sky.

It is explained by reflection by the sides of columnar ice crystals falling with their long axes horizontal. The term light pillar is sometimes used when the source of light is artificial, such as street lamps.

Green Thunderstorm
Green Thunderstorm

The perceptually dominant wavelength of light from green thunderstorms ranges from blue- green to yellow-green. The purity of the color is generally low and the physical mechanism that causes the green appearance is not understood. Although green clouds often occur in conjunction with severe weather, there is no evidence to support anecdotal attributions of the cause of this green to specific characteristics of severe storms, such as hail or tornadoes.

(Photo by NOAA on Unsplash)

growing degree-day
growing degree-day

A heat index that relates the development of plants, insects, and disease organisms to environmental air temperature.

GDD is calculated by subtracting a base temperature from the daily mean temperature and GDD values less than zero are set to zero. The summation over time is related to development of plants, insects, and disease organisms. The reference temperature (base temperature) below which development either slows or stops is species dependent. For example, cool season plants (canning pea, spring wheat, etc.): base temperature is 40°F (5°C); warm season plants (sweet corn, green bean, etc.): base temperature is 50°F (10°C); and very warm season plants (cotton, okra, etc.): base temperature is 60°F (15°C).

wave breaking
wave-breaking

A complex phenomenon in which the surface of the wave folds or rolls over and intersects itself.

In the process it may mix (entrain) air into the water and generate turbulence. The causes of wave breaking are various, for example, through the wave steepening as it approaches a beach, through an interaction with other waves in deep water, or through the input of energy from the wind causing the wave to steepen and become unstable.