Bureau - Glossary of Terms

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Glossary

Select a letter from the index given below,
to be shown those glossary items which begin with the same letter.

| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |

D

DALR

The Dry Adiabatic Lapse Rate (DALR) is the rate at which the temperature of unsaturated air changes as a parcel ascends or decends through the atmosphere.
The DALR is approximately 9.8 degree Celsius per 1 km.

Deciles

Used to give an element a ranking. For example, a decile rainfall map will show whether the rainfall is above average, average or below average for the time period and area you have already chosen. Click here for more information.

Delta-T

Delta T is used by the agricultural industry. It is an important indicator for acceptable spraying conditions. It is indicative of evaporation rate and droplet lifetime. Delta T is calculated by subtracting the wet bulb temperature from the dry bulb temperature. Click here for more information.

Dew

Droplets of water deposited when air cools and the water vapor in it condenses.

Dew-point temperature

This is a measure of the moisture content of the air and is the temperature to which air must be cooled in order for dew to form. The dew-point is generally derived theoretically from dry and wet-bulb temperatures, with a correction for the site's elevation.

If the dry-bulb temperature is the same as the dew-point, the air is said to be saturated and the relative humidity is 100%.

Diurnal variation

The changes of value, for example, of a meteorological element within the course of a (solar) day. More especially, it denotes the systematic changes that occur during the average day.

Downburst

Violent and damaging downdraught striking the surface of the Earth violently. Associated with a severe thunderstorm.

Drizzle

Fairly uniform precipitation (rain) composed exclusively of very small water droplets (less than 0.5 mm in diameter) very close to one another.

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Drought

Prolonged absence or marked deficiency of precipitation (rain).

Dry-bulb temperature

This is the shade temperature (degrees Celsius) registered by a mercury-in-glass thermometer exposed in a white louvered box or meteorological screen which is raised on legs one metre above the ground.

Dry

(As used by forecasters) Free from rain. Normally used when preceding weather has also been relatively dry, and dry weather is expected to continue for a day or so.

Dust storm

A storm which carries large amounts of dust into the atmosphere. Ensemble of particles of dust or sand energetically lifted to great heights by a strong and turbulent wind.

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