Weather dirctionary

Following summary is mostly taken from the book "Meteorolgy in keywords" by Stefan Emeis from the Borntraeger publishing house and the internet page of the Goettingen weather station.

D

Dewpoint

Temperature onto those ones the moist air must be cooled off, so that dew forms itself. The difference between current temperature and dewpoint is mentioned 'dewpoint difference'; it is a wetness measure. The dewpoint lies under the humidity temperature.

T

Temperature

With the temperature T the heat energy contained in the air is measured. Heat is that one - through continuous collisions of the air molecules - disordered (accidental) molecule movement. The temperature is the measure of the middle kinetic energy of the molecules. The warmer a material is, the stronger the movement of the molecules is. At the absolute zero, the deepest accessible temperature, every molecule movement comes to the succumbing. The Kelvin (K) is physical unit of measure of the temperature. There are 0 K at the absolute zero. Further fixed points for a definition of the temperature scale are the freezing point and the boiling point of pure water at 1013.25 hPa, the middle air pressure at the ground. The difference between freezing and boiling-point is divided into 100 parts (degrees). With this increment we find the freezing point of water at 273.15 K and the boiling point at 373.15 K.

S

Soil temperature

The ground temperature influences the plant growth together with the soil humidity in a substantially way. An important value therefore for the phenomenology as well as the agriculture. The higher the temperature, the higher also the vaporization and in this way the ground humidity sinks. A dry soil heats up under solar radiation more quickly and cools down at night more strongly than a moist one does.
The soil temperature is measured by the Markkleeberg weather station in 10 and 50 cm of depth on a grass-grown meadow, sent over 4.50 m of cables to a separate transmitter station and transmit then about 30 meters to the base station.
In addition the temperature of the soil surface is determined. Especially in radiation-strong, wind-quiet nights the air is temporarily extremely stratified: warm air increases up, cold air sinks down. Ground frost can occur, although the air temperature in 2 m is height still 4 °C.

Soil wetness

The humidity content of the soil is strongly dependent on the selection of the location and in addition affects the soil and the surface temperature: the moister the soil is, the more sluggishly the variations are. A very wet soil freeze only slowly and keeps on being long frozen because a large amount of energy is needed for changing the phase of the water.
This measured value is interesting for all professions using soil, particularly for the agriculture. In addition with these data the storage capability of the soil as well as ground water and high tide states predicts are done. Because of the great number of different soils and the large measure variance of the ground humidity the soil wetness is not determined physically, but it is calculated with different parameters. The DWD publishes the graphic result of this work in the Internet (Profile for Leipzig).
The humidity content is measured by the Markkleeberg weather station in 10 and 50 cm of depth on a grass-grown meadow, sent over 4.50 m of cables to a separate transmitter station and transmit then about 30 meters to the base station.
A dry soil consists of mineral components and cavities filled with air. If the soil is completely satisfied with moisture, the whole air is replaced by water. The low pressure of 0-200 cb (centibar) which the plants must overcome in order to be able to include water against the capillarity is measured. Less water is available in the soil, the larger the (negative) pressure is, the more highly the indication in cb. The result might be quite representative for alluvial, fine, slightly loamy grounds of the nearer area. Because of plants differently can live with dryness, so they are more or less strongly be able to withdraw the remaining moisture, the following table can be used only as coase orientation:

Value	Soil conditions
0-10 cb	Satisfied soil. Typical in the winter and after productive rainfalls.
10-20 cb	Soil is sufficiently wet. No irrigation necessary.
20-60 cb	Soil is just sufficiently moist. At very light soil an irrigation can be already adequate.
60-100 cb	Soil desiccates. Now also a heavy soil must be watered.
100-200 cb	Dry soil. Without irrigation there are already dry damages at middle-deeply rooting plants (to bush size) on all soil types.