© Dipl.-Geogr. Martin Werner
- Glossary
As weather we call the present condition of the atmosphere at a certain place of the earth.
All substantial weather-determining processes take place in the troposphere below 12 km height.
Weather contains the same factors and elements as the climate, which results from the
long-term operational sequence of the weather.
A special interest is the statement about the supposed further progress
of the weather. Therefore, the pressure distribution on ground and in height plays an
important role.
Climate is called the middle condition of the atmosphere at a certain place.
Climate is the summary of the weather taking place typical for a larger area
(e.g. region) during a longer period.
3 ranges are differentiated: the macroclimate (e.g. a region or a continent),
the mesoclimate (influenced by topography) and the microclimate (canopy layer).
The most important climatic parameters are global radiation, air pressure,
humidity, air temperature, wind velocity and direction,
evaporation, precipitation and cloud coverage.
The measured values of these parameters are collected in tables and
evaluated statistically after a period of at least 30 years. The
statistic analysis is made according to frequence, succession and extreme
values.
Lines that interconnect the points of same temperature in a spatiotemporal raster.
The diagrams serve the temperature for the visualization of the hourly progress within a month.
Climatic factors represent the characteristics of an area (e.g. a region), which
affect the climate. Characteristics are: geographical latitude, elevation, valley adjustment,
exposition, ground cover, settlement density etc.
The term climatic factors cannot be rigidly used because in a certain way climatic elements represent
also climatic factors.
Lot days are certain days from which the weather can be forecast for following
periods. The lot days have their origin in the people faith.
Examples are: The Ice Saints (11.-15.May), the Seven Sleepers.
The peasants' weather maxims are popular formulations for regularly returning
weather features and expirations.
However, many of the delivered rules are inaccurate and among other things by
climatic change also outdated. But some of them contain true information and can
be proven scientifically.
The state of heat in the atmosphere is called temperature. The warming of the air take place on the ground:
the surface (soil, waters) is warmed up by solar radiation and transmitted to the air layers above.
The most common instrument used to measure the temperature is a thermometer filled with alcohol
(formerly: mercury).
Inside a small tubule the liquid expands or contracts. With the help of a calibrated scale the temperature
can be read exactly.
Air humidity is usually measured with a hygrometer. The instrument consists
of a case with degreased human hairs. The hairs expand or contract in dependance
of the humidity. With a special fixture the change of length is transmitted
to a scale where the value can be read.
The dew point is the condition in the atmosphere where the air mass is fully
saturated. The ralative humidity amounts to 100%. If the air continues to cool down,
then condensation begins.
We all know this effect, if in the morning rope drop at the blades of grass.
Or if hoar frost in the winter covers the landscape.
Dew point is often reached by night.
Climate:
Climatic parameters:
Isoplethes of the temperature:
Climatic factors:
Lot days:
Peasants' weather maxim:
Air temperature
The progress of temperature can be registered by a thermograph. It consists of a bimetal stored
in a case that is painted white on the outside. The bimetal is fixed on one side. The other
end of the bimetal is able to freely expand and contract; with a recording stylus the temperature
is drawn upon a special coated paper. A cylinder moves the paper one revolution the week.
Digital instruments are based upon the dependance of temperature of semiconductors.
The resistance of semiconductors is influenced by changes in temperature: a certain
temperature represents an exact voltage, that can be measured by a voltmeter.
For measurements of temperature different units are used. In Germany we use
degrees Celsius (°C), but in most of the anglo-saxon countries the scale
according to Fahrenheit (°F) is common. French-influenced countries are familiar
with the scale of Reaumur (°R). However, the standard in all sciences is the
scale of Kelvin: he committed the state of rest of the molecules as the (absolute)
zero point (corresponding to -273°C).
Air humidity:
For permanent measures of the air humidity a thermohygrograph can be used.
The hairs have the characteristic that they become dry at an air-humidity
lower than 60 %. The result is an increase of 5 % up from normal.
The maximum of inaccuracy is reached after 3 weeks. This period of time
is still shortened by lower values of air humidity (e.g. drought).
Normally the instrument will regenerate itself due to the high humidity
by night.
Another instrument to measure air-humidity is the psychrometer according
to Assmann. The gadget consists of two thermometers: one of the thermometers
is covered by a wet piece of cloth. A blower pulls the ambient air through
both thermometers. Due to the evaporation the wet thermometer will cool down.
The difference of the temperature between both thermometers
determines the air humidity: the bigger the difference the dryer the
air. With the aid of a psychrometer-table the accurate value of air-humidity
(in %) can be determined.
Digital values of humidity can be obtained by sensors that work as capacitors:
dielectric material is used to measure air-humidity. A circuit arrangement
shows the voltage adequate to the air-humidity.
There are different units for air humidity: generally it is used r.h. %.
It is the relationship between the water vapour presently in the air to
the saturated water vapour. Other units used are
absolute humidity (measured in g/m3) or the specific humidity (g/kg).
Dew point: