Meteo Trnava

Physical background

Meteorological data – the temperature, pressure and sunshine intensity are gathered to demonstrate the typical experiment of remote sensing.

The Sun radiation is stemming from the thermonuclear fusion of hydrogen nuclei forming helium taking part in the Sun at the temperatures round 10 millions of kelvin. By means of the thermal radiation of the Sun the Earth surface and its atmosphere enormous radiation flux of about 1.7 x 1017 W. In principle, all the energy on the Earth is stemming from the Sun. The average intensity of the sun radiation above the atmosphere is called the solar constant and its value is 1,373 kW/m2. It represents the basic information for all sorts of Sun radiation exploitation.

The ISES unit for radiation intensity is a simple one direction relative radiometric unit, without aspiration to measure the integrated Sun radiation . The data are gathered in regular time intervals and are stored for subsequent retrieval and use.

By means of warming of the earth surface the atmosphere is also warmed . The average day temperature depends on the intensity of absorbed Sun radiation, depending in return on the slope of the Earth surface with respect to the direction to the Sun. This is the reason, why we observe substantial differences of the temperature in winter and summer The local changes in atmosphere temperature depend on the existence of clouds, which absorb the major part of the radiation and prevent their falling on the earth service. Temperature is naturally changing with the altitude and with the air circulation caused by the differences in temperature.

The outside temperature is measured by the ISES temperature with precision of about 1%.

Barometric (atmospheric) pressure is due to the weight of the air column above the earth surface. The quantity of the gas above the earth surface ( as its density, changing with the temperature ) is function of the altitude and time. The ascent to the higher layers of atmosphere is the height of the air column and its density diminished, so the pressure with altitude is decreasing. The equation describing this phenomenon is called the barometric equation or barometric law

1en_eq1,

Where p0, ρ0 represent the pressure and density of the air on the earth surface, g the acceleration of gravity and h the altitude. .

The local changes of the pressure strongly depend on the circulation of the air in the atmosphere. The average pressure on the sea level is approximately 101,3 kPa = 1013 hPa and is called normal atmospheric pressure.

The atmospheric pressure is measured by the ISES pressure gauge recalculated on the sea level ( with the correction on the altitude of the measuring point).

Literature D.Ilkovič: Fyzika I, Bratislava: Alfa & Praha: SNTL, 1972.