Definitions of Physical Parameters
Air Temperature (Dry-Bulb Temperature)
A thermodynamic parameter, quantifying the kinetic motion of gas molecules contained in air. In macroscopic scale this motion is translated in the degree of how cold or hot air is. Also, known as dry-bulb temperature this is the parameter measured by a conventional thermometer.
Relative Humidity of Air
The amount of water vapour in air, expressed as a percentage of the total possible (saturation) amount of water vapour at the same temperature. This parameter is important for many types of thermodynamic systems including all living organisms.
Barometric Pressure
The total weight of gas molecules exerted in the atmosphere at a given point on Earth. It is a fundamental environmental parameter for prediction of weather changes for hours in advance. In environmental measurements, it can also be found under the name “station pressure”.
Reduced to Sea Level Atmospheric Pressure
Equivalent atmospheric pressure at sea level, introduced globally to eliminate dependence of barometric pressure values on installation height (station elevation) of a weather station. This is the parameter reported in weather forecasts.
Dew Point (Dew Temperature)
The temperature at which water vapours in air begin condensing into water. This parameter finds valuable applications in industrial processes and agriculture.
Absolute Humidity of Air
The mass of water vapour present in a unit volume of air.
Vapor Pressure in Air
The pressure exerted by vapours that are in thermodynamic equilibrium with their solid or liquid form in air.
Saturated Vapor Pressure in Air
Under each given set of environmental conditions, saturated vapour pressure is the maximal vapour pressure exerted by vapours in thermodynamic equilibrium with their solid or liquid form.
Heat Index
An equivalent raised value of air temperature, perceived by a human body due to the presence of relative humidity in air. Heat index is a valuable indicator for heat stroke prevention in activities, involving people exposed to high levels of relative humidity – both indoors and outdoors.
Speed of Sound in Air
The distance travelled per unit of time by a sound wave in air. Speed of sound changes with air temperature and relative humidity.
Mixing Ratio of Moisture in Air
A measure of atmospheric humidity defining the ratio of mass of water vapor contained in air to mass of dry air. Also known as specific humidity.
Specific Enthalpy
The total thermal energy (sensible heat + latent heat), contained in a unit mass of mixture of dry air and water vapour.
Water Activity in Air
A dimensionless parameter of how efficiently the water amount present in air can take part in a reaction or in a physical process.
Boiling Point of Water
The temperature at which the water vapour pressure equals barometric pressure.
Wet-Bulb Temperature
Under each given set of environmental conditions, wet-bulb temperature is the lowest temperature that can be reached through cooling by means of evaporating water (e.g. human perspiration). It is an important parameter in many industrial thermal processes as well as in agriculture and farming.
Percentage Concentration of CO2 in Air
Abnormally high concentration of CO2 that may be reached in an enclosed space during fire burning or because of biological or technological processes. Percentage of CO2 in air is often monitored in safety applications.
Height Above Sea Level
Also referred to as “station elevation”, this is the vertical distance above mean sea level at which a meteorological station (a RHTP probe) is installed. This elevation is adopted as the reference datum level for all measurements of reduced to sea level atmospheric pressure by the station (by the RHTP probe).
Vertical Temperature Coefficient
The rate of temperature drop per every 100 meters of vertical elevation above sea level.