2.6 Pressure
Atmospheric
or barometric pressure can provide information to the meteorologist responsible
for reviewing data that may be useful in evaluating data trends, and is also
used in conjunction with air quality measurements. There are two
basic types of instruments available for measuring atmospheric pressure:
- the
mercury barometer and
- the aneroid barometer.
The
Mercury Barometer
The
mercury barometer measures the height of a column of mercury that is
supported by the atmospheric pressure. It
is a standard instrument for many climatological observation stations, but
it does not afford automated data recording.
The
Aneroid Barometer
The aneroid barometer consists
of two circular disks bounding an evacuated volume. As the pressure changes,
the disks flex, changing their relative spacing which is sensed by a
mechanical or electrical element and transmitted to a transducer.
A
barograph is usually an aneroid barometer whose transducer is a mechanical
linkage between the bellows assembly and an ink pen providing a trace on a
rotating drum. A more sophisticated aneroid barometer providing a digital
output has been developed consisting of a ceramic plate substrate sealed
between two diaphragms. Metallic areas on the ceramic substrate form one
plate of a capacitor, with the other plate formed by the two diaphragms. The
capacitance between the internal electrode and the diaphragms increases
linearly with applied pressure. The output from this barometer is an
electronic signal that can be processed and stored digitally [5].
2. PRIMARY METEOROLOGICAL VARIABLES
2.1 Wind Speed
2.1.1 Cup Anemometers
2.1.2 Vane-oriented and Fixed-mount Propeller Anemometers
2.1.3 Wind Speed Transducers
2.2 Wind Direction
2.2.1 Wind Vanes
2.2.2 U-V and UVW Systems
2.2.3 Wind Direction Transducers
2.2.4 Standard Deviation and Turbulence
Data
2.3 Temperature and Temperature Difference
2.3.1 Classes of Temperature Sensors
2.3.2 Response Characteristics
2.3.3 Temperature Difference
2.3.4 Sources of Error
2.4 Humidity
2.4.1 Humidity Variables
2.4.2 Types of Instrumentation
2.5 Precipitation
2.6 Pressure
2.7 Radiation
2.8 Recommendations
