A
PAPER
ON
LOCATION AND DESIGN OF A
WEATHER STATION
BY
AJILORE YEJIDE
ARC/O5/5583
AJAO OLAWALE
ARC/05/5581
AJIBOLA YEMI
ARC/05/5582
Submitted to the Department of Architecture
In partial fulfillment of the course
Environmental Control (CLIMATE) ARC 309
April, 2008
TABLE OF CONTENT
1.0
INTRODUCTION
1.1
WEATHER STATION
2.0
TYPES OF WEATHER STATION
3.0
INSTRUMENT IN A WEATHER STATION
4.0
3.1
THERMOMETER
3.2
BAROMETER
3.3
RAIN GUAGE
3.4
WIND VANE
3.5
ANEMOMETER
3.6
STEVENSONS SCREEN
FACTORS AFFECTING THE DATA GOTTEN FROM A WEATHER
STATION
5.0
4.1
DIFFERENCE IN ALTITUDE
4.2
COASTAL OR INLAND NATURE OF LOCATIONS
4.3
NEARNESS TO URBAN CENTERS
4.4
OBSTRUCTION CAUSED BY GROUND COVER AND TOPOGRAPHY
LOCATION AND DESIGN OF A WEATHER STATION
REFERENCES
1.0
INTRODUCTION
Weather is measured so as to determine the changes weather elements
and variations in factors affecting climate which cannot be achieved without
the use of a Weather Station which houses the various instrument that measures
the various weather elements .there are various types of weather stations with
respect to their functions-synoptic Synoptic Agricultural weather station,
Climatological weather station, Rainfall weather station. The design of a
weather station involves locating a suitable environment and siting the needed
instrument using the appropriate design.
1.1
WEATHER STATION
A weather station is a facility with instruments and equipment to make
Observations of atmospheric conditions in order to provide information to make
weather forecasts and to study the weather and climate of a particular area. It
could also be defined as a meteorological observation post where
meteorological conditions are observed and recorded.
2.0
TYPES OF WEATHER STATIONS.
Measurement of weather elements or weather observations are carried
out at various weather stations .there are specifically four types of weather
stations which can be recognized depending on the number of weather
elements measured, the frequency of measurement ,and the status of the
observer whether professional or amateur. There specifically four types of
weather station which includes:
1. Synoptic weather station
2. Agricultural weather station
3. Climatological weather station
4. Rainfall weather stations
1. Synoptic weather station: these are stations manned by full-time a
Professional observers who maintain continuous weather watch and make
Hourly instrumental observations of the weather elements on which
information is required for the compilation of the synoptic charts or weather
maps used in weather forecasting. Synoptic weather stations typically report
near real-time (hourly, 6-hourly, daily) automated weather information using a
communication system (satellite or modem). they collect detailed data on air
temperature, precipitation amount and intensity, wind speed and direction at a
height of 10 m above the ground, atmospheric pressure, visibility, cloud cover
and type, hours of bright sunshine, solar radiation ,humidity, dew point
temperature and, in a few cases, snow depth and evaporation. The information
from these stations is used in preparing weather forecasts and in calculating
climatic information.
2. Agricultural weather station: These are stations manned by part-time observers
making at least twice daily instrumental observations of the major weather
elements: evaporation, grass and soil temperatures, and solar radiation are also
usually measured in view of their obvious importance in agriculture
3. Climatological weather station: These are stations manned by part-time
observers making only once or twice daily instrumental observations of
temperature, humidity, rainfall, and wind. Climate stations typically report less
frequently (daily, twice-daily, weekly, monthly) and may be automated or
manually operated by professionals. These stations collect daily temperature
and precipitation information, and some used to collect precipitation only.
4. Rainfall weather stations: These are stations manned by part-time observers
who take daily readings of rainfall only. Rainfall is measured by catching it in a
calibrated rain gauge. At most climate stations, a volunteer observer measures
rainfall intensity using a standard Canadian rain gauge called a type b rain
gauge. The gauge sits about 40 centimeters (cm) above the ground and has a
circular opening 11.3 cm in diameter. The rain is funneled into a clear plastic
cylinder which measures the contents to the nearest 0.2 mm.
the majority of climate station observers measure the depth of new snow using a
ruler. They estimate the amount of moisture in the snow by assuming a snow
density of 100 kilograms per cubic meter. Snow depth is read to the nearest 0.2
cm with less than 0.1 cm is recorded as a trace. The Canadian nipper shielded
snow gauge system is the standard instrument for measuring fresh snowfall water
equivalent. It is used at a limited number of stations.
3.0
INSTRUMENTS USED IN A WEATHER STATION
The typical weather station
has the following instrument
-Thermometer for measuring temperature
-Barometer for measuring barometric pressure -Hygrometer for measuring
humidity
-Anemometer for measuring wind speed
-Wind vane for measuring wind direction
-Rain gauge for measuring precipitation
Except for those instruments requiring direct exposure to the elements (i.e
anemometer, rain gauge), the instruments should be sheltered in a vented box,
called a STEVENSON SCREEN, to keep direct sunlight off the thermometer and
wind off the hygrometer. The instrumentation may be specialized to allow for
periodic recording otherwise significant manual labor is required for record
keeping.
3.1
THERMOMETER
A Clinical Thermometer
A thermometer is a device that measures temperature or temperature gradient, using a
variety of different principles. The word thermometer is derived from two smaller word
fragments: thermo from the Greek for heat and meter also from Greek, meaning to
measure. A thermometer has two important elements, the temperature sensor (e.g. the
bulb on a mercury thermometer) in which some physical change occurs with
temperature, plus some means of converting this physical change into value (e.g. the
scale on a mercury thermometer). Industrial thermometers commonly use electronic
means to provide a digital display or input to a computer.
Thermometers can be divided into two groups according to the level of
knowledge about the physical basis of the underlying thermodynamic laws and
quantities. For primary thermometers the measured property of matter is known so well
that temperature can be calculated without any unknown quantities. Examples of
these are thermometers based on the equation of state of a gas, on the velocity of
sound in a gas, on the thermal noise (see Johnson–Nyquist noise) voltage or current of
an electrical resistor, and on the angular anisotropy of gamma ray emission of certain
radioactive nuclei in a magnetic field.
Secondary thermometers are most widely used because of their convenience.
Also, they are often much more sensitive than primary ones. For secondary
thermometers knowledge of the measured property is not sufficient to allow direct
calculation of temperature. They have to be calibrated against a primary thermometer
at least at one temperature or at a number of fixed temperatures. Such fixed points, for
example, triple points and superconducting transitions, occur reproducibly at the same
temperature.
Internationally agreed temperature scales are based on fixed points and
interpolating thermometers. The most recent official temperature scale is the
International Temperature Scale of 1990. It extends from 0.65 K to approximately 1358 K
(−272.5 °C to 1085 °C).
3.2
BAROMETER
A barometer is an instrument used to measure atmospheric
pressure. It can measure the pressure exerted by the atmosphere by
using water, air, or mercury. Pressure tendency can forecast short
term changes in the weather. Numerous measurements of air
pressure are used within surface weather analysis to help find
surface troughs, high pressure systems, and frontal boundaries.
Schematic drawing of a simple mercury Barometer with vertical mercury column
and reservoir at base.
WATER-BASED BAROMETERS
This concept of "decreasing atmospheric pressure predicts stormy weather" was
invented by Lucien Vidie and is the basis for a basic weather prediction device
called a weather glass or thunder glass. It can also be called a "storm glass" or a
"Goethe barometer" (the writer Goethe popularized it in Germany). It consists of
a glass container with a sealed body, half filled with water. A narrow spout
connects to the body below the water level and rises above the water level,
where it is open to the atmosphere. When the air pressure is lower than it was at
the time the body was sealed, the water level in the spout will rise above the
water level in the body; when the air pressure is higher, the water level in the
spout will drop below the water level in the body. A variation of this type of
barometer can be easily made at home.[3]
Mercury barometers
A standard mercury barometer has a glass tube of about 30 inches (about
76 cm) in height, closed at one end, with an open mercury-filled reservoir at the
base. Mercury in the tube adjusts until the weight of the mercury column
balances the atmospheric force exerted on the reservoir. High atmospheric
pressure places more force on the reservoir, forcing mercury higher in the
column. Low pressure allows the mercury to drop to a lower level in the column
by lowering the force placed on the reservoir. Since higher temperature at the
instrument will reduce the density of the mercury the scale for reading the
height of the mercury is adjusted to compensate for this effect.
Torricelli documented that the height of the mercury in a barometer changed
slightly each day and concluded that this was due to the changing pressure in
the atmosphere[2]. He wrote: "We live submerged at the bottom of an ocean of
elementary air, which is known by incontestable experiments to have weight".
The mercury barometer's design gives rise to the expression of atmospheric
pressure in inches or millimeters (torr): the pressure is quoted as the level of the
mercury's height in the vertical column. 1 atmosphere is equivalent to about
29.9 inches, or 760 millimeters, of mercury. The use of this unit is still popular in the
United States, although it has been disused in favor of SI or metric units in other
parts of the world. Barometers of this type normally measure atmospheric
pressures between 28 and 31 inches of mercury.
Design changes to make the instrument more sensitive, simpler to read, and
easier to transport resulted in variations such as the basin, siphon, wheel, cistern,
Fortin, multiple folded, stereometric, and balance barometers. Fitzroy
barometers combine the standard mercury barometer with a thermometer, as
well as a guide of how to interpret pressure changes.
On June 5, 2007, a European Union directive was enacted to restrict the sale of
mercury, thus effectively ending the production of new mercury barometers in
Europe.
Old aneroid barometer
Modern aneroid
barometer
ANEROID BAROMETERS
An aneroid barometer uses a small, flexible metal box called an aneroid cell.
This aneroid capsule(cell) is made from an alloy of beryllium and copper. The
evacuated capsule (or usually more capsules) is prevented from collapsing by a
strong spring. Small changes in external air pressure cause the cell to expand or
contract. This expansion and contraction drives mechanical levers such that the
tiny movements of the capsule are amplified and displayed on the face of the
aneroid barometer. Many models include a manually set needle which is used
to mark the current measurement so a change can be seen. In addition, the
mechanism is made deliberately 'stiff' so that tapping the barometer reveals
whether the pressure is rising or falling as the pointer moves. They are used for
measuring atmospheric pressure.
A barometer is commonly used for weather prediction, as high air pressure
in a region indicates fair weather while low pressure indicates that storms are
more likely. When used in combination with wind observations, reasonably
accurate short term forecasts can be made.[6] Simultaneous barometric
readings from across a network of weather stations allow maps of air pressure to
be produced, which were the first form of the modern weather map when
created in the 19th century. Isobars, lines of equal pressure, when drawn on such
a map, gives a contour map showing areas of high and low pressure. Localized
high atmospheric pressure acts as a barrier to approaching weather systems,
diverting their course. Low atmospheric pressure, on
the other hand, represents the path of least
resistance for a weather system, making it more likely
that low pressure will be associated with increased
storm activities. If the barometer is falling then
deteriorating weather or some form of precipitation will fall, however if the
barometer is rising then there will be nice weather or no precipitation.
Barographs
A barograph, which records a graph of some atmospheric pressure, uses an
aneroid barometer mechanism to move a needle on a smoked
Barograph using five stacked aneroid barometer cells.
Barographs may be calibrated for altitude and this type is often used to
preserve a record of balloon and glider flights.
3.3
RAIN GUAGE
Standard Rain Gauge
Tipping Bucket Rain Gauge Recorder
Close up of a Tipping Bucket Rain
Gauge Recorder chart
A rain gauge (also known as an udometer or a pluviometer[pluviograph] or a
cup) is a type of instrument used by meteorologists and hydrologists to gather and
measure the amount of liquid precipitation (as opposed to solid precipitation that is
measured by a snow gauge) over a set period of time.
Most rain gauges generally measure the precipitation in millimeters. The level of rainfall
is sometimes reported as inches or centimeters.
Types of rain gauges include graduated cylinders, weighing gauges, tipping bucket
gauges, and simple buried pit collectors. Each type has its advantages and
disadvantages for collecting rain data.
Rain gauges have their limitations. Attempting to collect rain data in a hurricane can
be nearly impossible and unreliable (even if the equipment survives) due to wind
extremes. Also, rain gauges only indicate rainfall in a localized area. One example of
this is in Seattle: the official weather station for the city is at Seattle-Tacoma
International Airport, the driest part of the city, which means that actual annual rainfall
for downtown Seattle is around 254 mm (10 in) greater than official records
indicate.[citation needed] For virtually any gauge, drops will stick to the sides or funnel
of the collecting device, such that amounts are very slightly underestimated, and those
of .01 inches or .02 mm may be recorded as a trace.
Another problem encountered is when the temperature is close to or below freezing.
Rain may fall on the funnel and freeze or snow may collect in the gauge and not permit
any subsequent rain to pass through.
Rain gauge amounts are read either manually or by AWS (Automatic Weather Station).
The frequency of readings will depend on the requirements of the collection agency.
Some countries will supplement the paid weather observer with a network of volunteers
to obtain precipitation data (and other types of weather) for sparsely populated areas.
In most cases the precipitation is not retained, however some stations do submit rainfall
(and snowfall) for testing, which is done to obtain levels of pollutants.
Rain gauges, like most meteorological instruments, should be placed far enough away
from structures and trees to ensure that any effects caused are minimized.
3.4
WIND VANE
A weather vane, also called a wind vane, is a movable device attached to an
elevated object such as a roof for showing the direction of the wind. Very often these
are in the shape of cockerels and are called weather cocks. Arrows are also popular,
but a multitude of designs have been used.
The weather vane must be balanced so that half its weight is on either side of its axis,
but also designed so that the momenta about the axis of the areas exposed to the
wind are unequal. This unequal momentum causes the vane to rotate to minimize the
force of the wind on its surface. The design of the vane causes the end with the smallest
momentum to turn into the wind, pointing to the source of the wind. Because winds are
named from their source direction, the pointer enables the viewer to name the wind
easily. Most simple weather vanes have directional markers beneath the pointer,
aligned with the geographic directions. The pointer must be able to move freely on its
axis.
Weather cocks, especially those with fanciful shapes, do not always show the real
direction of a very gentle wind. This is because the figures do not achieve the design
balance required in a weather vane: an unequal surface area but balanced in weight.
To obtain an accurate reading, the weather vane must be located well above the
ground and away from buildings, trees, and other objects which interfere with the true
wind direction. Changing wind direction can be meaningful when coordinated with
other apparent sky conditions, enabling the user to make simple short range forecasts.
3.5
ANEMOMETER
An anemometer is a device for measuring wind speed, and is
one instrument used in a weather station. The term is derived
from the Greek word, anemos, meaning wind. The first
anemometer was invented by Leon Battista Alberti.
Anemometers can be divided into two classes: those that
measure the velocity of the wind, and those that measure
the pressure of the wind, but as there is a close connection
between the pressure and the velocity, a suitable
anemometer of either class will give information about both
these quantities.
3.6
STEVENSON SCREEN
A Stevenson screen or Instrument shelter is a meteorological screen to shield
instruments against precipitation and direct heat radiation from outside sources,
while still allowing air to circulate freely around them. It forms part of a standard
weather station. The screen creates, as near possible, a uniform environment in
relation to the air outside. The Stevenson screen is usually designed to hold
various instruments including thermometers (ordinary, maximum and minimum),
a hygrometer, a dew cell, a psychrometer, a barometer and a thermograph.
Stevenson screens may also be known as a cotton region shelter, an instrument
shelter, a thermometer shelter, a thermoscreen or a thermometer screen. The
use of a standard screen allows temperatures to be compared accurately with
those measured in earlier years and at different places. The traditional
Stevenson screen however, is a box shape, constructed of wood, in a doublelouvered design. However, it is possible to construct a screen using other
materials and shapes, such as a triangle. The World Meteorological Organization
(WMO) agreed standard for the height of the thermometers is between 1.25 m
(4 ft 1 in) and 2 m (6 ft 7 in) above the ground.
Exterior of a Stevenson screen
Screen
Interior of a Steven
4.0
FACTORS AFFECTING DATA GOTTEN FROM A WEATHER STATION
Table extracted from Lecture notes on Climatic data by Prof O.O.
Ogunsote
Due to the variation at different regions of the world, climatic data gotten from
weather stations will differ with variation in climate. Variations in climate are
caused by
1) Difference in Altitude
2) Coastal or Inland nature of locations
3) Nearness to urban centers
4) Obstructions caused by ground cover and topography
4.1
DIFFERENCE IN ALTITUDE
It is noticed that there may be up to one degree celcius for every 100m increase
in altitude. Higher diurnal ranges and higher wind speed are also recorded.
There is also a general fall in temperature with altitude as a result of subsequent
cooling of air.
4.2
COASTAL OR INLAND NATURE OF LOCATIONS
The sea affects the climate of coastal regions for up to 30 km inland. This creates
a variation
between inland and coastal climates which is more marked in dry climates. With
increase in the distance from the sea there is a general decrease in relative
humidity, cloud cover, wind
speed and rainfall. At the same time solar radiation as well as diurnal and
annual temperature ranges are on the increase.
4.3
NEARNESS TO URBAN CENTERS
Urban centres with large populations tend to create microclimates different
from that of the surrounding region. The urban heat island is formed as a result of
high concentrations of buildings, factories, structures, machines and human
beings. This is manifested by higher temperatures in cities.
4.4
OBSTRUCTIONS CAUSED BY GROUND COVER AND TOPOGRAPHY
This affects mainly the wind speed. The wind speed is usually measured at a
height of 10 metres. The wind speed at the level of the human body is usually
less since wind speed increases with altitude. This decrease is more marked in
wooded, suburban and urban areas as opposed to open areas. This is a result of
the obstruction caused by trees, buildings and other elements of the
topography.
5.0
LOCATION OF A WEATHER STATION
To ensure that different weather stations are accurate and comparable, the
exposures of meteorological instruments should be similar. To this end, a weather
station irrespective of the type should be located on a level ground covered
with short grasses and measuring at least 9m by 6m in size. The station should not
be sited on or close to a hill, in a depression or on a steep slope. Likewise, it
should be far from any obstacles like buildings or trees. Weather observation is a
painstaking job that requires care, patience, honesty, and punctuality on the
part of the observer. Weather observations must not only be accurate but must
also be done on time.
5.1
DESIGN OF A WEATHER STATION
In the design of a weather station, it is necessary to understand the
instrumentation of the weather instruments. It is with this proper understanding
that weather parameters can be precisely read
Instrumentation
A weather station measuring not less than 6m by 9m houses. The
stevenson’s screen and other instruments should be fenced with barb wire to
prevent animals fro entering. The interior size of the stevenson’s screen will
depend on the number of instruments that are to be used. A single screen may
measure 765 mm high by 610 mm wide by 593 mm deep (30.1 in by 24.0 in by
23.3 in) and a double screen 765 mm high by 1050 mm wide x 593 mm deep
(30.1 in by 41.3 in by 23.3 in). The unit may be mounted on a wooden stand or a
metal pipe.
The top of the screen was originally composed of two asbestos boards
with an air space between them. These asbestos boards have generally been
replaced by a laminate due to health and safety reasons. The whole screen is
painted with several coats of whitewash to reflect radiation and will usually
require repainting every two years.
Thermometers to measure maximum and minimum air temperature and
sensors to determine relative humidity and dew point temperature are placed
1.2 m above the ground in a shelter called a Stevenson screen. The shelter has
horizontal, overlapping slats that protect the thermometers from direct sunlight
and precipitation, while allowing air to circulate around them.
Rainfall is measured by catching it in a calibrated rain gauge. At most climate
stations, a volunteer observer measures rainfall intensity using a standard
Canadian rain gauge called a Type B rain gauge. The gauge sits about 40
centimetres (cm) above the ground and has a circular opening 11.3 cm in
diameter. The rain is funneled into a clear plastic cylinder which measures the
contents to the nearest 0.2 mm.
The majority of climate station observers measure the depth of new snow using
a ruler. They estimate the amount of moisture in the snow by assuming a snow
density of 100 kilograms per cubic metre. Snow depth is read to the nearest 0.2
cm with less than 0.1 cm is recorded as a trace. The Canadian Nipher Shielded
Snow Gauge System is the standard instrument for measuring fresh snowfall
water equivalent. It is used at a limited number of stations.
REFERENCES
Luther M., Meteorological observation(weather
observation,analysis,and forecasting)
Ogunsote O.O. , Lecture notes prepared on Climatic data for the
course Environmental Control, Federal University of Technology,
Akure
www. Agric.gov.ab.ca (2008), Agroclimatic Atlas of Alberta:
{Understanding Weather and Climate Data}
www.tsrye.fsnet.ca, Meteorology (Stevensons screen)
www.wikipedia.org