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Home , Barograph, Snow gauge, Stevenson screen, Weather station, Weather vane

A PAPER

ON LOCATION AND DESIGN OF A 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 () ARC 309

April, 2008 TABLE OF CONTENT

1.0 INTRODUCTION

1.1

2.0 TYPES OF WEATHER STATION

3.0 INSTRUMENT IN A WEATHER STATION

3.1

3.2

3.3 GUAGE

3.4 VANE

3.5

3.6 STEVENSONS SCREEN

4.0 FACTORS AFFECTING THE DATA GOTTEN FROM A WEATHER STATION

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

5.0 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 . Synoptic weather stations typically report near real-time (hourly, 6-hourly, daily) automated weather information using a communication system ( or modem). they collect detailed data on air , amount and intensity, and direction at a height of 10 m above the ground, , , cloud cover and type, hours of bright sunshine, solar radiation ,, dew point temperature and, in a few cases, 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 , 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 . 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 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 - for measuring humidity

-Anemometer for measuring wind speed

-Wind vane for measuring

-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 , 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 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 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

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 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 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 , 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 , 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 , 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 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 double- louvered 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 Interior of a Steven Screen

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 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 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 , (Stevensons screen) www.wikipedia.org