Tour of a Weather Gauging Station
On this page I'll take you on a tour of the Moree Bureau of Meteorology Weather Observation station. If you're interested in the weather I thoroughly recommend taking a tour of an observation station. You can find contact details for your local BOM station here.
BOM weather observation stations typically feature both automated and manually read instruments. If you're a user of the Bureau's on-line real-time data it's useful to see how the data is collected.
Temperature data is measured inside a louvered wooden box known as a Stevenson's Screen. The BOM measure dry and wet bulb air temperature inside the screen. As discussed in the weather basics page the two temperature readings are used to estimate the humidity. The Stevenson's Screen at Moree has both manually read and automated thermometers inside. The screen is placed approximately 1.5m above ground level.
Inside the Stevenson's Screen at Moree AWS. Manually read dry and wet bulb thermometers are placed at the front left. Automated thermometers are placed at the back of the box. The thermometers placed horizontally measure daily minimum and maximum temperatures.
Rainfall measurements are recorded continuously by an automated gage (pictured below). Rain that falls into the cone is directed into a small tipping bucket. The bucket tips each time it fills with water representative of 0.2mm of rain at the gauge and the data logger records each tip. Automated gauges are notoriously inaccurate for measuring snowfall as they can freeze over and may be subjected to high winds. The collection cones of the gauging stations in the mountains are heated to combat these problems.
Automated rain gauge with cover on. Standard sized gauges are used across the world.
Under the rainfall collection cover of the rain gauge. Water is directed into the brass tipper bucket. The data logger records each tip and transmits the data to the station's computer and this information is transmitted to the BOM's database, which is accessible on the web.
A second standard rain gauge which drains to a measuring cylinder is also measured manually twice per day. Before the days of data loggers rainfall accumulation was plotted by the gauge pictured below. Rainfall was directed into the black container. The silver cyclinder on the right contained a marker that was attached to a float. The marker turned one full revolution in 24 hours and scribed the water level onto a piece of paper.
An early version of rainfall data logger.
A barometer is used to measure absolute air pressure at the station. As well as logging the data electronically the barometer also plots a paper log of air pressure.
Barometer and manual air pressure plotter.
Wind speed is measured by a 3 cup anemometer and direction is measured by a wind vane. These are placed at a standard height of 10m above ground level.
Anemometer (left) and wind vane (right).
Evaporation is measured daily using a standard sized evaporation basin. The basin is filled to the top of a reference point each day and the amount of water required to refill the basin is recorded as the previous 24 hours evaporation. A floating thermometer set records the daily minimum and daily maximum water temperatures. The basin is caged to prevent wildlife from consuming the water or adding to it!
Evaporation basin showing the floating thermometer set and filling reference point (in the centre of the white PVC tube).
Soil temperatures are measured manually at the Moree station. Soil temperatures are measured at depths of 0.05m, 0.10m, 0.25m, 0.50m and 1.00m below ground level. A manually read thermometer also records the daily minimum temperature at ground level, which is typically around 2 degrees C less than the daily minimum recorded inside the Stevenson's Screen.
Soil temperature thermometer set. As you go from left to right in this picture the thermometers measure temperatures at depths of 0.05m, 0.10m, 0.25m, 0.50m and 1.0m below ground level. The thermometer with the wooden base measures the daily minimum temperature at surface level.
The Bureau measures solar radiation intensity manually with the instrument shown below. The spherical glass ball focuses the suns energy onto a strip. A pattern is burnt into the strip and the solar intensity is determined by the size of the burn marks.
Measuring solar intensity. A pattern is burnt onto the material placed on the underside of the glass sphere.
The gadget pictured below measures visibility. The cameras shown provide an indication of the particulates in the atmosphere and use this to provide an estimate of atmospheric visibility.
Visibility measuring gadget.
The Moree weather radar is located on the roof of the station. It sends out a signal every 10 minutes and records the echo to assess the location and intensity of rainfall within a radius of around 250km.
Moree's weather radar.
Weather balloons are released twice a day at Moree. The 9.15am release measures wet and dry bulb temperatures, air pressure and wind speed and direction. The 3pm release measures wind speed and direction. The meters and data recording and transmitting devices are attached to the balloon on a 50m long string balloon. As the balloon is released the string unwinds to place the meters away from the balloon. The balloons are made of a highly stretchable latex rubber and are filled with hydrogen. When released at ground level, the balloons are approximately 1m in diameter. As the balloon gets higher in the atmosphere (ie. the air pressure drops) the balloon expands and can end up greater than 10m in diameter. The balloon collects data until it bursts and falls back to earth. At Moree the balloons are prepared for flight in an automated booth (pictured below). The integrity of the balloon and attached instruments is tested before the balloon is released.
Data collected from weather balloons measures conditions in the upper atmosphere. This data is fed into the computer forecast models.
Automated relaese of the weather balloon.
Data recording equipment unwinding away from the balloon as it ascends higher into the atmosphere.