Recording the Weather
in Armidale NSW
Early settlers on the Northern Tablelands in the early 1800s immediately noticed the similarity between the climate here and in some parts of England, warm summers and cold winters with severe frosts and occasional snowfalls, hence the region gaining the name "New England." Some of these pioneers made their own temperature and rainfall measurements with claims that temperatures as high as 39 degrees C (102 deg F) had been recorded, and as low as -12 degrees C (10 deg F).
POST OFFICE - 1857 TO 1965
In the second half of the 19th century the government started setting up a network of weather stations in the main cities and towns across the country. Post offices were mostly chosen as the sites for these weather stations with the postmaster being in charge of recordings. In Armidale the post office, which was located a short distance to the west of the present building, became the official weather station from December 1857. Daily readings taken included rainfall, temperatures, wind, pressure and cloud cover. In 1880 a new post office building was built at the corner of Beardy and Faulkner Streets where weather recordings continued until 1965.
RADIO STATION 2AD - 1965 TO 1997
Because the area at the back of the post office was gradually being "built out" the Bureau of Meteorology moved the weather station a distance of about 100 metres to the back yard of Radio Station 2AD in Rusden Street between Marsh and Faulkner Streets in July 1965. This was a more open area, and because the radio station was staffed almost around the clock seven days a week, it was convenient for staff to keep up the seven observations per day which the Bureau required.
Recordings continued there until June 1997 when a further move was necessary.
UNE EAST ARMIDALE SITE - FROM 1997
Over the years from 1965 the area around the back yard of the radio station slowly suffered the same problem as the rear of the post office. New buildings were built and bitumen car parks installed. In June 1997 when the 2AD backyard was about to be replaced by a carport and cement carpark, the weather station was relocated to the site of the University of New England (UNE) weather station in East Armidale which had been in operation at this location since October 1980. This was a move of about one kilometre to an area of slightly lower temperatures and greater incidence of frost, so the Bureau of Meteorology decided not to amalgamate records from the former and new sites, but to commence a new set of records at the UNE location. During the 16 years that both stations were operating in parallel maximum temperatures averaged 1.1 degrees lower and minimums 1.7 degrees lower at the UNE site.
AIRPORT WEATHER STATION - FROM 2001
In 2001 an automatic weather station (AWS) was set up at Armidale Airport by the Bureau of Meteorology to replace a similar AWS which had been operated in the same location by the Dumaresq Council since 1993. This new weather station is completely automatic providing the Bureau with continuous readouts of temperatures, humidity, rainfall, pressure, wind, visibility and cloud height.
The airport station is 93 metres higher and five kilometres from the East Armidale station often resulting in moderate differences in temperatures and rainfall. Because the airport is on a plateau and the East Armidale station is in the Armidale valley, the airport overnight temperatures are often around two to five degrees higher than the city. During the day the airport is windier than the more sheltered valley causing day temperatures to frequently be about one degree lower than the city.
The Bureau of Meteorology weather station is located in East Armidale within the valley of Dumaresq Creek at an elevation of 987 metres above sea level.
Temperatures are measured with mercury and alcohol thermometers which are read by observers at designated observation times daily. These thermometers are very accurate measuring the temperature in tenths of degrees.
They are housed within a Stevenson Screen which is a white painted timber box with louvred sides with the base about 1.1 metres above the ground. The louvres allow outside air to move slowly past the instruments while protecting them from direct sunlight, wind and rain, and temperatures recorded this way are referred to as screen or shade temperatures.
Mercury thermometers supply current dry and wet bulb temperatures.
A mercury thermometer records the maximum temperature for the 24 hours to each day when the thermometer is reset.
An alcohol thermometer records the minimum temperature for the 24 hours to each day when the thermometer is reset.
A thermograph records the temperature continuously onto a seven day graph which is used to determine the times at which maximum and minimum temperatures occur.
An alcohol minimum thermometer is placed on the surface of the grass each evening to record the overnight terrestrial or grass minimum temperature. The terrestrial minimum is usually between 2 and 5 degrees lower than the screen minimum.
Rainfall is recorded with a rain gauge set in the ground with the top 30 centimetres above the ground. It consists of a metal drum with a funnel 203 millimetres in diameter and a plastic measuring cylinder within. Rainfall is totaled for the 24 hours ending daily and registered against that day.
This is measured using an American Class A pan 1206 millimetres in diameter and 250 millimetres deep. At daily a measured quantity of water is added to the pan to replace the amount which has evaporated since the previous day. If it has rained then the rainfall amount is taken into account in the evaporation calculation. Pan coefficient (Kp): 0.7.
A wind vane mounted to a ten metre tower is used to determine the wind direction to 16 points of the compass. A cup anemometer, also mounted to the tower, is used to calculate the wind speed and the wind run for the 24 hour period ending at daily. Wind run is a measure of the amount of air or wind moving past the anemometer for a given period of time. Thus if the wind is blowing at a speed of exactly 5 kilometres per hour for exactly one hour, then the wind run is 5.0 kilometres.
Details of clouds including amount of cloud covering the sky in eighths, height of clouds, and the type of clouds are observed and recorded.
Horizontal visibility is estimated. This is reduced by precipitation, fog, and on some winter mornings and evenings by Armidale's woodsmoke haze trapped in the valley.
Other aspects of the weather referred to as phenomena are also recorded. These include: frosts, fogs, hail, snow, thunderstorms and strong winds.
Manually operated weather stations, such as the East
Armidale weather station, continue to remain a part of the Bureau of
Meteorology’s network as human observers can observe and report conditions that
automatic weather stations are unable to do, such as details of clouds,
thunderstorms, hail (size and quantity of hailstones) and snowfalls (depth of
snow on ground).
The Bureau, however, is gradually phasing out many of the manual weather stations, particularly those which are in close proximity to automatic stations.
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