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Airwatch – Running a Weather Station 1. The weather station While there are several types of weather station available, the Weather Monitor II + Weatherlink software from Davis Instruments, Hayward, CA, USA is a good choice. It is a comprehensive weather station, data management, analysis and display system. We recommend obtaining the full system, supplemented by a rainfall gauge. Contact the Australian agents:
We do not recommend you try to build your own weather station. 2. Using the weather station We have found that the manual that comes with the Davis system is easy tof ollow and use. There is little that we can add except to recommend a set up using 24-hour time, Celsius (0.1ºC) for temperature, metres per second for wind speed, high resolution (1º) for wind direction, millimetres for rainfall and millibar or hectoPascals for pressure. The weather station runs off a supplied mains power pack, or a 12 volt battery, such as the one used to power the particle sampler, can be used. A PC is only needed to set the sampling frequency of data and to download the data for analysis, plotting and display. Set up the anemometer on a post at least 1.5 m high, preferably at least 2 m high, in an area free of trees and buildings for a distance of at least 50 m. The rain gauge should be similarly located in an area free of trees and other obstructions.
3. Activities involving the weather station Temperature The weather station can record the current temperature, the minimum and the maximum temperatures over the past 24 hours. The weather station software will allow you to plot the data easily, so you can see how the temperature changes during the measurement period. Because the weather station can store temperature readings frequently, you can see the change that occurs if and when the sea breeze reaches you in summer, generally bringing cool, clean air to the region. Or, look for the change due to the arrival of a cold front after hot northerlies. Some suggested statistics include:
Pressure The changes in atmospheric pressure over a week or even over a day as a cold front passes can be used to predict changes in the weather. It is common in Australian cities to find higher air pollution when a high pressure system is near and to the east of the city. Then the winds are basically northerly (before arrival of a sea breeze in the afternoon), the sky is generally fairly clear, and the temperature is higher. While pressure can be measured using a mercury barometer, it is the trend in the pressure that is important and the best way to plot trends over many hours is to use the Weatherlink weather station software. There are no special set-up requirements for the pressure device, since pressure is not much affected by local events nor local set-up. Rain fall Air pollution can be strongly dependent on rainfall. Particles in the atmosphere are readily washed out in rain, so taking measurements of these in rainy conditions is not useful. However, pollutant gases are generally not much affected by rain and this observation can be tested using AIRWATCH by measuring nitrogen dioxide. It is useful to have measurements of rainfall in an air pollution study because the data can be used to help interpret other measurements. A heap of dirt will be blown around in strong winds if the heap is dry, but if it has rained in the past 48 hours the heap may well stay put. You can discover a relation between these fugitive emissions and wind speed and rainfall if you have good data obtained with the weather station. Visual range or visibility will be greater on days of rain than on other days. However, visibility may actually be lower soon after rain if the sky clears, due to formation of low cloud or fogs. The signal pulses from the tipping bucket instrument in the weather station kit can be used to control other instruments, such as a rainwater collector for acid rain studies. There is at least one commercial acid rain monitor that has taken this approach (see http://www.ecotech.com.au). Wind speed and direction Wind information is the key to many investigations. We describe two in some detail here. Many other studies are possible.
Contact: peter.manins@csiro.au Return to The Airwatch Index |
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Modified: 29 September 2003 |
The
temperature sensor should be place in a shaded location with free airflow.
It is not adequate to just put it out in the sun: it will give temperature
readings that are much too high because the black sensor will absorb solar
radiation directly. The sensor should be set up in the shade at a height
of approximately 1.2 m above ground level. For frequent use, you will
need to make a Stevenson Screen. This is a wooden box with a double roof,
slatted door and sides, like the one in the picture. It is painted white
and mounted, with the door facing south, so that the floor is 1.2 m above
ground level at a site that is free from close-by buildings, trees and
such.