This site provides useful practical information related to global and national weather observing practices and instruments, including independent equipment reviews.
You will find much of the background in my book The Weather Observer’s Handbook (published by Cambridge University Press), details of which can also be found on this site, together with useful links and downloads.
Author, The Weather Observer’s Handbook
A nation obsessed with the weather? Yes, certainly, but which nation?
Tip of The Day
Precipitation measurements are very sensitive to exposure – particularly to the wind – and the choice of site is very important to ensure comparable and consistent records are obtained. Choose an unsheltered (but not too exposed) spot for the raingauge/s – loss of catch through wind effects is the greatest single error in precipitation measurements, particularly in snow. A site on short grass or gravel is preferable. Wherever possible, obstructions (particularly upwind obstructions in the direction of the prevailing rain-bearing winds) should be at least twice their height away from the raingauge. Rooftop sites are particularly vulnerable to wind effects and should be avoided. The site should also be secure, but accessible for maintenance (grass cutting, etc.) as required.
The traditional method of measuring humidity is by using a pair of matched mercury-in-glass thermometers, known individually as dry-bulb and wet-bulb thermometers and in combination as a dry- and wet-bulb psychrometer. The wet-bulb is a thermometer whose bulb is kept permanently wet using a thin close-fitting cotton cap or sleeve. The wet-bulb is cooled by evaporation, and the difference in temperature between dry-bulb and wet-bulb thermometers is a measure of the humidity of the air. Using tables, an online calculator or formulae, the relative humidity (or any of the other humidity measures) can be quickly and easily determined from simultaneous readings of the two thermometers.
To obtain records of the timing and intensity of rainfall, one or more recording raingauges are often sited alongside the manual raingauge. The record from the manual gauge should be taken as the standard period total and sub-daily records (hourly totals, for instance) taken from the recording gauge adjusted to agree with the daily total taken from the manual gauge. The use of standalone recording gauges is not recommended when accurate or comparable rainfall totals are required.
Raingauges should be exposed with the rim at the national standard height above ground – in the UK and Ireland, this is 30 cm; in the United States, between 3 and 4 feet (90 to 120 cm). Most countries define a ‘standard rim height’ as between 50 cm and 150 cm above ground. Take care to set the gauge rim level, and to maintain it accurately so.
A good exposure for one sensor can be the exact opposite for another. For representative wind speed and direction readings, for example, an anemometer mounted on top of a tall mast in a very open expanse is ideal, but this would be a poor exposure for a raingauge owing to wind effects. No single exposure will provide a perfect fit for the requirements of all sensors.