Around the world, automatic weather stations measure parameters including temperature and humidity, with networks gathering data from multiple locations to generate shorttimescale weather forecasts. This data could also be used to make climate change predictions, but characterising long-term trends, such as global warming, requires better data quality.
Weather measurements can be affected by various unwanted influences, with poorly designed shielding, for example, causing potential errors when measuring air temperature. Consider how the temperature inside a car with its windows closed rises rapidly in sunshine, a similar affect can also be experienced by sensors inside weather station shielding introducing air temperature measurement errors. Poor weather station shielding designs can also expose temperature sensors to back-reflected solar radiation from their surroundings. In mountainous or polar regions, snow cover can act as a reflector, whilst for urban weather stations, buildings or roads nearby can raise temperatures artificially.
To make weather station measurements sufficiently accurate for use in climate predictions, unwanted effects of weather station design, siting and other local conditions need to be minimised. More accurate temperature measurement, for example, could be achieved with better shielding, as improved designs would minimise heat trapping and shield temperature sensors from high levels of back-reflected solar radiation such as that from snow cover.
The EMRP project Metrology for Essential Climate Variables assessed the effects on weather station measurement accuracyincluding the influence of nearby features such as buildings or trees, housing design, and other local conditions. The influence of these was shown to have a smaller effect on measurement parameters, including temperature, than previously estimated in a World Meteorology Organisation guide. This information has now been incorporated in to a recent revision of this important guide for the weather monitoring community, removing reliance on overestimated corrections.
Different solar shields for weather station instrumentation were tested in the project, with a new novel design that shields temperature sensors from direct and back-reflected solar radiation whilst minimising heat trapping effects demonstrating significantly reduced measurement errors. The results demonstrated that up to 3 °C in temperature variation was attributable to the “albedo effect” where snow reflects sunlight onto a temperature sensor. This demonstrates the importance of good solar shield design.
Barani Design, an SME producing weather station sensors, had a prototype solar shield independently validated in the project. In addition to the shielding of instrumentation from direct and reflected radiation, the prototype’s novel helix design was shown to allow free airflow over housed sensors so minimising heating effects. These design features improve ambient air temperature measurement accuracy by reducing errors caused by solar radiation heating and the trapping of warm air. The validated helical shielding will be launched commercially in 2019. The product’s affordability will make it attractive in regions currently lacking a developed meteorological infrastructure such as Africa and south-east Asia.
- EMN Climate and Ocean Observation,