Stevenson screen

Why instrument shielding matters in weather observation

Meteorological measurements are only as reliable as the conditions under which they are taken. The Stevenson screen plays a foundational role in ensuring that key weather readings—such as air temperature, humidity, and atmospheric pressure—are not distorted by direct exposure to the elements. Without a standardized housing like this, sensors can easily overheat in sunlight, cool too rapidly in shade, or collect moisture that skews readings.

Designed in the 19th century by British civil engineer Thomas Stevenson, the screen has become a global standard in meteorological observation. It allows instruments to be exposed to freely circulating air while shielding them from rain, solar radiation, wind, and other interfering factors. Its primary function is to create a controlled microenvironment that reflects true ambient conditions, making data more accurate and comparable across time and space.

From national weather services to agricultural field stations and climate research outposts, Stevenson screens remain a common sight wherever high-quality meteorological data is collected.

Key features and design principles

The classic Stevenson screen is a white, wooden box mounted at a standard height (usually 1.25 to 2 meters above ground) and designed with the following features:

• Louvered sides: These horizontal slats allow air to flow freely through the screen, ensuring that instruments inside are exposed to ambient air without being directly affected by wind gusts or rain.
• Double roof: The roof is constructed in two layers to insulate instruments from radiant heat from the sun, preventing artificial warming.
• White paint: The exterior is painted white to reflect solar radiation and minimize heat absorption.
• Placement guidelines: Stevenson screens are typically placed over natural grass surfaces and away from artificial heat sources, buildings, or large reflective surfaces to avoid localized heat effects.

Though modern materials and automation have led to the development of newer shelters (such as radiation shields made from UV-stable plastics), traditional Stevenson screens are still widely used and accepted in official weather stations, especially when consistency with historical climate records is important.

What instruments are kept inside a Stevenson screen

The Stevenson screen houses instruments that require shelter from direct exposure while remaining responsive to changes in ambient conditions. These typically include:

• Thermometers: Dry bulb and wet bulb thermometers measure air temperature and humidity. Maximum and minimum thermometers may also be included to track daily extremes.
• Hygrometers: Used to measure relative humidity, often in conjunction with dry/wet bulb thermometers.
• Barometers (occasionally): Though often placed indoors today, older stations sometimes kept barometers in Stevenson screens when ventilation was appropriate.
• Data loggers: In modern stations, digital temperature and humidity sensors with built-in memory are used instead of manual instruments.

Why Stevenson screens are still relevant today

Despite advances in automated weather stations and sensor technology, the Stevenson screen remains a benchmark for air temperature and humidity measurement. Because so many historical weather records were collected using this shelter design, continuing to use Stevenson screens—or their carefully calibrated modern equivalents—helps maintain data continuity in long-term climate monitoring.

They also remain especially valuable in education, research, and agricultural applications where understanding microclimates and surface-level atmospheric conditions is essential. By minimizing the influence of radiation, precipitation, and surface heat, Stevenson screens ensure that measurements reflect the true state of the atmosphere—not the quirks of the measuring setup.