* To minimize the influence of ground radiation: The ground both absorbs and radiates heat, which can significantly affect the temperature readings of instruments placed directly on it. By elevating the Stevenson screen, the instruments are exposed to a more representative temperature of the surrounding air, rather than being influenced by the ground's thermal fluctuations.
* To avoid direct sunlight: Direct sunlight can heat up the screen and the instruments inside, leading to inaccurate temperature readings. Placing the screen several feet from the ground ensures it is more likely to be shaded by trees or other structures, reducing the impact of direct solar radiation.
* To reduce the influence of wind: Wind can create localized changes in temperature, particularly near the ground. Placing the Stevenson screen at a higher level helps to minimize the influence of wind on the readings.
* To ensure proper ventilation: Proper ventilation is crucial for accurate readings, as it allows for air circulation and prevents the screen and instruments from overheating. Elevating the screen promotes better air flow.
In summary, the Stevenson screen's placement is carefully designed to minimize external influences on the instruments inside, ensuring more accurate measurements of air temperature, humidity, and other meteorological factors.