Air temperature and pressure

Air temperature is measured with a thermometer placed 2 m above the ground in shade, out of direct sunlight. To find the mean daily temperature we add the day’s readings (in the textbook 8 readings, every 3 hours) and divide by the number of readings; the mean monthly temperature is found by adding the daily means and dividing by the number of days, and the mean annual one by adding the 12 monthly means and dividing by 12. Temperature is highest around 14–15 h and lowest just before sunrise. The difference between the highest and lowest temperature is the amplitude: the daily amplitude is 1–2 °C over the sea and up to 15–20 °C in deserts; the annual amplitude increases from the equator to the poles (about 26 °C in Tashkent). With height, temperature falls by about 6 °C every 1000 m. Air pressure is the pressure of air on the Earth’s surface and everything on it: it presses with a force of about 1 kg on each cm². It is measured with a barometer; at sea level at 0 °C normal pressure is 760 mm of mercury (mm Hg), and near the ground pressure falls by about 10 mm Hg for every 100 m of rise. If a mercury thermometer or barometer breaks, do not touch the mercury – it is poisonous – and tell an adult.