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Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa ), which is equivalent to 1,013.25 millibars , [ 1 ] 760 mm Hg , 29.9212 inches Hg , or 14.696 psi . [ 2 ]
For example, if a barometer located at sea level and under fair weather conditions is moved to an altitude of 1,000 feet (305 m), about 1 inch of mercury (~35 hPa) must be added on to the reading. The barometer readings at the two locations should be the same if there are negligible changes in time, horizontal distance, and temperature.
This storm system had, in part, a large effect on the weather in the entire eastern half of the country. A number of different weather records (at the time) were set during the four days of this storm, especially in daily high temperatures, wind gusts, low barometric pressure readings, and number of tornadoes. [1]
Cyclone Dirk, this was the lowest barometric pressure observed at any site in the British Isles, and the deepest depression to pass close to the British Isles, since 8 December 1886, 936.4 hPa at Stornoway was reported on minute observations at 12:29, with 936.8 hPa recorded at the 13:00 hourly observation. [307]
Christopher C. Burt, a weather historian writing for Weather Underground, believes that the 1913 Death Valley reading is "a myth", and is at least 2.2 or 2.8 °C (4 or 5 °F) too high. [13] Burt proposes that the highest reliably recorded temperature on Earth could still be at Death Valley, but is instead 54.0 °C (129.2 °F) recorded on 30 ...
Measurements of barometric pressure and the pressure tendency (the change of pressure over time) have been used in forecasting since the late 19th century. [66] The larger the change in pressure, especially if more than 3.5 hPa (2.6 mmHg), the larger the change in weather can be expected.
There, barometer readings fell to 956.0 mb (28.23 inHg). [2] In Detroit, air pressure fell to 28.34 inches of mercury (960 mbar). At around the same time, the absolute low pressure was measured at Sarnia, in Southwestern Ontario, Canada, where barometer readings decreased to 955.5 mb (28.22 inHg). [2]
The changing height of the mercury in the barometer was recorded on a continuously moving photosensitive surface. [5] By 1847, a sophisticated temperature-compensation mechanism was also employed. Ronalds’ barograph was utilised by the UK Meteorological Office for many years to assist in weather forecasting and the machines were supplied to ...