<P> Atmospheric pressure shows a diurnal or semidiurnal (twice - daily) cycle caused by global atmospheric tides . This effect is strongest in tropical zones, with an amplitude of a few millibars, and almost zero in polar areas . These variations have two superimposed cycles, a circadian (24 h) cycle and semi-circadian (12 h) cycle . </P> <P> The highest adjusted - to - sea level barometric pressure ever recorded on Earth (above 750 meters) was 1084.8 hPa (32.03 inHg) measured in Tosontsengel, Mongolia on 19 December 2001 . The highest adjusted - to - sea level barometric pressure ever recorded (below 750 meters) was at Agata in Evenk Autonomous Okrug, Russia (66 ° 53'N, 93 ° 28'E, elevation: 261 m, 856 ft) on 31 December 1968 of 1083.8 hPa (32.005 inHg). The discrimination is due to the problematic assumptions (assuming a standard lapse rate) associated with reduction of sea level from high elevations . </P> <P> The Dead Sea, the lowest place on Earth at 430 metres (1,410 ft) below sea level, has a correspondingly high typical atmospheric pressure of 1065 hPa . </P> <P> The lowest non-tornadic atmospheric pressure ever measured was 870 hPa (0.858 atm; 25.69 inHg), set on 12 October 1979, during Typhoon Tip in the western Pacific Ocean . The measurement was based on an instrumental observation made from a reconnaissance aircraft . </P>

Differences between normal pressure station pressure and sea level pressure