# Effects of pressure at sea level

According to this answer atmospheric pressure can vary between 870 and 1070 mb.

Can you tell what (if any) effects would there be on sea level if such difference of pressure (200 mb) on two near areas of the ocean, has anything similar has ever been recorded? If there is an elevation (or depression) can you say to what difference in gravity it corresponds? How do pressure effects compare with Earth's non-homogeneous gravity which affects local sea levels?

• – arkaia Aug 9 '16 at 13:35
• also, you can check: youtube.com/watch?v=F37GnGFcdL0 – arkaia Aug 9 '16 at 14:25
• In reality the problem is that it might be 2m in the distance between high and low pressures (could be many hundreds of km). By comparison, the sea level gradient across the Gulf Stream is 1m/100km! The other problem is that the ocean adjusts dynamically to the differences in air pressure and the resulting sea level gradient might be smaller. – arkaia Aug 9 '16 at 17:23
• To convert pressure to force (acceleration), you can use P=rhogh. I don't see what you are after in terms of gravity. The biggest differences in g at the surface of Earth are around 50mgal (50microm/s2). The differences cause by the extra meter will be way smaller and can be considered negligible. – arkaia Aug 10 '16 at 15:19

The effect of atmospheric pressure on sea level is described as "inverted barometer" effect. The basic equation governing the effect (Wunsch & Stammer, 1997) is: $\delta_{IB} = -{\Delta P_{atm} \over \rho_{water}*g}$, where $\delta_{IB}$ is the change in sea level, $\Delta P_{atm}$ is the change in atmospheric pressure, and $\rho_{water}$ is the density of water.

A good example of the effect was observed by Close (1918) From Wunsch & Stammer, 1997.

In reality, while atmospheric pressure can vary between 870 and 1070 mb, the problem is that it might result in a change of 2m over a distance between high and low pressures that could be many hundreds of km. By comparison, the sea level gradient across the Gulf Stream is on the order of 1m/100km. The other problem is that the ocean adjusts dynamically to the differences in air pressure and the resulting sea level gradient might be smaller.

To convert pressure to force (acceleration), you can use $P=\rho g h$. The biggest differences in $g$ at the surface of Earth are around 50 mgal (50 $\mu m/s^2$) and caused by differences in latitude, altitude, and local topography and geology. The differences in gravity cause by the extra meter of water will be way smaller and can be considered negligible.

Wunsch, C., and D. Stammer (1997), Atmospheric loading and the oceanic “inverted barometer” effect, Rev. Geophys., 35(1), 79–107, doi:10.1029/96RG03037.

Close, C. (1918), The Fluctuations of Mean Sea-Level with Special Reference to Those Caused by Variations in Barometric Pressure. The Geographical Journal 52, no. 1, 51-58.

• The gravity pull from the Moon and the Sun that cause the tides have a 0.2 mGal effect on the apparent strength of Earth's gravity. The equation comes from basic hydrostatic: en.wikipedia.org/wiki/Hydrostatics. The effect of 1mGal in the ocean will be something like a 5-times stronger tide. – arkaia Aug 13 '16 at 10:43
• so the effect of .2 mgal will be a 1-times stronger tide, stronger means higher? so if the other parameters give 50 mbar, that is 50 cm elevation, 0,2 mGal due to the moon will make it 100 cm? Did I get it right? – user6402 Aug 13 '16 at 11:04
• The 0.2 mgal is what gives you the current tides. The 50mgal is the maximum difference of the effective gravity at the surface and it is in equilibrium with the latitude (varying height of the ellipsoid), altitude/depth (e.g., size of the mountains), and geology (varying densities). – arkaia Aug 13 '16 at 11:46
• Very low pressure is typically associated with storm systems, particularly hurricanes. The inverse barometer effect can then lead to a rise in water level by something like a metre (compared to average conditions) at a particular location, this is called a storm surge and one of the reasons for coastal flooding (the other reason is water being pushed towards the coast through wind drag, especially where the coast acts like a funnel). – Stephan Matthiesen Sep 14 '16 at 20:30