Storm surge is caused by two main factors-wind, which drags the water along and

Question

Storm surge is caused by two main factors-wind, which drags the water along and piles it up along the coastline, and the inverse barometer (IB) effect. The IB effect occurs because at some datum far below the surface of the ocean, the sum of the hydrostatic pressure from air and from water must be equal, i.e, Pair + Pwater constant. If not, a horizontal pressure gradient (force imbalance) occurs, causing water to move until a balance is restored. 5. Look up the lowest minimum atmospheric pressure (at sea-level) for hurricane Maria, and compare to standard atmospheric conditions. What is the pressure difference, in Pascals? Now, consider a datum that is below the water surface, for example,-100m below the mean sea level datum, what is the total pressure Ptotal (water pressure atmospheric pressure) under standard atmospheric conditions at this datum? Assume a water depth of 100m and a density of 1020 kg/m3. a. b. c. Assuming that Potal at -100m (sea level datum) is constant, how high must the water level rise above the sea level datum in order that Poir + Pwater constant underneath the eyewall of hurricane Maria? lgnore dynamic effects, such as the effect of wind or the time fo Why is this called the "inverse barometer" effect? r the system to reach an equilibrium. d.

Explanation / Answer

A. Lowest minimum atmospheric pressure for hurricane Maria was 909 millibar or 90900 pascals. Standard Atmospheric pressure is 101325 pascals. Therefore, difference is 10425 pascals.

B. Pwater = Depth * Water Density * Acceleration due to gravity

So Pwater = 100 m * 1020 kg/m3 * 9.8 m/s2 = 999600 N/m2

So Ptotal = Pwater + Pair = 999600+101325 = 1100925 Pascals  

C. Because total pressure at 100 m depth is greater than that on the sea surface, so water level will rise.

Now increase in water level = Difference in pressure / water density * Acceleration due to gravity

so increase in water level = 999600/1020*9.8 = 999600/9996 = 100 m

D.  Inverse barometer effect: The constantly changing weather increases or decreases atmospheric pressure on the sea water. So when low-pressure system prevails, the sea level rises by a relative amount, while high-pressure systems create a drop in sea level. This phenomenon is called the inverse barometer effect, as the higher the pressure, the lower the sea level, and vice versa.

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