Consider air with a constant density of 1.225 kg/m^3. As hurricane Sandy passed
ID: 3161728 • Letter: C
Question
Consider air with a constant density of 1.225 kg/m^3. As hurricane Sandy passed over a tide gauge at the coast, a pressure of 945 mBar was measured, well underneath standard atmospheric pressure of 1015 mBar. Note that one mBar = 100 Pa. Find the height of water would need to be removed from a water column (density 1000 kg/m^3) to produce the same absolute reduction in pressure as the hurricane Assuming that Pascal's law applies between point A at the tide gauge and point B far away from the storm pressure effects, determine the deflection (if any in the coastal waters due to the change in atmospheric pressure. Point A and point Bare a vertical distance of 5 m below mean sea-level. Neglecting wind, circulation or tidal effects, state whether water moves up, down, or stays the same. .Assume salt water with a density of 1030 kg/m^3 Winds of 72 km/hr blow steadily during the storm. It is empirically found that the shear stress on the water surface by the wind is tau = rho_air C_d U^2, where rho_air is the air density, U is the wind velocity [m/s] and C_d = 0.001 is a dimensionless drag coefficient. Draw a free body diagram showing the resultant shear force and pressure forces on a channel of depth H, width b and length L. Neglect friction on the sea-bed, assume equilibrium conditions, and consider what effect the shear stress has on the water. It has been found empirically that the San Francisco tide gauge water level varies as -1.65 cm/mBar (Bromirski et al., 2003) Considering the answer to (b) and (c) what processes may produce this observation?Explanation / Answer
a) reduction in pressure = 1015 - 945 = 70 mbar
water pressure = d g h where d = density h = height of water column
1000 * 10* h = 70*100 Pa => h = 0.7 m
b) water moves up due to reduction in air pressure.