A mercury barometer is carried in a car on a day when there is no wind. The temperature is \(20^{\circ} \mathrm{C}\) and the corrected barometer height is \(761 \mathrm{~mm}\) of mercury. One window is open slightly as the car travels at \(105 \mathrm{~km} / \mathrm{hr}\). The barometer reading in the moving car is \(5 \mathrm{~mm}\) lower than when the car is stationary. Explain what is happening. Calculate the local speed of the air flowing past the window, relative to the automobile.