Vertical Structure of the Atmosphere www assignmentpoint com

Vertical Structure of the Atmosphere www. assignmentpoint. com

VERTICAL STRUCTURE OF THE ATMOSPHERE Measurement of atmospheric pressure with the mercury barometer: vacuum Atmospheric pressure P = PA = PB = r. Hg gh h A B Mean sea-level pressure: P = 1. 013 x 105 Pa = 1013 h. Pa = 1013 mb = 1 atm = 760 mm Hg (torr) www. assignmentpoint. com

“SEA LEVEL” PRESSURE MAP THIS MORNING (2/4/14, 15 Z) …and the forecast: www. assignmentpoint. com weather. unisys. com

SEA-LEVEL PRESSURE CAN’T VARY OVER MORE THAN A NARROW RANGE: 1013 ± 50 h. Pa Consider a pressure gradient at sea level operating on an elementary air parcel dxdydz: P(x) P(x+dx) Pressure-gradient force Vertical area dydz Acceleration For DP = 10 h. Pa over Dx = 100 km, g ~ 10 -2 m s-2 a 100 km/h wind in 3 h! Effect of wind is to transport air to area of lower pressure a dampen DP On mountains, however, the surface pressure is lower, and the pressure-gradient force along the Earth surface is balanced by gravity: P(z+Dz) P-gradient gravity P(z) a. This is why weather maps show “sea level” isobars even over land; the fictitious “sea-level” pressure assumes an air column to be present between the surface and sea level www. assignmentpoint. com

MASS ma OF THE ATMOSPHERE Radius of Earth: 6380 km Mean pressure at Earth's surface: 984 h. Pa Total number of moles of air in atmosphere: Mol. wt. of air: 29 g mole-1 = 0. 029 kg mole-1 www. assignmentpoint. com

QUESTIONS 1. What is the fractional increase in volume of water-soluble aerosol particles when relative humidity increases from 90% to 95%? (assume that the particles are mainly water, so neglect the contribution of the solute to particle volume). Assuming that visibility degradation is proportional to the cross-sectional area of the particles, what is the resulting percentage decrease in visibility? 2. Why does it take longer to boil an egg in Denver than in Boston? www. assignmentpoint. com

CLAUSIUS-CLAPEYRON EQUATION: PH 2 O, SAT = f(T) PH 2 O, SAT (h. Pa) A = 6. 11 h. Pa B = - 5310 K To = 273 K www. assignmentpoint. com T (K)

VERTICAL PROFILES OF PRESSURE AND TEMPERATURE Mean values for 30 o. N, March Stratopause Tropopause www. assignmentpoint. com

Barometric law (variation of pressure with altitude) • Consider elementary slab of atmosphere: P(z+dz) P(z) hydrostatic equation unit area Ideal gas law: Assume T = constant, integrate: Barometric law www. assignmentpoint. com

Application of barometric law: the sea-breeze effect www. assignmentpoint. com