4. Atmospheric transport Forces in the atmosphere: Gravity
4. Atmospheric transport Forces in the atmosphere: Gravity g Pressure-gradient a p 1/ dp / dx for x-direction (also y, z directions) Coriolis ac 2 v sin to R of direction of motion (NH) or L (SH) Angular velocity = 2/24hh Friction a f kv Wind speed v Equilibrium of forces: Latitude Friction coefficient k In vertical: barometric law
ap In horizontal: geostrophic flow parallel to isobars v P P + P ac In horizontal, near surface: flow tilted to region of low pressure ap af v
ac P P + P The Coriolis force GEOSTROPHIC FLOW: equilibrium between pressure-gradient and Coriolis forces Isobar ap ac
steady parallel to isobars speed ~ pressure gradient ap ap ac N hemisphere example Circulation around Highs and Lows How Highs and Lows affect surface weather
air rises precipitation Surface Low air sinks dry weather Surface High Great red spot of Jupiter: lack of friction allows persistence of Highs and Lows Questions 1. The Coriolis force responsible for anticyclonic and cyclonic motions (rotation
around Highs and Lows) applies only when viewing motions from the perspective of the rotating Earth. Then how come we can see rotating hurricanes (strong cyclones) from weather satellites? 1. What happens to tropical cyclones when they cross the Equator? Do they start turning the other way? Satellite in geostationary orbit Cyclone tracks, 1985-2005 The Hadley circulation (1735): global sea breeze COLD Trade winds
HOT COLD Explains: Intertropical Convergence Zone (ITCZ) Wet tropics, dry poles Easterly trade winds in the tropics But Direct meridional transport of air between Equator and poles is not possible because of Coriolis force Hadley circulation only extends to about 30o latitude
Easterly trade winds in the tropics at low altitudes Subtropical anticyclones at about 30o latitude Westerlies at mid-latitudes Climatological surface winds and pressures (January) Climatological surface winds and pressures (July) Time scales for horizontal transport (troposphere) 1-2 months 2 weeks 1-2 months
1 year VERTICAL TRANSPORT: BUOYANCY Consider an object (density ) immersed in a fluid (density ): ap Fluid () Object ( g z+z z Buoyancy acceleration (upward) :
For air, Ma p RT p(z) > p(z+z) pressure-gradient force on object directed upward ab = a p - g g so as T
Barometric law assumes T = T ab = 0 (zero buoyancy) T T produces buoyant acceleration upward or downward ATMOSPHERIC LAPSE RATE AND STABILITY Lapse rate = -dT/dz Consider an air parcel at z lifted to z+dz and released. It cools upon lifting (expansion). Assuming lifting to be adiabatic, the cooling follows the adiabatic lapse rate : z stable
unstable = 9.8 K km-1 z dT g 9.8 K km -1 dz C p What happens following release depends on the local lapse rate dTATM/dz: ATM inversion
-dTATM/dz > upward buoyancy amplifies (observed) initial perturbation: atmosphere is unstable unstable -dTATM/dz = zero buoyancy does not alter perturbation: atmosphere is neutral T -dTATM/dz < downward buoyancy relaxes initial perturbation: atmosphere is stable dTATM/dz > 0 (inversion): very stable The stability of the atmosphere against vertical mixing is solely determined by its lapse rate. WHAT DETERMINES THE LAPSE RATE OF THE ATMOSPHERE?
An atmosphere left to evolve adiabatically from an initial state would eventually tend to neutral conditions (-dT/dz = at equilibrium Consider now solar heating of the surface. This disrupts the equilibrium and produces an unstable atmosphere: z z z ATM
ATM T Initial equilibrium state: - dT/dz = initial T Solar heating of surface: unstable atmosphere final
T buoyant motions relax unstable atmosphere back towards dT/dz = Fast vertical mixing in an unstable atmosphere maintains the lapse rate to Observation of -dT/dz = is sure indicator of an unstable atmosphere. Typical summer afternoon vertical profile over Boston 4 Altitude, km
10 Temperature, oC 20 30 IN CLOUDY AIR PARCEL, HEAT RELEASE FROM H2O CONDENSATION MODIFIES Wet adiabatic lapse rate W = 2-7 K km-1 z T RH Latent heat release
as H2O condenses RH > 100%: Cloud forms 100% W W2-7 K km-1 9.8 K km -1
SUBSIDENCE INVERSION typically 2 km altitude DIURNAL CYCLE OF SURFACE HEATING/COOLING: ventilation of urban pollution z Planetary Boundary Layer (PBL) depth Subsidence inversion MIDDAY
1 km Mixing depth 0 NIGHT MORNING T NIGHT
MORNING AFTERNOON VERTICAL PROFILE OF TEMPERATURE Mean values for 30oN, March Altitude, km Radiative cooling (ch.7) - 3 K km-1 +2 K km-1 Radiative heating: O3 + hO2 + O
O + O2 + M O3+M heat Radiative cooling (ch.7) - 6.5 K km-1 Latent heat release Surface heating TYPICAL TIME SCALES FOR VERTICAL MIXING tropopause (10 km) 10 years
1 month planetary 2 km boundary layer 0 km 1 day Questions A sea-breeze circulation often results in an inversion. Explain why. A classic air pollution problem is fumigation where a location downwind of a tall smokestack will experience a sudden burst of high pollution from that smokestack in mid-morning. Can you explain this observation on the basis of atmospheric stability?
Calibri Arial Symbol Times New Roman Lucida Grande Office Theme Microsoft Equation 3.0 Microsoft Excel Chart ISIS/Draw Sketch Titration of 25 mL of 0.100 M HCl with 0.100 M NaOH Adding NaOH to HCHO2 Slide 3 Slide 4 Slide 5...
Once a keypoint candidate has been found by comparing a pixel to its neighbors, the next step is to perform a detailed fit to the nearby data for location, scale, and ratio of principal curvatures. This information allows points to...
The preterite tense is used to talk about actions that are completed in the past. ... jugar, organizar. I practiced = ... Verbs with irregular stems in the preterite. Some verbs change . their stem in the . preterite. This...
What is a Science Fair Project? A journey of scientific inquiry. Students answer a scientific question by conducting an experiment. The process ends with a showcase event that shows students that their work matters to the school community.
Export promotion boards PROBLEM Since Greece has many smaller food businesses, market intelligence is not generally available in particular when it comes to market needs and preferences, e.g. on social responsibility, carbon footprint, organic food.
Folding the Graphic Organizer. 3. Cut along the dotted lines between each box. Stop cutting where the dotted lines end. ... Natural selection favors one extreme of the population for that trait. often happens when environment changes in a consistent...
Schlueter et al used CT to study head conformation and the nasolacrimal drainage system (NDS) in mesencephalic and brachycephalic cats (JFMS 2009). From their study, which of the following statements is NOT true? In severely brachycephalic cats: a) The root...
Utilize twins to understand importance of genetics and tease out environment effects. ... What economic factors might account for these variations? Teratogens (1 of 3) Teratogens are environmental and bodily conditions that could be harmful.
Ready to download the document? Go ahead and hit continue!