CHAPTER 4: ATMOSPHERIC TRANSPORT. Forces in the atmosphere: Gravity Pressure-gradient Coriolis Friction. to R of direction of motion (NH) or L (SH). Equilibrium of forces:. In vertical: barometric law In horizontal: geostrophic flow parallel to isobars. g p. P. v. P + D P.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Forces in the atmosphere:
to R of direction of motion (NH) or L (SH)
Equilibrium of forces:
In vertical: barometric law
In horizontal: geostrophic flow parallel to isobars
P + DP
In horizontal, near surface: flow tilted to region of low pressure
P + DP
Air converges near the surface in low pressure centers, due to the modification of geostrophic flow under the influence of friction. Air diverges from high pressure centers. At altitude, the flows are reversed: divergence and convergence are associated with lows and highs respectively
COLDTHE HADLEY CIRCULATION (1735): global sea breeze
But… Meridional transport of air between Equator and poles results in strong winds in the longitudinal direction because of conservation of angular momentum; this results eventually in unstable conditions.
Bright colors indicate the tallest clouds
where I’ll be
Consider an object (density ρ) immersed in a fluid (density ρ’):
P(z) > P(z+Δz) epressure-gradient force
on object directed upward
Buoyancy acceleration (upward) :
so ρ↑ as T↓
Barometric law assumes T = T’ e gb = 0(zero buoyancy)
T’ produces buoyant acceleration upward or downward
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 rateG :
G = 9.8 K km-1
What happens following release depends on the local lapse rate –dTATM/dz:
The stability of the atmosphere against vertical mixing is solely determined by its lapse rate.
state: - dT/dz = G
Solar heating of
surface/radiative cooling of air: unstable atmosphere
buoyant motions relax
unstable atmosphere back towards –dT/dz = G
Observation of -dT/dz = Gis sure indicator of an unstable atmosphere.
Wet adiabatic lapse rate GW = 2-7 K km-1
“Latent” heat release
as H2O condenses
GW = 2-7 K km-1
RH > 100%:
G = 9.8 K km-1
-20 -10 0 10 20 30
2 km altitude
- 3 K km-1
+2 K km-1
O3 + hn →O2 + O
O + O2 + M →O3+M
Latent heat release
- 6.5 K km-1