Physics of Atmosphere and Ocean Flashcards
fundamental forces to consider in atmospheric/ocean motions
gravitational force
pressure gradient
friction
Additional forces to consider in atmospheric/ocean motions
centrifugal
Coriolis
formula for gravitational force
F = G (m.m)/r^2
per unit mass (a) = -GM/r^2 = -g
quantitative formula for pressure gradient force
F (per kg) = -1/rho (∂P/∂x)
(in 3d ∂x, ∂y, or ∂z)
What can friction be caused by
- viscosity
- frictional drag at base of atm
- windstress on ocean
formula for centrifugal force (per unit mass)
c.f. = Ω^2 . R
Ω = angular velocity = ∆theta/∆t
R = radius = 6400km
what direction does Coriolis force act in northern and southern hemisphere
N: 90º to right
S: 90º to left
formula for Coriolis parameter
f = 2Ω.sin(theta)
equation for Coriolis acceleration
a = 2Ω.v
Where is maximum and minimum spin on the earth
max = poles
min = equator
magnitude of Coriolis force formula
mag = f.v
value for Coriolis parameter, f, at mid latitudes
10^ -4 (/s)
force balance equation in x, y, z direction
∂u/∂t = -1/rho (∂P/∂x) + fv
∂v/∂t = -1/rho (∂P/∂y) - fu
∂w/∂t = -1/rho (∂P/∂z) - g
What forces is geostrophic balance between
pressure gradient + Coriolis = 0
what is the significance of geostrophic balance
on a rotating planet, winds do not flow high->low pressure, but along constant pressure contours
equation for velocity of geostrophic winds
rearrange force balance equations for velocity in x and y directions
(p.g + Coriolis = 0)
directions of winds around pressure systems
in N:
anticlockwise around low
clockwise around high
= cyclonic
what is the effect on geostrophic wind balance of being close to the surface
additional frictional force
(moving slower = Coriolis weaker, cannot balance)
=> spiral into low pressure (ascent)
=> spiral out of high pressure (descent)
what are the forces involved in hydrostatic balance
pressure gradient force + gravity = 0
hydrostatic balance formula
∂P/∂z = -rho . g
rearrange force balance equation in z direction
how to use hydrostatic balance formula to find pressure at given point in atm
integrate between that point and infinity
= weight per unit area at that point = pressure
equation of state for ocean (what does density depend on)
rho = rho(T, S, P)
what does the TS diagram show
temperature more important for determining density at usual conditions
salinity becomes more important at polar temperatures
definition and formula for potential temperature, θ
θ = temperature a fluid parcel would be if brought adiabatically to the surface
θ = T . (Ps / P) ^ 2/7
What is thermal wind balance in words
combination of geostrophic and hydrostatic balance to show how geostrophic flow varies with height
How to find thermal wind equations
partially differentiate geostrophic velocity equations with respect to height, z, and sub in hydrostatic balance equation
example of how thermal wind balance works in oceans and atm
Gulf Stream
high temp, low density off coast
= +ve wind equation
= increase velocity of currents in y with height
Jet Stream in atm
meaning of westerly winds and easterly winds
westerly = west -> east
meaning of eastward ocean currents
eastward = west -> east
why does wind speed up as moves north from equator (westerlies)
air must conserve angular momentum = mass . velocity . radius
moving polewards = decrease r, therefore increase v
Where are the westerlies seen
almost everywhere except equator, strongest at mid latitudes - subtropical jet
how is heat transported to the poles
temperature gradient gets stronger across jet stream, strengthening it, flow becomes unstable, anomalies amplify into EDDIES
= baroclinic instability
How are the easterly trade winds formed
Air moving equator-ward at the surface in the hadley cell deflected by Coriolis force
what do eddies do in the atmosphere
eddies transport hot air northwards, and cold southwards (net flux=heat N) , by a lateral motion rather than overturning
trailing tails into tropics = move westerly momentum northwards
describe regional climate of near equatorial regions
- trade wind convergence
- rain
(tropical rainforests)
describe regional climate of subtropics
- descending air from Hadley cell
- hot and dry
(deserts)
describe the regional climate of the mid latitudes
- westerlies
- eddies dominate weather
- cyclone = wet+stormy
- anti = calm+fine
what are factors of the earth to also consider when describing general atmospheric circulation
- land/sea contrast (oceans warmer, mountains deflect wind)
- seasonal variations