The climatological mean circulation Deviations from the climatological mean Synthesis: momentum and the jets
Lecture 7: Atmospheric General Circulation
Jonathon S. Wright
11 April 2017 The climatological mean circulation Deviations from the climatological mean Synthesis: momentum and the jets
The climatological mean circulation Zonal mean energy transport Zonal mean energy budget of the atmosphere The climatological mean and seasonal cycle
Deviations from the climatological mean Transient and quasi-stationary eddies Eddy fluxes of heat, momentum, and moisture Eddies in the atmospheric circulation
Synthesis: momentum and the jets Vorticity and Rossby waves Momentum fluxes Isentropic overturning circulation The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
400 Outgoing longwave radiation 350 net energy loss in Incoming solar radiation ] 2
− 300 the extratropics m 250 W [
x 200 u l f
y 150 net energy gain g r e
n 100
E in the tropics 50 0 90°S 60°S 30°S 0° 30°N 60°N 90°N 6
4
2
0
2 Energy flux [PW] 4 JRA-55 6 90°S 60°S 30°S 0° 30°N 60°N 90°N
data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
400 Outgoing longwave radiation 350 Incoming solar radiation ] 2
− 300 m 250 W [
x 200 u l f
y 150 g r e
n 100 E 50 0 90°S 60°S 30°S 0° 30°N 60°N 90°N 6 Northward atmospheric energy transport 4 Northward ocean energy transport Total northward energy transport 2
0
2 Energy flux [PW] 4 JRA-55 6 90°S 60°S 30°S 0° 30°N 60°N 90°N
data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
400 Outgoing longwave radiation 350 Incoming solar radiation ] 2
− 300 m 250 W [
x 200 u l f
y 150 g r e
n 100 E 50 0 90°S 60°S 30°S 0° 30°N 60°N 90°N 6 Northward atmospheric energy transport 4 Northward ocean energy transport Total northward energy transport 2
0
2 Energy flux [PW] 4 CFSR 6 90°S 60°S 30°S 0° 30°N 60°N 90°N
data from CFSR The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
Energy budget of an atmospheric column
∂E a = R + LP + SH + TR ∂t net
300 LP SH Radiation Transport
200 latent heating ] 2 −
m transport 100 W [
x u l
f sensible heating
y g
r 0 e n E radiative cooling 100
JRA-55 200 90°S 60°S 30°S 0° 30°N 60°N 90°N data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
Energy budget of an atmospheric column
∂E a = R + LP + SH + TR ∂t net
300 LP SH Radiation Transport
200 latent heating ] 2 −
m transport 100 W [
x u l
f sensible heating
y g
r 0 e n E radiative cooling 100
CFSR 200 90°S 60°S 30°S 0° 30°N 60°N 90°N data from CFSR The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
The climatological mean
1 Z τ time mean: x = xdt τ 0
climatological zonal mean: [x]
1 Z 2π zonal mean: [x] = xdλ 2π 0 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
Zonal mean zonal wind subtropical jets 100
200
300
400
500
600 Pressure [hPa]
700
800 tropical midlatitude 900 easterlies westerlies
1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
30 24 18 12 6 0 6 12 18 24 30 1 extratropical jet Zonal wind [m s− ] data from JRA-55 (storm track) The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
Zonal mean zonal wind: energy and momentum transfer perspectives
energy budget angular momentum budget
Q 4 (1 − α) = σT M = (uearth + u) a cos ϕ 4 e pole Energy loss
Implied energy W Implied momentum transport transport Loss of angular momentum
Energy gain Gain of angular E momentum The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
Zonal mean zonal wind 100−15 m s−1 < [u] < 35 m s−1
200
300
400
500
600 Pressure [hPa]
700
800
900
1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
30 24 18 12 6 0 6 12 18 24 30 1 Zonal wind [m s− ] data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
Zonal mean uearth 100
200
300
400
500
600 u = Ωa cos ϑ u, particularly in the tropics Pressure [hPa] earth
700
800
900
1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
0 50 100 150 200 250 300 350 400 450 500 1 Angular velocity [m s− ] data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
Zonal mean angular velocity (uearth + u) 100
200
300
400
500
600 Pressure [hPa]
700
800
900
1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
0 50 100 150 200 250 300 350 400 450 500 1 Angular velocity [m s− ] data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
The mean meridional circulation
mass streamfunction 2πa cos ϕ Z p ΨM = [v] dp g 0
The mass flow between any two streamlines is equal to the difference between the streamlines
g ∂Ψ −g ∂Ψ [v] = M [w] = M 2πa cos ϕ ∂p 2πa2 cos ϕ ∂ϕ The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
Meridional mass streamfunction 100
200
300
400
500
600 Pressure [hPa]
700
800
900 contours streamfunction 1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
-5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 2 1 Vertical wind [ 10− Pa s− ] × data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
contours streamfunction
data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
Northward heat flux by mean meridional circulation 100
200
300
400
500
600 Pressure [hPa]
700
800
900 contours streamfunction 1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
15 10 5 0 5 10 15 1 Heat flux [K m s− ] data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
Northward water vapor flux by mean meridional circulation 100
200
300
400
500
600 Pressure [hPa]
700
800
900 contours streamfunction 1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
5 4 3 2 1 0 1 2 3 4 5 1 1 Water vapor flux [g kg− m s− ] data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
Northward momentum flux by mean meridional circulation 100
200
300
400
500
600 Pressure [hPa]
700
800
900 contours streamfunction 1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
30 20 10 0 10 20 30 8 3 2 Zonal momentum flux [ 10 m s− ] × data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
The MMC and energy transport Potential energy: PE = gz
Vertical Energy Distribution 100 100 100
200 200 200
300 300 300
400 400 400
500 500 500 PE 600 600 600
Pressure [hPa] 700 700 700
800 800 800
900 900 900 contours streamfunction 1000 1000 1000 30°S 20°S 10°S 0° 0 1 2 3 4 5 0° 30°N 60°N 90°N 5 1 Energy [ 10 J kg− ] × data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
The MMC and energy transport
Potential energy: PE = gz Latent energy: LE = Lvq
Vertical Energy Distribution 100 100 100
200 200 200
300 300 300
400 400 400
500 500 500 PE 600 600 600
Pressure [hPa] 700 700 700
800 800 800 LE 900 900 900 contours streamfunction 1000 1000 1000 30°S 20°S 10°S 0° 0 1 2 3 4 5 0° 30°N 60°N 90°N 5 1 Energy [ 10 J kg− ] × data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
The MMC and energy transport
Potential energy: PE = gz Latent energy: LE = Lvq Sensible heat: SH = cvT
Vertical Energy Distribution 100 100 100
200 200 200
300 300 300
400 400 400
500 500 500 PE 600 600 600
Pressure [hPa] 700 700 SH 700
800 800 800 LE 900 900 900 contours streamfunction 1000 1000 1000 30°S 20°S 10°S 0° 0 1 2 3 4 5 0° 30°N 60°N 90°N 5 1 Energy [ 10 J kg− ] × data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
The MMC and energy transport
Potential energy:27.1% PE = gz Latent energy:2.5%LE = Lvq Sensible heat:70.4%SH = cvT
moist static energy: h = gz + Lvq + cvT
Vertical Energy Distribution 100 100 100
200 200 200
300 300 300 MSE 400 400 400
500 500 500 PE 600 600 600
Pressure [hPa] 700 700 SH 700
800 800 800 LE 900 900 900 contours streamfunction 1000 1000 1000 30°S 20°S 10°S 0° 0 1 2 3 4 5 0° 30°N 60°N 90°N 5 1 Energy [ 10 J kg− ] × data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
creating potential energy releasing potential energy
Diabatic heating 100
200
300
400
500
600 Pressure [hPa]
700
800
900
1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
3 2 1 0 1 2 3 1 Diabatic heating rate [K day− ] data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle diabatic heating creates density gradients that drive the overturning circulation
contours: potential temperature Diabatic heating 100 400 400 380 380 360 200 350 340 320 330
300 310
400
500
600 290 Pressure [hPa]
300 700 280 290 800
270 300 280 270 900 contours potential temperature 1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
3 2 1 0 1 2 3 1 Diabatic heating rate [K day− ] data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
15 Inferred total energy transport Inferred atmospheric energy transport Potential energy 10 Latent energy Sensible heat Moist static energy
5 latent energy
0 Energy flux [PW] 5 sensible heat moist static energy 10 potential energy
JRA-55 15 90°S 60°S 30°S 0° 30°N 60°N 90°N data from JRA-55 The climatological mean circulation Zonal mean energy transport Deviations from the climatological mean Zonal mean energy budget of the atmosphere Synthesis: momentum and the jets The climatological mean and seasonal cycle
15 Inferred total energy transport Inferred atmospheric energy transport Potential energy 10 Latent energy Sensible heat Moist static energy
5 latent energy
0 Energy flux [PW]
5 sensible heat moist static energy 10 potential energy
CFSR 15 90°S 60°S 30°S 0° 30°N 60°N 90°N data from CFSR The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Eddies
climatological zonal mean: [x]
transient eddies: x0 = x − x deviations from the time mean (e.g., weather fluctuations) quasi-stationary eddies: x∗ = x − [x] deviations from the zonal mean (e.g., topographic effects)
fluxes by mean meridional circulation fluxes by quasi-stationary eddies fluxes by transient eddies [vx] = [v][x] + [v∗x∗] + v0x0 The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Northward heat flux by eddies 100
200
300
400
500
600 Pressure [hPa]
700
800
900
1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
15 10 5 0 5 10 15 1 Heat flux [K m s− ] data from CFSR The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Northward heat flux by stationary eddies 100
200
300
400
500
600 Pressure [hPa]
700
800
900
1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
10 8 6 4 2 0 2 4 6 8 10 1 Heat flux [K m s− ] data from CFSR The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
data from CFSR The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Northward momentum flux by eddies 100
200
300
400
500
600 Pressure [hPa]
700
800
900
1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
30 20 10 0 10 20 30 2 1 Zonal momentum flux [m s− ] data from CFSR The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Northward momentum flux by stationary eddies 100
200
300
400
500
600 Pressure [hPa]
700
800
900
1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
30 20 10 0 10 20 30 2 1 Zonal momentum flux [m s− ] data from CFSR The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Northward water vapor flux by eddies 100
200
300
400
500
600 Pressure [hPa]
700
800
900
1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
5 4 3 2 1 0 1 2 3 4 5 1 1 Water vapor flux [g kg− m s− ] data from CFSR The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Northward water vapor flux by stationary eddies 100
200
300
400
500
600 Pressure [hPa]
700
800
900
1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
5 4 3 2 1 0 1 2 3 4 5 1 1 Water vapor flux [g kg− m s− ] data from CFSR The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Total northward water vapor flux 100
200
300
400
500
600 Pressure [hPa]
700
800
900
1000 90°S 60°S 30°S 0° 30°N 60°N 90°N
5 4 3 2 1 0 1 2 3 4 5 1 1 Water vapor flux [g kg− m s− ] data from CFSR The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Evaporation Precipitation − CFSR JRA-55 4
2 ] 1 − d
m
m 0 [
P
−
E
2
4
90°S 60°S 30°S 0° 30°N 60°N 90°N
data from JRA-55 and CFSR The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Atmospheric water vapor flux convergence 60 Total MMC Eddy 40 ] 1 − d
1 − g k 20 g k [
e c n e g r
e 0 v n o c
x u l f
r
o 20 p a v
r e t a W 40
60 90°S 60°S 30°S 0° 30°N 60°N 90°N data from CFSR The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Standing eddies: subtropical highs and subpolar lows
90°N
60°N
30°N
0°
30°S
60°S
streamlines 850 mb wind 90°S 60°E 120°E 180° 120°W 60°W
980 985 990 995 1000 1005 1010 1015 1020 1025 1030 1035 1040 Pressure at mean sea level [hPa] data from JRA-55 The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Seasonal variations in standing eddies
streamlines 850 mb wind
data from JRA-55 The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation 4 4 8 4 4 4 4 4 4 8 8 4 4 8 4 4 Seasonal variations in standing eddies: monsoons 4
4
4 DJF sea level pressure and winds 4 JJA sea level pressure and winds 4
4 4
4 4 40°N 4 40°N 4 4 4 4 8 8 4 4
4 4 4 4 4 8 30°N 30°N 4 8 4 12 4 H L 4 4 16
8 4 12 16 8 20 20 4 4 20°N 20°N 8 12
4
12 16 8 20 4
8 4 4 16 12 8 12 4 4 8 8 16 16 12 4 4 12 12 12 8 4 10°N 8 10°N 16 12 20 16 8 12 8 20 20 16 16 12 8 8 12 12 12 4 12 8 12 12 8 12 8 8 8 8 8 8 4
8
0° 0° 12 8 8 8 8
8 8 4 8 12 8 12 8 12 12 8 16 8 4 12 8 8 12 16 8 4 12 8 8 12 4 8 8 12 8 12 8 8 12 4 10°S 12 10°S 8 8 streamlines 8 8 12 8 12 L H surface wind 8 8 4 8 8 20°S 20°S contours precipitation 8
4 40°E 50°E 60°E 70°E 80°E 90°E 100°E 40°E 50°E 60°E 70°E 80°E 90°E 100°E
4 4 4 4 980 985 990 995 1000 1005 1010 1015 1020 1025 1030 1035 1040 4 Sea level pressure [hPa] data from JRA-55 4
4 4 8
4 4 4 4 8
4
4
4 4 4 The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Standing eddies: outgoing longwave radiation
90°N
60°N
30°N
0°
30°S
60°S
streamlines 90°S 850 mb wind 60°E 120°E 180° 120°W 60°W
150 175 200 225 250 275 300 2 Outgoing longwave radiation [W m− ] data from JRA-55 and CERES SYN1deg The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Standing eddies: the surface water budget
90°N
60°N
30°N
0°
30°S
60°S
streamlines 90°S 850 mb wind 60°E 120°E 180° 120°W 60°W
10.0 7.5 5.0 2.5 0.0 2.5 5.0 7.5 10.0 1 Evaporation minus precipitation [mm d− ] data from JRA-55 The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Standing eddies: surface salinity
90°N
60°N
30°N
0°
30°S
60°S
streamlines 850 mb wind 90°S 60°E 120°E 180° 120°W 60°W
30 31 32 33 34 35 36 37 38 39 40 Salinity [psu] data from JRA-55 and ECMWF ORAS4 The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Standing eddies in the tropics: the Walker circulation a Z ϑN Z p Zonal mass streamfunction: Ψ = u∗dpdϑ Z g ϑS 0 Zonal mass streamfunction 100
200
300
400
500
600 Pressure [hPa]
700
800
900 contours streamfunction 1000 0° 60°E 120°E 180°E 120°W 60°W 0°
-5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 2 1 data from JRA-55 Vertical wind [ 10− Pa s− ] × The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Standing eddies in the tropics: the Walker circulation
Normal El Ni˜no La Ni˜na
WARM COLD WARM WARM COLD Maritime South Maritime South Maritime South Continent America Continent America Continent America The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Eddy activity in the extratropics: the storm tracks ∗ Maxima in u are collocated with maxima in v∗T + v0T 0
90°N
60°N
30°N
0°
30°S
60°S
contours 200 mb zonal wind 90°S 0° 60°E 120°E 180° 120°W 60°W
40 30 20 10 0 10 20 30 40 1 Northward eddy heat flux [K m− ] data from CFSR The climatological mean circulation Transient and quasi-stationary eddies Deviations from the climatological mean Eddy fluxes of heat, momentum, and moisture Synthesis: momentum and the jets Eddies in the atmospheric circulation
Eddy activity in the extratropics: the storm tracks The storm tracks also coincide with the sharpest meridional temperature gradients
90°N
60°N
30°N
0°
30°S
60°S
contours 200 mb zonal wind 90°S 0° 60°E 120°E 180° 120°W 60°W
240 250 260 270 280 290 300 310 Temperature [K] data from CFSR The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
Relative vorticity
∂v ∂u ζ = − ζ ∂x ∂y
ζ > 0
ζ < 0 ζ > 0 ζ < 0 The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
Absolute vorticity
η = ζ + f
relative vorticity planetary vorticity
absolute vorticity is conserved in the absence of sources or sinks: ∂η + (v · ∇) = 0 ∂t The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
Rossby waves f increases, so ζ must decrease
ϑN ζ < 0 η0 = ζ + fN north
η0 = f0 fN > f0 > fS ϑ0 ζ0 = 0
η0 = ζ + fS ζ > 0 ϑS f decreases, so ζ must increase The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
Rossby waves Rossby waves propagate toward the west relative to the background flow ∂f wavelength β = ϑN ∂ϑ ζ < 0 phase speed βL2
north c = − 4π2 ϑ0 always toward the west ζ > 0 ϑS The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
DJF 500 hPa Geopotential Height Standing Rossby waves 6.0
wave number = 2∼3 5.9
5.8
5.7
5.6
5.5
5.4
5.3 Geopotential Height [km]
5.2
5.1
5.0
data from CFSR The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
Transient eddies
isotherm
north L WARM WARM
COLD streamline H
under geostrophic balance, streamlines are also isobars The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
Transient eddies: synoptic systems
2007-01-01 00Z 850 hPa Geopotential Height Anomaly
75°N
60°N
45°N L L L H 30°N H H
180° 150°W 120°W 90°W 60°W 30°W
data from CFSR The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
Atmospheric zonal momentum flux convergence 2.0 Total MMC 1.5 Eddy
] The mean meridional circulation fluxes 2 − s 1.0 momentum into the subtropical jets... m [
e c n
e 0.5 g r e v n o c 0.0 x u l f
m u t
n 0.5 e m o m
l
a 1.0 n o Z
1.5
2.0 90°S 60°S 30°S 0° 30°N 60°N 90°N data from CFSR The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
Subtropical jets Friction adds angular momentum to the atmosphere in the tropics; the Hadley cell transports this momentum to the jets
poleward flux of angular momentum
Wa W
EQUATOR EQUATOR S N
E E N S E E
flux of angular momentum into tropical atmosphere The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
Atmospheric zonal momentum flux convergence 2.0 Total MMC 1.5 Eddy
] Eddies flux momentum out 2 − s 1.0 of the subtropical jets... m [
e c n
e 0.5 g r e v n o c 0.0 x u l f
m u t
n 0.5 e m o m
l
a 1.0 n o Z ...and into the storm tracks 1.5
2.0 90°S 60°S 30°S 0° 30°N 60°N 90°N data from CFSR The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
Midlatitude westerlies Eddies transport angular momentum from the subtropical jets downward and poleward, where it returns to the solid Earth poleward flux of angular momentum
Wa W
eddies eddies
return flux of angular W E E W return flux of angular momentum out of momentum out of midlatitude atmosphere midlatitude atmosphere flux of angular momentum into tropical atmosphere The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
Upper troposphere Northern high latitudes midlatitude westerlies and eddies subtropical jet Equator Hadley cell subtropical jet Southern high latitudes midlatitude westerlies and eddies
Lower troposphere Northern high latitudes storms and prevailing westerlies DRY northeasterly trade winds Equator WET southeasterly trade winds DRY storms and prevailing westerlies Southern high latitudes The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
CLIMATIC ZONES POLAR Earth’s Rotation VERTICAL CIRCULATION EASTERLIES POLAR CELL POLAR JET STREAM SUBPOLAR Low 60°N Polar front FERREL CELL TEMPERATE High SUBTROPICAL 30°N ‘Horse latitudes’ NORTHEASTERLY TRADES HADLEY CELL Clear skies Low rainfall ITCZ Intertropical 0 EQUATORIAL ° convergence Persistent zone (ITCZ) cloudiness SOUTHEASTERLY TRADES HADLEY CELL High rainfall SUBTROPICAL High ‘Horse latitudes’ 30°S FERREL CELL TEMPERATE ‘Roaring Forties’ WESTERLIES 60°S JET STREAM Frequent storms Antarctic front POLAR CELL
Antarctica Wells: The Atmosphere and Ocean 2012
Plate 6.13 Schematic representation of features of the general circulation of the atmosphere. Reproduced, with permission, from Charnock, H. In: Oceanography, Edited by S.A. Thorpe and C. Summerhayes. Manson Publishers. 1995: page 34, figure 2.9 The climatological mean circulation Vorticity and Rossby waves Deviations from the climatological mean Momentum fluxes Synthesis: momentum and the jets Isentropic overturning circulation
Isentropic perspectives on the mean meridional circulation Averaging the MMC in dry or equivalent potential temperature coordinates highlights Other Averaging the MMC in dry or equivalent potential temperature different aspects of the overturning circulation Perspectives coordinates highlights different aspects of the circulation Only one cell in each hemisphere Hadley cell Hadley cell
Implied mass transport twice as large! Ferrel cells Ferrel cells Pauluis et al., Science 2008
Pauluis et al., Science 2008 REPORTS
Similarly, the mass transport between two moist the flow when the circulation is integrated on computing the circulation on moist isentropes. isentropes qe1 and qe2 is given by the integral moist isentropes than on dry isentropes, and the The low potential temperature of these parcels is mass transport (Eqs. 5 and 6) is larger on moist typical of the lower troposphere. In Fig. 2, the DYqe Yqe qe2, f −Yqe qe1, f ¼ qe2 ð∞ Þ ð Þ isentropes than on dry isentropes. Because the black contour line shows the values of q and qe M qe, q dqdqe 6 equivalent potential temperature better separates found at Earth's surface: This additional mass ¼ ∫qe1 ∫0 ð Þ ð Þ poleward and equatorward flows, averaging on transport on moist isentropes corresponds to a The integral in Eq. 5 is taken between two moist isentropes includes a larger portion of eddy low-level poleward flow of warm moist air. Its vertical lines in Fig. 2, whereas the integral in mass transport into the global circulation. high equivalent potential temperature is indicative Eq. 6 is taken between two horizontal lines. It is The difference between the mass transports of air parcels that are nearly convectively unstable. apparent from Fig. 2 that the flow on moist isen- on dry and moist isentropes can be attributed to On the basis of these findings, we propose a The climatological mean circulation Vorticity and Rossbytropes (corresponding waves to horizontal lines in the the contribution from the upper left quadrant of revised description of the global atmospheric cir- figure) tends to point uniformly either toward the the distribution shown in Fig. 2. This corresponds culation in Fig. 3. It includes the previously Deviations from the climatological mean Momentum fluxespole (at high values of qe)ortowardtheequator to poleward moving air parcels with high qe and identified global circulation on dry isentropes Synthesis: momentum and the jets Isentropic overturning(at low values circulation of qe). In contrast, the flow on dry low q.Thepolewardmasstransportfromthis (black and blue arrows): Air rises to the upper isentropes (corresponding vertical lines) has con- upper left quadrant cancels out with the equator- troposphere within the precipitation zones of the tributions in both the equatorward and poleward ward flow at low q and low qe when computing equatorial regions and moves poleward; although directions. There is thus less cancellation be- the mass transport on dry isentropes but is added some air subsides in the subtropics, the rest is tween equatorward and poleward components of to the poleward flow at high qe and high q when advected poleward across the storm tracks by syn- optic eddies, subsides over the poles, and returns equatorward near the surface (4, 5). The addi- Isentropic perspectives on the mean meridional circulation tional mass transport found in the moist isen- tropes is associated with a “moist” branch of the Other The MMC on equivalent potential temperature coordinates circulation (red and blue arrows) in which low- The MMC on equivalent potential temperature coordinates better accounts for mass level warm moist air in the subtropics is advected poleward by synoptic-scale eddies and rises within the storm tracks before subsiding over the
Perspectives better accounts for mass transport in moist poleward flow on October 7, 2011 transport in moist poleward flow poles and returning equatorward near Earth's surface. This moist branch is reminiscent of the Palmén-Newton circulation (12, 13), which stresses the role of ascending warm air in mid-latitude eddies. These two branches of the circulation trans- port roughly the same amount of air: Half of the air parcels in the polar upper troposphere have risen within the storm tracks, whereas the other half rose within the equatorial regions.
This revised circulation emphasizes the im- www.sciencemag.org portance of moist processes in mid-latitude dy- isotherm namics. Although previous studies have noted some impacts of the moist processes on the isen-
north L tropic circulation (5)andthetransformedEuler- ian mean circulation (10)inthemid-latitudes,we Fig. 2. Joint distribution of the mass transport as a function of q and qe at 40°N during December, have shown that an analysis based on a dry frame- January, and February, averaged between 1970 and 2004. The combinations of (q, qe)foundwithinthe work systematically underestimates the atmo- WARM, MOIST black contour line have aWARM, high probability to beMOIST found at Earth's surface at 40°N, defined as having a spheric circulation by averaging out the moist Downloaded from probability density function larger than 0.001 K−2. branch of the circulation from the total mass transport. The moist branch is closely tied to the Fig. 3. Schematic rep- latent heat transport, which accounts for roughly COLD, DRY resentation of the global half of the poleward energy transports (2). Ascent atmospheric circulation. of warm, moist air within the storm tracks occurs Black and blue arrows through a combination of deep and slantwise indicate isentropic circu- convection (14, 15)andresultsinenhancedpre- streamline H lation on dry isentropes, cipitation. A key question is to what extent moist with air rising at the equa- processes play an active role in setting the atmo- tor, moving poleward in spheric lapse rate in mid-latitudes, as has been the upper troposphere, suggested recently (16, 17). Without fully answer- and returning equator- ing this question, our findings confirm that the ward near the surface. Red and blue arrows show circulation provides an ample supply of warm, black and blue: onthe dry moist branch isentropes of the moist air that should have a direct impact on the circulation corresponding temperature structure in the mid-latitudes. As red: only on moistto the additional isentropes mass Earth's temperature rises, the amount of water transport on moist isen- vapor present in the atmosphere is extremely tropes, with warm moist likely to increase as well (18). Understanding how air moving toward the changes in temperature and humidity affect the mid-latitudes at low levels, rising into the upper troposphere within the stormPauluis tracks, and et subsiding al., overScience the dynamics2008 of the storm tracks and, in particular, pole and dry cold air moving toward the equator near the surface. the mass transport in the two branches of the cir-
www.sciencemag.org SCIENCE VOL 321 22 AUGUST 2008 1077 Pauluis et al., Science 2008