3
Global atmospheric circulation,
modes and variability
3.1 Mean conditions
3.2 Modes in atmospheric circulation
3.3 Changes in upper-level atmosphere
3.4 Monsoon system
General introduction
ATMOSPHERIC VERTICAL STRUCTURE
The troposphere (0 - ~10 km)
contains ~80% of the
atmospheric mass,
Temperatures increase with altitude in
the stratosphere (10 - 50 km) due to
absorption of UV light by ozone (O3),
There is limited exchange of material
between the troposphere and the
stratosphere,
ATMOSPHERIC
PRESSURE
Atmospheric pressure decreases rapidly with
height,Climbing to an altitude of only 5.5 km,
where the pressure is 500 mb,would put you
above one-half of the atmosphere's molecules,
Example,
T= 15C = 288 K
r = 1.2 kg /m3
R = [287.05 J K-1 kg-1 ]
[1 J = 1 N m]
?
p = 1.013 x 105 N/m2
= 1013 mb
Ideal Gas Law
p =r R T
Atmospheric circulation
Descending Air
High
Pressure
Ascending Air
Low
Pressure
Descending Air
High
Pressure
Ascending Air
Low
Pressure
THERMALLY-
DIRECT
CIRCULATION COLD WARM
THERMALLY
INDIRECT
CIRCULATION WARM COLD
Equator N S
HADLEY CELL IS A THERMALLY-DIRECT
CIRCULATION
THERMALLY-
DIRECT
CIRCULATION IN
AN IDEALIZED
NON-ROTATING
EARTH
The prevailing circulation of the atmosphere
0 30 30 60 60 N S
Latitude
High High Low Low
Surface Pressure Systems
HADLEY CELLS ARE THERMALLY DIRECT
CIRCULATIONS
FERREL CELLS ARE THERMALLY-INDIRECT CIRCULATIONS
As are (weak) polar cells
Low
Precipitation
occurs in bands
of surface
convergence (low
pressure regions)
0 30 30 60 60 N S
Low
Latitude
High High Low Low
Atmospheric Vertical Circulation
Surface Pressure Centers
0 30 30 60 60 N S
Westerly
Easterly Surface Winds
2WVgsin f= -(1/r) Dp/ Dy
Geostrophic Balance,Responsible for east-west
component of wind at surface
Dp/ Dy>0 ? Vg <0
(easterlies)
Dp/ Dy<0 ? Vg >0
(westerlies)
At the equator there are weak
easterlies (“doldrums”)
Global mean atmospheric
circulation
January
July
Note the seasonal changes in the global atmospheric circulation
ITCZ migrates with Sun,but lags it..,
Seasonal changes in upper air (500mb level)
atmospheric circulation
January
Seasonal changes in upper air (500mb level)
atmospheric circulation
July
50mb geopotential height Jan
50mb geopotential height July
Atmospheric center of action
January
July
3.1 Mean conditions
3.2 Modes in atmospheric circulation
3.3 Changes in upper-level atmosphere
3.4 Monsoon system
Modes in surface circulation,
Atmospheric oscillations
Sir G,T,Walker
Walker’s NAO
Walker and Bliss,1932
Walker and Bliss,1932
Walker and Bliss,1932
Walker’s NPO
Walker and Bliss,1932
Walker and Bliss,1932
Walker and Bliss,1932
NPO as simulated in CGCM (Shneider and
Kinter III,1994)
Walker’s SO
Walker and Bliss,1932
Walker and Bliss,1932
Walker and Bliss,1932
Antarctic Oscillation
25S
50S
70S
P T O
P G A
S T A
G R Y
S I G
O R C
I 3 C
I 3 B
C H A
AU C
C H R
C AM
H O B
I 3 A
T P I
A O I
M1
Z1
Z2
0
180
90W
90E
L SA
25S
50S
70S
P T O
P G A
S T A
G R Y
S I G
O R C
I 3 C
I 3 B
C H A
AU C
C H R
C AM
H O B
I 3 A
T P I
A O I
M1
Z1
Z2
0
180
90W
90E
L SA
Antarctic Oscillation (AAO)
南半球纬圈平均 SLP的相关系数
南半球月平均 SLP的 EOF分析第一模态
Gong & Wang,1999
GFDL R15,800yr,hPa
Hall & Visbeck,2001
Atmospheric oscillations and their
climatic influence
a b
c d
四个大气涛动对 SLP的解释率
四个大气涛动对全球 SLP的解释率
观测资料中 NAO与 SST距平的相关系数分布
Zhou et al.2000
NAO and Hurricane
NAO NPO and Arctic
Oscillation
0102030405060708090
-0,4
-0,2
0,0
0,2
0,4
-0,4
-0,2
0,0
0,2
0,4
N
U
H
500hPa纬圈平均冬季纬向风
(U)与位势高度 (H)奇异值分
解 (SVD)的第一对模态
1000hPa纬圈平均冬季纬向
风 (U)与位势高度 (H)奇异值
分解 (SVD)的第一对模态
0102030405060708090
- 0, 4
- 0, 2
0, 0
0, 2
0, 4
- 0, 4
- 0, 2
0, 0
0, 2
0, 4
N
U
H
1 9 6 0 1 9 7 0 1 9 8 0 1 9 9 0 2 0 0 0
-3
0
3
m
/
s
- 1 0 0
- 5 0
0
50
1 0 0
g
p
m
U 55
H 40 - H 65
Cor=0.96
Winter,SLP,High Index 1989 1988 1945 1982 1991
Low Index 1968 1962 1955 1946 1967
Baldwin and Dukerton(1999)
The evolution of the 90
day low-pass filtered
projection of geopotential
height on the AO
computed from
NCEP/NCAR reanalysis
data,
12－ 3月瑞士 Arosa站臭氧总量 (实线 )与 NAO指数 (虚线 )
Appenzeller et al.,2000
Long-term changes
Teleconnection map between snow accumulation at the NASA-U drill site (*) and mean
pressure at sea level,Contours indicate pressure variation associated with 1 SD in snow
accumulation,Contour interval is 0.5 hPa and for clarity values are scaled with -1.0,
Regions with significant correlation (above 99% c.l.) are shaded,Both data sets are
monthly mean ECMWF reanalysis data for 1979-1993,(Appenzeller et al.,1998)
Normalized proxy NAO index based on western Greenland ice accumulation
rates (shaded) and normalized instrumental NAO index (thick line),Data are
annual means averaged from spring to spring,Linear trends and high-
frequency parts are removed,Also shown is a 15-year running median of the
proxy index (thin line),
Appenzeller et al.,1998
3.1 Mean conditions
3.2 Modes in atmospheric circulation
3.3 Changes in upper-level atmosphere
3.4 Monsoon system
Stratospheric and mesospheric wind systems
Polar-night westerlies
Summer easterlies
In middle and high latitudes there is indeed a reversing vortex
in both hemispheres,In the winter hemisphere the
mesospheric westerlies (so called because their jet cores lie in
the mesosphere) are believed strongest at about 65 kilometres
in mid-latitudes,where winds average more than 80 metres per
second,The polar-night area is bitterly cold (down to below -
80 C in the 25–35-km layer),and strong westerlies are usually
present in the intensely baroclinic zone around this cold core,
These westerlies,which are often visible on charts as low as
20 kilometres,have become famous since 1952,when the first
explosive warming in them was observed over Berlin,Their
relation to the main mesospheric jet is not clear,and they may
be distinct,
Summer easterlies
The polar-night westerlies of the Northern Hemisphere
are deformed by standing waves (mostly of the two-
wave sort),with a ridge over and west of Alaska and
troughs over eastern Siberia and eastern North
America,which are often continuous with similar
waves in the Ferrel westerlies below,The southern
polar-night system lies over the ocean for much of the
winter and is less well known,but it is probably more
nearly a pure zonal westerly,Both systems are subject
to transient disturbances involving strong vertical
motion,as is the whole depth of the mesospheric
westerlies,
These disturbances show themselves by sudden warmings,
sometimes more than 30C in a day,through substantial
depths of the stratosphere,The warmings,once thought to
result from some kind of extraterrestrial impulse,are
almost certainly due to subsidence on the order of one or
two kilometres per day,They temporarily destroy or even
reverse the westerly circulation,The last of these
warmings brings winter to an abrupt and spectacular end,
usually at or before the spring equinox,These invisible
events also transfer much ozone downward into the lower
stratosphere from the layers of rapid formation higher up,
giving the high-latitude belts the curious phenomenon of a
spring ozone
Summer easterlies
Summer easterlies at high levels,established after
some weeks of further vacillation,blow continuously
until September (March in the Southern Hemisphere),
They are probably strongest at about 70 kilometres in
about 50° latitude,where they attain 60 metres per
second,They probably tilt equatorward as one
descends,and below 40 kilometres the strongest winds
are in about 15° latitude,These easterlies lack the
spectacular disturbances of winter but contain rather
feeble westward-drifting troughs and ridges,
Between these vast zonal currents,in broadly equatorial
latitudes,mean wind speeds are low,In the layer above
about 15 kilometres and up to at least 40 kilometres
within the 30° parallels,there is a remarkable regime in
which the zonal wind reverses on a unique 26-month
cycle with easterlies giving way to westerlies all around
the Earth and then reappearing 26 months later,It has
been shown that a 26-month component of variation
occurs in many atmospheric phenomena,but in the
equatorial stratosphere it dominates the motion of the
winds,
Q B O
Verical lines indicate the Januaries,The index is the concatenation of
values at Canton Island (3S,172W) for Jan 1953 - Aug 1967;
Gan/Maledives (1S,73E) for Sep 1967 - Dec 1975; and Singapore
(1N,104E) for Jan 1976 - Feb 1999,
B,Naujokat and C,Marquardt 2000
30 hPa zonal wind (m/s)
W
E
Time-height section of zonal wind,1993-98
W E W W E E
Teleconnections
EA
PNA
WA
WP
EUP
P J
1650 1 7 0 0 1750 1 8 0 0 1850 1900 1 9 5 0 2000
-2
0
2
-2
0
2
E
U
EU序列 (冬季,上下分别为不同方案重建结果 )
Luterbacher(1999)
3.1 Mean conditions
3.2 Modes in atmospheric circulation
3.3 Changes in upper-level atmosphere
3.4 Monsoon system
7月海平面气压分布 (张家诚,林之光,1985)
1) low-level cross equatorial flow,2) southwesterlies,3) EASM trough,4) subtropical
high,5) Mei-Yu front zone,6) midlatitude westerlies,7) Tibetian high,and 8) upper
level return flow,
(J,Zhou,K.-M.Lau,1998)
图 2.3a 1月海平面气压分布 (张家诚,林之光,1985)
30E 60E 90E 120E 150E
0N
30N
60N
90N
西伯利亚高压中心区平均气压变化一个标准差时温度
的相应变化 (?C),
30E 6 0 E 90E 120E 150E
0N
3 0 N
6 0 N
9 0 N
- 2 0 t o - 1 5
- 1 5 t o - 1 0
- 1 0 t o - 5
- 5 t o 0
0 t o 5
5 t o 1 0
1 0 t o 1 5
西伯利亚高压中心区平均气压变化一个标准差时降水量的相应
变化 (％ )
1 8 8 0 1 8 9 0 1 9 0 0 1 9 1 0 1 9 2 0 1 9 3 0 1 9 4 0 1 9 5 0 1 9 6 0 1 9 7 0 1 9 8 0 1 9 9 0 2 0 0 0
Y e a r
-4
-2
0
2
4
I
n
t
e
n
s
i
t
y
I
n
d
e
x
/
h
P
a
冬季西伯利亚高压强度指数
192 2 - 197 5 1976 -200 0
图 2,1 922 - 197 5 及 197 6- 200 0 年冬季海平面气压的线性趋势,( N C A R 资料 )
1 9 2 0 1 9 3 0 1 9 4 0 1 9 5 0 1 9 6 0 1 9 7 0 1 9 8 0 1 9 9 0 2 0 0 0
-4
0
4
(
m
b
)
-4
0
4
(
m
b
)
-4
-2
0
2
4
T
e
m
p
e
r
a
t
u
r
e
(
C
)
温度
- 2 0
- 1 0
0
10
20
P
r
e
c
i
p
i
t
a
t
i
o
n
(
m
m
)
降水
o
平
距
度
温
平
距
水
降
平
距
压
气
平
距
压
气
亚洲大陆中高纬平均温度与降水序列及其与西伯利亚高压强
度 (虚线 )的关系
1 9 5 0 1 9 6 0 1970 1980 1990 2000
Y e a r
-2
0
2
T
e
m
p
e
r
a
t
u
r
e
(
C
)
-2
0
2
A O + S H C I + E U + S O T r e n d = + 0, 2 7 C / d e c a d e
R e s i d u e T r e n d = + 0, 1 1 C / d e c a d e
o
o
o
西伯利亚高压，北极涛动，欧亚遥相关型及南方涛动拟合的温度值
(上图 )及与实际观测值之间的差别 (下图 ),虚线是线性趋势