Changing tropical water vapour
transports in high resolution
atmospheric data
Matthias Zahn supervised by Richard Allan
ESSC
University of Reading
m.zahn@reading.ac.uk
March 22, 2012
fg:logo
My Background
◮
Polar Lows (regional scale Arctic Storms)
PhD in Hamburg with Hans von Storch
resulted in a series of papers (e.g.
GRL[Zahn and von Storch(2008)],
Nature[Zahn and von Storch(2010)])
◮
Hydrological Cycle/ Moisture Transports
Post Doc with Richard Allan and Lennart Bengtsson
one paper so far (JGR [Zahn and Allan(2011)])
one about to be submitted
Data
high resolution instantaneous data
◮
◮
◮
◮
in space and time (≈ 0.5◦ , ≈ 30 vertical levels,
6h )
reanalysis (ERAint) 1989 -2008
model (ECHAM5)
C20: 1960-1989, A1B: 2070-2100
ω, U and V, q, pressure information
Method, two steps
1. define ASC and DESC regions
◮
◮
based on monthly mean and instantaneous ω
4 ∗ 365 ∗ 20 = 29200 ASC/DESC masks
2. calculate moisture transport across
boundary
◮
◮
◮
linking wind vectors with water content
along all boundary segments (horizontally and
vertically)
monthly mean and instantaneous
Examples of monthly mean and
instantaneous ω fields
10˚
20˚
30˚
40˚
50˚
60˚
70˚
80˚
90˚
100˚ 110˚ 120˚ 130˚ 140˚ 150˚ 160˚ 170˚ 180˚ −170˚ −160˚ −150˚ −140˚ −130˚ −120˚ −110˚ −100˚ −90˚ −80˚ −70˚ −60˚ −50˚ −40˚ −30˚ −20˚ −10˚
0˚
40˚
40˚
30˚
30˚
20˚
20˚
10˚
10˚
0˚
0˚
−10˚
−10˚
−20˚
−20˚
−30˚
−30˚
−40˚
−40˚
Jun 2008
10˚
20˚
30˚
40˚
50˚
60˚
70˚
80˚
90˚
100˚ 110˚ 120˚ 130˚ 140˚ 150˚ 160˚ 170˚ 180˚ −170˚ −160˚ −150˚ −140˚ −130˚ −120˚ −110˚ −100˚ −90˚ −80˚ −70˚ −60˚ −50˚ −40˚ −30˚ −20˚ −10˚
0˚
30˚
30˚
20˚
20˚
10˚
10˚
0˚
0˚
−10˚
−10˚
−20˚
−20˚
−30˚
−30˚
22 Jun 2008, 0:00
Frequency distribution of ASC
(1989-2008)
20˚
40˚
60˚
80˚
100˚
120˚
140˚
160˚
180˚
−160˚
−140˚
−120˚
−100˚
−80˚
−60˚
−40˚
−20˚
0˚
30˚
30˚
20˚
20˚
10˚
10˚
0˚
0˚
−10˚
−10˚
−20˚
−20˚
−30˚
−30˚
from monthly mean ω fields
20˚
40˚
60˚
80˚
100˚
120˚
140˚
160˚
180˚
−160˚
−140˚
−120˚
−100˚
−80˚
−60˚
−40˚
−20˚
0˚
30˚
30˚
20˚
20˚
10˚
10˚
0˚
0˚
−10˚
−10˚
−20˚
−20˚
−30˚
−30˚
%
0
10
20
30
40
50
60
70
80
90
100
from instantaneous ω fields
Vertical Profile of MT (1989-2008)
0
MTii
MTim
MTmm
200
Pressure level [hPa ]
◮
400
600
◮
800
1000
0
0.5
MT [kg *s-1 * m-1]
1
implication for the budget !
1.5
lower
level MT
similar
mid-level
MT
different
mean and trend for MT in different
experiments
acronym
MTii
MTim
MTmm
P-E in ASCm
mean [km3 · day −1 ] trend [per year ]
651.1
320.3
404.6
320.0
0.612
0.236
0.514
0.274
Vertical Profile of MT C20/C21
0
MTm
MTm
MTi
MTi
Pressure level [hPa ]
200
C20
C21
C20
C21
◮
400
600
◮
800
1000
0
0.02
0.04
0.06
MT [kg *s-1 * m-1 * hPa-1]
0.08
0.1
0.12
lower
level MT
strengthened
mid-level
MT
strengthened
MTii percentiles (C21 - C20)
0
900
99%
97%
95%
90%
75%
50%
25%
10%
5%
3%
1%
920
200
Pressure level [hPa ]
940
400
960
980
600
1000
0.01
0.011
0.012
0.013
0.014
0.015
0.016
800
1000
-0.005
0
0.005
MT [kg *s-1 * m-1 * hPa-1 ]
C21 - C20
0.01
0.015
MTii percentiles at lower levels (C21 C20)
0.12
0.1
0.1
0.08
0.08
lev 31
lev 30
lev 29
lev 28
lev 27
lev 26
lev 25
lev 24
lev 23
0.015
0.01
0.06
0.06
0.04
0.04
0.02
0.02
0
0
-1
-1
-1
MT [kg *s * m * hPa ]
0.12
0.005
0
0
20
40
60
80
percentile [ % ]
(a)
C21
100
0
20
40
60
80
100
0
percentile [ % ]
(b)
C20
20
40
60
80
percentile [ % ]
(c)
C21 - C20
100
Changes of wind and humidity
0
0
99%
97%
95%
90%
75%
50%
25%
10%
5%
3%
1%
200
Pressure level [hPa ]
Pressure level [hPa ]
200
99%
97%
95%
90%
75%
50%
25%
10%
5%
3%
1%
400
600
800
400
600
800
1000
0
0.005
0.01
0.015
0.02
-2
PWC [kg * m
(d)
0.025
0.03
0.035
1000
-0.005
-1
PWC
-0.004
-0.003
-0.002
-0.001
0
0.001
-1
* hPa ]
effective wind [ m * s ]
(e)
effective wind[Sohn and Park(2010)]
Tropical Circulation pattern. Changing
frequency of ASC (C21 - C20)
20˚
40˚
60˚
80˚
100˚
120˚
140˚
160˚
180˚
−160˚
−140˚
−120˚
−100˚
−80˚
−60˚
−40˚
−20˚
0˚
30˚
30˚
20˚
20˚
10˚
10˚
0˚
0˚
−10˚
−10˚
−20˚
−20˚
−30˚
−30˚
%
−10
−8
−6
−4
−2
0
2
4
6
8
10
ASCi
20˚
40˚
60˚
80˚
100˚
120˚
140˚
160˚
180˚
−160˚
−140˚
−120˚
−100˚
−80˚
−60˚
−40˚
−20˚
0˚
30˚
30˚
20˚
20˚
10˚
10˚
0˚
0˚
−10˚
−10˚
−20˚
−20˚
−30˚
−30˚
%
−30 −25 −20 −15 −10 −5
0
5
10
ASCm
15
20
25
30
Results
1.
MT should be calculated instantaneously
◮
◮
2.
MT projected to intensify with warming
◮
◮
3.
definition of ASC/DESC region
mid level outward MT underestimated otherwise
especially at higher percentiles
due to higher humidity
(Changes of tropical circulation less distinct
if based on instantaneous ω)
◮
to be investigated in more detail ...
Thank you very much for your attention
http://www.nerc-essc.ac.uk/ maz/
References
Sohn, B. J., and S.-C. Park, Strengthened
tropical circulations in past three decades
inferred from water vapor transport, J. Geophys.
Res., 11 , 2010.
Zahn, M., and R. P. Allan, Changes in water
vapor transports of the ascending branch of the
tropical circulation, J. Geophys. Res., 116 , 2011.
Zahn, M., and H. von Storch, A long-term
climatology of North Atlantic polar lows,
Geophys. Res. Lett., 35 , 2008.
Zahn, M., and H. von Storch, Decreased
frequency of north atlantic polar lows associated
Bonus material
http://www.nerc-essc.ac.uk/ maz/
Vertical structure of percentiles
0
0
99%
97%
95%
90%
75%
50%
25%
10%
5%
3%
1%
200
Pressure level [hPa ]
Pressure level [hPa ]
200
400
600
800
1000
-0.02
99%
97%
95%
90%
75%
50%
25%
10%
5%
3%
1%
400
600
800
0
0.02
0.04
0.06
MT [kg *s-1 * m-1 * hPa-1 ]
(f)
C20
0.08
0.1
1000
-0.02
0
0.02
0.04
0.06
MT [kg *s-1 * m-1 * hPa-1 ]
(g)
C21
0.08
0.1
Method
define ASC and DESC regions
◮
◮
based on monthly mean and instantaneous ω
4 ∗ 365 ∗ 20 = 29200 ASC/DESC masks
calculate moisture transport across boundary
MTt =
nl
nb X
X
b
Wbl · PWCbl
l
MT: moisture transport
W: wind vector ( positive towards ASC)
PWC : precipitable water content
t: time, b: boundary segment, l: level
(1)
PWC along boundaries C21 relative to
C20.
0
i
m
Pressure level [hPa ]
200
400
600
800
1000
100
120
140
160
180
200
220
240
PWC in C21 [ % compared to C20]
Figure:
Percentage of precipitable water content along ASC/DESC boundary of ASCi and ASCm in C21
relative to C20. Unit of transport is mass of water [kg] per time [s] and area [hPa ∗ m]. Note that the vertical unit
of the area is given in pressure [hPa].
-1
7
8
9
10
11
12
-1
-3.2
-3
-2.8
-2.6
-2.4
-2.2
-2
-1.8
-1.6
2069
2072
2075
2078
2081
2084
2087
2090
2093
2096
2099
MTi, C20out
MTi, C20in
MTi, C21out
MTi, C21in
MTm, C20out
MTm, C20in
MTm, C21out
MTm, C21in
61
64
67
70
73
76
79
82
85
88
-1
-1
[ kg *s * m ]
5
6
7
Budi, C20
Budi, C21
Budm, C20
Budm, C21
61
64
67
70
73
76
79
82
85
88
-1
[ kg *s * m ]
8
9
10
2069
2072
2075
2078
2081
2084
2087
2090
2093
2096
2099
Temporal evolution of moisture transport into the
ascending region.
2069
2072
2075
2078
2081
2084
2087
2090
2093
2096
2099
61
64
67
70
73
76
79
82
85
88
Time series of MT above and below RL
-1
[ kg *s * m ]
Examples of monthly mean and
instantaneous ω fields, ECHAM5 C20
10˚
20˚
30˚
40˚
50˚
60˚
70˚
80˚
90˚
100˚
110˚
120˚
130˚
140˚
150˚
160˚
170˚
180˚
−170˚ −160˚ −150˚ −140˚ −130˚ −120˚ −110˚ −100˚
−90˚
−80˚
−70˚
−60˚
−50˚
−40˚
−30˚
−20˚
−10˚
0˚
30˚
30˚
20˚
20˚
10˚
10˚
0˚
0˚
−10˚
−10˚
−20˚
−20˚
−30˚
−30˚
downward
0.0
10˚
20˚
30˚
40˚
50˚
60˚
70˚
80˚
90˚
100˚
110˚
120˚
130˚
140˚
150˚
160˚
Mar 1965
170˚
180˚
−170˚ −160˚ −150˚ −140˚ −130˚ −120˚ −110˚ −100˚
−90˚
−80˚
−70˚
−60˚
−50˚
−40˚
−30˚
−20˚
−10˚
0˚
30˚
30˚
20˚
20˚
10˚
10˚
0˚
0˚
−10˚
−10˚
−20˚
−20˚
−30˚
−30˚
downward
0.0
22 Mar 1965, 6:00
Vertial profile of in an outflows, separately
0
MTini C20
MTinm C20
MTini C21
MTinm C21
MTouti C20
MToutm C21
MTouti C21
MToutm C21
MTini ERAint
MTinm ERAint
MTouti ERAint
MToutm ERAint
Pressure level [hPa ]
200
400
600
800
1000
-0.4
-0.3
-0.2
-0.1
0
-1
0.1
-1
0.2
0.3
0.4
-1
MT [kg *s * m * hPa ]
MT outwards also strongest at low levels, Hadley
pattern only exists in theory, average