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Thomas Moelg (1, 2), N.J. Cullen (3), D.R. Hardy (4), G. Kaser (1)
(1) University of Innsbruck, A U S T R I A
(2) University of California - Berkeley, U. S. A.
(3) University of Otago, N E W Z E A L A N D
(4) University of Massachusetts, U. S. A.
AGU Fall Meeting 2007 (San Francisco)
KILIMANJARO (Tanzania)
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Š climate conditions?
Š importance of melt?
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Š Rapid climate change in East Africa in late 19th century (~1880)
O ver-lake rain fall [m m ]
2600
extents (Kilimanjaro, Mt. Kenya, Rwenzori)
- 2glacier
400
2200
(Meyer, 1900; Hastenrath, 1984)
ea n
000
levelm accounts
- 2lake
(Lake Victoria)
1 8 58 -1 8 7 8
1800
(Nicholson and Yin, 2001; Yin and Nicholson, 2002)
1600
- lake sediment composition (Lake Naivasha)
1400
1200
(Verschuren et al., 1999, 2000)
1000
1860
1880
1900
1920
1940
1960
1980
2000
T im e [year]
m o is tu re re g im e 1 (w e tte r)
tra n sitio n
m o is tu re re g im e 2 (d rie r)
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O ver- lake rain fall [m m ]
2 60 0
2 40 0
2 20 0
2 00 0
m ean
1 8 5 8 -1 8 7 8
surface level
1 80 0
1 60 0
1 40 0
1 20 0
1 00 0
18 6 0
1 88 0
1 9 00
19 2 0
1 94 0
1 9 60
19 8 0
2 00 0
T im e [year]
m o isture re gim e 1 (w e tter)
tra nsitio n
m o isture reg im e 2 (d rie r)
mid troposphere??
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AWS3, 5873 m a.s.l.
02/2005 to 01/2006
Š T = -6.6 °C
Š vp = 1.7 hPa
Š solar rad. = 340 W m−2
Š v = 5.1 m s−1
Š albedo, LW fluxes, surface
height change, air pressure
T, RH, p, v, P
sublimation, melt
energy balance
snowfall
LWÈ
LWÇ
-
GLACIER
energy fluxes
+
g
in
-
ez
f re
re
+
n
tio
SWÇ
QS, QL
+/-
si
po
de
SWÈ
+/QG
SNOW
(20-30 levels)
mass fluxes
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Moelg et al. (2007), Int. J. Climatol. 27, doi: 10.1002/joc.1589.
2/8 /05
270
268
266
264
262
m easured
m odeled
R M S D = 0.92 K
260
258
0
50
10 0
15 0
2 00
T im e (d ays)
2 50
300
5/6 /05
8 /1/0 5
1 0/27/05
a
0
r = 0.89
A ccu m u lat ed lo werin g (cm )
Glacier su rf ace t emp erature (K )
a
m easured
m odelled
-4 0
-8 0
-1 2 0
-1 6 0
350
0
1 /22/06
100
200
T im e ( d ay)
)LJ9DOLGDWLRQVXUIDFHWHPSHUDWXUHDQGORZHULQJ
300
/RFDOVFDOHGDWD
Precipitation (snowfall amount & frequency) governs glaciers
20 0
Sublimation accounts for ~70% of mass loss (melt ~30%)
0.9
15 0
n et LR
QL
10 0
0.8
0.7
QS
ALB
0.6
50
0.5
0
0.4
DATA G AP
-5 0
0.3
-1 0 0
S h o r tw a v e s ur fa c e a lbe d o
E n e rg y flu x d e n s ity (W m -2 )
n et S R
0.2
M -0 A -0 M -0 J-0 J-0 A -0 S -0 O -0 N -0 D -0 J-1 F-1 M -1 A -1 M -1 J-1 J-1 A -1 S -1 O -1 N -1 D -1 J-2 F-2
Tim e (m onth)
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m
as
s
eq
ui
l ib
ri u
m
inverse mass balance
modeling
18
80
m
or
a
Š first step (to detect
basic climate change):
- constant thickness
in
es
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- ∆h/yr (AWS3) = 0
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∆P = +60%
∆GR = −4%
∆vp = +12%
~ 1880
∆T = −8K
present
∆K DWVWDWLRQ
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/DUJHVFDOHFRQWH[W
Š What is responsible for precipitation fluctuations in East Africa?
Æ Indian Ocean Zonal Mode (IOZM): OND wet season
Š IOZM activity 19th & 20th century?
Paleoclimate simulation AOGCM
5° S
model captures dynamics!
Moelg et al. (2006), GRL 33.
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Standar diz ed S O N DMI
3
2
D ipole M ode Index & Proxy D ata
A lake levels (LL) start to rise
B LL drop from highstand, glaciers begin retreat
1820-1880
3 strong events /dec
1
after 1880
1 strong event /dec
0
-1
-2
18 0 0
p e rio d
p e rio d
A
B
1840
1880
1 9 20
1960
2 0 00
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Š historical ship observations: easterly winds more frequent prior to 1880
(Hastenrath, 2001) Æ when did wet period begin?
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Š Measurements, modeling, proxies Æ Kilimanjaro glaciers governed by
precipitation (snowfall), ~+60% prior to 1880 (last maximum extent)
Š Lake levels & sediments Æ moisture drop at low altitudes, regional scale
Š These phenomena reflect large-scale tropical climate change Æ decrease
in moisture transport from Indian Ocean into East Africa
(AOGCM experiments and historical-source proxy data)
Š Outlook: refine inverse mass balance modeling on Kilimanjaro Æ robust
validation basis for climate change in tropical mid-troposphere (500 hPa)