Meteorological modelling in polar regions

Meteorological modelling in polar regions
Prof. Nicole van Lipzig
Department of Earth- and Environmental Sciences
K U Leuven Celestijnenlaan 200E,
K.U.Leuven,
200E B
B-3001
3001 Heverlee
Meeting Royal Meteorological Society at British
Antarctic Survey 21 March 2012
Overview
• What were the model developments in recent
decades?
• For which purposes can we use atmospheric
models?
– How does the present and future climatology of the
Greenland and Antarctic ice sheet look like?
– How big is the mass loss from the polar ice sheets?
– How does precipitation variability affect the ice core
signals?
– What are the mechanisms behind recent observed
changes?
• Which future model developments are needed?
Development and improvement of atmospheric models
In the middle of the ‘90-ies the basis for modelling of polar
regions
eg o s was
as laid
a d ((e.g.
g Connolleyy and Cattle,, 1994;; Lynch
y
et al.
1995; Hines et al., 1997; Heinemann 1997; van Lipzig et al. 1999;
Gallee et al., 2000; Bromwich et al. 2001; van den Broeke et al., 2001;
Cassano et al. 2001; Klein et al. 2001; King et al., 2001).
Key issues that were addressed:
• Proper digital elevation models
• Proper land sea mask
• Subgrid orography
• Albedo
physics
y
((including
g snowdrift))
• Snow surface p
• The stable boundary layer
• Cloud physics
• Sea ice treatment
Snow surface physics
• IIn the
th original
i i l model,
d l th
the diff
diffusivity
i it and
dh
heatt
capacity of ice was used for ice sheets
Van Lipzig et al., 1999
Snow surface physics
• For Greenland,
Greenland
subsurface model
(ice/firn/snowpack)
needs to be included
that takes into account
penetration and ref
freezing
i off meltwater
lt t
• Implemented in
RACMO ((Ettema et al.,,
2010)
The stable boundary layer
• St
Standard
d db
boundary-layer
d
l
parametrizations
t i ti
were found to be inadequate for the stable
Antarctic boundary-layer
boundary layer
Van Lipzig et al., 1999
The stable boundary layer
•
•
•
Sensitivity test: The surface exchange coefficients and eddy
diffusivities decrease more rapidly with increasing stability than they
do in the standard parametrization used in the HadAM2 model
reductions in downward heat flux occur almost everywhere over the
continent
Wind along the coast increases
Sensitivity of surface heat flux
sensitivity of wind speed
•
King et al., 2001
Ho
ow big
g is the
e mass
s loss ffrom th
he
po
olar ice
e shee
ets?
Study surface mass
balance and calving
separately to
understand physical
processes and
predict changes, Van
den Broeke et al.,
2009, 2011
How big is the mass loss from the polar ice sheets?
• M
Monthly
thl surface
f
mass balance
b l
and
d yearly
l iice
discharge
Antarctica
Greenland
Ri
Rignot
t ett al.,
l 2008
How does the present and future climatology of the Greenland and
Antarctic ice sheet look like?
JJA near-surface
wind RACMO55
1980 1993
1980-1993
Van Lipzig et al., 2004
Van den Broeke and van Lipzig, 2003
How does the present and future climatology of the Greenland and
Antarctic ice sheet look like?
• Representation
NAO determines
correct atmospheric
dynamics in GrIS
• Good
G dd
dynamics
i no
guarantee for good
near-surface climate
• HadGEM1 and
ECHAM5 best
performance in
Arctic (and Antarctic
– see Connolley
and
dB
Bracegirdle,
i dl
2007)
Franco et al., 2011
What are the mechanisms behind recent observed changes?
31 January 2002
MODIS beelden van NASA's Terra satellite,
National Snow and Ice Data Center, University
of Colorado, Boulder
What are the mechanisms behind recent observed changes?
17 February 2002
What are the mechanisms behind recent observed changes?
23 February 2002
What are the mechanisms behind recent observed changes?
05 March 2002
What are the mechanisms behind recent observed changes?
Increase in Sam index (meridional pressure gradient):
stronger westerlies
Marshall et al., 2003
What are the mechanisms behind recent observed changes?
Increase in westerlies leads to stronger temperatures
at the lee side of the mountain barrier
Marshall
M
h ll ett al.,
l 2006
Orr et al., 2008
Van Lipzig et al., 2008
How does precipitation variability affect the ice core signals?
•
•
•
Full isotopic models under development, but aGCMs’ currently
cannot represent isotopic depletion over inland Antarctica
probably due to inadequate representation of cloud
microphysics (Masson et al., 2008).
Insight in the effect of precipitation variability can help
interpretation of ice cores (e.g.
(e g Krinner et al.,
al 1997; Werner et al
al.
2000, Noone et al., 1999;
Steig et al., 1994; van
p g, 2002;; Helsen et al.,,
Lipzig,
2007)
1. Weight the Inversion
p
with the
temperature
net accumulation
Ti , w
1
= N
∑
1
N
j =1, N
∑
Ti , j B j
j =1, N
Bj
How does precipitation variability affect the ice core signals?
2. Determine spatial relation between Ti,w and the surface
temperature
e pe a u e
T s,core = - 160.19 + 1.59 T i,w
How does precipitation variability affect the ice core signals?
3. Use spatial relation to derive temporal variability in surface
temperature as if it was derived from ice core signals
Insignificant at 90% level
Significant at 99% level
Significant at 90% level
Future model developments
Test of the Polar Weather Research and Forecasting (WRF) model
still points to the need for improving (Hines and Bromwich, 2008):
• the stable boundary layer
• snow surface physics
• sea ice treatment
• cloud physics
Annual average cloud
cover IPCC AR4 AMIP
model simulations
(Bromwich et al., 2012)
Airborne studies of
clouds
l d are conducted
d t d
(Lachlan-Cope, 2010
Future model developments
M. La
azzara,, AMRC
C, U Wissconsin
n-Madisson
AWS and cloud observatory at the Belgian Antarctic base
Future model developments
K-band Radar
AWS
Ceilometer
Infrared Radiation
Pyrometer
Microwave Radiometer
Phase II (to be installed)
AWS and cloud observatory at the Belgian
Antarctic base
N
W
E
S
Accumulation stake line
installed in Jan 2010
x
AWS
Synoptic
Kataba
atic
Gorodetskaya et al, 2012
Synoptic
S
c
winds
W
Future model developments
Summary
• Model have substantially improved during the last two
decades
• These developments have enabled applications of the
models to address pressing scientific questions related to
climate of polar regions
• Further improvements of the models is still necessary