Irina Gorodetskaya, Michael S. Town, Hubert Gallée Laboratoire de Glaciologie et Géophysique de l’Environnement, Grenoble,France EGU, Vienna 23 Apr. 2009 Mechanisms behind synoptic-scale variability in South Pole meteorology from observations and a regional model
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Mechanisms behind synoptic-scale variability in South Pole meteorology from observations and a regional model. Irina Gorodetskaya, Michael S. Town, Hubert Gall é e Laboratoire de Glaciologie et G é ophysique de l’Environnement, Grenoble,France. EGU, Vienna 23 Apr. 2009. - PowerPoint PPT Presentation
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Irina Gorodetskaya, Michael S. Town, Hubert Gallée
Laboratoire de Glaciologie et Géophysique de l’Environnement, Grenoble,France
EGU, Vienna 23 Apr. 2009
Mechanisms behind synoptic-scale variability
in South Pole meteorologyfrom observations and a regional model
acknowledgements:
Gerhard Krinner for support and discussions
Von P. Walden for providing computer time and space
Stephen G. Warren for antarctic cloud discussions
Ells Dutton and Tom Mefford of NOAA-GMD, and BSRN for radiation and meteorology data and advice.
Gorodetskaya, Town, Gallée, LGGE : EGU 2009
•importance of synoptic activity over Antarctica
•data sets and model description
•the climate of the South Pole
•model evaluation: wavelets
•cluster analysis
•conclusions
Gorodetskaya, Town, Gallée, LGGE : EGU 2009
Outline
1911
1960 1970 1980 1990 20001950
1957 1975 2003
surface meteorology/observations
radiosondes
radiation
accumulation
clouds
snow temperatures
NOAA CMDL/GMD
South Pole climate data set: A review
See poster M. Town and V. Walden, Session AS2.4, XY105
Atmospheric model: mesoscale hydrostatic primitive equation model (Gallée 1994, 1995)
Terrain following vertical coordinates (normalized pressure) Turbulence: 1 1/2 closure (Duynkerke 1988) Bulk cloud microphysics (Kessler 1962 and Lin et al 1983 + improvements of Meyers et al. 1992 and Levkov et al. 1992) Solar and infrared radiative transfer scheme (Morcrette 2002, Ebert and Curry 1992) Snow fall included into infrared radiation scheme
Snow model: conservation of heat and water (solid and liquid), description of snow properties (density, dendricity, sphericity and size of the grains), melting/freezingBlowing snow model (Gallée et al, 2001)
FS
FS
FL T4 HLatHSen
Sn
ow
HMelt HFreez
HCond
Tsfc
Pe
rco
lati
on
Liquid water
Blowingsnow
coupling to sea ice, land ice, vegetation...
Horizontal resolution 80 km 33 vertical levels (lowest ~9m, one level each 10 m below 50 m; top = 10hPa) Initial and boundary conditions: ECMWF ERA-40
Modèle Atmosphérique Régional (MAR)
Gorodetskaya, Town, Gallée, LGGE : EGU 2009
The climate of the South Pole
altitude = 2835 m
accumulation rate = 8 cm yr-1
mean temperature = -50oC
Gorodetskaya, Town, Gallée, LGGE : EGU 2009
Sfc air temperature
MAR. ERA40. South Pole. 1994
a
..-65oC
..-45oC
Goro
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GE : E
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Importance of synoptic activity over Antarctic interior
Time series of the five snow accumulation eventsclose to the South Pole (860S, 460W)from acoustic depth gauge
Braaten 2000
Nor
mal
ized
w.e
.A
ccum
ulat
ion
(10-3
m)
Goro
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e, LG
GE : E
GU
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Importance of synoptic activity over Antarctic interior
The 700hPa height and 500hPa wind field at 1200 UTC on Nov 5, 1997
Noone, Turner, Mulvaney 1999
Goro
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allé
e, LG
GE : E
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Directional distribution of hourlynear surface winds during warm and cold events
Isobaric temperature advectionwhen 300 hPa wind is from SW or NW (warm events)and from SE (cold events)
Neff, JGR (104) 1999
Warming eventsCooling events
Down-slope (“East”)Along-slope (“North”)
Warming Cooling
SE
SW
NW
Thermal advection (0C/day)Direction Class Intervals
Nu
mb
er i
n i
nte
rval
Hei
gh
t, m
Goro
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aya, T
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n, G
allé
e, LG
GE : E
GU
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Convolve wavelets of increasing sizewith time series to obtain scaling coefficients.
T(a,b) = w(a) x(t) dt
Wavelets applied to time series:
t-ba
power spectrum
time
b
a
T(a,b)
Wavelets give information in temporal and frequency domains.
Gorodetskaya, Town, Gallée, LGGE : EGU 2009
Model validation : wavelet analysis
Power spectrum (units2/time) Goro
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GE : E
GU
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Variables measuredat South Pole:
Sfc temperature Water vapor pressure (from frost point) Sfc wind speed downwelling LW flux downwelling SW flux
6 hour time step, 1994
5 variables...
Cluster analysis applied to time series: G
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GE : E
GU
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• Sfc air temperature amplitude is good in MAR (both synoptic and seasonal)
• Wind speed underestimated during some warm events
• Increased humidity and LW fluxes during warm events in obs and MAR
Variables simulated by MAR:
Sfc temperature Sfc pressure tropospheric water vapor downwelling LW flux downwelling SW flux U,V near surface U,V at 300 hPa tropospheric cloud liquid tropospheric cloud ice stratospheric cloud ice
6 hour time step, 1994
Cluster analysis applied to time series:
12 variables...
Goro
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allé
e, LG
GE : E
GU
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MAR : 6 meteorological regimes
Tair,
0C
Rad Trop
Hum
Trop
Clds
Strat
Clds
Sfc
wind
300hPa
wind
Cold -60 - - -
Warm-I -40 LW -
Warm-II -45..
-50
LW -
Warm-III -40..
-60
LW -
Summer -20..
-40
SW
LW - -
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
E
NW NE
NE
NE
E
NE
E
SW
SE
NW N
SES
E
SW...
Gorodetskaya, Town, Gallée, LGGE : EGU 2009
7%
24%
54%
11%
4%
Accum,
%
warm events
Sno
w a
ccum
ulat
ion,
mm
.w.e
Inte
grat
ed s
now
,m
m.w
.e
Snow accumulationG
oro
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aya, T
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n, G
allé
e, LG
GE : E
GU
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Con
clu
sio
ns
III. warm events correlated with high stratospheric ice content together with slight increase in tropospheric moisture content
7% snow accumulation
Goro
detsk
aya, T
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n, G
allé
e, LG
GE : E
GU
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Modèle Atmosphérique Régional (MAR): shows good skill in synoptic-scale simulations
Cold events are more or less similar: - low tropospheric humidity, clear sky, low downwelling LW flux - NE-E near surface wind (“inversion” wind) - weak SE wind at 300 hPa
11% snow accumulation
Warm events happen for a variety of reasons:
I. warm air advection from W-SW (West Antarctica) with increase in tropospheric humidity and tropospheric cloud liquid 54% snow accumulation
II. warm air advection from N-NW (Weddell Sea) - slight increase in tropospheric moisture content- no tropospheric clouds but stratospheric clouds form
24% snow accumulation
Plans
Goro
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aya, T
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GE : E
GU
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Extend cluster analysis to the entire period (1994-2000)