some observations from observing antarctic weather and climate · 2019. 12. 23. · according to...
TRANSCRIPT
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Some observations from observing
Antarctic Weather and [email protected]
Manager Antarctic Meteorology
Co-authors:
Andrew Klekociuk (AAD), Simon Alexander (AAD), Jonathan Willie (Universite Toulouse); Ben
Galton-Fenzi (AAD), Tas Van Ommen (AAD), Alain Protat (BoM), Phil Reid (BoM), Jan Lieser
(BoM), Fiona Smith (BoM), Chris Tingwell (BoM)
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Poleward of Latitude 40 deg
Upper Air
Surface Synop
N of 40N S of 40S
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Sensor height is an issue
(snow accumulation)
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Maintenance is an issue
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Remoteness is an Issue
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Optical Satellite: Worldview
Radar Satellite: TerraSAR-X
Safe field operations: Calibration (right) tests of
satellite images (left) with helicopter radar (bottom-
right)
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Antarctic staffed stations + AWS
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Antarctic staffed stations + AWS + POLENET
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Cold Temperatures
The lowest measured air temperature (2m) on Earth is −89.2°C (−129 F)
on 23 July 1983, observed at Vostok Station in Antarctica
(Turner et al., 2009, https://doi.org/10.1029/2009JD012104).
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Ultralow Surface Temperatures in East Antarctica From Satellite
Thermal Infrared Mapping: The Coldest Places on Earth
Scambos et al 2018 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL078133
Geophysical Research Letters, Volume: 45, Issue: 12, Pages: 6124-6133, First published:
25 June 2018, DOI: (10.1029/2018GL078133)
Using TIR temps from Landsat and Modis:
The lowest temperatures are found in
small (<200 km2) topographic basins of
~2 m depth above 3,800 m elevation.
Approximately 100 sites have observed
minimum surface temperatures of
~−98°C during the winters of 2004–2016.
Comparisons of surface snow
temperatures with near‐surface air
temperatures at nearby weather stations
indicate that ~−98°C surfaces imply
~−94± 4°C 2‐m air temperatures.
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Dome C tall tower measurements
http://polarmet.osu.edu/AMOMFW_2016/0608_0840_Vignon.pdf
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Minimum Wind Speed
for Sustainable
Turbulence
2 regimes:
Diffusive (left) and turbulent (right)
http://polarmet.osu.edu/AMOMFW_2016/0608_0840_Vignon.pdf
Note BL depth… how many
vertical layers does NWP resolve?
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aerodynamic
adjustment of sastrugi
Sastrugi are a direct manifestation of drifting snow and form the main surface roughness elements.
In turn, sastrugi alter the generation of atmospheric turbulence and thus modify the wind field and
the aeolian snow mass fluxes.
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aerodynamic
adjustment of sastrugi
In summary, for friction velocities (wind speeds) around 1 (20)m/s and above, the sastrugi streamlining timescale can
be as fast as 3 h. For a wind flow initially aligned with the sastrugi, a deviation of 20–30 deg from the streamlining direction
has the potential to both increase the drag cooeficient CDN10 by 30–120% and to significantly reduce (up to 80 %) the aeolian
snow mass flux, even under increasing friction velocity.
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Tsurface Trends from READER
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(1970-2017)
Tmean °C/century
-0.2-0.1
+0.0
-1.5
Mirnyi-0.7
Dumont D’Urvlle
(-0.4)
(+0.5) (+0.8)
(-0.5)
(+0.4)
(-1.5)
Values in brackets 1970-2009 when analysis/homogenisation of temperature completed.
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Jones 2016 dataset
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(1970-2017)
Rainfall mm/decade
+63.4(+64.6)
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Home of the Blizzard
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Solid Precipitation Intercomparison Experiment
(SPICE)
http://amrc.ssec.wisc.edu/meetings/meeting2015/presentations/AMOMF-
Day1/BAS%20precipitation%20measurements.pdf
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Antarctic Precipitation System
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Double Fenced Reference Site
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(King et al. 2012)Mass Accumulation 2002-2010
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Accumulation at Dronning Maud Land
https://www.mmm.ucar.edu/sites/default/files/terpstra_transport.pdf
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Episodic snow events
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Atmospheric Rivers
Precipitable water composite
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The Dominant Role of Extreme Precipitation Events (defined at the
heaviest 10% of daily precipitation amounts) in Antarctic Snowfall Variability
Geophysical Research Letters, Volume: 46, Issue: 6, Pages: 3502-3511, First published: 19 February 2019, DOI: (10.1029/2018GL081517)
Fig. 1 The contribution of HPEs tothe annual precipitation. Thenumber of days of the highest,ranked precipitation that gives 50%of the annual total. Darker coloursindicate where the HPEs are moreimportant.
(From Turner et al. 2019)
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Total sea level rise equivalent per Basin
Fricker et al (2019)
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KEY SCIENCE QUESTIONS
▪ What will be the rate and magnitude of
sea level rise from Antarctica,
particularly over the coming decades?
▪ When are the points where abrupt or
large changes in the ice sheet become
committed and what are the key regions
susceptible to rapid change?
▪ How will a warming atmosphere and
oceans drive evolution of the ice sheet,
and what are the feedbacks with other
parts of the climate system?
IPCC. Global average: 20 cm of sea level leads to 100 fold increase in flood frequency. A 1 in 100 year flooding event occurs annually. Regional variability (left)
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Sea level monitoring
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Global total sea level rise (SLR) estimates exceeding 2m by 2100 now lie within the 90% uncertainty bounds for a high emission scenario according to NOAA study (Structured Expert Judgement)
…We find it plausible that SLR could exceed 2 m by 2100 for our high-
temperature scenario, roughly equivalent to business as usual (ie +5 C by
2100). This could result in land loss of 1.79 M km2, including critical regions of
food production, and displacement of up to 187 million people. A SLR of this
magnitude would clearly have profound consequences for humanity.
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KEY UNCERTAINTIES
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Monitoring the ice sheet and contributions
to sea level
A range of techniques are used to understand
the vulnerability and behaviour of the Antarctic
Ice Sheet, including field deployments of
instruments (GPS and phase sensitive radar
to measure ocean melting, strain thinning and
firn compaction; right), active seismic and
other on ice traverses (bottom) remote
sensing from satellites and airborne
geophysics surveys.
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Numerical weather processes – static sea ice within
NWP
Zhaohui Wang
An increase of 1.4 Million square kms
After 10 days
A decrease of 1.7 Million square kms
After 10 days
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Polar Prediction Matters
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Antarctic contribution to YOPP-SH
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ACCESS-G model performance during YOPP-SH
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The importance of upper-air observations
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45
Forecast Sensitivity to Observations (FSO) in ACCESS-G Global NWP System
Sondes SYNOPS
Neutral
Mostbenefit
Mostbenefit
Neutral
Detrimental
FSO: a technique which projects error reduction in a +24 hour NWP forecast (when compared to a +30h forecast) onto all assimilated observations. FSO impacts can be aggregated by station, observation type, etc. Forecast error is measured globally in this case.
Negative FSO impacts (yellow-red colours) represent stations whose observations are doing the most to reduce 24 hour forecast error.
Sonde and SYNOP observations from remote stations, and especially Antarctic stations, do most to reduce forecast error.
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About 85% of all data used in forecast models are from polar-orbiting satellites and these attribute to nearly 60% of the reduction in forecast error, chiefly via:
o Microwave sounders o Hyperspectral infrared;o AMVs (to a lesser degree)
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Usage of channels sensitive to the lower troposphere is limited
because of inability to forward model or interpret data
Surface-sensitive and lower tropospheric channels cannot be used over
ice and snow surfaces at the present time
Upper tropospheric channels have excellent polar coverage
Observations from the ATMS microwave sounding instrument used in an ACCESS-G3 configuration
in a six-hour assimilation cycle
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(Rubino et al., 2013)
Carbon cycle reconstruction
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Australian rainfall teleconnection: SWWA and snowfall
Australian rainfall teleconnection: Eastern Au & salt (winds)
(Vance et al., 2013; 2015)
(van Ommen & Morgan 2010; van Ommen, in prep)
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Past Sea Ice Extent
Sea ice reconstruction
(Curran et al., 2003; Curran in preparation)
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CMIP5
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Global Mean Cloud Droplet Concentration
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4x daily radiosondes all summer = ~600 launches
Aerosol Sampling
Cloud, radiation & precipitation instruments on monkey island
Radiosonde
Radars
Photos all © Doug Thost, Australian Antarctic Division
US DoE ARM MARCUS (Measurements of Aerosols, Radiation, and Clouds over the Southern Ocean) campaign
Summer 2017/18 aboard Aurora Australis – three round-trips Hobart – Antarctica; one Hobart – Macquarie Island round-trip
YOPP-endorsed
W-band radar, radiosondes, lidar, ceilometer, Parsivels, radiometers, aerosol suite etc.
All data publically available
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SOCRATES flights
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Davis Ozone Measurements (AAD-BoM-CAMS)• Weekly ozonesonde flights since 2003 are used for studies stratospheric
dynamics and trends.
• The 2019 stratospheric warming strongly influenced ozone in early Sep.
• Small but significant positive trends are apparent in Sep-Oct stratospheric ozone.
Sep-Oct linear trends by height 2003-2018 (Tully et al., in prep.)
21-24 km ozone highlighting unusual behaviour in Sep-Oct
2019
Summary of 2019 measurements showing weak effects from the ozone hole and strong overburden in Sep.
A. K
leko
ciu
k
A. K
leko
ciu
k
M. T
ully
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Gravity Wave Analysis of Radiosonde Data
• Over Davis, gravity waves propagate close to the horizontal and are strongly advected by the background wind in the wintertime.
• About half of the stratospheric waves between early May and mid-October propagate downward.
• A source due to imbalanced flow that is distributed across the winter lower stratosphere best explains the observations.
Climatological percentage of (a) upward and (b) downward propagating gravity waves above Davis for 2001-2012.
Murphy et al. (2014, JGR 119, doi:10.1002/2014JD022448)
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Observation-Model Comparison of Winds
• UM simulations are performed at differing fine horizontal resolutions for a case study of orographic gravity wave (OGW) activity observed with the Davis VHF radar.
• Simulations improve at finer resolution and indicate synoptic winds and coastal topography interact to form OGWs.
• Temperature fluctuations induced by OGW influence local cloud presence.
Case study for 18 Feb 2014: (a) The time-height hourly VHF radar horizontal wind field. (b–d) The same but for UM simulations of differing horizontal resolutions.
Alexander et al. (2017, JGR 122, 122, doi:10.1002/2017JD026615.)
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Antarctica is:
• Sparsely observed;
• Hostile to people and instrumentation;
• A complex and unique environment that requires improved
representation in NWP and GCM;
• Fundamental to improved predictive services globally.
Conclusions
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