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6/25/2019 - David P . S chneider (NCAR ); Jan Lenaerts (CU ); J ennifer Kay (CU ); Matthew G entry (CU ); C la ra Deser (NCAR )
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6/25/2019
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David P . S chneider (NC AR ); J an L enaerts (C U); J ennifer K ay (C U); Matthew Gentry (C U); C lara
Deser (NC AR )
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It snows a lot in Antarctica and it’s cloudy
MODIS mosaic image from Jan 27, 2009, earthobservatory.nasa.gov
Annual SMB (mostly snow): ~2000 Gt/yr
~6mm sea level equivalent
Clouds!
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Meanwhile, Antarctica is loosing mass…
IMBIE Team (2018), Nature Average rate of mass change over 25 years:
-109 Gt/yr
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-change in S MB over ~40 years
IMBIE Team (2018), Nature
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CMIP5 multi-model ensemble Precip could increase by ~45% or not much at all!
RCP 8.5
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Kay et al., 2016
modified shallow convection scheme increases supercooled
cloud liquid, brightens low-level clouds
CESM 1.1 ‘LENS’ CESM 1.1 ‘CLDMOD’
ASR = absorbed shortwave radiation at TOA
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Large Ensemble “LENS” 1850 controlYear 1
year 2000
CLDMOD 1850 control
CLDMOD 1850 control (same as LENS, except for the aforementioned parameterization change + tuning)
Year 1year 400+
10 “low ozone”ensemble members50 years each
10 “low ozone”ensemble members50 years each
overlap period used to calculate responses (first 5 years excluded)
overlap period used to calculate responses(first 5 years excluded)
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Prescribed ozone change over 60S-90S
”WACCM” ozone
• relatively strong Antarctic ozone hole; compares well with obs (Marsh et al., 2013)
• ozone data is global, includes troposphere
• control runs have an 1850s ozone climatology
• “low ozone” is a monthly varying climatology from years 1996-2005
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-mean responses (DJ F )
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-mean responses (DJ F )
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-mean responses (DJ F )
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P recipitation & Z500 responses (DJ F )
LENS CLDMOD CLDMOD-LENS
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P recipitation response (annual)
LENS
+ 34.1 Gt/yrCLDMOD
+109.6 Gt/yr
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Z500 & interbasin correlationshigh-low precip years) (basin8) Basin 13
CLDMOD-LENS
Fyke et al., (2017), The Cryosphere
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LENS CLDMOD CLDMOD-LENSTS
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LENS CLDMOD CLDMOD-LENS
TGCLDLWP
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LENS CLDMOD CLDMOD-LENS
LHFLX
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• A significant increase in Antarctic precipitation in response to ozone forcing is enhanced in a cloud-modified version of CESM1.1. • CLDMOD average increase: 110 Gt/yr• LENS average increase: 34 Gt/yr; consistent with Lenaerts et
al. (2018)
• Dynamics: A poleward shift in the storm track, combined with amplified stationary waves as the flow interacts with Antarctic orography
• Thermodynamics: Increase in SSTs, tropospheric warming, and evaporation in CLDMOD, driven in part by a more positive shortwave cloud feedback
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-CLDMOD-LENS (DJF)
Precip & Z500 (total) Precip & Z500 (stationary component)
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LENS CLDMOD CLDMOD-LENSCLDTOT
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Shortwave radiation biases– a key source of uncertainty?OBS (CERES) CESM 1.1
ASR
OLR
RT
Obs.&
Diffs
2000-2014
Figure: courtesy K Trenberth & J Fasullo
S. Ocean – too much
Tropics – too little
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Meanwhile, Antarctica is loosing mass…
• Ice shelf thinning• Calving• Acceleration of outlet glaciers
