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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 )

6/25/2019

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!

6/25/2019

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

6/25/2019

CMIP5 multi-model ensemble Precip could increase by ~45% or not much at all!

RCP 8.5

6/25/2019

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

6/25/2019

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)

6/25/2019

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

6/25/2019

Meanwhile, Antarctica is loosing mass…

• Ice shelf thinning• Calving• Acceleration of outlet glaciers