the impact of the ozone hole on the antarctic surface...

The impact of the ozone hole on

the Antarctic surface energy budget

G.Chiodo¹, L.Polvani¹ and M.Previdi²

1.Applied Physics and Applied Mathematics, Columbia University, NY

2.Lamont Doherty Observatory, Columbia University, NY

1

-Poleward shift of the tropospheric Jet (SAM increase)

-Year-round loss of sea-ice around Antarctica

Polvani et al 2011

Bitz and Polvani 2012

The impact of the ozone depletion on

Southern Hem. Climate is well known

2

Cooling over E-Antarctica, and warming of Peninsula (SAM-driven,

…so “indirectly” induced.)

What is the (direct) radiative effect of ozone depletion?

Thompson and Solomon, 2002

Did ozone depletion have an impact on

Antarctic climate?

3

Direct (radiative) impact of ozone depletion

Ramanathan and Dickinson, JAS 1979

Ramaswamy et al, NAT 1991

-Cooling of the troposphere mostly

due to reduced downward LW

emission, but surface warming due

to increased SW heating.

-Solar forcing change from idealized O3

forcing offset by reduced LW emission

resulting from stratospheric adjustment.

-What is the impact of a realistic O3 forcing in a comprehensive

GCMs, with dynamic ocean and land ice? 4

Experiments with WACCM4 and CAM5-LE

WACCM: 6 members with O3 depletion (“historical”)vs 6 members without (“fixedODS”)

CAM5-LE: 8 members with imposed O3 depletion from WACCM (“historical”) vs 8

members with O3 fixed at 1960 levels (“fixO3”)

400

300

200

100

1960 1970 1980 1990 2000

DU

Column ozone (SON)

5

Clear-sky downward SW radiation

WACCM SON CAM5

DJF

6

Full-sky downward SW radiation

SON CAM5WACCM

DJF2 W/m² SW-forcing, after clouds are taken into account.

Does O3 depletion warm Antarctica?

7

O3-hole effect on SAT

DJF

SONCAM5WACCM

No detectable effect of ozone depletion over Antarctica.

…why?

8

GHG-effect only (long term d LW rad increase)

The O3 depletion does not induce decrease in downwelling

LW radiation at surface, so the SW forcing dominates!

LW compensating SW forcing?

Surface downwelling LW radiation (SON) CAM5WACCM

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Why does the SW forcing have no impact

on Antarctic SAT?

-Slight increase in surface albedo in both models compensates

the 2 W/m2 SW forcing, leading to 0-change in net surface SW!

CAM5WACCM Clear-sky albedo (SON)

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Is the surface albedo related to changes in

large-scale snowfall?

Increase in DJF snowfall in WACCM, and to lesser extent, in CAM5.

CAM5 WACCM DJF LS snowfall rate

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Does DJF snowfall affect surface

albedo in other seasons?

-In CAM5, a smaller change in albedo-precip is needed to counter act increased

SW forcing than in WACCM (background albedo is higher).

-Surface albedo in CISM is f(snow age + depth). Since there is no melting

in Antarctic interior, a change in DJF precip can alter albedo all-year round

CAM5WACCM

LS snowfall rate LS snowfall rate

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Conclusions

1) O3 depletion leads to a detectable increase in SW forcing

over Antarctica.

2) The SW forcing is balanced by an increase in large-scale

snowfall, possibly associated with O3-driven SAM increase,

which make Antarctica “brighter”.

3) Without increase in albedo, Antarctica would receive a net

SW forcing of 0.4 W/m² from O3-depletion, which, if

unbalanced and sustained over period of 25 years, could

have significantly altered the Antarctic energy budget.

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Total cloud cover

Disparate long-term trends in clouds in WACCM and CAM5.

In WACCM, increase is mostly due to high-clouds (see Grise et al., 2013)

Increase in SW forcing not related to long-term changes in cloud fraction or

cloud properties! 14

Does O3-hole induce zonal asymmetries in SW-heating?

15

Karen Smith, private communication

16

10/26/2015

Does O3-hole “cool” E-Antarctica?

McLandress et al., 2011

17

Grise et al., 2013 18