Sea Ice Update · 2017. 8. 15. · •Snow cover in Arctic sea ice reduced due to changing...
Transcript of Sea Ice Update · 2017. 8. 15. · •Snow cover in Arctic sea ice reduced due to changing...
Sea Ice Update
Marika Holland and David BaileyNational Center for Atmospheric Research
University of TorontoNovember 2012
NCAR is sponsored by the National Science Foundation
CESM WorkshopJune 2017
8/2/2017 28/2/2017 28/2/2017 28/2/2017 2CESM Workshop June 2016
Marika [email protected]
Run 79. NH Sea Ice
Ann Mean Thickness (Years 72‐91)
Run 36
Run 79
Where we were one year ago
CESM2 Update• Multiple issues have put us behind schedule (see Jean‐Francois Lamarque’s talk yesterday)
• Test runs we will discuss are short (<100 years for PI controls)
• Only showing results from PI control runs• We focus on aspects of the sea ice and heat budgets that seem to be robust across test runs
• Focus mostly on Arctic conditions • Caveat that these are not the final CESM2 integrations and things are still subject to change
CESM2 Update
• Changes have been made to the land ice runoff outside of Greenland and Antarctica
• Heat is now being used from the atmosphere to melt water before it enters ocean
• No longer have excessive (~100m) thick ice in the Canadian Archipelago
NH Sea Ice Extent
Annual cycle of NH Extent
CESM2 Test Runs –
• Typically have a smaller annual cycle
• Less ice in winter than CESM‐LE
• More ice in summer than CESM‐LE
CESM‐LECESM2 TestObs
Arctic Sea Ice – Snow Thickness
Snow ThicknessCESM‐LECESM2 Test
Summer (JAS) Mean Snow Thickness
Arctic Sea Ice – Snow Thicknesshs Arctic Ocean Mean
J F M A M J J A S O N D
0.1
0.2
0.3
0.4CESM‐LECESM2 Test
Snow thickness on Arctic Sea IceArctic Ocean Mean
CESM2 Test Runs –
• Have thinner snow on sea ice throughout the year
• Have snow‐free summers unlike CESM‐LE
• May now have a bit too little snow compared to observations
rain Arctic Ocean Mean
J F M A M J J A S O N D0.00
0.02
0.04
0.06
snow Arctic Ocean Mean
J F M A M J J A S O N D
0.03
0.04
0.05
0.06
0.07
0.08 Arctic PrecipitationCESM‐LE
CESM2 Test
CESM‐LE
CESM2 Test
CESM2 Test Runs
• Less snowfall throughout the year
• More rainfall present throughout year
• Realistic??
Snowfall rate in cm/day
Rainfall rate in cm/day
As discussed in Light et al. (2015) excessive snow cover in summer is related to episodic summer snowfall events
CESM‐LE has excessive
incoming SW Radiation in the
Arctic
CESM‐LE ISCCP
CESM‐LE minus ISCCP
JJA Incoming Surface SW RadiationArctic Surface Heat Budget‐Incoming SW
Arctic Surface Heat Budget‐Incoming SWCESM2 Test RunsIncoming SW Bias is largely alleviated
fswdn
J F M A M J J A S O N D0
50
100
150
200
250
300
W m
-2
Incoming SW Radiation Averaged over Arctic Ocean
CESM‐LECESM2 Test
Diamonds show SHEBA data for a real world reference
• Associated with mixed phase clouds
• Increase in super‐cooled water within clouds, which is more realistic
CESM‐LE has too little incoming LW Radiation in the
Arctic
CESM‐LE ISCCP
CESM‐LE minus ISCCP
Annual Incoming Surface LW RadiationArctic Surface Heat Budget‐Incoming LW
flwdn
J F M A M J J A S O N D
160
180
200
220
240
260
280
W m
Arctic Surface Heat Budget‐Incoming LW
CESM2 Test RunsIncoming LW Bias
is improved
Incoming LW Radiation Averaged over Arctic Ocean
CESM‐LECESM2 Test
Diamonds show SHEBA data for a real world reference
Also associated with simulation of mixed
phase clouds
Arctic Ice‐Ocean Heat Exchange
fhocn_ai Arctic Ocean Mean
J F M A M J J A S O N D
5
10
15
20
25
fhocn_ai Arctic b.e20.B1850.f09_g17.pi_control.all.180-LE
J F M A M J J A S O N D-6
-4
-2
0
2
4
CESM2 Test minus CESM‐LE
CESM‐LECESM2 Test
CESM2 has
• Less ocean heat flux to ice in summer – due to decreased incoming SW radiation
• More ocean heat flux to ice in winter • Due to ocean transport • May not be robust as
ocean is still spinning up
Antarctic Sea Ice Extent
Annual cycle of SH Extent
CESM2 Test Runs –
• Typically have a smaller annual cycle
• Less ice all year compared to CESM‐LE
• Captures min in Feb
CESM‐LECESM2 TestObs
Antarctic Sea Ice ThicknessCESM‐LECESM2
Test Run
CESM2 Test Runs –
• Improved thickness pattern in SH
• Thicker ice present in Weddell Sea
Summary• While CESM2 is not yet completed, some robust features are present in polar regions
• Snow cover in Arctic sea ice reduced due to changing precipitation
• Radiative fluxes over sea ice are much improved • Less SW and more LW• Associated with cloud changes
• Antarctic sea ice extent is reduced (improved) and thickness pattern is improved
Questions?