1. Extratropical Climate and Variability in CCSM3
Michael Alexander & James Scott
NOAA-CIRES
Climate Diagnostics Center
Clara Deser
NCAR

2. Overview: A Broad Survey
Long term means and variance
SST, Net Surface Heat Flux, Mixed Layer Depth
Upper Ocean Processes
Winter-to-winter SST anomaly recurrence: the “re-emergence mechanism”
Winter Atmospheric Circulation
Mean & Variance SLP and Z500
Patterns: NAO/AO, PNA, PDO

3. Annual Mean SST (ºC) Years 1-799
Equatorial cold bias much improved: diurnal cycle, chlorophyll. Still have warm bias along coastal upwelling regions as in CCSM2. Generally too cold in higher latitudes, may be related to a too vigorous atmospheric circulation.

4. Annual Mean Net Surface Heat Flux (W m-2)
>0
into
ocean
Generally
anti-correlated
with SST biases
Heating the equatorial cold tongue, oceanic western boundary currents (Kuroshio, Gulf Stream) venting heat to the atmosphere. Heat flux biases are generally anticorrelated to SST biases: too much heat released to atm where SSTs are too warm (maritime continent, WBCs, coastal upwelling regions).

5. Monthly Surface Temperature Standard Deviation (C)
Too
large
CCSM
Too
small
Max variability along KEX and Gulf Stream and in the equatorial Pacific, as observed. KEX and GS are too variable in model compared to obs and too variable in CCSM3 compared to CCSM2.

6. March Mixed Layer Depth (m)
Generally
deeper than
“observed”
March Mixed Layer Depth (m)
CCSM3
Levitus
Peter Gent pointed out the importance of MLD in how much heat and CO2 the ocean uptakes from the atm.
Here is MLD at its deepest during the seasonal cycle (NH). MLD too deep in WBC regions and along subduction pathway and throughout the tropics.

7. Annual Cycle of Temperature (ºC) & MLD Kuroshio Extension Region: 25ºN-45ºN,165ºE-175ºW
CCSM
Levitus
May
May X
March
Too deep in winter, but good in summer and good seasonal cycle; not warm enough in summer.
March

8. Re-emergence in the Kuroshio Extension Region Lead-lag Correlations between T´(month,depth) and T´ in summer at depth
0 m
60 m
120 m
180 m 1 2
summer MLD 3
0.3
0.6
0.6 T’
Depth (m)
Central North Pacific region is 25-45N, 165E-175W
Note correlations were computed at grid points and then averaged
Mar Sep Mar

9. Generalized Re-emergence: Local Lead-lag Correlations of SST with T’ in summer at depth along 42º-52ºN
Feb+1
Sep+0
Apr+0
SST Lags
Time
SST Leads
Correlations are computed at each point (1 x 1 grid) and then averaged between 42 and 52N

10. Northern Hemisphere Wintertime Atmospheric Variability
Mean & Standard Deviation SLP & Z500
Years 1-799
Variability Patterns (EOFs) (from Mark Steven’s Web page)
Years

11. Mean SLP (mb) DJF
Too strong
Zonal circ.

12. Standard Deviation SLP (mb) DJF

13. Standard Deviation Z500 (m) DJF

14. North Atlantic Oscillation (NAO) EOF 1 500 mb Height (m) DJFM
CCSM3
46.8%
NCEP
49.4%

15. Pacific Variability (PNA) EOF 1 500 mb Height (m) DJFM
CCSM
38.4%
NCEP
40.1%
Note one could flip the sign on one of these for a better comparison

16. Arctic Oscillation: SLP EOF 1
NCEP
CCSM3
31.5%
33.7%

17. Pacific Decadal Oscillation 1st EOF of Monthly North Pacific SSTA
24.5%

18. Pacific Decadal Oscillation Index: PC1 of North Pacific SST

19. “Pacific Decadal Oscillation” T42 Control Run years 100-500
r (1 yr) = 0.3

20. “Pacific Decadal Oscillation” T85 Control Run years 100-309

21. Summary Many processes are simulated reasonably well:
e.g. North Pacific SST “Re-emergence”
NAO
Other processes differ somewhat from the real world
e.g. PNA (AO?)
Hope these preliminary findings will motivate you to have a closer look.

22. Correlation of PDO Index with TS and SLP
CCSM3
TS is the surface temperature
Note should invert sign for either NCEP or the CCCSM to compare them.
Note Correlations in NCEP extend much deeper into the tropics
NCEP

23. Total Cloud (%) JJA

24. Annual Cycle of Monthly Mean & Standard Deviation of SST (°C) along 42ºN
CCSM3
NCEP

25. Temperature Variance (°C2) of Annual Means at 200 m
CCSM3
White
Variability is based on annual anomalies (at least in the model).
Note I tried to match the shading with Figure 1 in Lysne and Deser (2002):
Grey shading in both marks the 0.1 contour, hen the contour interval is .4 starting at 0.4
White is the same as SIO in L&D while Levitus is the same as WOA98
In the N.H. the two more variable areas. 1 northwest of Hawaii and the other off the
West coast correspond to subduction pathways in the model
Levitus

26. Mean Z500 (m) DJF