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

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

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.

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).

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.

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.

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

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

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

Northern Hemisphere Wintertime Atmospheric Variability Mean & Standard Deviation SLP & Z500 Years 1-799 Variability Patterns (EOFs) (from Mark Steven’s Web page) http://www.cgd.ucar.edu/cms/stevens/ccsm3/ccsm3.T42.html Years 750-850

Mean SLP (mb) DJF Too strong Zonal circ.

Standard Deviation SLP (mb) DJF

Standard Deviation Z500 (m) DJF

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

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

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

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

Pacific Decadal Oscillation Index: PC1 of North Pacific SST

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

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

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.

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

Total Cloud (%) JJA

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

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

Mean Z500 (m) DJF