Seminar in Atmospheric and Oceanic Sciences
Seminar in Atmospheric and Oceanic Sciences ATOC 6020
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This 30 page Class Notes was uploaded by Jon Johns on Thursday October 29, 2015. The Class Notes belongs to ATOC 6020 at University of Colorado at Boulder taught by Baylor Fox-Kemper in Fall. Since its upload, it has received 18 views. For similar materials see /class/232045/atoc-6020-university-of-colorado-at-boulder in Marine Science at University of Colorado at Boulder.
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Date Created: 10/29/15
Ocean Mixed Layer Dynamics and its Impact on Climate Variability Michael Alexander Earth System Research Lab httpwwwcdcnoaaqovpeople michaelalexander Seasonal Cycle of Temp amp MLD the Northeast Pacific 50 N 145 W 30 A 60 E v C 4 8 D 90 120 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Climetczlegical Mixed Layer Depth m C 303 90E 120E 150E 180 150W 20 60W 30W 0 1 JEl J 50 100 150 200 250 300 30 400 450 50 600 b mld m Levitus Clim Sep 60N 39 39 30N o 303 90E 120E 150E 180 150w 120w 9w 60W 30w 0 1 1 quot 1 15 0 45 60 75 90 1051015150 Vertical Flux entrainment and MLD h Entralnmmt To pull or draw along after ltself w gtgt w Haney et al 1983 Alexander 1992 w from Turbulent Klnetlc Energy TKE equatlon Nuler ac Kraus 1977 Gaspar 1988 wnendeepenrn htWs39hVgt w MhBrD DrS ere M Mechanlcal Turbulence wk am in B Buoyancy ForclngQmEP D Dlsslpatloneh Dr DensltyjumpatbaseoftheML s Shear across ML not In all models wnensnoalrng w 0 no delrarnrnenc n reforms closer to the surface n M B e Mean ML Budget terms Wm392 in January From an AGCM couple to a mixed layer ocean model V b V wvw o 4 Surface Flux We 2 o f 2 39 g an 8 we 50 n e A Qnet 4O 50 h 39 I 224 i a r a 30 r Egan a X 2039 9nn lg 50 L t 10 4 120E 150E 180 150W 120W 90W 60W 0 Ekman Qek 150w 120w 7O lt Entrainment a szve 40 30 C 3 V W 3953 1 k i w HEB XW inn ii HEB Hl EEG 42 8 ififfi39 4m 90W 60W HEM 180 150W 120W Mean Mixed Layer Budget terms Wm2 in August Qnet CLIIVI AUG Wm2 7O w39w x GV mS b ay 23 Eo f 5 60 r f n P 7 v 4 39 7 39 39 39 i V we 50 1 3 A 39 4 39 1 39 100 39 4039 100 7quot 30 V 20 r r 10 180 150w 120w 90w 60W 0 5O 0 50 100 150 200 Q k CLIM AUG ltWm2 gt 39 j335 V2ltE l JfJ b 0 120E 180 150W 120W 1020 20 10 o Qwe CLIM AUG Wm2 7O w w39wxia m a Miss a quota 30 60 Pk P 3 g x i 39 I 53 V 50 Dr Ii 3 e g 1 43 K4 5 39 YEW f 39 L a 39 39 w V 30 O391 o I 2039 3O quot quot 2 am quot 120E 7505 180 150w 120w ow 60W 0 ltQi 8O 7O 60 50 4O 3O Standard Deviation of Fluxes in August 70 52 quot39 i A 60 Qnet 5O 40 W m392 30 20 10 7O 60 Qwe 50 40 30 20a 39 3C E 391 5C E 1 3 39 50W E39C39 W 9039 60W NW C QWe Qnet2 05 in winter Terms in the SST39 heat budget role in rapidly warming temperatures Expand variables into time mean 39 and departure C n 1h AT TbTm I 8T C0mposite of 6 components on a m OCm0n 20 70 N t 12 1 08 06 04 02 07 o2 I I I I I I I I I I JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC O Q IJCU EI IQ n39 QT Ipcun WeAT W 117 9601 We IIV A EFTMVI Observed Standard Deviation of SST Anomalies C 65N 60N 55N SON 45N 4ON 35N 3ON 25N ZON 120E 140E 7 180 160W 65N 60N 55N 5ON 45N 40N 35N 3ON 25N ZON 120E 140E 180 160W The Reemergence Mechanism Qnetj 7200 Namias and Born 1 970 1974 JAN FEB MAR ARR MAY JUN JULUGEP OCT MOM DEC JAN FB MAR V nter Surface ux anomalies Create SST anomalies which spread over ML ML reforms close to surface in spnng Summer SST anomalies strongly damped by airsea interaction Temperature anomalies persist in summerthermocline Reentrained into the ML in the following fall and winter Alexander and Deser 1995 JPO Alexander et al 1999 Reemergence in three North Pacific reoions a lan Mar May Jul Sep NewI Jan Mar Regression between SST anomalies in AprilMay with monthly temperature anomalies as a function of depth depth m Reglons E 39Vr A t J a Iquot 13 MN 39 39 entral IWeat JON Central 3 East 3 39le 15hr 1813 16m 1439nw iz39nw depth m Alexander et a1 1999 J Climate a Jan Mar May Jul Sep N09 Jan Mar North Atlantic Regional Time Depth EOFs 48 quot 50w 30W 10w Remote reemergenceTemperature anomalies advected by currents de Coetogon and Frankingou 2003 J Climate Impact of reemergence on SST Persistence Extending the Stochastic SST Model Stochastic Model for SSTs Hasselmann and Frankignoul 1977 Heat uxes associated with weather events random stochastically force ocean Ocean integrates forcing slowly developing SST anomalies Heat uxes damp these anomalies dT pch quot F AT dt F forcing A linear damping coef cient rr exp trpch r autocorrelation at lag 395 Originally h set as a constant Single Depth Entraining Atmosphere lF39 MT F39 1T Tr Illilixed l T ayer 1 T I l Ocean I Interior Summer Winter Winter eff SST Autooorrelation wwo variable MLD North Atlantic Monthly SST Log Correlation 50N 65N 6OW lOW 1 1 7777777777 7777 1 1 1 1 1 635532 3 CBS 1 3 3 1 0 quot39 quot 39 quot39r392 7 fiTquot quoteg quotquot rquot 39 39 39 39 rquot739139 3903 1 1 1 ijgfj 31 N 1 1 1 07 r r r r r r r r r r r r r r r r r r r r r r r r r r r r7 r7ENEairj 75 07 1 MLM quotlf775 05quotH39 3 f391quotVV 139 37 1quot 39 39139139w39xr 7201706 At quot 05 r r r r r r r r r r r r r r r r r r r r r r r rm r r r r r wwr r r r r r r r r r r r r r r r rr 75 05 1 1 1 1A 1 A 775 04 r r r r r r r r r r r r r r r r r r r r r r r r r r r r r 7 r r r r r r r r r r r r r r r r r r r r r r47 20 04 1 1 1 03 r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r rwrrwrrrrer r r r 77 703 3 3 3 3 3 3 1 h 50m 0239quot393quot393quot39fhm0171th391y39 02 1 1 MLM 1 1 1 1 1 1 1 1 1 1 1 1 1 1 01rvrrrrawrampw1rwrrarrwraw 1w1rwrrriwrawrampw1rrr01 0J F M A M J J A s o N D J F M A M J J A 30 YrO Yr 1 NPAC MLD Obs and Entroining Model 50 ntralnlng 100 lode EM 150 dashed 200 3 Feb Apr Jun Aug Oct Dec Log Autocorrelotion from March 0 8 I Heat content lEM 39 l 06 04 02 QeS SST OBS O2 I l3 l Jun Dec Jun Dec Jun Dec Yr 0 Yr 1 Yr 2 Deser et al 2003 J Climate Heff winter MLD for interannual variability in a stochastic model Do the reemerging SST anomalies impact the atmosphere First examine relationship between atmospheric circulation and SSTs in the Atlantic to determine leading pattern of SSTs forced in winter and see if they reemerge Then use AGCM NCAR CAM2 coupled to a mixed layer ocean model predicts h Cassou Deser and Alexander J Climate 2007 Atmosphere forcing the ocean in winter NAO amp the Atlantic SST tripole March SST EOF1 shade Regressed JFM SLP contour PC time series March SST bars JFM MSLP line 1950 1960 1970 1 980 1990 2000 Correlation063 NCEP MSLP 19502003 eg Deser and Timin 1997 J Clim Reemergence of SST Tripole Leading EOF of March SST Autocorrelation of EOF PC time series r Lag in months From March MJSDMJSDMJSDM 10 1IIii A 06 04 00 Level of significance Correlation quotlquotlquotlquot quotlquotlquotlquot quotIquotlquotlquot39 o 3 6 9121518212427303336 Lag in months From March ERSSTVZ Datasets 19502003 07 05 03 01 01 03 05 07 Watanabe and Kimoto 2000 Timin et al 2002 Deser et al 2003 J Clim De Coetlogon and Frankignoul 2003 all J Climate Experimental Design FMA Sea Level Pressure contours JAS temperature at 50m depth shading m nk Temperature Degrees C 049 035 O21 007 007 021 035 049 39 Use SVD between SLP Winter amp Ocean Temp summer in the control run to obtain ocean conditions associated with NAO at depth in the following summer 39 Specify subsurface 40450m temperature anomalies on August 1 39 Run model integrations for 1 year Aug 1 July 31 with different initial atmospheric conditions 39 60 runs with positive polarity 39 60 with with negative polarity 39 Response ensemble average of the positive negative integration Timing of the Reemerging Signal Evolution of the REM anomalies over a year starting in August 15 Section 60 400W from 25 to 68 N Depth m 30 50 75 100 I25 150 200 1 August 1 E c Q 93 w 0 x 3 390 D i Y T i T I SON 4SN SON 15 O9 O3 03 09 15 21 ML heating rate 1 e7 Cday ML heating rate 1 6397 Cday Labrador 20 16 12 539 3 390 08 2 9 C 04 a 00 9 O4 l I I I I l I l 1Sept10ct 1Nov1Dec 1Jan 1Feb1Mar 1Apr 04 i l 04 Winter NDJFM Sea Level Pressure Response Forcing A SLP Response Modest 20 but signi cant SLP response that acts as a positive feedback eg in this model reemergence enhances the wintertoWinter persistence of the North Atlantic Oscillation 21 15 09 03 03 09 15 21 Relation to Observations Lag Autocorrelation of the detrended 3month observed NAO Index Yr2 Yr1 NDJ2 DJF2 JFM2 NDJ1 DJF1 JFM1 011 The Model results indicate that reemerging tripole SST anomalies favor the same phase of the NAG that created them the previous winter Summary Entainment amp concept of MLD important for SST evolution Eg SST anomalies larger in summer than winter due to shallow MLD Reemergence Adds predictability for SST and potentially for the atmosphere as well Extends the stocashtic model for SSTs Also occurs for salinity Reemergence extends oceanic impact of atmospheric teleconnections Other roles for mixing Interaction with the deeper ocean Subduction ML water leaves the surface Rossby wave propagation to the Kuroshio region Remix temperature anomalies due to thermocline variability back to the surface Biological Bring nutrients to the surface if not enough nutrient limited Mix phytoplankton if too much light limited Additional Slides More on the experiment of reemergence in the Atlantic Rossby waves that are 1 What is the oceanic reemergence 2 Surface signature of reemergence in the Labrador Sea Autocorrelation of the Labrador SST time series Starting from March eg for lag1 March and April time series are correlated for lag 2 March and May etc Sea Surface Temperature Lag in months From March MJSDMJSDMJSDM lllllll i 39 10 I V quot 39 39 i 39 r quot J x 06 s c 39 9 x E a 39 t 04 O s o Levelof significance 0 ERSSTV2 Datasets 19502003 0 o s 1 3 7111519 23 27 3 0369121518212427303336 Lag in months all months considered Deser et al 2003 JClim Autocorrelation of the Labrador SST time series all months considered eg for lag1 Jan50 eb50 3ecoo values are correlated with Feb50 Vlar50Jan01 values AtmosphereOcean Ice Model Atmospheric GCM NCAR CAM2 T42 resolution Ice Thermodynamic portion of NCAR CSIMV4 Ocean Mixed layer Model MLM An individual column model with a uniform mixed layer Atop a layered model that represents conditions in the pycnocline Prognostic ML depth Same grids as the atmosphere 128 lon x 64 lat 36 vertical levels from 0m to 1500m depth 0 higher resolution close to surface and a realistic bathymetry Flux correction needed to get reasonable climate Cassou et al 2007 J Clim Alexander et al 2000 JGR Alexander et al 2002 JClim Gaspar 1988 JPO The Mean NDJFM Atmospheric Response I Surface windamplce concentration I 14 80N 5 1o 1 6 2 2 Q ibbLOANwhmmw Afi I 07 28 r 7 S A 05 39 2 A 39 y w E 03 12 39 5 x 01 04 7 quot 39 o1 04 39 03 12 o5 2 07 Pressure 400 500 700 850 Atmospheric Vertical profile of Temperature Anomalies in Labrador Region 045 O15 015 075 105 Degrees C 045 Late stage w Height km Positive feedback Storm Track Changes 28 day band pass filtered 2500 m Variance Clim CTL Stormtrack Eady Baroclinic Growth Rate 850 hPa 35 25 15 05 05 15 25 35 Monthly Evolution of the SLP Response Nov Additional Topics The flux components and their variability Schematic of the mixed layer model Pattern of atmospheric circulation SLP and the underlying fluxes Basinwide reemergence The Pacific Decadal Oscillation Wind generated Rossby waves and its relation to SSTs The Latif and Barnett mechanism for the PDO and problems with this mechanism