Exploring North Atlantic jet and storm track behaviour in glacial climates

Transcription

1 Exploring North Atlantic jet and storm track behaviour in glacial climates 23 January 2015 Ateliers de Modélisation de l Atmosphère, Toulouse

2 H H H relationship between jets and storminess Pole L L H H H sharper jet more baroclinic more stormy J T L L J Wallace & Hobbs

3 H H H relationship between jets and storminess Pole L L H H H sharper jet more baroclinic more stormy J T for the North Atlantic: seasonal cycle interannual variability (e.g., Raible 2007) L L J Wallace & Hobbs

4 relationship between jets and storminess jets (u250 contours) and storm tracks (u v colours) present glacial sharper jet more baroclinic less stormy Li & Battisti 2008 Camille 7/13 Li

5 relationship between jets and storminess jets (u250 contours) and storm tracks (u v colours) present glacial sharper jet more baroclinic less stormy Li & Battisti 2008 Camille 7/13 Li

6 relationship between jets and storminess jets (u250 contours) and storm tracks (u v colours) present glacial sharper jet more baroclinic less stormy reproduced in coupled and uncoupled simulations Li & Battisti 2008 Camille 7/13 Li

7 outline simulating the Last Glacial Maximum origin of glacial North Atlantic changes jet-storm track (baroclinicity-stability) relationship

8 simulating the LGM (last glacial maximum) boundary conditions radiative forcing insolation changes decreased atmospheric greenhouse gas concentrations Radiative forcing Greenhouse gas concentration LGM 6 ka LGM 6 ka PI W m 2 Wm 2 CO ppm 280 ppm 280 ppm CH ppb 650 ppb 760 ppb N ppb 270 ppb 270 ppb Otto-Bliesner et al. 2006

9 simulating the LGM (last glacial maximum) boundary conditions radiative forcing insolation changes decreased atmospheric greenhouse gas concentrations continental ice sheets albedo topography (~120 m sea level) altered coastlines topography over N America 4km 3km LGM 2km 1km today 120W 90W 60W ICE-5G reconstruction data from Peltier 2004

10 simulating the LGM (last glacial maximum) boundary conditions radiative forcing insolation changes decreased atmospheric greenhouse gas concentrations continental ice sheets albedo topography (~120 m sea level) altered coastlines vegetation river routing dust and other aerosols etc. topography over N America 4km 3km LGM 2km 1km today 120W 90W 60W ICE-5G reconstruction data from Peltier 2004

11 simulating the LGM (last glacial maximum) a cooler, drier climate P. Braconnot et al.: New results from PMIP2 Part 1: experiments and large-scale features (a) PMIP2 OA mean model surface air temperature 267 precipitation (b) PMIP1 SSTf mean model Braconnot et al (see also Kageyama et al. 2006)

12 simulating the LGM (last glacial maximum) a cooler, drier climate P. Braconnot et al.: New results from PMIP2 Part 1: experiments and large-scale features (a) PMIP2 OA mean model surface air temperature 267 precipitation (b) PMIP1 SSTf mean model IPCC AR5 WG1; Braconnot et al (see also Kageyama et al. 2006)

13 North Atlantic sharper zonal jet, weaker storm track jets (u250 contours) and storm tracks (u v colours) present glacial reproduced in coupled and uncoupled simulations Li & Battisti 2008; see also Hall et al. 1996

14 North Atlantic sharper zonal jet, weaker storm track jet changes more robust than storm track changes total eddy energy 500 hpa LGM control Laîné et al. 2009; see also Kageyama et al. 1999, Justino et al. 2005

15 outline simulating the Last Glacial Maximum origin of glacial North Atlantic changes jet-storm track (baroclinicity-stability) relationship

16 U 200 h ice sheets matter for circulation changes u200 DJF response western Atlantic u200 NDJFMA NDJFMA MJJASO LGM - PI D. Hofer et al.: Sensitivity to glacial boundary conditions LGM - - PI + GHG + ice albedo + ice topography + albedo&topo Latitude PI speed (m/s) 0 Hofer et al (CCSM4/CAM4), Pausata et al (IPSL); see also Unterman et al. 2011, Merz PhD thesis 2014

17 D. Hofer et al.: Sensitivity to glacial boundary conditions ice sheets matter for circulation changes u200 DJF response LGM + forcing western Atlantic u200 NDJFMA PI + forcing U 200 h NDJFMA LGM with small Laurentide Latitude LGM - PI D. Hofer et al.: Sensitivity to glacial boundary conditions MJJASO LGM - - PI + GHG + ice albedo + ice topography + albedo&topo glacial d at 200 hpa for DJF. The mean value for PIEQ are shown in (a) while in (b g) the anomalies of the different espect to PIEQ are presented. For the anomalies only values that are statistically significant at the 5 % level based on the t s200 for DJF. The mean value for PIEQ are shown in (a) while in (b) (g) the anomalies t-test hpa are coloured. 30 al simulations with respect to PIEQ are presented. For the anomalies only values that are stream and of the storm and cyclone center, found in simulations where the Laurentide ice sheet height ronounced thelevel easternbased part ofon thethe North is altered, but also twhen is nt at the 5in% two-sided Student s testthe aretopography colored.of Greenland PI sembles findings of other PMIP simulations changed even though the mechanism is different (Dethloff outheastward extension of the winter storm et al., 2004; Petersen et al., 2004; Junge et al., 2005) a et al., 1999; Laine et al., 2009). In our simthe analysis of the two LGM simulations with different speed (m/s) a direct relationship between changes in the ocean surface forcings shows that the observed atmospheric precipitation anomalies in the North Atlantic changes for a high Laurentide ice sheet are amplified when, our study is based on only one model and the meridional temperature gradient in the North Atlantic al (CCSM4/CAM4), al. result 2011is(IPSL); seewith also Unterman ine et al.hofer (2009)et suggest that such a relationis Pausata increased. et This consistent Toracinta et al.et al. 2011, Merz PhD thesis 2014 odel-dependent. Note also that a meridional (2004) who used a lower resolved atmospheric model forced h University Atlantic storm track in winter is not only either by the CLIMAP SST fields or by artificially adapted of Bergen

18 D. Hofer et al.: Sensitivity to glacial boundary conditions D. Hofer Sensitivity to glacial boundary conditions ice sheets matter foret al.:circulation changes especially Laurentide topography u200 DJF response LGM + forcing western Atlantic u200 NDJFMA PI + forcing U 200 h NDJFMA LGM with small Laurentide Latitude LGM - PI D. Hofer et al.: Sensitivity to glacial boundary conditions MJJASO LGM - - PI + GHG + ice albedo + ice topography + albedo&topo glacial d at 200 hpa for DJF. The mean value for PIEQ are shown in (a) while in (b g) the anomalies of the different espect to PIEQ are presented. For the anomalies only values that are statistically significant at the 5 % level based on the t s200 for DJF. The mean value for PIEQ are shown in (a) while in (b) (g) the anomalies t-test hpa are coloured. 30 al simulations with respect to PIEQ are presented. For the anomalies only values that are stream and of the storm and cyclone center, found in simulations where the Laurentide ice sheet height ronounced thelevel easternbased part ofon thethe North is altered, but also twhen is nt at the 5in% two-sided Student s testthe aretopography colored.of Greenland PI LGM with relatively is different (Dethloff sembles findings of other PMIP simulations changed even small though FS, the mechanism large Laurentide+others outheastward extension of the winter storm et al., 2004; Petersen et al., 2004; Junge et al., 2005) a et al., 1999; Laine et al., 2009). In our simthe analysis of the two LGM simulations with different speed (m/s) a direct relationship between changes in the ocean surface forcings shows that the observed atmospheric precipitation anomalies in the North Atlantic changes for a high Laurentide ice sheet are amplified when, our study is based on only one model and the meridional temperature gradient in the North Atlantic al (CCSM4/CAM4), al. result 2011is(IPSL); seewith also Unterman ine et al.hofer (2009)et suggest that such a relationis Pausata increased. et This consistent Toracinta et al.et al. 2011, Merz PhD thesis 2014 odel-dependent. Note also that a meridional (2004) who used a lower resolved atmospheric model forced h University Atlantic storm track in winter is not only either by the CLIMAP SST fields or by artificially adapted of Bergen

19 D. Hofer et al.: Sensitivity to glacial boundary conditions ice sheets matter for circulation changes smaller effects from radiative forcing and surface ocean forcing u200 DJF response LGM + forcing western Atlantic u200 NDJFMA PI + forcing U 200 h NDJFMA PI Fig ka insolation, GHG + small SST changes Latitude LGM - PI D. Hofer et al.: Sensitivity to glacial boundary conditions MJJASO LGM - - PI + GHG + ice albedo + ice topography + albedo&topo Fig. 8. Zonal wind at 200 hpa for DJF. The mean value for PIEQ are shown in (a) while in (b g) the anomalies of the different glacial speed (m/s) simulations with respect to PIEQ are presented. For the anomalies only values that are statistically significant at the 5 % level based on the Zonal wind at 200 for DJF. The mean value for PIEQ are shown in (a) while in (b) (g) the anomali two-sided Student s t-test hpa are coloured. different glacial simulations with respect to PIsee are Unterman presented.etfor the anomalies Hofer of et the al (CCSM4/CAM4), Pausata et al (IPSL); al. 2011, Merz PhD only thesisvalues 2014 EQ also that a eddy-driven jet stream and of the storm and cyclone center, found in simulations where the Laurentide ice sheet height whichsignificant is more pronounced thelevel easternbased part ofon thethe North is altered, but also twhen is statistically at the 5in% two-sided Student s testthe aretopography colored.of Greenland

20 D. Hofer et al.: Sensitivity to glacial boundary conditions ice sheets matter for circulation changes smaller effects from radiative forcing and surface ocean forcing u200 DJF response LGM + forcing western Atlantic u200 NDJFMA PI + forcing U 200 h NDJFMA PI colder (North Atlantic) SSTs Latitude LGM - PI D. Hofer et al.: Sensitivity to glacial boundary conditions MJJASO LGM - - PI + GHG + ice albedo + ice topography + albedo&topo warm 60 SSTs speed (m/s) Hofer et al (CCSM4/CAM4), Pausata et al (IPSL); see also Unterman et al. 2011, Merz PhD thesis 2014

21 North Atlantic sharper zonal jet, weaker storm track jets (u250 contours) and storm tracks (u v colours) present glacial sharper jet more baroclinic less stormy Li & Battisti 2008

22 North Atlantic sharper zonal jet, weaker storm track jets (u250 contours) and storm tracks (u v colours) present glacial sharper jet more baroclinic less stormy 1. baroclinicity alone does not determine stability in real (3D) world 2. variance statistics may confound some aspects of storm activity Li & Battisti 2008

23 glacial North Atlantic is more baroclinic u and temperature present PRESENT DAY glacial LGM 200 p(mb) ATL latitude ATL latitude m/s/deg K Li & Battisti 2008

24 glacial North Atlantic is more baroclinic u and temperature Eady growth rate hpa present PRESENT DAY glacial LGM glacial 200 p(mb) present PRESENT DAY ATL latitude ATL latitude m/s/deg K f N u h z oriolis paramete Li & Battisti 2008

25 expected baroclinicity-stability relationship holds (with some modifications by 3D effects) Framework Glacial more unstable by... Eady (1D) 80% QG β-channel meridional structure (2D) 50% QG β-channel meridional+zonal structure (3D) 30%

26 expected baroclinicity-stability relationship holds (with some modifications by 3D effects) Framework Glacial more unstable by... Eady (1D) 80% meridional scale alters efficiency of baroclinic energy conversion (Ioannou & Lindzen 1986, James 1987); consistent with Laîné et al QG β-channel meridional structure (2D) QG β-channel meridional+zonal structure (3D) 50% 30% growth rate (1/day) present glacial 100W longitude 10W

27 back to the simulations... jets (u250 contours) and storm tracks (u v colours) present glacial sharper jet more baroclinic less stormy 1. baroclinicity alone does not determine stability in real (3D) world 2. variance statistics may confound some aspects of storm activity Li & Battisti 2008

28 less efficient energy conversion from mean flow storm activity geopotential height Z variance (m 2 ) baroclinic conversion (m 2 /s 2 ) energy from mean flow into storms

29 less efficient energy conversion from mean flow storm activity geopotential height Z variance (m 2 ) glacial present baroclinic conversion (m 2 /s 2 ) energy from mean flow into storms

30 storms grow more rapidly in the glacial Atlantic... Hinman (1888) global distribution of storm activity (Chang et al. 2002) normalized probability glacial --- present normalized probability Donohoe & Battisti 2009

31 storms grow more rapidly in the glacial Atlantic... but they are smaller and fewer to begin with Hinman (1888) global distribution of storm activity (Chang et al. 2002) normalized probability glacial --- present # storms Donohoe & Battisti 2009

32 outline simulating the Last Glacial Maximum origin of glacial North Atlantic changes jet-storm track (baroclinicity-stability) relationship

33 less variability and different variability modes in glacial present glacial SLP mean (contours) and std dev (colours) Z500 NAO (Atlantic EOF1) IPSL results from Pausata et al. 2009, Rivière et al. 2010

34 cause of reduced seeding of storm tracks in glacial steered away by mean flow? Hinman (1888) global distribution of storm activity (Chang et al. 2002) geopotential height Z500 present glacial

35 a role for seeding in the Pacific midwinter suppression 75 latitude JAN APR JUL OCT JAN APR eddy heat flux 850mb [Km/s] eddy heat flux u 250mb T(E P) 850mb JAN APR JUL OCT JAN APR sharper jet weaker storm track Yin & Battisti 2004; Li & Battisti 2008

36 a role for seeding in the Pacific midwinter suppression Amplitude and frequency of disturbances from central Asia are reduced in midwinter Penny et al. 2010

37 summary points expected relationship between jet and storm activity isn t found in some simulations of the glacial North Atlantic sharper jet more baroclinic less stormy growth rates are linked to baroclinicity, but changes in seeding win Laurentide ice sheet largely determines mean circulation, variability and leading variability pattern in North Atlantic how exactly to link to the wave-breaking and stationary wave points of view? watch out for changes in the link between atmospheric variability patterns and climate variables

38 proxy-climate relationships A common goal in selecting proxy sites is to find locations where local variability represents larger spatial scales. present glacial CCSM3 (IPSL) HadCM3 (MIROC) NAO-SAT correlation maps

39 proxy-climate relationships A common goal in selecting proxy sites is to find locations where local variability represents larger spatial scales. present glacial CCSM3 (IPSL) HadCM3 (MIROC) NAO-SAT correlation maps SAT coherence maps

40 proxy-climate relationships A common goal in selecting proxy sites is to find locations where local variability represents larger spatial scales. present glacial

41 Text

42 jet variability std dev (lat) W 10W 0 10E latitude west histogram (%) east histogram (%) present 14 ka 21 ka (LGM) Text

43 a reminder... global precipitation (mm/d) CMAP Text

44 transient eddies in the midlatitudes earthobservatory.nasa.gov GEOS5 Text

45 storm tracks westerly jets (u200 contours) & storm tracks (colours) EKE at 200 mb mb v T at mb mb u v at mb mb ERA 40 reanalysis DJFM, Li & Battisti 2008 Text