Atmospheric Circulation, Climate and Ice Sheets. Atmospheric Circulation, Climate and Ice Sheets

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1 Atmospheric Circulation, Climate and Ice Sheets David S. Battisti University of Washington Atmospheric Circulation, Climate and Ice Sheets 1. Albedo, Absorbed Insolation and Meridional Heat Transport 2. East-West Asymmetries in orography and heating: Impact on Stationary Waves and Climate 3. Storminess and Patterns of Climate Variability Basic model for the NAO, NPO, SAM 4. The Impact of Ice Sheets on Circulation, Storminess, and Climate during the LGM 5. Increased Greenhouse Gases, Circulation and the Ice Sheets

2 Annual Radiation Balance The meridional gradient in Absorbed Solar Radiation (ASR) drives circulation. In an equilibrium, the resultant Meridional Heat Transport (MHT) is such that ASR = OLR + MHT where OLR is the Outgoing Longwave Radiation at the TOA Meridional Energy Transport Ocean does most of the transport in the deep tropics (15ºS-15ºN) Atmosphere does most of the transport poleward of 30ºN,S

3 Definitions Write all quantities in terms the global average and a perturbation. Example: the Solar Radiation at the Top of the Atmosphere (TOA) would be S: S = S + S ' Total TOA insolation Global Average Deviation from the Global Average Absorbed Solar Radiation ASR can be written ASR " S a = S a + a S ' + a ' S + a ' S ' where is the co-albedo and a = 1 " # p ( ) " p x is the planetary albedo. Definitions The meridional gradient in Absorbed Solar Radiation drives all circulation. It is due to: geometry (angle of incidence) spatially inhomogeneous planetary albedo a ' S + a ' S ' Climate state a S ' geometry ASR ' total

radiation, which is responsible for circulation In the present climate, geometry is responsible for about ~ two-thirds of the meridional gradient in ASR that drives all circulation Approx.

4 What causes circulation: geometry or optical processes internal to the climate system? We define ASR* to be the deficit in the integrated ASR over the area poleward of where ASR = 0: ASR " = #2$R 2 1 % ASR' dx x(asr' =0) ASR ' = 0 ASR* is a measure of the gradient in absorbed SW radiation, which is responsible for circulation In the present climate, geometry is responsible for about ~ two-thirds of the meridional gradient in ASR that drives all circulation Approx. 1/3 of the meridional gradient in ASR is due to processes internal to the climate system What causes the meridional gradients in albedo (that drive circulation)? Gradients in planetary albedo are due to gradients in atmospheric properties that reflect shortwave radiation gradients in the (shortwave) optical properties of the surface (e.g., sea ice, snow, trees, land, ocean) Which matters most to ASR*: atmosphere or land? Annual Average Planetary Albedo

5 Estimating the contributions of surface and atmosphere to the planetary albedo Consider the simple model S Atmosphere with absorptivity A and reflectivity R Surface with albedo " Knowns from data (4): upwelling and downwelling radiation at the TOA and surface Unknowns: ", R and A. Solve by least-squares fit Estimating the contributions of surface and atmosphere to the planetary albedo In this framework, the shortwave flux at the TOA F " TOA is F " TOA = S[R + #(1$ R $ A) 2 + # 2 R(1 $ R $ A) 2 + # 3 R 2 (1 $ R $ A) 2... (1 $ R $ = SR + S#(1$ R $ A) 2 [1+ (#R) + (#R) 2 A)2...] = SR + S# 1 $ #R Hence, the planetary albedo is Atmospheric contribution to " p by clouds, water vapor, etc F " TOA S (1$ R $ A)2 = # p = R + # 1 $ #R Surface contribution to where : ", R and A are the surface albedo, atmospheric reflectivity and absorptivity. " p

6 Estimating the contributions of surface and atmosphere to the planetary albedo (1 # R # A)2 " 1 # "R " (1 # R # A)2 " p = R + " 1 # "R R Wither surface albedo.. " (1 # R # A)2 " 1 # "R Surface Contribution to " p Surface Albedo " = (1# R # A)2 1# "R Surface Albedo Surface contribution to Planetary Albedo

7 Estimating the contributions of surface and atmosphere to the planetary albedo: the global average In the global mean or in either hemisphere. " p = Atmosphere + Surface = Fully 88% of the globally averaged planetary albedo is due to atmospheric processes; only 12% is due to surface properties. What causes circulation: geometry or optical processes internal to the climate system? Contributions to ASR* Geometry Atmos. Surface NH SH The angle of incidence is responsible for 2/3 of the gradient in ASR* that is responsible for all circulation Gradients in the optical properties in the atmosphere account for 31% (36%) in the NH (SH) Gradients in surface properties account for only 5%

8 Implications Large changes in the equator-to-pole gradient in ASR (ASR*) that drives the large scale circulation are likely to come from (in order of importance): changes in atmospheric optical properties (clouds and water vapor) changes in orbital forcing (~5%) Hence, ASR* is a strong function of the state of the climate system (mainly water vapor and cloud composition/distribution) Affects: A A & R In contrast, very large changes in surface albedo will have a very small affect the gradient in planetary albedo and hence on the meridional gradient in ASR* Implications In equilibrium, the equator-to-pole gradient in ASR (ASR*) must be balanced by energy transported by circulation and by OLR. The nodes of ASR and MHT are nearly co-located, so the maximum Meridional Heat Transport (MHT) is related to ASR* by MHT = "2#R 2 1 $ [ ASR(x) " OLR(x) ] dx % ASR & " OLR & x(asr =OLR ) Implications: MHT should be highly dependent of atmospheric processes that affect ASR* (and not to changes in surface composition)

9 Meridional Heat Transport and Optical Properties of the Atmospheric Across fifteen climate models simulation of the present day climate, and simulations of the LGM and under 1020ppm CO 2 (4xPI) * = one climate model (NH, SH) The blue (red) lines are the linear best fits to the PI model simulations in the NH (SH). the Maximum MHT is largely dependent on atmospheric composition and not related to changes in surface properties or OLR Atmospheric Circulation, Climate and Ice Sheets 1. Albedo, Absorbed Insolation and Meridional Heat Transport 2. East-West Asymmetries in orography and heating: Impact on Stationary Waves and Climate 3. Storminess and Patterns of Climate Variability Basic model for the NAO, NPO, SAM 4. The Impact of Ice Sheets on Circulation, Storminess, and Climate during the LGM 5. Increased Greenhouse Gases, Circulation and the Ice Sheets

East-West Asymmetries in the Midlatitudes There are two major players: 1.

regional temperature greatly Localize the storm tracks in the northern hemisphere winter to two nearly independent branches: the

East-west gradients in the heating the atmosphere due to different thermal capacities of atmosphere and ocean Presently, the jury is

10 East-West Asymmetries in the Midlatitudes There are two major players: 1. Large orography of the Himalaya and the Rockies cause Time mean (standing) waves that transport energy poleward in the NH and affect regional temperature greatly Localize the storm tracks in the northern hemisphere winter to two nearly independent branches: the Pacific and Atlantic 2. East-west gradients in the heating the atmosphere due to different thermal capacities of atmosphere and ocean Presently, the jury is out as to which is more important Climatological Flow (Near Surface Wind) DJF The orography (mainly Tibet and the Rockies) and east-west gradients in surface heating produce stationary (standing) waves in the NH winter These stationary waves transport heat polewards (2.5PW NH and ~0PW in SH) (ms -1 ) JJA

The Basics of Orographically Forced Waves Conservation of potential vorticity: barotropic Conservation of potential vorticity: stratified fluid

squashing and meridional advection of low planetary vorticity are balance by zonal advection of relative vorticity Opposite for down slope flow

11 The Basics of Orographically Forced Waves Conservation of potential vorticity: barotropic Conservation of potential vorticity: stratified fluid Stationary Waves Forced at the Surface Orographic gradients with sufficiently large scales and amplitude force stationary waves Upslope flow: squashing and meridional advection of low planetary vorticity are balance by zonal advection of relative vorticity Opposite for down slope flow Downstream wave is due to downstream propagation of energy Stationary waves forced by orography transport a lot of heat poleward in the NH (winter) DJF near surface flow

12 East-West Asymmetries in the Midlatitudes Heating also produces standing eddies that flux momentum and heat. The forcing enters through the thermodynamic equation The forcing enters through the thermodynamic boundary condition at the surface (w/ QG scaling) u " "x "# ' "z + "#' "x " u "z + N 2 f o w ' = R f o H J Cp Zonal temp advection Anom meridional temp advection Adiabatic Cooling Diabatic Heating Orography imparts vorticity Heating (surface upward) imparts vorticity East-West Asymmetries in the Midlatitudes A classic look from Isaac Held R15,L9 AGCM; fixed clouds; 15 year equilibrium runs two experiments forced by same observed climatological SST and sea ice I.M Held, 1983: Stationary and quasistationary eddies in the extratropical troposphere: theory. In Large-Scale Dynamical Processes in the Atmosphere, eds Hoskins B. J., Pearce R. P. (Academic, London), pp

, Pearce R. P. (Academic, London), pp 127 168.

13 East-West Asymmetries in the Midlatitudes A cross-section of geopotential along 45N Control Control minus no mts Thermal ( no mts ) I.M Held, 1983: Stationary and quasistationary eddies in the extratropical troposphere: theory. In Large-Scale Dynamical Processes in the Atmosphere, eds Hoskins B. J., Pearce R. P. (Academic, London), pp The importance of orgraphy for surface temperature Experiment with an Atmospheric GCM coupled to a slab ocean w/ prescribed ocean heat flux convergence Compared to the zonal mean, Oceans are 20ºC colder than land NE Canada is 25ºC colder than over Europe Winds, SLP and Eddy Temperature in January Seager et al 2000

, Northeast US would be 12-15 C warmer w/o the Rockies; China would be ~ 10 C warmer in winter w/o the Tibetan Plateau) Contributes

14 The importance of mountains in wintertime Mountains No Mountains Winds, SLP and Eddy Temperature in January Seager et al 2000 The importance of mountains in wintertime (e.g., Northeast US would be C warmer w/o the Rockies; China would be ~ 10 C warmer in winter w/o the Tibetan Plateau) Contributes up to 20% of the annual cycle of surface air temperature in some places (e.g., Norway would be ~ 4C colder in winter w/o the Rockies) Europe is warm in winter because of the Rockies and atmospheric heat transport Seager et al 2000

Quiz: What explains the missing half of the temperature difference between

Experiments with an Atmospheric GCM coupled to a slab ocean w/ prescribed

colder than Europe NE Canada 5-10ºC warmer than Europe + 20ºC - 21ºC Reverse

Albedo, Absorbed Insolation and Meridional Heat Transport 2.

15 Quiz: What explains the missing half of the temperature difference between Eastern Canada and Western Europe? Experiments with an Atmospheric GCM coupled to a slab ocean w/ prescribed ocean heat flux convergence Forward Rotation Reverse Rotation NE Canada 25ºC colder than Europe NE Canada 5-10ºC warmer than Europe + 20ºC - 21ºC Reverse minus Forward Atmospheric Circulation, Climate and Ice Sheets 1. Albedo, Absorbed Insolation and Meridional Heat Transport 2. East-West Asymmetries in orography and heating: Impact on Stationary Waves and Climate 3. Storminess and Patterns of Climate Variability Basic model for the NAO, NPO, SAM 4. The Impact of Ice Sheets on Circulation, Storminess, and Climate during the LGM 5. Increased Greenhouse Gases, Circulation and the Ice Sheets

Climatological Flow (200hPa Zonal Wind) DJF JJA (ms -1 ) The winter jets

while the jet in the SH is nearly zonally symmetric Jets demark regions

Hence they are regions with high potential energy and flow instability

5PW in SH) Variability in the Midlatitudes Localized Storm Tracks (due

patterns: NAO, NPO/WP, SAM NH Winter Storminess (e.g.

16 Climatological Flow (200hPa Zonal Wind) DJF JJA (ms -1 ) The winter jets are stronger than the summer jets The jets in the NH are localized, while the jet in the SH is nearly zonally symmetric Jets demark regions of strong temperature gradients. Hence they are regions with high potential energy and flow instability -> the storm tracks which transport heat polewards (3PW NH and 5.5PW in SH) Variability in the Midlatitudes Localized Storm Tracks (due to orography) plus Storm-low frequency interaction leads to preferred patterns: NAO, NPO/WP, SAM NH Winter Storminess (e.g., eddy heat transport; color) poleward heat flux 850mb (Km/s) 250 hpa Zonal Wind (contour in 10 m/s, starting at 30) C. Li (2007) Positive Phase NAO

17 Climate variability associated with storm tracks # 1) In the midlatitudes, climate variability is due to storm-track dynamics that are intrinsic to the atmosphere 2) The dynamical time scale tau associated with these modes is ~ 5 days, and is set by the interactions between the storms and the jets that form them 3) Key patterns of climate variability (the modes ) are co-located with the jets, which are determined by gross boundary conditions (e.g., rotation rate, orography, gross land-sea contrasts, etc). These modes include: The North Atlantic Oscillation (NAO) The North Pacific Oscillation (NPO) The Southern/Northern Annular Mode* (SAM/NAM; aka AO/AAO) # Not governed by this dynamics: ENSO, PNA * Need one more piece of physics Where does variability come from? * Storms owe their existence to the jets. * Over their life cycle, storms both take and give momentum to the jet Storm Growth Storm Decay A Pattern is the expression the changes in the jets due to storms.

18 Positive Phase The North Atlantic Oscillation Negative Phase NAO Time Series The North Atlantic Oscillation Correlation of NAO with winter air temperature The NAO is a wintertime phenomenon, with ~ no predictability

ocean that is not in motion (time scale 6-12 months) 2) On decadal and longer time scales, the memory for reddening may come from

, - 10 years: gyre circulations, arctic sea ice, - 100 years: intermediate water masses; ice streams - 1000 years: deep oceans 3)

19 Where does the memory come from? 1) The redness of spectrum (presence of enhanced decadal variability is guaranteed because of the interaction with the thermodynamic ocean that is not in motion (time scale 6-12 months) 2) On decadal and longer time scales, the memory for reddening may come from other physics: e.g., - 10 years: gyre circulations, arctic sea ice, years: intermediate water masses; ice streams years: deep oceans 3) The amplitude of the spectrum and the spatial pattern can be nudged by changes in geometry e.g., ice sheets, continent configuration, orography, sea ice, orbital forcing, stratospheric aerosols), greenhouse gases, and perhaps solar variability Example: Reddening of the NAO Regression of the NAO on the surface heat flux and SST Marshall et al 2001

The Default Model: Atmospheric phenomenon that are reddened by coupling to the upper ocean The dynamical white noise forcing Dynamical Atmosphere The NAO (D.

20 The Default Model: Atmospheric phenomenon that are reddened by coupling to the upper ocean The dynamical white noise forcing Dynamical Atmosphere The NAO (D. Stephenson) Storms interacting with the mean flow create advective surface temperature anomalies Forcing Ocean T a T o Turbulent Heat Flux Coupling leaves an SST footprint that, in turn, affects the atmosphere H m The Default Model for these climate patterns: Atmospheric phenomenon that are reddened by coupling to the upper ocean via surface heat fluxes Ocean Thermal Inertia Storm Dynamics Time Scale Coupling enhances the low frequency variability (t > 2*pi tau) by a factor of 2-4, but the increase in the total atmospheric variance is small (5%).

Time series of the NAO 1860 Time 2000 0 0.1 0.2 0.3 0.4 0.

pattern in winter than summer The spectrum is statistically indistinguishable from red noise (e.

jets, exactly as in the NAO SAM is special, however, because: The jet in the southern

waves The life-cycle associated with a storm is ~5 days.

21 Time series of the NAO 1860 Time Frequency (/yr) For the NAO (and the other patterns): There is more variance captured by this pattern in winter than summer The spectrum is statistically indistinguishable from red noise (e.g., Desser; Hurrell; Goodman) The time scale is determined by the thermal inertia of the upper ocean (including re-emergence). The Southern Annular Mode (SAM) The SAM is an aggregate of the storms interacting with the jets, exactly as in the NAO SAM is special, however, because: The jet in the southern hemisphere is nearly zonally symmetric because there is little orographic forcing of stationary waves The life-cycle associated with a storm is ~5 days. Hence, the storm/jet interactions that give rise to the NAO play out over a distance d = 800km/day * 5 days = 4000km Thus, the SAM can be thought of as the average of ~4 independent storms interacting with the time mean jet along the same latitude

22 Southern Hemisphere Eddy-Driven Jet. First EOF represents N-S shift of eddy driven jet. 1.5 standard deviation of PC-1 corresponds to 10 latitude shift of surface westerlies. Hartmann and Lo, 1998 Southern Hemisphere Eddy-Driven Jet. First EOF of zonal wind almost independent of season. Amplitude of EOF 1 is slowly varying, with most variance > 20 days Hartmann and Lo, 1998

The Southern Annular Mode (SAM; aka AAO) Time Series 1979-2006 Where does the memory come from?

23 The Southern Annular Mode (SAM; aka AAO) Time Series Where does the memory come from? 1) The redness of spectrum (presence of enhanced decadal variability is guaranteed because of the interaction with the thermodynamic ocean that is not in motion (time scale 6-12 months) 2) On decadal and longer time scales, the memory for reddening may come from other physics: e.g., - 10 years: gyre circulations, arctic sea ice, years: intermediate water masses; ice streams years: deep oceans 3) The amplitude of the spectrum and the spatial pattern can be nudged by changes in geometry e.g., ice sheets, continent configuration, orography, sea ice, orbital forcing, stratospheric aerosols), greenhouse gases, and perhaps solar variability

Other issues concerning patterns of climate variability The NAO is not the same as the NAM ENSO is the only true mode of the climate system The NAO vs NAM/AO (Z500 variability) NAO NAM AO Leading EOF

24 Other issues concerning patterns of climate variability The NAO is not the same as the NAM ENSO is the only true mode of the climate system The NAO vs NAM/AO (Z500 variability) NAO NAM AO Leading EOF of the 500 mg NH (monthly averaged): rotated (NAO) and unrotated (NAM/AO) The Atlantic and Pacific jets/stormtracks/associated climate patterns (e.g., NAO and NPO) are regional independent phenomenon The NAM/AO is a stratospheric phenomenon that has similar physics to the NAO, it is driven by variability in planetary (not synoptic) scale waves A reasonable estimate is that the NAM explains ~5% of the monthly variance in each storm track in the NH; the local patterns NAO/NPO explain the remaining variance

El Nino/Southern Oscillation: ENSO ENSO is the leading pattern of

Temperature Anomalies Precipitation Anomalies Nino3.

Oscillation: ENSO Small changes in the distribution of sea surface

circulation and rainfall patterns Sea Surface Temperature and Sea

25 El Nino/Southern Oscillation: ENSO ENSO is the leading pattern of climate variability on seasonal to interannual time scale Temperature Anomalies Precipitation Anomalies Nino3.4 or CT SOI (Tahiti -Darwin) Sea Level Pressure El Nino/Southern Oscillation: ENSO Small changes in the distribution of sea surface temperature are tightly coordinated with changes in atmospheric circulation and rainfall patterns Sea Surface Temperature and Sea Level Pressure CT r = 0.93 SOI ENSO is the only true climate mode (eigenmode) of the climate system

26 Atmospheric Circulation, Climate and Ice Sheets 1. Albedo, Absorbed Insolation and Meridional Heat Transport 2. East-West Asymmetries in orography and heating: Impact on Stationary Waves and Climate 3. Storminess and Patterns of Climate Variability Basic model for the NAO, NPO, SAM 4. The Impact of Ice Sheets on Circulation, Storminess, and Climate during the LGM 5. Increased Greenhouse Gases, Circulation and the Ice Sheets The Impact of Ice Sheets on Circulation, Storminess, and Climate during the LGM Contributions of ice sheet orography, albdeo and greenhouse gas changes to the change in temperature, LGM minus modern Changes in storminess and energy transport in the LGM (mainly due to ice sheet orography) Equatorward shift in the jet (and SAM variability) in the Southern Hemisphere?

27 Forcing at the LGM 21K BP Insolation Land Ice CLIMAP Ice4G Reconstruction Hewitt et al 1987 Surface Temperature Change LGM - Today Broccoli 2000

28 Surface Temperatures: LGM Today Estimated by running climate models, with and w/o component forcings Manabe and Stouffer 1987 Globe N.Hemis S.Hemis Land Ocean Hewitt & Mitchell 1997 Contributions of ice sheet orography, albdeo and greenhouse gas changes to the change in temperature: LGM minus modern Orbitally induced insolation changes do pace the Glacial cycles, but In the Southern Hemisphere the simulated changes in temperature depend on: CO 2 changes In the Northern Hemisphere: Albedo changes associated with land ice Changes in the ice sheet orography (increased evaportation due to increased with over the ocean CO 2 changes (small) In both hemisphere, insolation changes are small

29 The Impact of Ice Sheets on Circulation, Storminess, and Climate during the LGM Contributions of ice sheet orography, albdeo and greenhouse gas changes to the change in temperature, LGM minus modern Changes in storminess and energy transport in the LGM (mainly due to ice sheet orography) Equatorward shift in the jet (and SAM variability) in the Southern Hemisphere? Pop Quiz How did storminess during the LGM in the northern hemisphere compare to storminess in the modern climate?

Ice Mountains and Storminess During the LGM, the meridional temperature gradient increased but storminess decreased compared to today Atlantic Jet Cross Section

, eddy heat transport) Modern Height 20N 60N 20N 60N Contours are west-to-east (zonal) wind speed; Temperature is colored poleward heat flux 850mb (Km/s) 250 hpa Zonal

30 Ice Mountains and Storminess During the LGM, the meridional temperature gradient increased but storminess decreased compared to today Atlantic Jet Cross Section Amplitude of Storms (e.g., eddy heat transport) Modern Height 20N 60N 20N 60N Contours are west-to-east (zonal) wind speed; Temperature is colored poleward heat flux 850mb (Km/s) 250 hpa Zonal Wind (contour in 10 m/s, starting at 30) Li and Battisti 2007 Ice Mountains and Storminess The Regime that the Atlantic resides in is a strong function of the ice volume (orography) over N. America Maximum Jet Speed T Stormy Quiet 0% LGM Fraction of N. American Land Ice (100% = LGM Ice5G) T = Today Rennert et al (in prep)

d) Mountains and Midlatitude Storminess Dogma: as the equator-to-pole temperature gradient (dt/dy) increases,

A modern day counter example: midwinter suppression of the Pacific storm track Going from November to January

decreases by ~25% and the atmospheric heat transport goes down.

31 d) Mountains and Midlatitude Storminess Dogma: as the equator-to-pole temperature gradient (dt/dy) increases, so should storminess increase. A modern day counter example: midwinter suppression of the Pacific storm track Going from November to January (increases dt/dy) and the Jet increases by ~20 m/s, Yin and Battisti (2005), Li (2007) but storminess decreases by ~25% and the atmospheric heat transport goes down. Mountains and Midlatitude Storminess Mean zonal wind, 300mb Storms across E (Z300mb) Nov. Land genesis Jan. Ocean genesis X Storm Path Apr. Orogrpahy contour 1500m Shading every 10 m/s over 20 m/s (example from one year) Penney et al. (2009)

32 Mountains and Midlatitude Storminess Storms that cross E (Z300mb) Avg. magnitude (m 2 s -2 ) #/month (30-day running mean smoother applied) Mid-winter suppression is due to the reduced NUMBER of storms Obs. in all tested variables (Z, VO, V) and levels (300, 500, 700, 775, 850). Reduction is ~15-40% depending on variable, level, and location w/in W. Pac No corresponding reduction in magnitude of storm Penney et al. (2009) Mountains and Midlatitude Storminess Storms that cross E (Z300mb) Average Number magnitude per month (m 2 s -2 ) Land Starts Ocean Starts All Starts Aug Jan Jun Aug Jan Jun Penney et al. (2009)

Mountains and Midlatitude Storminess Storms that cross 160 0 E (Z300mb) Average Number magnitude per month (m 2 s -2 ) Genesis frequency (All Storms) Ocean Starts Land Starts All Starts Aug Jan Jun

33 Mountains and Midlatitude Storminess Storms that cross E (Z300mb) Average Number magnitude per month (m 2 s -2 ) Genesis frequency (All Storms) Ocean Starts Land Starts All Starts Aug Jan Jun Aug Jan Jun January minus November Wintertime lee cyclogenesis is significantly reduced in January Increased atmospheric stability over China Reduced horizontal temperature gradients? Penney et al. (2009) Ice Mountains and Storminess Amplitude of disturbances seeding the Atlantic storm track pdf LGM Modern Storminess is reduced in the Atlantic during the LGM because the ice sheet orography greatly reduces the disturbances that perturb the faster (and more unstable) jet Donohoe and Battisti 2008

34 The Impact of Ice Sheets on Circulation, Storminess, and Climate during the LGM Contributions of ice sheet orography, albdeo and greenhouse gas changes to the change in temperature, LGM minus modern Changes in storminess and energy transport in the LGM (mainly due to ice sheet orography) Equatorward shift in the jet (and SAM variability) in the Southern Hemisphere? There are limited data that address this possibility, but they suggests a significant poleward displacement of the SH jet Not yet supported by models Atmospheric Circulation, Climate and Ice Sheets 1. Albedo, Absorbed Insolation and Meridional Heat Transport 2. East-West Asymmetries in orography and heating: Impact on Stationary Waves and Climate 3. Storminess and Patterns of Climate Variability Basic model for the NAO, NPO, SAM 4. The Impact of Ice Sheets on Circulation, Storminess, and Climate during the LGM 5. Increased Greenhouse Gases, Circulation and the Ice Sheets

Increased GH gases are expected to move the jet in the SH poleward Physics: Eddy-mean flow interactions Since the troposphere is deeper in the tropics than polar regions, warming of the troposphere

35 Increased GH gases are expected to move the jet in the SH poleward Physics: Eddy-mean flow interactions Since the troposphere is deeper in the tropics than polar regions, warming of the troposphere enhances the poleward surface gradient aloft and thus enhances the jet Barolclinic eddies growing at the base of the jet propagate energy upward and (more) equatorward and momentum (more) equatorward This acts to strengthen and move the jet poleward Enhanced stratospheric Ozone Also increases poleward pressure gradient aloft and moves jet poleward thought to account for some fraction in the observed positive trend in SAM over the past 30 yrs. Stratospheric aerosols should also lead to a positive shift in SAM Warms the low strasphere due absorption of SW; also increases poleward pressure gradient aloft and moves jet poleward Increased GH gases are expected to move the jet in the SH poleward Simulated Trends Simulated and observed summer trend in SAM due to ozone loss and increasing GH gases Similar atmospheric physics is expected to dry (wet) the mid (high) latitude regions of North America

Increased GH gases are expected to move the jet in the SH poleward Southward moving intensified surface winds energize the Antarctic Circumpolar Current

2009; Boning et al 2009) These important ocean process are poorly represented in climate models Impact on the ice sheets: likely to further warm the

caused changes in rainfall in these regions that have been teleconnected to western Antarctica MCA #2 of tropical SST (color) with Z200 height (contour)

36 Increased GH gases are expected to move the jet in the SH poleward Southward moving intensified surface winds energize the Antarctic Circumpolar Current (ACC) and warm the sub-surface water by either doming isopycnals in the ACC (Fyfe et al 2005, 2007) or enhancing eddy mixing across the ACC (Screen et al 2009; Boning et al 2009) These important ocean process are poorly represented in climate models Impact on the ice sheets: likely to further warm the near-surface water surrounding the Antarctic Increased Greenhouse Gases, Circulation and the Ice Sheets Trends in the western tropical Pacific SST have caused changes in rainfall in these regions that have been teleconnected to western Antarctica MCA #2 of tropical SST (color) with Z200 height (contour) The expansion coefficient of the Z200 (red) and SST (blue) mode in SON The Z500 map and time series are reproduced by a GCM forced by the observed tropical SST

Z200 Explains the positive trend in surface air temperature and precipitation in western Antarctica

37 The cause for the warming trend that Adrian modeled in the Amundsen Sea? Surface temperature (brown/blue shading) anomalies regressed on the expansion coefficients of the Z200 Explains the positive trend in surface air temperature and precipitation in western Antarctica Does it cause upwelling of warmer water along the shelf edge? The cause for the warming trend that Adrian modeled in the Amundsen Sea?

38 Summary: Atmospheric Circulation, Climate and Ice Sheets 1. Albedo, Absorbed Insolation and Meridional Heat Transport Planetary albedo and meridonal energy transport is controlled greatly by atmospheric processes (clouds and water vapor) surface albedo is negligible 2. East-West Asymmetries in orography and heating: Impact on Stationary Waves and Climate Orography has a profound impact on the mean circulation, the meridional heat transport mechanism (stationary vs eddies) in the northern hemisphere winter 3. Storminess and Patterns of Climate Variability Basic physics for the NAO, NPO, SAM (and their associated climate patterns of variability) is storms interacting with the jets Summary: Atmospheric Circulation, Climate and Ice Sheets The Impact of Ice Sheets on Circulation, Storminess, and Climate during the LGM In the mean, the orography and albedo of the ice sheet cools the NH and the reduced CO2 cools the SH during the LGM compared with the modern day (MD) climate The ice sheets have a large and surprising impact on storminess, reducing storminess in the Atlantic in the LGM compared with M Increased Greenhouse Gases, Circulation and the Ice Sheets Increased GH gases are expected to move the jet in the SH poleward This is likely to add to the direct warming of the subsurface near Antarctica Trends in the western/central tropical Pacific SST have caused changes in rainfall in these regions that have had teleconnected to western Antarctica Explains the warming trends in western Antarctica temperature and precipitation and perhaps the warming trend that Adrian modeled in the Amundsen Sea

Introduction to Climate ~ Part I ~

2015/11/16 TCC Seminar JMA Introduction to Climate ~ Part I ~ Shuhei MAEDA (MRI/JMA) Climate Research Department Meteorological Research Institute (MRI/JMA) 1 Outline of the lecture 1. Climate System (