Dynamics of general circulation atmosphere and climate changes V. - - PowerPoint PPT Presentation

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Международная конференция ENVIROMIS-2014, 28 июня -05 июля 2014 года, Томск, Россия Секция 2. Моделирование регионального климата.

Dynamics of general circulation atmosphere and climate changes

• V. Krupchatnikov(1,2,3,4) , Yu. Martynova (1,3) I. Borovko (1,2 )

(1) SibRHMI, (2) ICMMG SB RAS, (3) IMCES SB RAS , (4) NSU

e-mail: vkrupchatnikov@yandex.ru Web: http://sibnigmi.ru

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Outline

Introduction Water vapor and climate changes Dynamics of General Curculation Atmosphere and Climate:

• the poleward of expansion of the tropical circulation (HC);

extratropical eddies and jets, formation of jets by baroclinic turbulence; atmospheric energy transport: moisture transport, dry static energy transport The Role of SST Forcing Sea ice extent Summary and Conclusions

Introduction

An evidence of our understanding of the general circulation is whether we can predict changes in the general circulation that might be associated with past or future climate changes. It would be especially useful to predict changes associated with global warming. Changes in the location, intensity or seasonality of major climatological features of the general circulation could be more important than average temperature changes, particularly where these changes might affect local hydrology, energy balances and etc.

One of main problems of our researches is to understand the genesis, evolution and decay of weather patterns that produce extreme events, such as heavy precipitation, floods, heat/cold waves, etc. For present and future climate, these extreme events are what affect most of society on a regional scale. Planning to face the threat of global warming requires detailed predictions of climate changes in different parts of the world. This will require an array of climate models, from the global to the regional scale, to explore various scenarios of change, and associated uncertainties. Our ability to simulate and understand these phenomena is critical in climate studies and to improve weather prediction

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• Water vapor dynamics is more important in warmer than in colder climates because the atmospheric water

vapor concentration generally increases with surface temperature.

Water vapor and climate changes

(From: Walker and Schneider, 2006; Frierson et al., 2007b; Korty and Schneider, 2008;

• T. Schneider et al, 2009)

* * 2 v

e L T e R T δ δ ≈

that is, the saturation vapor pressure increases 6–7% if the temperature increases 1K

• In Earth’s atmosphere in the past decades, precipitable water (columnintegrated specific humidity) has

varied with surface temperature at a rate of 7–9% /K, averaged over the tropics or over all oceans

• Global mean precipitation and evaporation (which are equal in a statistically steady state) increase

more slowly with temperature than does precipitable water.

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Global mean precipitable water and precipitation vs global mean surface temperature in idealized GCM simulations. (T. Schneider et al, 2009)

That global mean precipitable water and precipitation change with climate at different rates has one immediate consequence: the water vapor cycling rate

TROPICAL CIRCULATIONS

Water vapor cycling rate vs globalmean surface temperature in idealized GCM simulations

A decreasing water vapor cycling rate may be interpreted as a weakening of the atmospheric water cycle and may imply a weakening of the atmospheric circulation, particularly in the tropics where most of the water vapor is concentrated and precipitation is maximal

Dynamics of General Curculation Atmosphere and Climate:

• the poleward of expansion of the tropical circulation (HC);
• extratropical eddies and jets, formation of jets by

baroclinic turbulence;

• atmospheric energy transport: moisture transport, dry

static energy transport

Observation-Based Evidence The Hadley Circulation. Climatology, Variability, Change

Rosenlof (2002) was probably the first to investigate long-term trends in the width of the tropics by studying the latitudinal extent of the upwelling branch of the Brewer–Dobson circulation in the lower stratosphere. This circulation represents a slow meridional overturning that extends through troposphere and stratosphere, with upwelling in the tropics and downwelling in higher latitudes. Rosenlof applied this indicator to reanalyses and found that the width of the tropics has increased by about 3 latitude per decade during the period 1992–2001. This rate is rather large and likely contains considerable observational uncertainty. Continuing the pioneering work by Rosenlof, a subsequent study by Reichler and Held (2005) focused on the structure of the global tropopause as another indicator of tropical width. This indictor is based on the well-known distinction between the tropics, where the tropopause is high, and the extratropics, where the tropopause is low

Tropical vertical mass flux and scaling estimates vs globalmean surface temperature in idealized GCM simulations. Figure shows ψ and evaluated at 4° latitude and at a pressure of approximately 825 hPa

Strength of Hadley Circulation

Strength of the Hadley circulation in simulations with (solid with circles) and without (dashed–dotted with squares) ocean heat transport

These arguments, based on energetic and hydrologic balances alone constrain how the tropical gross upward mass flux changes with climate, are generally insufficient to constrain how the net vertical mass flux and thus the strength of the Hadley circulation change The reason why the strength of the Hadley circulation responds differently to climate changes than the gross upward mass flux is that the Hadley circulation is not only constrained by energetic and hydrologic balances but also by the angular momentum balance, which it must obey irrespective of water vapor dynamics

(a) Coldest simulation (global

mean surface temperature

[Ts] = 259K. (b) Reference simulation [Ts] = 288K. (c) Warmest simulation [Ts] = 316K.

Total Meridional circulation - streamfunction units: 1010 kgm/sec

S N

latitude

DJF JJA

200 mb (hPa) 200 mb (hPa)

THE POLEWARD EXPANSION OF THE TROPICAL CIRCULATION

Tropopause Height

• Analysis of radiosonde and reanalysis data shows that the height
• f the global tropopause has increased over the past decades, and
• GCM experiments indicate that climate change is likely

responsible for this

• increase. This increase has been suggested as a

possible reason for the poleward expansion of the tropical circulation.

The dependence of the HC boundary of the tropopause height. In the small angle approximation: yH = sin(θH), (Held and Hou, 1980)

1 2 H 2 2

5 3

t h

gH T a ϕ ⎛ ⎞ Δ ≈ ⋅ ⋅ ⎜ ⎟ Ω ⎝ ⎠

(3)

Model-Based Evidence

The studies demonstrate that GCMs respond to anthropogenic forcings in expected ways, that is, the tropical edges and other aspects of the general circulation move poleward . However, the model simulated trends seem to be smaller than in the observations

Высота тропосферы (км).. На этом рисунке и далее пунктирной линией показаны графики, соответствующие контрольному эксперименту, сплошной - эксперименту, моделирующему потепление

декабрь-февраль июнь-август

Hadley circulation width vs globalmean surface temperature in idealized GCM simulations

inmcm3

Model simulated widening of the tropics - A2, A1B, and B1 scenarios of the IPCC-AR4 simulations. SH NH

The Role of SST Forcing

• Surface temperatures over the tropical oceans undergo

changes over time, which have been shown to have important consequences for the global atmospheric

• circulation. These SST changes are primarily related to the

natural ENSO phenomenon.

• Various studies have demonstrated that the tropics are

contracting during the warm phase of ENSO (El Nin˜o), as indicated by equatorward displacements of the jet,

storm track, eddy momentum divergence, and

edge of the HC.

STORM TRACKS

Good understanding of the mechanisms controlling storm track is important for many reasons. Extratropical eddies and jets, formation of jets by baroclinic turbulence; atmospheric energy transport: moisture transport, dry static energy transport

The role of the storm - tracks in the dynamics of weather and climate The storm - tracks are defined as the region of strong baroclinicity (maximum meridional temperature gradient), which are determined on the basis of eddy statistics like eddy fluxes of angular momentum, energy, and water (with the use of high - band pass - filter). In the Northern Hemisphere, there are two major storms in the region - Atlantic and Pacific. Baroclinic eddies:

• bring heavy rains and other hazardous weather phenomena in the middle latitudes;
• play an important role in the global energy cycle and the hydrological cycle

• We provide our study using the idealized

climatic system model (Fraedrich K., Jansen

H., et al., 2005).

• Together with sensitivity of storm-track

dynamic other features of “warm” climate in comparison with “current” climate dynamic is considered.

Semi-implicit time stepping

Model Physics – Parameterizations:

Surface Fluxes and Vertical Diffusion; Radiation; Moist Processes and Dry Convection; Land Surface and Soil; Sea Surface;

Ocean: Mixed Layer; Slab Ocean Model; Dynamic Vegetation

Sea ice model;

Climatic scenario we used reproduces both the atmospheric CO2 concentration increase due the anthropogenic pressure and its further decrease till return to preindustrial value (http://climate.uvic.ca/EMICAR5). Thus, the scenario of the atmospheric CO2 concentration change consists of four parts:

(i) For a time period from 850 to 2005 CO2 concentration was set according to the protocol \Historical simulations" of CMIP5. (ii) During the 21{23 century CO2 concentration was set according to the most aggressive scenario RCP 8.5. (iii) During 24{29 century CO2 was fixed on the level of the year 2300. (iv) During 30{31 century CO2 was returned to the preindustrial value. At this period during the rst 100 years CO2 concentration was decreasing linearly to preindustrial value and then fixed.

+

Trends - 21st Century (Wu, Y., et al, 2010) -

zonal climatic characteristics: T, Ty , N

Observations as well as model experiments indicate that the global warming signal in the upper troposphere is stronger than in the lower troposphere and that it maximizes in the tropical upper troposphere

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E

g T N T y σ ∂ ⋅ ⋅ ∂ :

The length scale vortices at 300 hPa for 12 AGCM simulations with the reference period 1981-2000 (solid line) and for the A2 scenario modeling to the period 2081-2100 (dashed line) (Project CMIP3)

• J. Kidston et al, 2010

R

NH L f = ( )

Rh

rms eddy vel L β =

INM RAS model

( ' ') u fv u v u t y α ∂ ∂ = − − ∂ ∂

( ' ') ' ' u u v v t y ξ ∂ ∂ = − = ∂ ∂

2

1 ' ' ' ' ' 2

av

d v F dt ξ β ξ ξ ⎛ ⎞+ = ⎜ ⎟ ⎝ ⎠

Уравнение энстрофии Уравнение баланса импульса

( )

2 2 2 2

2

i

yy kc t i

U kc d uv A e dy U c β χ − − =− −

( )

2 2 2 2

2

i

yy kc t i

U kc U d uv A e t dy U c β χ − ∂ =− − =− ∂ −

(J. Pedlosky, 1979)

'2

1 2

av

U ξ β = −

Zonal mean surface wind (м/sec), and pressure (hpa) in NH. Blue – Г = 0, red – Г = 4 (strong vortex)

• The intensity of the lower level baroclinicity (forcing amplitude) seems to be a

determining factor for the quality of upper-level wave breaking.

• For weak intensities, the strong effective beta asymmetries due to the earth sphericity

produce anticyclonic wave breaking and a poleward shift of the zonal jet will occur.

• By increasing the forcing, the cyclone centers become considerably more intense than

the anticyclones (CVC) and they are able to deform and thin the anticyclones, thus moving the jet equatorward. This transition is very abrupt; above a threshold amplitude, the lifecycle bifurcates to a cyclonic wave breaking.

Thorncroft, C.D., Hoskins, B.J., and McIntyre, M.E., 1993; Orlanski, I., and B. D. Gross, 2000

Through radiative forcing by increased atmospheric carbon dioxide and water vapor and increased solar absorption due

to less low cloud cover in the subtropics, more energy is gained within the tropics and subtropics, while in the middle and high latitudes energy is reduced through increased outgoing terrestrial radiation in the Northern Hemisphere and increased ocean heat uptake in the Southern Hemisphere. This enhanced energy imbalance in the future climate requires larger poleward atmospheric energy transports in the midlatitudes which are partially accomplished by the intensifed storm tracks. This strong connection between intensifed storm track energy transports and intensifed energy imbalance in the atmosphere is also confrmed in CMIP3/IPCC AR4 models.

Why do we need to study dynamics of storm tracks?

• Recent studies have indicated a poleward shift of the storm tracks and

midlatitude precipitation zone in the warming world that will contribute to subtropical drying and higher latitude

moistening.

Therefore we need to investigate the storm track response to increased warming and the dynamical mechanisms driving the changes in the storm tracks using climate models.

38 A figure from an 1888 geography text showing storm frequency distribution as viewed in the

mid-nineteenth century. The stipling denotes high storm frequency, while the arrows indicate individual storms. Reproduced from Hinman (1888). (From E. CHANG et al, 2002)

[U’v’] - 250

1801-1900 RCP85

[U’v’] - 250

2901-3000 RCP85

[U’V’] - 250 3901-4000 (100 year) RCP85 [u’v’] - 250 3901-4000 (1000 year) RCP85

Comparison of band-pass filtered variance of meridional velocity, produced in the GFDL CM2:1 model simulations (right column) with that derived in the NCEP-NCAR reanalysis (left column).

NCEP-NCAR GFDL CM2:1 The variance of eddy meridional velocity (v'v') at 250 mb

[V’v’] - 250

1801-1900 RCP85 [v’v’] - 250 2901-3000 RCP85

[V’v’] - 250

3901-4000 (100 year) RCP85 [v’v’] - 250 3901-4000 (1000 year) RCP85

[v’T’] - 700 1801-1900 RCP85 [v’T’] - 700 2901-3000 RCP85

[v’T’] - 700 3901-4000 (100 year) RCP85 [v’T’] - 700 3901-4000 (1000 year) RCP85

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 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 rotation rate, orography, gross land-sea contrasts, etc. These modes include:

• The North Atlantic Oscillation (NAO)
• The North Pacific Oscillation (NPO)
• The Northern Annular Mode (NAM / AO)

poleward heat flux 850mb (Km/s)

Positive Phase NAO

Sea ice extent

Легенда: квадратики - значения величины при росте концентрации СО2 и ее экстремально высоком значении (с 1701 г. по 3000 г.) черная сплошная линия - значения величины при падении концентрации СО2 до преиндустриального значения за 100 лет и при удержании ее далее на достигнутом значении до конца расчета (с 3001 г. по 4000 г.) серая сплошная линия - значения величины при падении концентрации СО2 до преиндустриального значения за 1000 лет (с 3001 г. по 4000 г.)

Summary and Conclusions

Summing up the above we can conclude that in our case the variation of atmospheric CO2 concentration signicantly aects storm track behavior. In general the areas of maximal storm track activity shift in the meridional direction to high latitude simultaneously with the atmospheric CO2 concentration increase and shift back with further CO2 concentration decrease. But the amplitude of the storm track activity doesn't change back to preindustrial value with the CO2 concentration decrease. At the end of simulations when CO2 concentration is already returned to preindustrial value and xed, the storm track amplitude continues to decline. Thus the amplitude of the storm track activity exhibits weak hysteresis

• eect. We associate this eect with a

presence of so-called recalcitrant component in the climate system. This component is slow and cannot be driven by atmospheric CO2 concentration variation

• nly. The
• btained storm track behavior is very interesting and requires further

detailed study.

We have examined the future projections in the location and amplitude of the storm tracks from the global coupled climate model simulations, the A2 and – A2 scenarios. We have identified a poleward expansion, and intensification on the poleward flank, of storm tracks in the future climate from band-pass filtered transient eddy statistics. The future projections in transient eddy activity and its heat transport well correspond to the changes in baroclinic instability. As have been noted, the enhanced planetary energy imbalance is primarily radiative driven and provides more available potential energy in the atmosphere. However, till now there is no general point of view on that as distribution and intensity a storm – tracks will vary at change of a climate in 21 century, i.e. can the transient eddies maintain themselves in forming the storm track, or are they controlled by other sources such as diabatic heating, surface damping, or stationary waves?

53 After a rise of 0.5 °C in the 25 years starting in the mid-1970s, the change in Earth’s global mean surface temperature has been close to zero since the turn of the century. Although the rise in carbon dioxide and other greenhouse gases explains many aspects

• f the overall warming trend over the past century (including the heat uptake by the
• ceans and the spatial and seasonal patterns of the warming), it cannot explain the

multi-decadal fluctuations superimposed on this trend Forcing agents such as anthropogenic and volcanic aerosols and variations in the Sun’s energy output are often called on to explain these features. Internal fluctuations of the atmosphere–ocean system, the low-frequency tail of

• ur chaotic weather, could also be responsible (I. Held, 2013).

But though

54 Despite ongoing increases in atmospheric greenhouse gases, the Earth’s global average surface air temperature has remained more or less steady since 2001. Are historical simulations of surface temperature trends, obtained using climate models with the best available estimates of past climate forcings, consistent with observations? Where on the globe can observed temperature trends be attributed to anthropogenic forcing?

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| Observed trends in winds, SLP, sea surface height, SST and SAT during 1992–2011. a, Observed trends in surface wind stress (Nm-2 yr-1) shown as vectors with observed trends in atmospheric SLP overlaid in colour shading (Payr-1). The maximum vector is 0.003 Nm-2 yr-1 and only vector trends that are significant at the 95% confidence level are shown. b, Observed trends in sea surface height (cmyr-1) from satellite altimetry. c,d, Observed trends in SST (c) and surface layer air temperature (d), respectively (Cyr-1). In all panels, stippling indicates where the trends are significant at the 95% confidence level given the linear regression standard error over the entire period of 1992–2011. (Matthew H. England et al., 2014)

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Global average SAT and Pacific trade wind anomalies over the past century. a, Temperature anomalies are shown as the annual mean relative to 1951–1980, with individual years shown as grey bars and a five-year running mean overlaid in bold. b, Pacific wind stress anomalies are computed over the region 6 N–6 S and 180–150W

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Geographical distribution of surface temperature trends (from Knutson et al, 2013): (b) HadCRUT4 ( The observed surface temperature dataset used in this study is the Met Office Hadley Centre–University of East Anglia Climatic Research)

• bservations

(d) CMIP5 seven-model ensemble mean (all-forcing, volcanic models). (f) compares observed trends with trends from the CMIP5 seven-model subset

For period (1981–2010) the observed warming trends over about 30% of the globe are assessed as having a detectable anthropogenic contribution. These regions include parts of the tropics, subtropics, and midlatitudes (within about 40°–45° of the equator) and a narrow zonally oriented band near the Arctic Ocean.

Coupled atmosphere–ocean general circulation models

(AOGCMs) are themost comprehensive tool to study climate changes and perform climate projections. Simple climate models (SCMs)

Energy-balance models (EBMs)

Unperturbed state Equilibrium response

β the derivative of the outgoing flux to space with respect to T

• exchange between shallow and deeper ocean layers

Energy-balance models (EBMs) (O. Geoffroy et al, 2013)

Analytical solutions

f f

c τ β γ = +

D

F T T γ β γ + ≈ +

D D D

dT c T F dt βγ γ β γ β γ ≈ ⋅ + + +

D S

c β γ τ β γ + ≡ ⋅

If F only varies on time scales >> Substituting into the evolution equation for the slow component then gives TD relaxes to the equilibrium response F/β on the slow time scale:

The role of the upper-ocean and deep-ocean heat uptakes in the fast and slow responses is discussed. One of the main weaknesses of the simple EBM discussed here is its ability to represent the evolution of the top-of-the-atmosphere radiative imbalance in the transient regime. We must taking into account the efficacy factor of deep ocean heat uptake. The simple model calibration applied to AOGCMs constitutes a new method for estimating their respective equilibrium climate sensitivity and adjusted radiative forcing amplitude from short-term step-forcing simulations and more generally a method to compute their global thermal properties.

As the climate evolves towards equilibrium, the spatial pattern of the warming evolves, so that the relationship between global mean surface temperature and outgoing flux to space changes. Because this evolving spatial pattern can be related to the oceanic heat uptake, Winton et al (2010) argue that a natural way of retaining the global mean perspective is by introducing an efficacy factor ε for H:

f D D

dT c T H F dt dT c H dt β ε = − − + =

( 1) ( )

f D

dT c T T T H F dt β ε γ = − − − ⋅ − − +

physical assumption is more apparent if one rearranges the first of these equations to: with the sum of the first two terms on the RHS now thought of as the parameterization

• f perturbations to the radiative flux at the top of the atmosphere.

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Thanks for attention if you listened to me