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 1
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 2
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
Water vapor and climate changes (From: Walker and Schneider, 2006; Frierson et al., 2007b; Korty and Schneider, 2008; T. Schneider et al, 2009) • Water vapor dynamics is more important in warmer than in colder climates because the atmospheric water vapor concentration generally increases with surface temperature. * e L δ T ≈ δ that is, the saturation vapor pressure increases 6–7% if the temperature increases 1K * 2 e R T v • 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. 5
Global mean precipitable water and precipitation vs global mean surface temperature in idealized GCM simulations. ( T. Schneider et al, 2009) 6
TROPICAL CIRCULATIONS That global mean precipitable water and precipitation change with climate at different rates has one immediate consequence: the water vapor cycling rate 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
The Hadley Circulation. Climatology, Variability, Change Observation-Based Evidence
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
Strength of Hadley Circulation 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 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.
THE POLEWARD EXPANSION OF THE TROPICAL CIRCULATION 200 mb (hPa) DJF 200 mb (hPa) JJA S N latitude Total Meridional circulation - streamfunction units: 10 10 kgm/sec
Tropopause Height - Analysis of radiosonde and reanalysis data shows that the height of 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: y H = sin( θ H ), (Held and Hou, 1980) 1 gH 5 ⎛ ⎞ 2 Δ t h ϕ ≈ ⋅ ⋅ ⎜ ⎟ H 2 2 3 a T Ω ⎝ ⎠ 0 (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
декабрь - февраль июнь - август Высота тропосферы ( км ).. На этом рисунке и далее пунктирной линией показаны графики , соответствующие контрольному эксперименту , сплошной - эксперименту , моделирующему потепление
Hadley circulation width vs globalmean surface temperature in idealized GCM simulations
NH inmcm3 SH Model simulated widening of the tropics - A2, A1B, and B1 scenarios of the IPCC-AR4 simulations.
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.
Extratropical eddies and jets, formation of jets by baroclinic turbulence; atmospheric energy transport: moisture transport, dry static energy transport STORM TRACKS Good understanding of the mechanisms controlling storm track is important for many reasons.
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.
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