Anomalies of the Snow Cover: Origin and Climatic Role

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Anomalies of the Snow Cover Origin and
Climatic Role

• (some results of experiments with global climate
  model)

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Global Climate Model of Laboratory of Climatology
IGRAS (LC IGRAS)
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• The climatic model is created on the basis of
  model of Oregon State University (OSU),
  developed under direction of Prof. M.Schlesinger
  (1984). Under direction of Prof. G.L.Stenchikov
  this model was further developed at the Computer
  Center of the Russian Academy of Sciences. The
  version of this model is improved at the
  Laboratory of climatology of IGRAS.

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• Two-Level Atmospheric General Circulation Model.
  The centers of layers approximately correspond to
  levels 800 mbar and 400 mbar.
• Above 200 mbar up to the top border of the
  atmosphere there is a modelling thermodynamic
  stratosphere whose dynamics is not considered,
  and the temperature is calculated based on its
  radiation balance. In the stratosphere, annual
  change of distribution of ozone and water vapor
  is set.

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• Horizontal approximation is executed in s -
  system of coordinates on grid with resolution of
  4 by latitude and 5 by longitude.
• The spectral radiation model is used.
  Calculation of radiation fluxes is done at 5
  levels by vertical (4 levels in troposphere and 1
  in stratosphere) for 40 spectral intervals.
• Precipitation large-scale condensation and
  moist convective adjustment.

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• Cloudiness 4 types (the bottom level,
  "stratus", "cumulonimbus", top level
  ("cirrus")).
• The sensitive and latent heat fluxes between the
  surface and the atmosphere are calculated based
  on vertical gradients of temperature and
  humidity. The factor of the turbulent exchange is
  calculated depending on parameter of the
  aerodynamic roughness and Richardson number.
• Evapotranspiration Factor is set to be equal to
  one soon after precipitation, while for the lack
  of precipitation it decreases monotonously up to
  the minimal value prescribed for each type of
  landscape.

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• Active land layer represents a layer with the
  fixed thermal capacity set various for various
  types of the landscape, and its temperature is
  calculated on the basis of the heat balance
  equation.
• The temperature of ocean surface and
  distribution of sea ice is set on empirical data.
• Landscapes 10 types (tropical forest, steppe,
  semidesert, desert, extratropical forest,
  tundra, cultivated landscape, continental ice,
  sea ice, ocean).

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• Snow cover it is formed at tsn lt 0C
• tsn 0.5 (tg (t3
  ?Z3)) , (1)
• where tg mean active layer temperature (C),
  t3 and Z3 - temperature (C) and height at the
  bottom level of model (about 800 mbar), ? - moist
  adiabatic gradient.
• Snow cover melts if daily average values of tsn
  exceeds 0C. Thus the quantity of the melted snow
  is defined by the formula
• Smel Kmel ?rb tsn ,
  (2)
• where Smel - the snow water equivalent (SWE)
  which have melted during a day, cm
• Kmel - temperature factor of melting,
  0.3 cm SWE/?C
• ?rb - the correcting factor for
  large values of net radiation of the surface. It
  is calculated by the formula
• ?rb max(1, 0.025 R) ,
  (3)
• where R - net radiation of the surface,
  W/m2.
• With the Smel value, necessary expenses of heat
  for its melting are calculated.

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Calculation of Modern Climate

• Sea level pressure
• Sea-level air temperature
• Precipitation (mm/day)
• Snow depth (cm). January
• Snow depth (cm). Maximal winter

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Sea-level Pressure (Mbar)
January
July
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Sea-level air temperature (?)
January
July
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Precipitation (mm/day)
January
July
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Snow depth (cm). January

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Snow depth (cm). Maximal winter
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Experiments on the role of snow cover anomalies
in climate system

• Spring anomalies of snow water equivalent over
  Eurasia
• Winter anomalies of the area of snow cover over
  Eurasia

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Role of Spring Anomalies of snow water equivalent
of Eurasia

• Spring anomalies of the snow cover were
  simulated as follows on March 1st of each
  modelling year, the snow water equivalent (SWE)
  at each point of Eurasia was multiplied by factor
  K
• 1) K 1 2Cv for it is abnormal small,
• 2) K 1 2Cv for it is abnormal great
  values of the spring SWE.
• Here Cv - average for Eurasia coefficient of
  variation of SWE , calculated according to
  empirical data it was set to be equal to 0.18.
• The difference between the two experiments is
  analyzed.

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Changes of the some meteorological fields under
positive anomaly of spring snow cover over Eurasia

• Air temperature. April
• Air temperature. May
• Air temperature. June
• Radiation balance of the Earth-atmosphere system

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Change of radiation balance of the
Earth-atmosphere system (W/m2)
May
June
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Change of air temperature. April
Bottom of Troposphere
Surface
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Change of air temperature. May
Bottom of Troposphere
Surface
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Change of air temperature. June
Bottom of Troposphere
Surface
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Role of winter anomalies of the area of snow
cover over Eurasia

• For base calculation was suggested that from
  November till March of each year, the snow cover
  over Eurasia can form only to the north from 52º
  N, and to the south from it, solid precipitation
  is not formed. For the forced calculation, during
  the same time interval of each year the snow
  cover can form only to the north from 40º N.
• The difference between two experiments is
  compared.

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Changes of some meteo elements at shift of the
snow cover border from 52N to 40N

• Radiation balance of the Earth- atmosphere
  system
• Air temperature. January
• Air temperature. February
• Precipitation

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Change of radiation balance of the
Earth-atmosphere system (W/m2)
January
February
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Change of air temperature. January
Bottom of Troposphere
Surface
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Change of air temperature. February
Bottom of Troposphere
Surface
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Change of precipitation (mm/day)
January
February
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The origin of anomalies of the snow cover

• Role of winter anomalies of air temperature in
  formation of spatial structure of anomalies of
  the snow cover over Northern Eurasia.
• Role of winter anomalies of evaporation and
  temperature of Atlantic ocean surface in
  formation of the snow cover features over
  Northern Eurasia.

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Role of negative winter anomalies of air
temperature in formation of the spatial structure
of snow cover anomalies over Northern Eurasia.

• For simulation of the negative anomalies of
  air temperature, a dependence between descending
  atmospheric flows and quantity of clouds was
  used. For the testing regions, climatic regimes
  with cloudiness decreased by 50 due to
  descending atmospheric movements from November
  till February of each year,were evaluated.

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Experimental regions

• A North Eurasia to the north from 52?N
• B North Eurasia to the north from 52?N and to
  the east from 22.5?E
• C North Eurasia to the north from 52?N and to
  the east from 57.5?E
• D North Eurasia to the north from 48?N and to
  the east from 87.5?E

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Temperature and snow water equivalent changes for
experiment A
Temperature January
Snow () March
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Temperature and snow water equivalent changes for
experiment B
Temperature January
Snow () March
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Temperature and snow water equivalent changes for
experiment C
Temperature January
Snow () March
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Temperature and snow water equivalent changes for
experiment D
Temperature January
Snow () March