Climate Modeling MEA 719 Lecture Set 8 Monsoons

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Climate Modeling MEA 719Lecture Set 8
Monsoons
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Main Topics of Lecture

• Definition of Monsoons
• Monsoon General Climatology
• ii) International Monsoon Observational Programs
• Theoretical Modeling
• Variability of the American Monsoons (VAMOS)

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Original Definition

• The word monsoon has its origins in the Arabic
  word, Mausam which means Season
• However, it has also come to be associated with
  wind directions

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Quantitative Definition

• Many versions of the definition for Monsoons
  See examples of different attempts
• Hann (1908)
• Shick (1953)
• Khromov (1957)
• GOAL A definition that separates monsoon regions
  from non-monsoon regions

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References

• Hann J. V (1908) Results of Meteorological
  Observations in Upper Egypt and Sudan.
  Meteorologische Zeitschrift, 25, 559-562.
• Shick M. (1953) Die Geographische Verbreitung
  Des Monsuns. NOVA Acta Leopoldina, 16, No. 12.
• Khromov S.P. (1957) Geographical Distribution of
  the Monsoons. Vsesoiusnoe Geographicheskoe
  Ovshchesivo, Leningrad, Izvvestiia, 89(1), 7-13

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Ramage (1971) Definition(widely adopted by
monsoon researchers throughout the world)

• Defines a monsoon area by the following criteria
• The prevailing wind direction shifts by at least
  120deg between January and July
• The average frequency of the respective
  prevailing wind direction in January and July
  exceeds 40
• The mean resultatnt wind in at least one of the
  months exceeds 3 m/s

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Monsoon General Climatology (Monsoon Regions)

• Monsoon of India and nearby regions
• Monsoon over southeast China
• Monsoon over north Australia
• Monsoon over East Africa
• Monsoon over West Africa
• Monsoon over the Americas

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East Africa
S.A Monsoon
North Australia
http//www.sandiego.edu/weather/N-N/O16.jpg
J A N U A R Y
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NA Monsoon
SE Asia
India monsoon
West Africa
http//www.sandiego.edu/weather/N-N/O16.jpg
J U L Y
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Indian Monsoon CirculationFasullo Webster
(2004)
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International Monsoon Observational Programs

• To understand the monsoons we need both
  observations and theory
• International Indian Ocean Expedition (IIOE)
  during 1963-64
• GARP Atlantic Tropical Experiment (GATE, 1974)
• Monsoon Experiment (MONEX) during 1979 as a
  component of the First GARP Global Experiment
  (FGGE)
• Between GATE and FGGE there was two less
  extensive Programs
• Indo-Soviet Monsoon Experiment in 1973 ISMEX-73
• In 1977 MONEX-77

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IIOE-MONEX-ISMEX Observations

• Concentrated mostly on the Indian Ocean region.
  Observations were collected from
• Routine surface upper air platforms
• Commercial ships
• Special research ships
• Commercial aircrafts
• Special research aircrafts
• Buoys
• Satellites

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Theoretical Modeling of the Monsoon System
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Governing Equations Quasi-geostrophic
formulation Asnani Mishra, Diabatic Heating
model of the Indian Monsoon, 1975 MWR., 103,
115-130
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Key Symbols
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Dynamical formulation of MonsoonsQuasi-geostroph
ic formulation Asnani Mishra, Diabatic
Heating model of the Indian Monsoon, 1975MWR.,
103, 115-130)

• Quasi-geostrophic conditions
• Latitude 5deg North 35deg North
• Beta-plane geometry centered at 20deg North
  (therefore a source of error as we approach the
  equator)

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Boundary Conditions

• Convergence of heat due to horizontal advections
  is supposed to be inconsequential compared to in
  situ diabatic heating Q and
• Vertical velocity at the bottom of the atmosphere
  is due to frictions pumping in Ekman layer
  (Brunt, 1939 Charney and Eliassen, 1949 see
  full references next page)

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Ekman Pumping References

• Brunt, D.,1939 Physical and Dynamical
  Meteorology. Cambridge University Press, 2nd
  Edition, 428 pp. 2nd Edition Printed in 1941)
• Charney J. G., Eliassen, 1949 A numerical
  method for predicting the perturbations of the
  middle latitude westerlies. Tellus, 1, 38-54.

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Basis of Theoretical Model Formulation

• Basic Observed Monsoon Structure
• It is noted that the monsoon circulation is the
  sum of the annual mean and annual oscillation
  for pressure and circulation
• Hypothesis
• The annual oscillation in the pressure and wind
  is a result of the annual diabatic heating
  oscillation
• Modeling Strategy
• If diabatic heating can be shown to produce the
  observed pressure oscillation in the model, then
  we can claim that we have gained some insight
  into the mechanism

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The Primary Objective is to Study the Response
of the Atmosphere to Two Plausible types of
Diabatic Heating Q
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Two Types of Diabatic Heating
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Structure of the Diabatic Heating Functions

• TYPE I Has largest value at the bottom, i.e., at
  the earth-atmosphere interface and decreases
  upwards. This heating occurs through sensible
  heat exchange. Assumed to be sinusoidal in the
  horizontal and in time.
• Type II This is the heating due to latent heat
  release during condensation and it has a maximum
  in the middle and upper troposphere. Assumed to
  be sinusoidal in the horizontal and in time.

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Other Forms of Diabatic Heating

• Direct heat absorption in the stratosphere is
  considered to be secondary and ignored
• Other diabatic heating and cooling are also
  neglected

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Theoretical Investigation of the Influence of
Diabatic Heating Surface Friction on the Annual
Cycle

• Diabatic Heating Type I, without friction
• Diabatic Heating Type II, without friction
• Diabatic Heating Type I, with friction
• Diabatic Heating Type II, with friction
• Diabatic Heating Type I II, with friction

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Main Results

• Heating of Type I II both produce low pressure
  in the lower levels and high pressure aloft, with
  phase reversal in the lower or middle
  troposphere.
• The horizontal dimension of the diabatic heating
  have a remarkable influence on the character of
  the Low and the High pressure perturbations, the
  larger he horizontal dimensions, the larger is
  the amplitude of the pressure oscillation, at
  higher levels
• Surface friction reduces the amplitude of the
  pressure oscillation in the in the lower layers
  but enhances it in the upper layers.
• When the annual mean is superimposed on the
  annual oscillation the resulting zonal flow along
  the 77.5deg E meridian the observed features of
  the monsoon system are simulated very well, such
  as, the westerly jet stream over north India
  during winter and the easterly jet stream over
  south India during summer

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Main Results
Model
Observations
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Variability of the American Monsoon System
(VAMOS)
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Guiding question

• What are the primary characteristics of the
  Variability of the American Monsoon
  System(VAMOS)?
• ii) What are the primary factors responsible for
  the existence of the American Low-Level-Jets?
• What is the role of the American Low-Level-Jets
  in modulating regional atmospheric hydrological
  budgets?
• What are the main objectives of the SAME NAME
  research programs

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Primary characteristics of the Variability of the
American Monsoon System
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Climatology of Low-Level Jets
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Theories of the cause of the South North
American LLJs

• The blocking effect of the Andes play a prominent
  role in the intensification of the low-level
  circulations of the South America. However,
  important elements of LLJ interaction with
  topography and precipitation still are marginally
  understood.
• The low-level flow is strongly influenced by the
  proximity of the Bermuda anticyclone, with
  enhanced southerlies with a strong high close to
  the continent
• Cold air incursions
• Although diurnal and seasonal oscillations of the
  Great Plains LLJ are contained in atmospheric
  models, related aspects are poorly simulated, and
  therefore marginally understood

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The role of the American Low-Level-Jets in
modulating regional atmospheric hydrological
budgets
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• Low-level atmospheric jets over the Americas
  circulations promote exchange of atmospheric
  water vapor from low to mid-latitudes and its
  subsequent condensation

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American Low Level Jets modulate much of the
moisture supply to the fertile plains located
east of the North American Rockies, and situated
over the LaPlata river basin
LaPlata river basin
18 S
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Total precipitation from gridded analysis
(Higgins et al. 1996a) of station data, for July
1993 (top) and  June 1988 (bottom). Contour
interval is 0.05m - based on gridded Analyses
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The Great Plains jet in drought episodes similar
to that of summer 1988 was only about half as
strong as those observed for flood conditions
similar to summer 1993 (Mo et al., 1995)
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Guiding Question

• Outline the main goals of the VAMOS SAME and
  NAME Programs of the Americas

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South American Monsoon Experiment (SAME
www.clivar.org)

• The ultimate goal is to improve short and long
  term prediction through the following strategy
• obtain an improved description of the temporal
  and spatial structure of the LLJs based on
  expanded monitoring activities and special field
  experiments,
• evaluate numerical representation (forecasts and
  analyses) of LLJs against special observations
  and,
• determine improvements of initial state
  representation and model parameterizations
  required to improve prediction

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South American Monsoon Experiments (SAME)

• The ultimate goal of SAME is to improve short and
  long term prediction. This will be achieved
  through a series of coordinated projects (see RHS)

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North American Monsoon Experiment (NAME
www.clivar.org)

• The scientific objectives of NAME are to promote
  a better understanding and more realistic
  simulation and prediction of
• (1) The evolution of the North American monsoon
  system and its variability
• (2) The response of the warm season atmospheric
  circulation and precipitation patterns to slowly
  varying, potentially predictable surface boundary
  conditions (e.g. SST, soil moisture and
  vegetation)
• (3) The diurnal heating cycle and its
  relationship to the seasonally varying mean
  climate
• (4) Intraseasonal variability of the monsoon.
• In addition to these scientific objectives, NAME
  researchers will interact with applications,
  assessment, and human dimensions researchers on
  the potential use of NAME science by end users.

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NAME REGION