A Simple Model of Atmospheric developments during El-Nino
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Transcript of A Simple Model of Atmospheric developments during El-Nino
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A Simple Model of Atmospheric developments during El-Nino
Mentor: doc dr. Nedjeljka Žagar Author: Aljoša Slameršak
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Structure of my seminar
• Description of El Nino.
• Significance and impacts of El Nino Southern Oscillation.
• Presentation of the model.
• Interpretation of model’s results and their coherence with measurements.
• Advanced models.
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Definition and description of El Nino
• El Niño (EN) is characterized by a large scale weakening of the trade winds and warming of the surface layers in the eastern and central equatorial Pacific Ocean. (NOAA definition).
• It is a quasiperiodic occurance (t : 2-7 years)
• The expression was coined in 19th century, as the warm currents around Peru become most intense around christmas.
East – west overturning of sea surfaceTemepratures / Source: Holton
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Development of El-Nino
• Rise of sea surface pressure over Australonesia and fall over eastern pacific.
• Easterly trade winds weaken over the Pacific or change direction towards west.
• This change of wind stress excites Kelvin waves, which transfer the warm waters towards Eastern Pacific.
• This results in percipitation suprpluss over eastern and deficit over western part of the Pacific.
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El Nino animation
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Effects of El Nino
• Effects vary, depending on intensity of seasonal occurence
• Intensification of weather systems developments (hurricanes, droughts).
• Disruption of fishing, agriculture.
• Loss of life, infrastructure.
• Economic damage is measured in billions.
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The model
• Our task is to describe the atmospheric component of El Nino, that is the change of the wind stress, due to temperature changes.
• We use simple shallow water equations and continuity equation,which will later be modified accordingly to our assumptions.
Shallow water equations
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Assumptions and transformations:- Lower boundary condition w(0) = 0
- Equatorial beta plane for Coriolis parameter
- Geopotential instead of pressure gradients
- Linear tranfsormation of variables for time and scale
- We obtain a modified set od equations:
Pressuposed solution form:
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• The solutions for our homogenous set are:
• This is not the end of story. Sofar we have not mentioned any forcing or dissipative terms in equations. However these are crucial even for a rough description of macroscopic atmospheric systems.
Hermite polynomial
ε stands for Newtonian cooling
Q is parameterized heating
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Parameterization of heating
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Results and coherence with measurements
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Advanced models
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