A Simple Model of Atmospheric developments during El-Nino

Mentor: doc dr. Nedjeljka Žagar Author: Aljoša Slameršak

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.

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

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.

El Nino animation

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.

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

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:

• 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

Parameterization of heating

Results and coherence with measurements

Advanced models