Turbulance, Vorticity and atmospheric waves

1. Turbulance,Vorticity and
Atmospheric waves.
Presented by,
Harithalekshmi V

2. Turbulance
Turbulent flow is any pattern of fluid motion characterized
by chaotic changes in pressure and flow velocity.
It is in contrast to a laminar flow regime, which occurs when
a fluid flows in parallel layers, with no disruption between
those layers.

3. How it happens?
• Turbulence is caused by excessive kinetic energy in
parts of a fluid flow, which overcomes the damping
effect of the fluid's viscosity.
• For this reason turbulence is easier to create in low
viscosity fluids, but more difficult in highly viscous
fluids.

4. • The onset of turbulence can be predicted by a
dimension less constant called the Reynolds number.
• The Reynolds number is calculated as,
•
• ρ is the density of the fluid (SI units: kg/m3)
• u is the velocity of the fluid with respect to the object (m/s)
• L is a characteristic linear dimension (m)
• μ is the dynamic viscosity of the fluid (Pa·s or N·s/m2 or kg/m·s)
• ν is the kinematic viscosity of the fluid (m2/s).
Laminar flow occurs at low Reynolds
numbers.
Turbulent flow occurs at high
Reynolds numbers.

5. Examples of turbulence in nature.
• Most of the terrestrial atmospheric circulation.
• The oceanic and atmospheric mixed layers and intense oceanic currents.
• The external flow over all kind of vehicles such as cars, airplanes, ships and
submarines.
• Snow fences work by inducing turbulence in the wind.
• Billowing storm clouds.
• Smoke from a chimney.

6. Vorticity
• Vortex: Area of closed circular or near circular
fluid motion.
Vorticity
• Measure of the local spinning motion of the
flow.
• Vector quantity.
• Denotes the local axis of rotation and local
magnitude.

7. Stoke’s Theorem
• Vorticity and circulation can be related by
stokes theorem.

8. • In accordance with geostropic balance positive
vorticity is associated with cyclonic rotation in the
northern hemisphere.
• Negative vorticity is associated with anticyclonic
rotation in the northern hemisphere.

9. Planetary vorticity
Component of vorticity due to rotation of earth around the axis.

10. Atmospheric waves
An atmospheric wave is a periodic disturbance
in the fields of atmospheric variables
like surface pressure,temperature, or wind
velocity which may either propagate (traveling
wave) or not (standing wave).

11. Causes and effects
• Obstruction of the flow of air currents by mountain ranges,
• Heating effects can be:
 small-scale
Eg:like the generation of gravity waves by convection.
 Large scale
Eg:The formation of Rossby waves by the temperature
contrasts between continents and oceans in the Northern
hemisphere winter.

12. Types of atmospheric waves
Gravity waves
Waves generated in a fluid medium or at the interface between
two media when the force of gravity or buoyancy tries to
restore equilibrium.
Eg: Waves generated at the interphase between
the atmosphere and ocean.

13. • A gravity wave results when fluid is displaced from a
position of equilibrium.
• The restoration of the fluid to equilibrium will
produce a movement of the fluid back and forth,
called a wave orbit.
• In the Earth's atmosphere, gravity waves transfer
momentum from the troposphere to
the stratosphere and mesosphere.

14. Rossby wave
 Rossby wave are formed due to earth’s rotation.
 Also known as planetary waves .
 Rossby waves were first identified by Carl Gustaf Rossby
 These waves explain about the dominant weather
systems at the higher latitudes.
 It is induced by variation of coriolis force with latitude.

15. Atmospheric rossby waves
Rossby waves are formed when polar air moves toward
the Equator while tropical air is moving poleward.
• The tropical air carries heat poleward, and the polar
air absorbs heat as it moves toward the Equator.
• The existence of these waves explains the low-
pressure cells (cyclones) and high-pressure
cells (anticyclones).