Slide 1

Transient and Eddy

Transient: deviations from time mean

Eddy: deviations from zonal mean

Why transients/eddies matter to zonal and time means?

Flux Components

Three components contribute to the zonal- and time-mean transport:

Mean Meridional Circulation (such as the three-cell circulation)

Stationary planetary Waves (such as the wavenumber 1-3 eddies in the Northern Hemisphere).

Transient Eddies (such as the weather systems = midlatitude cyclones and anticyclones).

Climate Roles of Eddies

Stationary and transient eddies are important to the poleward fluxes of temperature, moisture, energy, and angular momentum.

Poleward Flux of Temperature

Transient eddy fluxes dominant the meridional flux of temperature except in the Northern Hemisphere during winter, when stationary eddies contribute up to half of the flux.

The low-level maximum in the troposphere is associated with the structure of growing mid-latitude cyclones (I.e., weather systems).

Poleward Flux of Moisture

Both the mean meridional circulation and eddies transport water and play an important role in determining the nature of the hydrological cycle.

Moisture convergence in the tropics is dominated by the transport provided by the mean meridional circulation.

The subtropcs serves as source regions for water vapor.

Eddies remove water from the tropics and supply it to middle and high latitudes.

Poleward Flux of Energy

Mosit Ststic Energy

= sensible + latent + potential energy

= Cp*T + L*q + g*z

In a stably stratified atmosphere, moist static energy increases with altitude.

A mean meridional circulation will transport energy in the direction of flow in the upper branch of the cell.

The meridonal flux in mid-latitudes is dominated by the transient eddy fluxes, which is associated with the weather systems.

Poleward Flux of Momentum

In the tropical easterlies, eastward angular momentum is transferred from Earth to the atmosphere via frictional forces and mountain torque.

This westerly angular momentum is transported upward and then poleward inb the Hadley Cell.

Eddies then transport angular momentum poleward and downward into mid-latitude westerlies.

In the mid-latitude, the westerly momentum is returned to the Earth.

Stationary Planetary Waves

Stationary: These waves do not move around much and are fixed in certain geographic locations.

Planetary: These waves have large wavelengths, one the order of several thousands of kilometers.

Wave: Their structures vary in the zonal direction.

Stationary planetary waves are forced by large-scale mountains (such as Himalaya and Rocky mountain ranges) and heat contrasts between continents and oceans.

Stationary planetary waves are stronger in winter than in summer.

Transient Eddies

Mid-latitude cyclone and anticyclone are the major transient eddies that play an important role in meridional transports of heat, momentum, and moisture.

These mid-latitude weather systems grow from the baroclinic instability associated with the strong north-south temperature gradients in mid-latitudes.

Mid-latitude cyclones have typical spatial scales of wavenumbers 5-6 and have typical time scale of 7-10 days.

Mid-latitude cyclones are marked by well-defined fronts separating the warm air mass from the south and the cold air mass from the north. (Very different from tropical hurricanes, which do not have frontal features).

Cold and Warm Fronts

How Cyclone Grows?

Life Cycle of Mid-Latitude Cyclone

Cyclogenesis

Mature Cyclone

Occlusion

Tropical Hurricane

The hurricane is characterized by a strong thermally direct circulation with the rising of warm air near the center of the storm and the sinking of cooler air outside.

The warm core of the hurricane serves as a reservoir of potential energy, which is continuously being converted into kinetic energy by the thermally direct circulation.

They Are the Same Things…

Hurricanes: extreme tropical storms over Atlantic and eastern Pacific Oceans.

Typhoons: extreme tropical storms over western Pacific Ocean.

Cyclones: extreme tropical storms over Indian Ocean and Australia.

Slide 17

Mid-Ocean Eddies

The Gulf Stream and the Kuroshio spin off long-lived eddies via baroclinic and barotropic instabilities.

The role of eddies for heat transport in the ocean is likely much less than in the atmosphere.

The oceanic eddies are best developed well poleward of the latitude of the maximum oceanic transport.

The wind-driven and thermohaline circulations are likely to provide much more important contributions to the meridional heat flux in the subtropics.


	Transient: deviations from time mean



	Eddy: deviations from zonal mean



	Why transients/eddies matter to zonal and time means?


	Three components contribute to the zonal- and time-mean transport:
	Mean Meridional Circulation (such as the three-cell circulation)
	Stationary planetary Waves (such as the wavenumber 1-3 eddies in the Northern Hemisphere).
	Transient Eddies (such as the weather systems = midlatitude cyclones and anticyclones).


	Stationary and transient eddies are important to the poleward fluxes of temperature, moisture, energy, and angular momentum.


	Transient eddy fluxes dominant the meridional flux of temperature except in the Northern Hemisphere during winter, when stationary eddies contribute up to half of the flux.

	The low-level maximum in the troposphere is associated with the structure of growing mid-latitude cyclones (I.e., weather systems).


	Both the mean meridional circulation and eddies transport water and play an important role in determining the nature of the hydrological cycle.
	Moisture convergence in the tropics is dominated by the transport provided by the mean meridional circulation.
	The subtropcs serves as source regions for water vapor.
	Eddies remove water from the tropics and supply it to middle and high latitudes.


	Mosit Ststic Energy
	= sensible + latent + potential energy
	= CpT + Lq + g*z
	In a stably stratified atmosphere, moist static energy increases with altitude.
	A mean meridional circulation will transport energy in the direction of flow in the upper branch of the cell.
	The meridonal flux in mid-latitudes is dominated by the transient eddy fluxes, which is associated with the weather systems.


	In the tropical easterlies, eastward angular momentum is transferred from Earth to the atmosphere via frictional forces and mountain torque.
	This westerly angular momentum is transported upward and then poleward inb the Hadley Cell.
	Eddies then transport angular momentum poleward and downward into mid-latitude westerlies.
	In the mid-latitude, the westerly momentum is returned to the Earth.


	Stationary: These waves do not move around much and are fixed in certain geographic locations.
	Planetary: These waves have large wavelengths, one the order of several thousands of kilometers.
	Wave: Their structures vary in the zonal direction.
	Stationary planetary waves are forced by large-scale mountains (such as Himalaya and Rocky mountain ranges) and heat contrasts between continents and oceans.
	Stationary planetary waves are stronger in winter than in summer.


	Mid-latitude cyclone and anticyclone are the major transient eddies that play an important role in meridional transports of heat, momentum, and moisture.
	These mid-latitude weather systems grow from the baroclinic instability associated with the strong north-south temperature gradients in mid-latitudes.
	Mid-latitude cyclones have typical spatial scales of wavenumbers 5-6 and have typical time scale of 7-10 days.
	Mid-latitude cyclones are marked by well-defined fronts separating the warm air mass from the south and the cold air mass from the north. (Very different from tropical hurricanes, which do not have frontal features).


	The hurricane is characterized by a strong thermally direct circulation with the rising of warm air near the center of the storm and the sinking of cooler air outside.
	The warm core of the hurricane serves as a reservoir of potential energy, which is continuously being converted into kinetic energy by the thermally direct circulation.


	Hurricanes: extreme tropical storms over Atlantic and eastern Pacific Oceans.
	Typhoons: extreme tropical storms over western Pacific Ocean.
	Cyclones: extreme tropical storms over Indian Ocean and Australia.


	The Gulf Stream and the Kuroshio spin off long-lived eddies via baroclinic and barotropic instabilities.
	The role of eddies for heat transport in the ocean is likely much less than in the atmosphere.
	The oceanic eddies are best developed well poleward of the latitude of the maximum oceanic transport.
	The wind-driven and thermohaline circulations are likely to provide much more important contributions to the meridional heat flux in the subtropics.