Chapter 8 Flashcards
Rossby waves
also known as planetary waves, are a natural phenomenon in the atmosphere and oceans of planets that largely owe their properties to rotation of the planet.
Rossby waves, also known as planetary waves, are a natural phenomenon in the atmosphere and oceans of planets that largely owe their properties to rotation of the planet. Rossby waves are a subset of
inertial waves.
Atmospheric Rossby waves on Earth are
giant meanders in high-altitude winds that have a major influence on weather.
Atmospheric Rossby waves on Earth are giant meanders in high-altitude winds that have a major influence on weather. These waves are associated with
pressure systems and the jet stream.
Atmospheric Rossby waves result from
the conservation of potential vorticity and are influenced by the Coriolis force and pressure gradient.
A fluid, on the Earth, that moves toward the pole will deviate toward the
east
A fluid, on the Earth, that moves toward the pole will deviate toward the east; a fluid moving toward the equator will deviate
toward the west (true in either hemisphere).
The deviations are caused by the
the Coriolis force and conservation of potential vorticity which leads to changes of relative vorticity.
The deviations are caused by the Coriolis force and conservation of potential vorticity which leads to changes of relative vorticity. This is analogous to
conservation of angular momentum in mechanics.
In planetary atmosphere, Rossby waves are due to the
variation in the Coriolis effect with latitude.
One can identify a terrestrial Rossby wave as its
its phase velocity, marked by its wave crest, always has a westward component.
One can identify a terrestrial Rossby wave as its phase velocity, marked by its wave crest, always has a westward component. However, the collected set of Rossby waves may appear to move
in either direction with what is known as its group velocity.
However, the collected set of Rossby waves may appear to move in either direction with what is known as its group velocity. In general, shorter waves have an
eastward group velocity and long waves a westward group velocity.
The terms “barotropic” and “baroclinic” are used to distinguish
the vertical structure of Rossby waves.
Barotropic Rossby waves
do not vary in the vertical, and have the fastest propagation speeds.
The baroclinic wave modes
on the other hand, do vary in the vertical. They are also slower, with speeds of only a few centimeters per second or less.
Most investigations of Rossby waves have been done on those in
Earth’s atmosphere.
Most investigations of Rossby waves have been done on those in Earth’s atmosphere. Rossby waves in the Earth’s atmosphere are
easy to observe as (usually 4-6) large-scale meanders of the jet stream
Most investigations of Rossby waves have been done on those in Earth’s atmosphere. Rossby waves in the Earth’s atmosphere are easy to observe as (usually 4-6) large-scale meanders of the jet stream. When these deviations become very pronounced,
masses of cold or warm air detach, and become low-strength anticyclones and cyclones, respectively, and are responsible for day-to-day weather patterns at mid-latitudes.
The action of Rossby waves partially explains why
eastern continental edges, such as the Northeast United States and Eastern Canada, are colder than Western Europe at the same latitudes.
Poleward-propagating atmospheric waves
Deep convection (heat transfer) to the troposphere is enhanced over very warm sea surfaces in the tropics, such as during El Niño events.
Deep convection (heat transfer) to the troposphere is enhanced over very warm sea surfaces in the tropics, such as during El Niño events. This tropical forcing generates
atmospheric Rossby waves that have a poleward and eastward migration
Poleward-propagating Rossby waves explain
many of the observed statistical connections between low- and high-latitude climates
Poleward-propagating Rossby waves explain many of the observed statistical connections between low- and high-latitude climates. One such phenomenon is
is sudden stratospheric warming
Poleward-propagating Rossby waves are an important and unambiguous part of the
variability in the Northern Hemisphere, as expressed in the Pacific North America pattern.
Some things to note regarding Rossby waves::
· The frequency is always
negative, and becomes larger in magnitude for the longer wavelengths (smaller wave numbers).
Some things to note regarding Rossby waves::
· The frequency is always negative, and becomes larger in magnitude for the longer wavelengths (smaller wave numbers).
· The zonal phase speed is
always negative in the absence of mean flow
Some things to note regarding Rossby waves::
· The frequency is always negative, and becomes larger in magnitude for the longer wavelengths (smaller wave numbers).
· The zonal phase speed is always negative in the absence of mean flow.
· The zonal group speed may be
either positive or negative, depending on the horizontal wave number.
Some things to note regarding Rossby waves::
· The frequency is always negative, and becomes larger in magnitude for the longer wavelengths (smaller wave numbers).
· The zonal phase speed is always negative in the absence of mean flow.
· The zonal group speed may be either positive or negative, depending on the horizontal wave number.
o Long waves propagate
energy westward in the same direction as the phase speed.
Some things to note regarding Rossby waves::
· The frequency is always negative, and becomes larger in magnitude for the longer wavelengths (smaller wave numbers).
· The zonal phase speed is always negative in the absence of mean flow.
· The zonal group speed may be either positive or negative, depending on the horizontal wave number.
o Long waves propagate energy westward in the same direction as the phase speed.
o Shortwaves propagate
energy eastward, opposite to the phase speed.
Some things to note regarding Rossby waves::
· The frequency is always negative, and becomes larger in magnitude for the longer wavelengths (smaller wave numbers).
· The zonal phase speed is always negative in the absence of mean flow.
· The zonal group speed may be either positive or negative, depending on the horizontal wave number.
o Long waves propagate energy westward in the same direction as the phase speed.
o Shortwaves propagate energy eastward, opposite to the phase speed.
· The meridional phase speed is
negative, but the meridional group speed is positive.
