chapter 7: Jet and Jet streaks Flashcards
Weather processes strongly depend on
the structure and dynamics of jet streams
There are ………………….major ……………………jet streams in the upper ………………………in each hemisphere
two
westerly
troposphere
There are two major westerly jet streams in the upper troposphere in each hemisphere
– Polar jet stream
– Subtropical jet stream
The structure of jet streams are related to
temperature distribution through the thermal wind relationship
Warm air to the south results in
westerly geostrophic winds through the thermal wind relationship.
Draw the jet stream (box)
The thermal wind relationship also explains why
the jet stream tends to be collocated with the polar front.
Large horizontal temperature gradients > > >
large horizontal temperature gradients
Large thickness gradients>
Large horizontal pressure gradient aloft>
strong winds
The polar jet is the band of
(speed ) (found in)
meandering strong winds (~100 knots) found at the tropopause.
The polar jet moves
meridionally (30°-60° latitude) and vertically (10-15 km) with the seasons.
Large vertical extent: maximum usually near ……………….. but can be seen at ……………….
300 mb
200mb - 500mb
At times, the polar jet will split into …………………………….and possibly merge with ………………………..
northern and southern branches
the subtropical jet
Polar Jet and thermal wind balance:
it is associated with:
strong quasi-horizontal temperature gradients in the lower troposphere and strong vertical wind shear.
It is associated with strong quasi-horizontal temperature gradients in the lower troposphere and strong vertical wind shear.
• These features are often associated with
the polar front.
Meridional undulations of the jet stream are associated with
poleward and equatorward displacements of warm and cold air, respectively.
The subtropical jet is associated with……………………………………. between……………………… usually found between…………………….
subtropical front between the tropical and mid-latitude air masses and is usually found between 25° and 30° N.
It meanders less than…………………………., but in rare cases has been observed as far…………………………
the polar jet
north as 60°N
Subtropical jet is ………………………
shallow
subtropical jet stream is rather shallow – sometimes less than ……………………………..and may not show up on……………………………..
3 km in depth
either of the 200 mb or 300 mb standard levels
Subtropical Jet Stream directly influences …………………………..
low-level flow only when it becomes coupled through deep cumulus convection and interactions with the polar jet
what are the two cases that subtropical jet streams affect low:
- when it becomes coupled through deep cumulus convection and
- interactions with the polar jet
Like the Polar-Front jet, the subtropical jet is associated with a
change in height of the tropopause.
The meridional temperature gradient associated with the
vertical shear under the subtropical jet is concentrated in a shallow layer
Sometimes the subtropical jet is associated with a
a portion of the Polar-Front jet that has migrated equatorward into the subtropics and has lost its low-level baroclinicity.
define Barcoclinicity
surfaces of pressure intercect surfaces of temperature and density (occure at fronts)
FRONT HAS BAROCLINITY
Subtropical Jet position is …………….. than polar jet
higher
subtropical jets and polar jet separate ……..
cells
The presence of the subtropical jet relates to the
conservation of absolute angular momentum in the context of the Hadley cell.
