QG theory Flashcards
governing equations describe
the behavior of the atmosphere
cons if governing equations
they are complex and thus it’s difficult to conceptualize the dynamical essence of synoptic-scale weather systems using the full set of equations.
How was the governing equations simplified?
- by utilizing the observation that the flow in synoptic-scale weather systems is approximately geostrophic.
- By using a carefully designed set of assumptions
Define the quasigeostrophic theory
simplified the governing equations of motion and combined them in ways that retain the fundamental dynamics of weather systems and yet are simple enough to comprehend.
The QG framework simplifies the equation of motions into a set of diagnostic equations
- QG omega equation
- QG geopotential tendency
geostrophic balance represents the
fundamental balance condition for mid-latitude synoptic-scale flow
The geostrophic wind approximation is only strictly valid in
regions of zero wind acceleration
There are two broad categories of flow in the atmosphere that will violate geostrophic balances
- Wind speed changes along the flow (i.e. jet streaks, regions of speed convergence/divergence)
- Wind direction changes along the flow (i.e. troughs and ridges, regions of confluence/diffluence)
Define ageostrophic wind
The degree of departure from geostrophic balance that characterizes synoptic-scale motions can be assessed by considering the difference between the actual wind at a location and the calculate geostrophic wind at the same point.
Ageostrophic wind is defined mathematically as
………………………, this implies that the geostrophic wind is non-divergent.
Because all divergence/convergence necessarily implies an acceleration of the wind field,
ALL…………………… in the synoptic-scale………………………………. is due to the presence of ageostrophic motion.
divergence , wind field
ALL divergence in the synoptic-scale wind field is due to the
presence of ageostrophic motion.
all vertical motion is due to the presence of
ageostrophic motion.
ageostrophic wind is entirely responsible for
- the distribution of cyclones,
- anticyclones,
- clouds,
- and precipitation in the atmosphere.
Despite the fact that the mid-latitude atmosphere is predominately in geostrophic balance, all of the important weather with which we are confronted develops as a direct result of the ……………………………….
often relatively small ageostrophic portion of the wind.
To derive the relationship between ageostrophic wind and vertical motion, we first will write the
continuity equation in isobaric coordinates.
if the geostrophic wind is nondivergent, we have
the equation is for
relationship between ageostrophic wind and vertical motion
the equation means
divergece of ageostrophic wind in upper air causes upward motion
Equation for ageostrophic wind and horizontal acceleration:
Equation for ageostrophic wind and horizontal acceleration
Explain the following equation
Vag = Acceleration term in momentum equation and 1/f
Based on the equation we conclude three properties
- The ageostrophic wind is a measure of the horizontal acceleration in the atmosphere
- The ageostrophic wind is perpendicular to the horizontal acceleration vector
- The ageostrophic wind is directed to the left of the acceleration vector in the Northern Hemisphere.
The ageostrophic winds converge on ……………………….of the upper trough (on its ………………side)
the western side, upstream
The ageostrophic winds converge on the western side of the upper trough (on its upstream side), leading to ………………..
downward vertical motion.
The ageostrophic winds divergence on the …………………side of the upper trough (on its …………………………side),
eastern , downstream
The ageostrophic winds divergence on the eastern side of the upper trough (on its downstream side), leading to …………………..vertical motion.
upward
……………………………………. explains why there tends to be cloudy/stormy weather downstream of an upper level trough
divergence on the eastern side of the upper trough (on its downstream side), leading to upward vertical motion.
Centripital acceleration
ageostrophic wind
