Midlattitude cyclones

Question 1

The single most common weather element in the middle-latitudes is the

Answer 1

frontal cyclone (also called the midlatitude cyclone).

Question 2

Extratropical cyclones are

Answer 2

large low-pressure systems named by their cyclonic rotation and latitude of formation.

Question 3

Extratropical cyclones are synoptic-scale phenomena that has a life span

Answer 3

on the order of one week.

Question 4

Cyclogenesis

Answer 4

the process by which a surface cyclone initially develops and subsequently intensifies.

Question 5

Intensification is often measured in terms of

Answer 5

negative sea level pressure tendency

or

positive low-level vorticity tendency.

Question 6

Including the effects of …………………and …………………………., the four QG forcing functions that are associated with

Answer 6

friction

diabatic heating

Question 7

Including the effects of friction and diabatic heating, the four QG forcing functions that are associated with …………………. and ……………………..at the surface

Answer 7

rising motion and pressure falls

Question 8

Including the effects of friction and diabatic heating, the four QG forcing functions that are associated with rising motion and pressure falls at the surface are

Answer 8

• Increasing positive vorticity advection with height
• Local maximum in temperature advection
• Local maximum in diabatic heating
• Curl of the frictional force becoming more cyclonic with height

Question 9

Type B cyclones

Answer 9

Surface cyclones that form mainly in response to vorticity advection

Question 10

Type A cyclones

Answer 10

urface cyclones that form mainly in response to temperature advection along frontal zones

Question 11

By QG theory, geostrophic temperature advection increasing ………………… is associated with …………………

Answer 11

upward is associated with height falls

Question 12

for a developing cyclone, there is …………………………… and …………………………….

Answer 12

strong low-level warm advection below and downstream of the trough axis.

Question 13

In a developing midlatitude cyclone, height rises usually occur to the

Answer 13

east of the sea-level pressure minimum (in the vicinity of the cyclone’s warm front).

Question 14

Height falls usually occur to

Answer 14

the west of the sea-level pressure minimum (in the vicinity of the cold front)

Question 15

Diabatic heating alone may be responsible for the……………………………….. if the ….

Answer 15

formation of a surface cyclone, if the region of diabatic heating represents a local maximum

Question 16

What may form a low or trough?

Answer 16

Intense localized diabatic heating owing to latent heat release from cumulus convection

Question 17

what may form a high or ridge?

Answer 17

region of diabatic cooling owing to evaporation of rain in an unsaturated layer below

Question 18

Movement of surface low pressure

Answer 18

• toward a region of rising motion
• towards regions in which vorticity advection is becoming more cyclonic with height.
• regions of local maxima in warm advection.
• towards regions of local maxima in diabatic warming.

Question 19

The two ……………………..that are important for the formation of upper-level troughs and ridges are

Answer 19

QG forcing terms

Question 20

The two QG forcing terms that are important for the formation of upper-level troughs and ridges are

Answer 20

• Geostrophic vorticity advection
• differential temperature advection

Question 21

geostrophic vorticity advection will

Answer 21

not amplify the upper level systems

Question 22

………………………………… and ……………………………can affect the height field so that upper- level system form or intensify.

Answer 22

Differential temperature advection and diabatic heating

Question 23

low on surface causes

Answer 23

ridge

Question 24

When the strongest winds are ………………from the trough, the trough tends to ”dig” ……………………..

Answer 24

upstream

equatorward

Question 25

When the strongest winds are …………………….from the trough, the trough tends to ”lift out”……………………..

Answer 25

downstream

poleward

Question 26

The lifecycle of a midlatitude cyclone consists of four basic stages

Answer 26

1. Perturbation stage
2. Cyclogenesis stage
3. Mature stage
4. Decay stage

Question 27

Nearly all cyclogenesis events proceed from a

Answer 27

precursor upper-level disturbance in the flow

Question 28

Nearly all cyclogenesis events proceed from a precursor upper-level disturbance in the flow. This disturbance manifests itself as a

Answer 28

relative vorticity maxima

Question 29

The disturbance will propagate in the direction of the ………………… by ……………..

Answer 29

flow by vorticity advection.

Question 30

Cyclogenesis Stage:

Since the disturbance is often initially largest at ………………………….levels

Answer 30

middle and upper tropospheric levels,

Question 31

Since the disturbance is often initially largest at middle and upper tropospheric levels, there will be

Answer 31

upward-increasing PVA downstream of the disturbance

Question 32

Since the disturbance is often initially largest at middle and upper tropospheric levels, there will be upward-increasing PVA (NVA) downstream (upstream) of the disturbance

By QG theory, this circumstance is associated with

Answer 32

upward vertical motion downstream of the trough axis.

Question 33

Under the influence of the ………………………..associated with the developing lower tropospheric disturbance

Answer 33

cyclonic circulation

Question 34

Under the influence of the cyclonic circulation associated with the…………………….

Answer 34

developing lower tropospheric disturbance

Question 35

Under the influence of the cyclonic circulation associated with the developing lower tropospheric disturbance, ………………………….will occur ……………………………..of the…………………………..

Answer 35

low-level warm advection

downstream

upper-level trough axis.

Question 36

QG theory also predicts that such a circumstance will serve to raise the ……………………………….in the middle troposphere to the………………………….. of the surface low

Answer 36

geopotential heights

east

Question 37

The distribution of upper tropospheric convergence and divergence associated with the………………………………….

Answer 37

vertical motion couplet

Question 38

The distribution of upper tropospheric convergence and divergence associated with the vertical motion couplet will tend to

Answer 38

increase the upper tropospheric vorticity in the vicinity of the trough axis while decreasing it in the vicinity of the downstream ridge.

Question 39

A more intense upper-level vorticity maximum leads to …………………………. by …………………………………. and ……………………………………. which……………………………..

Answer 39

greater PVA by the thermal wind and attendant upward vertical motions which further intensify the surface cyclone downstream of the upper feature.

Question 40

As the upper disturbance continues to develop and progress eastward, it begins to

Answer 40

outrun its surface reflection.

Question 41

As the upper disturbance continues to develop and progress eastward, it begins to outrun its surface reflection.

• As a result,

Answer 41

the convergence at the surface (maximized at the location of the sea-level pressure minimum) gradually becomes disconnected from its divergence valve aloft and the surface cyclone can no longer intensify.

Question 42

During the mature stage of the cyclone, the axis of…………………….. is tilted to the …………………………..

Answer 42

minimum geopotential height is tilted to the west.

Question 43

As the cyclone matures, the vertical tilt of the geopotential minimum axis gradually becomes

Answer 43

more vertical by the time of occlusion.

Question 44

As the cyclone matures, the vertical tilt of the geopotential minimum axis gradually becomes more vertical by the time of occlusion.

As a consequence of the eastward displacement of the upper-level divergence at this stage of the life cycle, there is no mechanism available to

Answer 44

evacuate the accumulating mass near the center of the surface cyclone and the surface pressure rises as a consequence.

Question 45

By QG theory, this rise in surface pressure is associated with a

Answer 45

decrease in the near surface geostrophic vorticity

Question 46

By QG theory, this rise in surface pressure is associated with a decrease in the near surface geostrophic vorticity and therefore qualifies as a

Answer 46

cyclolysis event.