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Flashcards in Midlattitude cyclones Deck (46):
1

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

frontal cyclone (also called the midlatitude cyclone).

2

Extratropical cyclones are

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

3

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

on the order of one week.

4

Cyclogenesis

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

5

Intensification is often measured in terms of

negative sea level pressure tendency

or

positive low-level vorticity tendency.

6

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

friction

diabatic heating

7

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

rising motion and pressure falls

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

  • 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

9

Type B cyclones

Surface cyclones that form mainly in response to vorticity advection

10

Type A cyclones

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

11

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

upward is associated with height falls

12

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

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

13

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

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

14

Height falls usually occur to

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

15

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

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

16

What may form a low or trough?

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

17

what may form a high or ridge?

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

18

Movement of surface low pressure

  • 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.

19

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

QG forcing terms

20

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

  • Geostrophic vorticity advection
  • differential temperature advection

21

geostrophic vorticity advection will 

not amplify the upper level systems

22

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

Differential temperature advection and diabatic heating

23

low on surface causes

ridge

24

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

upstream

equatorward

25

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

downstream

poleward

26

The lifecycle of a midlatitude cyclone consists of four basic stages

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

27

Nearly all cyclogenesis events proceed from a

precursor upper-level disturbance in the flow

28

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

relative vorticity maxima

29

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

flow by vorticity advection.

30

Cyclogenesis Stage:

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

middle and upper tropospheric levels,

31

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

upward-increasing PVA downstream of the disturbance

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

upward vertical motion downstream of the trough axis.

33

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

cyclonic circulation

34

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

developing lower tropospheric disturbance

35

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

low-level warm advection

downstream

upper-level trough axis.

 

36

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

geopotential heights

east

37

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

vertical motion couplet

38

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

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

39

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

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

40

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

outrun its surface reflection.

41

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

• As a result,

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.

42

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

minimum geopotential height is tilted to the west.

43

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

more vertical by the time of occlusion.

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

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

45

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

decrease in the near surface geostrophic vorticity

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

cyclolysis event.