Chapter 3

Question 1

The potential vorticity (PV)

Answer 1

the absolute circulation of an air parcel that is enclosed between two isentropic surfaces

Question 2

…………………………………………. then it is officially called IPV (isentropic potential vorticity).

Answer 2

If PV is displayed on a surface of constant potential temperature

Question 3

PV is simply expressed as

Answer 3

Question 4

Static (hydrostatic) stability refers to

Answer 4

the resistive force offered to the motion by the vertical density structure of the atmosphere in the gravitational field, and specifically when the atmosphereis in hydrostatic equilibrium.

Question 5

Thus, PV in contrast to vorticity on isobaric surfaces, consists of two factors

Answer 5

dynamic alelement and a thermodynamical element

Question 6

Potential Vorticity units:

Answer 6

Question 7

In the middle and upper troposphere, PV is ranging from

Answer 7

0.5 to 1.0 PVU

Question 8

In the middle and upper troposphere, PV is ranging from 0.5 to 1.0 PVU. In the stratosphere

Answer 8

PV > 3.0 PVU

Question 9

In the middle and upper troposphere, PV is ranging from 0.5 to 1.0 PVU. In the stratosphere PV > 3.0 PVU due to

Answer 9

the strong increase of the static stability

Question 10

In terms of the PV concept, the tropopause in mid‐latitudes may be represented by the surface of

Answer 10

constant PV = 1.5 PVU, and considered as thedynamical tropopause.

Question 11

positive PV‐anomaly

Answer 11

An abrupt lowering of the dynamical tropopause

Question 12

A positive PV anomaly is produced by

Answer 12

the intrusion of stratospheric air into the
upper troposphere

Question 13

A positive PV anomaly is produced by the intrusion of stratospheric air into the upper troposphere. An upper level PV anomaly,

Answer 13

advected down to middle troposphere is called: tropopause dynamic anomalyor folding of the tropopause

Question 14

Due to PV conservation, the PV anomaly leads to

Answer 14

deformations invertical distribution of potential temperature and vorticity

Question 15

…………………….. produces a vertical motion

Answer 15

In a baroclinic flow increasing with height, the intrusion of PV anomaly in the troposphere

Question 16

The deformation of the isentropes imposes

Answer 16

ascending motion ahead of the anomaly and subsiding motion behind

Question 17

An idealized cross section of an positive PV anomaly is shown below. The wind speed ……………… 1.5 PVU surface ………………………………….. where ………………. and ……………………..

Answer 17

increases with height. 1.5 PVU surface separates the very stable stratosphere, where the isentropes are close to each other, and the much less stable troposphere.

Question 18

An idealized cross section of an positive PV anomaly is shown below. The wind speed increases with height. 1.5 PVU surface separates the very stable stratosphere, where the isentropes are close to each other, and the much less stable troposphere. Ahead of the PV anomaly there is

Answer 18

ascent, behind it descent

Question 19

In the water vapour image the anomaly appears as

Answer 19

a dark, roundish area

Question 20

A

Answer 20

Question 21

B

Answer 21

Question 22

C

Answer 22

Question 23

D

Answer 23

Question 24

E

Answer 24

Question 25

F

Answer 25

Question 26

G

Answer 26

Question 27

Analyses of PV appear to have more structure than

Answer 27

height analyses on an isobaric surface.

Question 28

Analyses of PV appear to have more structure than height analyses on an isobaric surface. The reason for this is

Answer 28

a mathematical consequence of the dynamical principles.

Question 29

If the gradient wind formula is examined, one can establish that

Answer 29

the wind is related to the gradient of the geopotential height

Question 30

The horizontal gradient of PV is related to ............................. and show ....................................

Answer 30

second derivatives of the geopotential height, and show a lot more structure than the geopotential height field.

Question 31

The practical consequence is that using PV can identify

Answer 31

e.g. short wave troughs in the geopotential height field more easily.

Question 32

Since fast‐moving troughs can

Answer 32

influence weather dramatically

Question 33

Since fast‐moving troughs can influence weather dramatically, PV is a useful tool to

Answer 33

notify this kind of small‐scale structures.

Question 34

When there is a mismatch between the PV and the imagery it can be an indicative of

Answer 34

a model forecast or analysis error

Question 35

The three types of mismatches between WV imagery and PV fields are:

Answer 35

temporal, location/spatial, and magnitudes/heights

Question 36

To ensure the best comparison between the WV and PV fields make sure to

Answer 36

Compare the NWP analysis with the same time in water vapour imagery. If the times don't match, then an accurate representation of the other components will hinder your ability to accurately adjust the forecast NWP

Question 37

To ensure the best comparison between the WV and PV fields make sure to: 1. Compare the NWP analysis with the same time in water vapour imagery. If the times don't match, then an accurate representation of the other components will hinder your ability to accurately adjust the forecast NWP

Answer 37

2. Compare the locations of synoptic features. Mesoscale or smaller diabatic processes are often not matched well between the NWP and the WV. Only in the largest complexes of diabatic processes comparing those features can be done directly.

Question 38

To ensure the best comparison between the WV and PV fields make sure to: 1. Compare the NWP analysis with the same time in water vapour imagery. If the times don't match, then an accurate representation of the other components will hinder your ability to accurately adjust the forecast NWP 2. Compare the locations of synoptic features. Mesoscale or smaller diabatic processes are often not matched well between the NWP and the WV. Only in the largest complexes of diabatic processes comparing those features can be done directly.

Answer 38

3. Compare the magnitudes/heights of the major synoptic features This can be hard to compare unless the contour interval of the PV surface is high enough to match the gradients of the water vapour imagery.

Question 39

Comparing the water vapour imagery and 1.5PVU surface, will be able to show

Answer 39

the differences well between observations and model

Question 40

Because the 1.5PVU surface and water vapour surface are

Answer 40

so similar in vertical structure and height, we can make a nearly direct comparison

Question 41

Limitations of Comparison

Answer 41

* The images will likely NOT match in areas of diabatic processes or strong frictional forces, and work best in developing systems, not in old systems. * Anticyclonic systems won't match between the WV and 1.5PVU surface as they have an inverse relationship.

Question 42

In the WV image, the areas where the PV field doesn't match because of NWP errors, and not due to

Answer 42

diabatic/frictional processes or anticyclonic flow are identified.

Question 43

In the WV image, the areas where the PV field doesn't match because of NWP errors, and not due to diabatic/frictional processes or anticyclonic flow are identified. Comparison is made to

Answer 43

look for location and magnitude mismatches, as there are no temporal differences.

Question 44

Location a

Answer 44

The dry area east of southern Greenland Mismatch in magnitude (too large in PV, not extended far enough east)

Question 45

location b

Answer 45

The PV anomaly over Denmark • Mismatch in location (too far north compared to dry maximum)

Question 46

location c

Answer 46

The PV anomaly in western Russia • Mismatch in location (too far east in PV) • Mismatch in magnitude (too deep in PV)

Question 47

location D

Answer 47

Location D: The warm dark region over Sweden and Finland • Mismatch in location (not tilting far enough east in PV)

Question 48

Location E

Answer 48

The jetstreak aimed toward the southern UK and Northern France • Mismatch in magnitude (dark area not represented well in PV)