Chapter 3

Question 1

Turbulence statistics differ case by case because of

Answer 1

• different surface forcing,
• geostrophic wind, or
• different sounding

Question 2

Turbulence statistics differ case by case because of different surface forcing,

geostrophic wind, or different sounding.

 But with proper …………….., most turbulent statistics of the PBL collapse onto some ……………….

Answer 2

scaling

universal curves, even though data are taken from different cases.

Question 3

Turbulence statistics differ case by case because of different surface forcing, geostrophic wind, or different sounding.

 But with proper scaling, most turbulent statistics of the PBL collapse onto some universal curves, even though data are taken from different cases.

 In other words, ………………

Answer 3

if we can come up with proper scaling parameters, turbulent statistics obtained from a wide range of meteorological conditions can be normalized in such a way that their non‐dimensional statistics are similar.

Question 4

Employing typical characteristic ……………………………enables us to derive …………………………….

Answer 4

length, time, and velocity scales

governing equations in a non‐dimensional form.

Question 5

Employing typical characteristic length, time, and velocity scales enables us to derive governing equations in a non‐dimensional form.

 The advantage is that we can

Answer 5

compare the relative importance of each contribution and reduce the number of parameters needed to study the atmospheric flow

Question 6

Variables that frequently appear in combination with one another are grouped to form

Answer 6

new variables that may be nondimensional, such as the Richardson number,

Question 7

Variables having simple dimensional units such as

Answer 7

velocity, length, or time in some cases are related to the most important scales of motion in the eddies

Question 8

Turbulence Scales

Answer 8

• length scales
• Velocity scaales
  
  • deardoff velocity scale (w^*)
  • Friction velocity scale (u^*)
• time scales

Question 9

length scales

Answer 9

• Altitude of the capping inversion, z_i,
  
  • for the whole boundary layer
  • for statically unstable and neutral conditions.
• Aerodynamic roughness length z₀
  
  • _​for the surface layer (bottom 5% of PBL)
  • indicates the roughness of the surface
• Obukhov lenght (L)
  
  • for statistically nonneutral conditions in the surface layer

Question 10

Obukhov length (L)

Answer 10

Question 11

Velocity Scales

Answer 11

• Deardorff velocity scale (w^*)
  
  • characterizing the turbulent mixing due to free convection in an unstably stratified BL
• Friction velocity velocity scale (u^*)
  
  • applicable to statically neutral conditions in the surface layer (the turbulence is mostly mechanically generated)

Question 12

Deardorff velocity scale (w*) ‐

Answer 12

Question 13

Friction velocity scale ‐ Another scale u*,

Answer 13

Question 14

Time Scales

Answer 14

Question 15

In summary, For convective boundary layers (ie………..) the relevant scaling parameters are ………….

Answer 15

(ie., unstable mixed layers)

w* and Zi

Question 16

For the neutral surface layer, ……………… are applicable.

Answer 16

u* and z0

Question 17

Scaling parameters for surface layers are

Answer 17

u*, z0, and L, provided that the stratification is not neutral.

Question 18

Scaling laws describe

Answer 18

the functional relationship between two physical quantities that scale with each other over a significant interval.

Question 19

Scaling laws describe the functional relationship between two physical quantities that scale with each other over a significant interval.

 An example of this is

Answer 19

the scaling law for wind profile in the ABL

Question 20

Wind profile ‐ the wind profile law

Answer 20

Question 21

For non‐neutral situations. the wind profile

Answer 21

deviates slightly from logarithmic.

Question 22

In stable boundary layers. the wind profile

Answer 22

is concave downward on a semi log plot

Question 23

unstable boundary layers wind profile

Answer 23

are concave upward

Question 24

Air stability refers to

Answer 24

the vertical moving tendency of an air parcel in response to a small disturbance.

Question 25

The amplification of a small vertical disturbance in an............... atmosphere, represents the ................................

Answer 25

unstable mechanism by which buoyancy produces turbulence

Question 26

Under neutral conditions, turbulence is generated

Answer 26

mechanically by wind shear

Question 27

the flow is dynamically unstable when

Answer 27

the presence of wind shear and a viscous force such that a small initial perturbation will become amplified, leading to overturning motion.