Meteorology

Question 1

How far does the troposphere extend and why is it significant?

Answer 1

11km, it is where weather occurs

Question 2

What characterises a region of convergent flow?

Answer 2

Air flows in toward a central point at ground level and rises before diverging near the upper limit

Question 3

What characterises a region of divergent flow?

Answer 3

Air flows together high in the troposphere and descends before parting near the ground

Question 4

What force causes wind flow to deviate from a straight path?

Answer 4

Coriolis force

Question 5

What is a typical size and speed of a depression?

Answer 5

4000km diameter
15-25 m/s

Question 6

Which type of front causes severe weather?

Answer 6

Cold front

Question 7

What is the lapse rate?

Answer 7

Decrease in temperature with height

Question 8

What is the equation for the polytropic law?

Answer 8

p=k * rho^n

Question 9

What is the equation of state?

Answer 9

p=rho * R * T

Question 10

What does adiabatic mean?

Answer 10

No transfer of heat or mass outside the system

Question 11

What is the density ratio?

Answer 11

rho2/rho1 = (p1/p2)^(gamma-n/gamma*n)

Question 12

What is n in these equations? What is its equation?

Answer 12

Polytropic index
n = g/(g-RL) where L is lapse rate

Question 13

What is assumed for Earth-fixed motion?

Answer 13

Linear acceleration di V/dt = 0
Rotational acceleration di Omega/dt = 0

Question 14

What is the pressure gradient force?

Answer 14

-delta p/rho

Question 15

What are the forces denoted by Ff and g respectively?

Answer 15

Friction force
Gravity force

Question 16

What is the equation for coriolis force relative to motion?

Answer 16

-2 * Omega * Vm

Question 17

Gravity force is not used directly in acceleration calculations, what is used instead?

Answer 17

Effective gravity force
g - Omega(Omega * r)

Question 18

What are the unit vectors s, n and k?

Answer 18

s is along the particle path
n is normal to the path
k is vertically up from the Earth’s surface

Question 19

How is coriolis force different to the other involved forces when resolving into s and n?

Answer 19

Coriolis force only has an n component, all others have both

Question 20

What is the coriolis parameter f?

Answer 20

2 * Omega * sin phi

Question 21

What are the conditions for geostrophic wind?

Answer 21

Negligible friction
Negligible curvature
Pressure gradient and coriolis force are balanced

Question 22

What is the equation for geostrophic wind speed?

Answer 22

Vg = -1/(f*rho) * dp/dn

Question 23

How do you begin the derivation of gradient wind speed?

Answer 23

(dv/dt)s = 0
(dv/dt)n = v^2/r

Question 24

If centripetal acceleration is positive, what is the direction of circulation?

Answer 24

Anti-clockwise

Question 25

What direction is cyclonic flow in the northern hemisphere?

Answer 25

Anti-clockwise

Question 26

What is the equation for solutions of gradient wind speed?

Answer 26

Vgr = -f*r/2 * (1+- sqrt(1+ 4Vg/f*r))

Question 27

For a regular low in the northern hemisphere (acw circulation) which solution for Vgr is used?

Answer 27

The negative

Question 28

What is the Rossby number?

Answer 28

Ratio of centrifugal to coriolis actions Ro = v/f*r

Question 29

What does it mean when the Rossby number is large?

Answer 29

Coriolis force can be neglected

Question 30

What is cyclostrophic wind speed? What is the equation?

Answer 30

Gradient wind speed neglecting coriolis force Vc = sqrt(-r/rho * dp/dn)

Question 31

What is the radius of maximum winds in relation to the fitting factors A and B?

Answer 31

Rw = A^(1/B)

Question 32

What is the name of the height, delta, at which wind speed becomes equal to gradient wind speed?

Answer 32

Boundary layer depth

Question 33

What is the equation for maximum shear stress at the ground surface?

Answer 33

Tao 0 = rho * u*^2 Where u* is friction velocity

Question 34

What is z0?

Answer 34

Roughness length, used to scale relative height z

Question 35

What is the function g(x) which relates x = z/z0 to y = Vz/u*?

Answer 35

2.5ln(x) + (34.5*f*z)/u*

Question 36

For what heights is the mean velocity equation using z0 applicable?

Answer 36

Up to 300m Below 30m the 34.5fz/u* part is neglected

Question 37

What is the power law Vz/Vr?

Answer 37

Vz/Vr = (z-d/r-d)^alpha Where d is the zero level, r is reference height and alpha is tabulated based on terrain

Question 38

How is turbulent wind speed quantified?

Answer 38

A sum of mean and fluctuating components

Question 39

How is turbulence intensity found?

Answer 39

Standard deviation of wind speed divided by mean wind speed

Question 40

What is the gust factor Ktao?

Answer 40

Peak wind speed (V^)/ mean wind speed (V-)

Question 41

What is the autocovariance function used for?

Answer 41

Measuring the persistence of turbulent eddies

Question 42

What is the autocovariance function Cuu(Tao)?

Answer 42

The time-averaged product of velocity and times t and t+tao

Question 43

What is the autocorrelation function rhouu?

Answer 43

rhouu(tao) = Cuu(tao)/variance

Question 44

What is the equation for time period of turbulence?

Answer 44

The integral of autocorrelation by tao

Question 45

Similarly to time based covariance and correlation equations, what else can be represented in this way?

Answer 45

Velocity measured simultaneously at two different points in SPACE

Question 46

How is the Power Spectral Density equation Suu defined?

Answer 46

Variance = integral of Suu over frequency range n

Question 47

What is the PSD function used for?

Answer 47

Finding the frequency distribution of kinetic energy of fluctuations

Question 48

What are the 3 types of anemometer?

Answer 48

Pressure Rotation Research (Hot wire/sonic)

Question 49

What are advantages and disadvantages of pressure anemometers?

Answer 49

+ Robust, low maintenance + Quick response to fluctuation - Many factors affecting calibration - Poor accuracy at high yaw

Question 50

What are advantages of rotation anemometers?

Answer 50

+ Calibration unaffected by temperature, humidity etc + Linear response + Robust + Omnidirectional

Question 51

What are disadvantages of rotation anemometers?

Answer 51

- Slow response at low wind speeds - Cannot record wind direction - Differently calibrated for smooth and turbulent flow - Overspeeding possible

Question 52

What are generally the main advantage and disadvantage of research anemometers?

Answer 52

Very accurate Very expensive

Question 53

What distribution is commonly used to approximate cumulative probability of wind speeds in storm conditions?

Answer 53

Weibull distribution

Question 54

What is the notation Px signifying? What about Pxn?

Answer 54

Px is the probability that the extreme value is less than x in any one year Pxn is the probability x is not exceeded in n years

Question 55

How do you create a quadratic in the gradient wind speed derivation?

Answer 55

Substitute in the equation for geostrophic wind speed

Question 56

In what direction does coriolis force act relative to wind motion as viewed from above?

Answer 56

To the right of wind direction in the Northern Hemisphere, to the left in the Southern Hemisphere

Question 57

Why is (dV/dt)s = 0 in gradient wind?

Answer 57

Flow is steady so there is no streamwise acceleration

Question 58

How do you convert bar to Pascals?

Answer 58

Divide by 1e-5

Question 59

What is the equation for peak wind speed in a hurricane?

Answer 59

sqrt(B/rho*e (pn -pc))

Question 60

What is typically assumed of Omega if no information about rotational acceleration is given?

Answer 60

Omega = 2pi/86400 Where 86400 is the number of seconds in a day

Question 61

What is true in adiabatic conditions?

Answer 61

n = gamma