met 61 introduction to meteorology - lecture 10

57
MET 61 1 MET 61 Introduction MET 61 Introduction to Meteorology to Meteorology MET 61 Introduction to Meteorology - Lecture 10 Atmospheric Dynamics Dr. Eugene Cordero Ahrens: Chapter 9 W&H: Chapter 7, pg 271-296 Class Outline: Principle forces in the atmosphere Pressure gradient Coriolis Geostrophic wind

Upload: salaam

Post on 21-Jan-2016

68 views

Category:

Documents


0 download

DESCRIPTION

MET 61 Introduction to Meteorology - Lecture 10. Atmospheric Dynamics Dr. Eugene Cordero Ahrens: Chapter 9 W&H: Chapter 7, pg 271-296 Class Outline: Principle forces in the atmosphere Pressure gradient Coriolis Geostrophic wind. Atmospheric forces. - PowerPoint PPT Presentation

TRANSCRIPT

Page 1: MET 61 Introduction to Meteorology - Lecture 10

MET 61

1 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

MET 61 Introduction to Meteorology - Lecture 10

Atmospheric DynamicsDr. Eugene CorderoAhrens: Chapter 9

W&H: Chapter 7, pg 271-296 Class Outline:

Principle forces in the atmosphere Pressure gradient Coriolis Geostrophic wind

Page 2: MET 61 Introduction to Meteorology - Lecture 10

MET 61

3 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Atmospheric forcesAtmospheric forces

Fundamental Forces in the atmosphereFundamental Forces in the atmosphere– Pressure Gradient ForcePressure Gradient Force– GravityGravity– Rotation of the Earth Rotation of the Earth – FrictionFriction

Page 3: MET 61 Introduction to Meteorology - Lecture 10

MET 61

4 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

PressurePressure

Ultimately responsible Ultimately responsible for our weatherfor our weather

Page 4: MET 61 Introduction to Meteorology - Lecture 10
Page 5: MET 61 Introduction to Meteorology - Lecture 10

MET 61

6 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Horizontal Pressure ChangesHorizontal Pressure Changes

Determines the direction and speed of winds:Determines the direction and speed of winds:– Predominate force in atmospheric flowsPredominate force in atmospheric flows

Can help explain general circulation of Can help explain general circulation of atmosphere.atmosphere.

Page 6: MET 61 Introduction to Meteorology - Lecture 10

MET 61

7 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 7: MET 61 Introduction to Meteorology - Lecture 10
Page 8: MET 61 Introduction to Meteorology - Lecture 10

MET 61

9 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 9: MET 61 Introduction to Meteorology - Lecture 10

MET 61

10 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 10: MET 61 Introduction to Meteorology - Lecture 10

MET 61

12 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Pressure Gradient ForcePressure Gradient Force

Pressure gradient: Pressure gradient: – Dependent on spacing between isobarsDependent on spacing between isobars– Dense or tight clustering of isobars - strong or large Dense or tight clustering of isobars - strong or large

pressure gradientpressure gradient– Weak clustering of isobars - weak pressure gradientWeak clustering of isobars - weak pressure gradient

Pressure gradient directed from high to low pressurePressure gradient directed from high to low pressure

Page 11: MET 61 Introduction to Meteorology - Lecture 10

MET 61

13 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 12: MET 61 Introduction to Meteorology - Lecture 10

MET 61

14 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Reading a weather mapReading a weather map

Orient yourself (location, date and time)Orient yourself (location, date and time)

Identify what you are looking atIdentify what you are looking at

Determine the interval of the fieldDetermine the interval of the field

Page 13: MET 61 Introduction to Meteorology - Lecture 10

MET 61

15 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 14: MET 61 Introduction to Meteorology - Lecture 10

MET 61

16 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 15: MET 61 Introduction to Meteorology - Lecture 10

MET 61

18 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

1.1. At what local time is this map valid?At what local time is this map valid?2.2. What fields are we looking at?What fields are we looking at?3.3. Indicate the direction of the pressure gradient force at points A-C.Indicate the direction of the pressure gradient force at points A-C.

• AA

• CC

• BB

Page 16: MET 61 Introduction to Meteorology - Lecture 10

MET 61

19 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 17: MET 61 Introduction to Meteorology - Lecture 10

MET 61

20 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Atmospheric Thickness

Page 18: MET 61 Introduction to Meteorology - Lecture 10

MET 61

21 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 19: MET 61 Introduction to Meteorology - Lecture 10

MET 61

22 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Hypsometric EquationHypsometric Equation Combination of ideal gas law with hydrostatic balance.

Relates atmospheric thickness with average temperature.

Thickness of atmosphere relates to difference between two atmospheric layers; z t (m) = thickness between two pressure levels

2

112 lnz

p

pT

g

Rz d

Page 20: MET 61 Introduction to Meteorology - Lecture 10

MET 61

23 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 21: MET 61 Introduction to Meteorology - Lecture 10

MET 61

24 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 22: MET 61 Introduction to Meteorology - Lecture 10
Page 23: MET 61 Introduction to Meteorology - Lecture 10

MET 61

26 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

knotsknots

Page 24: MET 61 Introduction to Meteorology - Lecture 10

MET 61

28 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

The rotation of the EarthThe rotation of the Earth

Rockets, migrating birds, and large scale weather Rockets, migrating birds, and large scale weather systems are all deflected due to the rotation of the systems are all deflected due to the rotation of the Earth.Earth.

The Earth’s rotation causes bothThe Earth’s rotation causes both– Translational movementTranslational movement– Rotational movement Rotational movement

The The Coriolis ForceCoriolis Force is the name of this rotational is the name of this rotational force that deflects motion.force that deflects motion.

Page 25: MET 61 Introduction to Meteorology - Lecture 10

MET 61

29 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 26: MET 61 Introduction to Meteorology - Lecture 10

MET 61

30 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 27: MET 61 Introduction to Meteorology - Lecture 10

MET 61

31 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 28: MET 61 Introduction to Meteorology - Lecture 10

MET 61

33 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Coriolis ForceCoriolis Force

• Affects direction, not speed of object• Maximum at the poles• Zero at the equator (only translational

movement)

Fc=2v sin

- omega - Earth’s rotational rate =360 degrees/24 hours or

v - wind speed - latitude

2 radians/86400 seconds=7.27x10-5 s-1

Calculate Coriolis force for wind moving at

10m/s

2(7.27x10-5 s-1)(10m/s)(sin37)=8.8e-4 m/s2

Page 29: MET 61 Introduction to Meteorology - Lecture 10

MET 61

34 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Coriolis Force

Take home message:– N. Hem - deflects air to the

right– S. Hem - deflects air to the

left– Relatively small

acceleration, thus requires long periods of time to influence motion.

Page 30: MET 61 Introduction to Meteorology - Lecture 10

MET 61

36 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Geostrophic balance

Geostrophic balance is balance between:

Pressure gradient force and

Coriolis force

Result: flow of air is parallel to isobars

friction is assumed to be zero

Page 31: MET 61 Introduction to Meteorology - Lecture 10

MET 61

38 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Geostrophic Wind exampleGeostrophic Wind example

L

H

1000 mb

1004 mb

1008 mb

Pressure Gradient Force

Geostrophic Wind

Coriolis Force

Northern Hemisphere

Page 32: MET 61 Introduction to Meteorology - Lecture 10

MET 61

39 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 33: MET 61 Introduction to Meteorology - Lecture 10

MET 61

40 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 34: MET 61 Introduction to Meteorology - Lecture 10

MET 61

41 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 35: MET 61 Introduction to Meteorology - Lecture 10

MET 61

42 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 36: MET 61 Introduction to Meteorology - Lecture 10

• AA

• CC

• BB

1.1. Indicate with arrows the pressure gradient and Coriolis force at A, B and C.Indicate with arrows the pressure gradient and Coriolis force at A, B and C.2.2. Indicate the direction of the wind at each point.Indicate the direction of the wind at each point.3.3. Which point do you think the wind will be stronger?Which point do you think the wind will be stronger?

Page 37: MET 61 Introduction to Meteorology - Lecture 10

MET 61

45 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Geostrophic WindGeostrophic Wind

• Assume friction is zero• Flow is parallel to isobars• Balance between pressure gradient and

Coriolis force

- density, f - Coriolis parameter (=2 sin Vg - geostrophic wind speedd – distance between isobars p – pressure difference

d

p

fVg

1

Page 38: MET 61 Introduction to Meteorology - Lecture 10

MET 61

46 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

http://www.met.sjsu.edu/weather/avn.html

Page 39: MET 61 Introduction to Meteorology - Lecture 10

MET 61

47 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Estimate the geostrophic wind speed for this situation

Page 40: MET 61 Introduction to Meteorology - Lecture 10

MET 61

49 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

http://www.met.sjsu.edu/weather/avn.html

Page 41: MET 61 Introduction to Meteorology - Lecture 10

MET 61

51 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Geostrophic Wind with Geostrophic Wind with FrictionFriction

L

H

1000 mb

1004 mb

1008 mb

Pressure Gradient Force

Geostrophic Wind

Coriolis Force

Northern Hemisphere

Friction

Friction decreases speed of wind, thusFriction decreases speed of wind, thusCoriolis force is weaker.Coriolis force is weaker.

Page 42: MET 61 Introduction to Meteorology - Lecture 10

MET 61

52 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 43: MET 61 Introduction to Meteorology - Lecture 10

MET 61

53 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 44: MET 61 Introduction to Meteorology - Lecture 10

MET 61

54 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 45: MET 61 Introduction to Meteorology - Lecture 10

MET 61

55 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

•A

•B

Page 46: MET 61 Introduction to Meteorology - Lecture 10

MET 61

56 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

•A

•B

Page 47: MET 61 Introduction to Meteorology - Lecture 10

MET 61

57 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 48: MET 61 Introduction to Meteorology - Lecture 10

MET 61

59 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 49: MET 61 Introduction to Meteorology - Lecture 10

MET 61

60 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 50: MET 61 Introduction to Meteorology - Lecture 10

MET 61

61 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 51: MET 61 Introduction to Meteorology - Lecture 10

MET 61

62 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Page 52: MET 61 Introduction to Meteorology - Lecture 10

MET 61

64 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Terminology

Cyclone: Anticyclone:

At the surface, pressure cells are often closed. However, at higher altitudes, pressure cells are often elongated, forming ridges and troughs. – Low pressure systems -– High pressure systems -

refers to closed low pressure systemrefers to a closed high pressure system

Troughs

Ridges

Page 53: MET 61 Introduction to Meteorology - Lecture 10

MET 61

65 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Upper atmosphere pressure gradients

Meteorologist often examine the upper level pressure gradients to determine the prevailing weather conditions.

However, it is not convenient to simply calculate the pressure gradient because of it’s dependence on density.

Rather, meteorologist calculate the height of a particular pressure surface. The slope of these heights determines the pressure gradient force.

Page 54: MET 61 Introduction to Meteorology - Lecture 10

MET 61

68 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Quiz 3: Part A

1. Write down the component form of the Geostrophic wind.

2. Explain the difference between the total derivative and the local derivative, and show how these are different mathematically.

Pf

kVg 1ˆ

Page 55: MET 61 Introduction to Meteorology - Lecture 10

MET 61

69 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Quiz 3: Part B

1. Write down the component form of the momentum equations. Be sure to show all your work (how you got each term).

2. For each term in your above equations, provide a physical description (explanation) for what it means.

Page 56: MET 61 Introduction to Meteorology - Lecture 10

MET 61

70 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

3. Indicate the temperature advection at points A and B. Justify your answer.

• B

• A

Page 57: MET 61 Introduction to Meteorology - Lecture 10

MET 61

72 MET 61 Introduction to MET 61 Introduction to MeteorologyMeteorology

Activity 9: Due April 11th

1.Use links found on the department web page to explore wind speed and direction from maps of model output such as shown in class. From these maps, calculate geostrophic wind using either pressure or height information (if you use height , then use equations given on pg 188-189 of Stull). Compare your answer with model wind information (isotachs). Show calculations and maps from at least two locations. 2. Compute by how much a soccer ball will be deflected during a 12m penalty kick due to the coriolis force.