Wednesday, September 15, 2010 Coriolis force, 3 dimensions (p 65)

Transcription

1 Wednesday, September 15, 2010 Coriolis force, 3 dimensions (p 65) Weather fronts (p 63) General circulation on a rotating Earth (p 65) Geostrophy force balance (p 66) Local effects (no coriolis force) - Sea Breeze (p 71) Continental effects (p 71-75)

2 A couple of questions for you: What does the Coriolis Force do to a moving air mass? Where is the Coriolis Force the greatest?

3 Does the Coriolis Force affect an air parcel that is moving East to West? So the answer is YES! Because of the horizontal component 2 components

4 Remember the Hadley Cell Cooling Cooling Heating

5 Hadley Cell Hadley Cell

6 Surface Winds Add Hadley Circulation and Coriolis effect and we get the generalized surface wind pattern.

7 Which gets more energy, the poles or the equator? Equator receives more radiation than poles. Leads to a surplus of radiation at the equator and deficit at poles. Direct rays at equator and indirect rays at poles. Remember solar flux. Emitting more than entering Enter more than emit. Atmospheric circulation moves energy from the equator to the poles.

8 Fronts (cold or warm) When warm and cold air masses meet, they form fronts. Fronts are typically found between the equator and pole at midlatitudes. When a region is in a warm sector, temperatures and humidities are more like tropical air, when a region is in a cold sector, air is cool and dry. Fig. 4.6

9 The Geostrophic Wind Balance between the Pressure gradient Force and the Coriolis Force. High altitude -> little friction Mid to high latitudes - > large Coriolis Force In the Northern Hemisphere, high pressure is to the right of the geostrophic wind direction. Wind direction is perpendicular to the pressure gradient force (pgf) Board work

10 The Geostrophic Wind

11 The Geostrophic Wind Friction Disrupts the balance between the COF and PGF. Incorporate friction and wind is no longer geostrophic. This creates waves in the atmosphere. The Polar Jet Stream

12 What causes the Jet Streams? Upper Level Flow 1. Atmosphere is thicker at the tropics than the poles. 2. So change in pressure due to height more gradual in tropics. This is due to temperature difference. 3. Connect points of constant pressure and find area of the steepest gradient (indicated by J)

13 What causes the Jet Streams? Air moves from high to low pressure. The force created by the difference in pressure is the Pressure Gradient Force, indicated by Pg. BUT the Coriolis effect (C) turns that air to the right. The resulting direction that the air travels is EAST. The resulting wind is called the geostrophic wind. The Jet Stream is a belt of high windspeed (at the 300 mb level) caused by this geostrophic balance.

14 Local temperature contrasts can also produce winds We think of the sea breeze in the same way that we explained the Hadley Circulation it is a convectively driven circulation Fig. 4.17

15 Sea Breeze/ Land Breeze During the day land heats faster than the ocean. Creates: Relatively low pressure over the land. Relatively high pressure over the ocean. Winds blow high to low, so blow from the ocean to land. During the night land cools faster than the ocean. Creates: Relatively high pressure over the land. Relatively low pressure over the ocean. Winds blow high to low, so blow from the land to ocean. The sea/land breezes regulate the temperature of the coastal regions. In-land regions experience bigger temperature swings.

16 We can now start to build a more complicated picture of climate at Earth s surface. We need to start with some basic information let s look at maps of temperatures (summer and winter).

17 July temperatures Fig. 4.18

18 January temperatures Fig. 4.18

19 Summer/winter temperature differences Fig. 4.18

20 Average sea-level pressure patterns - January L H L H H Fig. 4.19

21 Northern hemispheric average winds, January L H L H H Air flows in a direction that keeps high pressure the right of the wind direction in the NH Fig. 4.19

22 Average sea-level pressure patterns - July H H L Fig. 4.19

23 Mean wind directions in NH, July H H L Fig. 4.19

24 Using geostrophy to deduce climates West Coast of US mean wind direction from the north-northwest during July, keeping weather cool. H H L In January, the mean flow towards Washington state is from the southwest, bringing warm, wet air from near Hawaii (the pineapple express ) L L H H Fig. 4 H

25 Using geostrophy to deduce climates United Kingdom Note that weather in the UK comes from the west-southwest both months, even though the pattern switches from high to low. H H L This is because the position of the highs and lows shifts. The UK typically has wet weather in both July and January. L L H H Fig. 4 H

26 Monsoon flow in southeast Asia the importance of topography (land/sea interactions) Fig. 4.21

27 Monsoons NH Summer Land heats, creates low pressure over central Asia. High pressure in Indian Ocean Winds blow high to low. Moist air carried towards land. Because of Himalayan mountains, air rises, cools, condenses, rains. NH Winter Land heats, creates low pressure over central Asia. Low pressure in Indian Ocean Winds blow high to low. Dry air carried towards sea.

28 Water and it s phases Fig. 4.23

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31 Biomes (regions with distinct types of plants) can tell us something important about climate! Fig. 4.27

32 tundra deciduous forest alpine taiga grasslands rainforest savanna desert chaparral

33 chaparral

34 alpine

35 deciduous forest

36 savanna

37 desert

38 taiga