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UGA / Geography / GEOG 1112 / What is geometric height?

What is geometric height?

What is geometric height?


School: University of Georgia
Department: Geography
Course: Intro to Weather & Climate
Professor: Andrew grundstein
Term: Fall 2019
Cost: 50
Name: Exam 3 Study Guide
Description: These notes cover all the information that will be on the test Tuesday.
Uploaded: 10/31/2019
7 Pages 21 Views 6 Unlocks

Danea Sanders

What is geometric height?

GEOG 1112:

Intro to Weather and Climate

Midterm #3 Study Guide 

Pressure Gradient Force (PGF):

 In the horizontal direction, air pressure creates wind, which blows from  regions of high pressure to lower pressure 

 Isobars are used to visualize lines of constant pressure on maps  PGFs show the rate of pressure change over a distance

 Gradients are seen on maps by the spacing between isobars  Strong gradients = close isobars Weak gradients = spread apart  isobars 

 Clear skies and sinking motion occurs around high pressure centers  Cloudy skies and rising motion occurs around low pressure centers 

What is called coriolis force?

Upper Level Pressure Differences (Geopotential  Height):  

 Geopotential height maps are used to determine circulation of upper  atmosphere

Geopotential height- the height at a constant pressure (different  heights are shown on the graph; the numbers on the graph are the  different heights, instead of different pressure as seen on surface  maps) If you want to learn more check out What are the modes of movement in microbial eukaryotes?

 High geopotential height = high pressure (air moves away from the  region) and low geopotential height = low pressure (air moves toward  the region) 

 You can have pressure differences in the upper atmosphere even with  the same surface pressures because of the changes in height in the  upper atmosphere

 A warm region will have higher heights and higher pressure  A cold region will have lower heights and lower pressure  Heights are lower in the North and higher in the south on geopotential  

Where do geostrophic winds occur?

height maps, so the PGF goes South to North, because it is warmer in  the South (more pressure) and colder in the North (less pressure)

Coriolis Force:


 Motion already initiated by pressure differences (Coriolis force can’t  create motion; it causes the motion already created to veer/turn)  Only acts on motion for long distances and time


 Northern Hemisphere: Turns winds to the right 

 Southern Hemisphere: Turns winds to the left 


 Higher latitude = bigger Coriolis  

 Stronger wind = bigger Coriolis If you want to learn more check out What is the site of rna translation?

 Equator = no Coriolis 

 No wind = no Coriolis 

Geostrophic Flow:

 Upper air also moves from areas of higher pressure to lower pressure,  undergoes Coriolis deflection, and flows parallel to height contours  Geostrophic flow occurs when PGF balances Coriolis 

Gradient Flow:

 Isolines and geopotential height lines are not parallel, but curve around  Wind follows a curved path adding centripetal force, and making wind  either super geostrophic (around highs) or sub geostrophic (around  lows) 

 *Just remember super = high sub= low* 


 Acts in the opposite direction of wind 

 Coriolis deflection still occurs but is reduced 

 Winds at the surface low due to friction are not parallel to isobars,  instead they cross 

 Friction is initiated at the surface but extends and decreases up  Friction is important for wind in about 1.5 km of the surface, the  planetary boundary layer

Cyclones: Don't forget about the age old question of What do slopes mean?

 Cyclones occur when air converges toward low pressure centers at the  surface 

 Cyclones are characterized by ascending air with a counter-clockwise  flow in the Northern Hemisphere and clockwise flow in the Southern  Hemisphere

 Cyclones only develop around low pressure centers, where clouds and  rain develop because of rising motion

Stages of a cyclone:

1.) Forms along stationary polar front separating Polar and Ferrell cells 2.)Cyclogenesis, which is the first stage when cold air moves south and  warm air moves north

3.) Mature cyclone forms with low pressure is at the surface and  divergence is in the upper atmosphere If you want to learn more check out What is achaia?

4.)Cyclone begins to breakdown when the cold front spreads beneath the  warm front and cuts off the supply of moist warm air. This is known as  dissipation.

Extratropical Cyclones:

 Extratropical cyclones are important in the midlatitudes  Extratropical cyclones are large, moving circulations with a low  pressure center 

 Clouds and rain form near the low center and along the front  These cyclones involve movement of many air masses 

 They can last days-weeks, can cover large parts of the U.S., and can  create a drastic change

Jet Stream:

 In winter, the jet stream position is directly over the U.S.  In summer, the jet stream moves over Canada If you want to learn more check out Why is loneliness so harmful?

 So, there are better extratropical cyclone conditions in winter than  summer


 Anticyclones are caused by air diverging away from high pressure  centers at the surface 

 They are characterized by descending air, and clockwise flow in the  Northern Hemisphere and counterclockwise flow in the Southern  Hemisphere (the opposite directions for cyclones) 

Global Scale Winds: (Three Cell Model)

 Hadley Cell

o Heating at the equator creates low press area called the Inter  Tropical Convergence Zone (ITCZ)

o Air sinks to surface at 20-30 degrees to form the subtropical high o Surface air moving toward the equator is turned by Coriolis,  creating the trade winds 

o Rainiest latitude (which is near the equator) 

 Polar Cell

o Circulates air from polar highs to subpolar lows 

o Surface air moving toward the equator is moved by Coriolis  creating the polar easterlies If you want to learn more check out What is the role of bystanders?

 Ferrell Cell

o Circulates air from subtropical highs to subpolar lows 

o Surface air moving toward the poles is turned by Coriolis,  creating the westerlies winds 

Surface Winds:

Latitude Lines

 ITCZ- low pressure

 Subtropics- high pressure

 Subpolar- low pressure

 Polar- high pressure

Winds Created In-between the Latitude Lines

 NE Trade Winds (above ITCZ/equator)

 SE trade Winds (below ITCZ/equator)

 Westerlies 

 Polar Easterlies 

*The PGF points high to low, and the wind is turned to the right (from the  perspective of the high pressure latitude*

Jet Stream and Fronts:

 Upper level winds are not explained well by the 3 cell model  Due to colder temperatures at the poles and higher geopotential  height at the equator, upper-level winds are turned by Coriolis and  mostly flow west to east 

 In the midlatitudes the polar front marks the largest temperature  difference between cold air over the poles and warm air in the south  The polar jet stream occurs at the polar front in the upper troposphere

Semipermanent Pressure and Shifting ITCZ:

 Because there are land and mountains differences, there are not  cohesive pressure belts circling Earth, instead there are semi permanent regions of high and low pressure changing in strength and  position with the seasons 

 Shifting ITCZ causes monsoon circulation  


 Monsoon indicates a seasonal reversal in large scale winds  Monsoons often occur due to thermal differences between land and  water and shifting ITCZ, which causes seasonal rainfall 

Sea and Land Breezes:

 Sea and land breezes are wind due to temperature differences  between land and sea, which are from different heat capacities of  water and land 

 During the day, land surface is warmer than water surface  During the night, water surface is warmer than the land surface  So, the land heats faster than the water

 A low pressure center develops over the warm region, where air  converges into the low, ascends, and produces clouds and could  possibly rain

Source Regions:

 Source regions are areas where air masses form 

 Long-term heating/cooling creates air with specific characteristic  The air masses reflect the temperature and humidity characteristics of  their source regions, as the move and collide they form fronts  P= polar T= tropical A= arctic

 Winter: Summer:   cP very cold and dry cool and dry  mP cool and humid mild and humid  cT cool and dry very hot and dry  mT warm and humid warm and humid  cA bitter-cold and dry -----

c = Continental = dry m = Maritime = humid Fronts:

 Cold front (represented as blue triangles; Cumulonimbus clouds form)  Warm front (represented as red semi-circles; Stratus clouds form)

 Stationary front (represented as blue triangles and red semi-circles; the cold and warm fronts are by each other, but not colliding)

 Occluded front (represented as purple triangles and semi-circles;  collided cold and warm front)

o Cold type occlusion occurs in eastern half of the Us when cP air  behind the cold front is colder than mP air ahead of the warm  front

o Warm type occlusion can occur in the west, which is the opposite of cold front occlusion

 Dry line (two air masses with similar temperatures, but different  humidities; Ex: Air formed over the Gulf of Mexico and air formed over  the country Mexico)

Santa Ana Winds (High Press Systems):

 These winds occur in California during the transition seasons especially in autumn when there is high pressure to the east 

 Hot and dry wind blows from the desert toward the west coast  These winds can often contribute to the spread of wildfires 

Ocean Circulation:

 Strong warm poleward currents are on the west side of midlatitude  oceans and weak cold currents are on the east side

 Within the western portion of a current, warm water is moved north  and within the eastern portion cold water is moved south. This occurs  in the Northern Hemisphere in a clockwise direction 

 The opposite occurs in the Southern Hemisphere. Within the western  portion of the current, warm water moves south and within the eastern boundary cold water moves north in a counterclockwise direction  Major US currents:

o Gulf Stream – fast moving, warm water on the east coast of the  U.S.

o California Current- slower, colder water on the west coast of the  U.S.

Deep Currents (Thermohaline-Density driven):

 Cold, salty, dense water sinks in the north around Greenland and goes  south

 The current flows south and picks up more cold, salty water near  Antarctica

 The current splits into 2 sections, one that travels into the Indian  Ocean, and the other into the Pacific Ocean

 The 2 branches of the current warm and rise as they move north, then  loop back around to the Southern Ocean

 The now-warm waters in the mid-level continue to circulate around the  globe and eventually return to the North Atlantic where the cycle  begins again

Walker Circulation:

 The Walker Circulation describes east-west atmospheric circulation in  the tropics, air rising in the West Pacific and sinking in the East  Winds along the surface push warm surface water to the west, making  the surface warmer with lower pressure and clouds/rain in the west  The ocean circulation pulls cold water up (upwelling) in the East  High ocean surface = low atmospheric pressure 

 Low ocean surface = high atmospheric pressure 

La Nina and El Nino:

La Nina

 In La Nina, the normal Trade Winds are stronger

 Warmer water piles up in the West Pacific with cold water upwelling in  the East

 Atmospheric pressure is low in the West with clouds and rain El Nino

 In El Nino, trade winds weaken, so the East Pacific is warmer and the  West is cooler

 Atmospheric pressure is low in the Central/East Pacific

 More clouds and rain in the East and less in the West

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