AOSC 200: Weather and Climate ­ Discussion Quiz 2 Review Answers Chapter 7: Atmospheric Circulations Lecture: “Winds” and “Global Winds” 1) What is the thermal circulation (thermal wind), how does it form, and what does it imply for the height of the isobars in different areas? a) Figure 7.4 b) circulation brought on by changes in air temperature, in which warm air rises and cold air sinks 2) What causes the sea breeze and land breeze? a) differing temperatures between water and land b) type of thermal circulation c) sea breeze: land heats more quickly during the day and so low develops, while H develops over the water d) at night this reverses so it becomes a land breeze 3) Describe the mountain breeze and valley breeze. a) valley breeze: sunlight warms valley during day creating low pressure, so air rises as a gentle upslope wind b) at night the flow reverses because the mountain slope cools quickly, so air slides downslope 4) What is a Katabatic wind? a) downslope wind b) usually we use it to describe downslope winds that are much stronger than mountain breezes c) forms when top of mountain cools quickly and a strong high is created, forcing air downslope quickly 5) What are the chinook winds? What is the main reason they are warm? a) warm, dry downslope wind that descends the eastern side of the Rockies b) temperature rises sharply when they pass through c) occur when strong westerly winds aloft flow over a north­south mountain range d) source of warmth is compression heating e) enhanced by cloud formation on windward side 6) What type of winds are the Santa Ana winds? a) Katabatic but not chinook 7) What is a monsoon? How does the Indian Monsoon relate to the ITCZ? What are the lifting mechanisms that play a role in the Indian Monsoon? a) monsoon wind system is one that changes direction seasonally b) a monsoon is a type of thermal circulation ­ kind of like a large scale sea breeze c) air over continent becomes much colder than over the ocean in the winter and there is clockwise circulation ­ fair weather ­ winter monsoon d) during summer a low forms because land heats up a lot more than the ocean and there is counterclockwise rotation ­ brings in moisture from the ocean ­ summer monsoon e) the ITCZ goes south in the summer, allowing the low to suck in moisture from the ocean f) India is in the southern hemisphere in the summer and the northern hemisphere in the winter g) lifting mechanism: convergence i) warm humid ocean air being sucked in converges with drier continental air ­­ lifting occurs which creates thunderstorms 8) What is the Three Cell Model and what does it assume? Does it perfectly represent the real world? ● The Three Cell Model is a atmospheric circulation model that, unlike the single cell model, accounts for the Earth’s rotation. ● It assumes that the earth’s surface is uniformly covered with water and that the sun is always directly over the equator (this is the assumption for a single cell model) ● Surface high pressure at the poles and a trough of surface low pressure is at the equator. Also high pressure at 30 N and low pressure at 60 N ● does not perfectly represent world obvi 9) Does the tropopause height increase or decrease as we move from the equator to the north pole? Based on this answer, does the pressure gradient force generally want to push air aloft from south to ​ ​ north or from north to south? ● tropopause decreases in height towards the poles because warm air is taller than cold air → creates pressure gradient force that drives winds toward the lower, colder columns of air in the north 10) Where do jet streams form? What are the names and latitudinal locations of the two jet streams in the Northern Hemisphere? ● where the fronts meet aloft → division between the cells ● subtropical jet: 30 north ● polar jet: 60 north ● both are westerlies 11) Here in the U.S.A and much of Canada, our prevailing winds are called _____westerlies____ and they move in the ___eastward___ direction. While these winds prevail, are we ALWAYS going to have surface winds blowing that way or will surface lows and highs sometimes spice things up? a) we won’t always have surface winds going this way because changes in surface pressure will change things sometimes b) important to note that surface winds AND upper level winds are both westerlies 12) What is the underlying cause of the general atmospheric circulation we see on Earth? ● unequal heating of the earth’s surface, which creates thermal convection cells 13) Where are the trade winds and in what direction do they blow? Between what latitudes do they exist? ● The trade winds are winds that occupy most of the tropics and below from the subtropical highs to the equatorial low ● From horse latitudes (around 30 degrees) to equator ● Blow from the northeast in the Northern hemisphere and from the southeast in Southern hemisphere 14) Do we have surface lows at the pole or at the equator, based on our atmospheric circulation model? a) Lows are at the equator, highs are the poles 15) What are the doldrums and what kind of weather usually happens there? How does this weather drive the Hadley cell? ● over the equator where PGF is low and winds are weak ­­ lots of upward convection and thunderstorms which hit tropopause, which acts as a barrier as forces air to laterally spread outwards towards both poles 16) Why is 30 N called the horse latitudes? (great bar trivia question) ● Sailing ships traveling to the New World were frequently becalmed in this region. As food and supplies dwindled, horses were either thrown overboard or eaten. ● Has anyone ever eaten horse? 17) What is the polar front? The subpolar low? What weather happens here? ● polar front: the barrier between air masses of contrasting temps at 60 N ● A zone of low pressure (the subpolar low) where surface air converges and rises, and storms/clouds develop 18) Be able to locate the three circulation cells on a figure of the globe. Know their names and the latitudes at which each starts and stops. Also be able to locate and label the two jet streams on the same map. See spring 2015 Quiz 2 for this question. 19) Where are the semipermanent highs and lows in the northern hemisphere? a) Bermuda high between 25 and 35 N b) Pacific high between 25 and 35 N c) these develop in response to convergence of air aloft at around 30 N (the boundary between Hadley and Ferrel cells) d) same thing for the two others but they are in the division between the Ferrel and polar cells: The Icelandic low and the Aleutian low e) Tim isn’t very concerned with knowing the names 20) What is the Intertropical Convergence Zone? How/why does its position change seasonally? Know where the highs and lows are in the summer and winter. ● where the NE and SE trade winds meet (surface winds) ● shifts northward in summer and southward in winter ○ this is because the zone of maximum surface heating shifts seasonally thanks to tilt of Earth ● in NH winter: Siberian high forms in Asia because of intense cooling of land , bringing cool winds down to India and the ocean ● As summer comes, the land warms and the Siberian high vanishes, and a thermal low appears close by. As thermal low intensifies it draws in warm moist air from the ocean and this leads to wet summer monsoon in India ● the shift of the ITCZ to the north in the summer allows this to happen because the wind direction has changed because India is changing hemispheres seasonally ● look at figure 7.28 and 7.20 21) What is a gyre? What are they driven by? What way do they circulate in the Northern Hemisphere? a) correspond to our semipermanent highs in Pacific and Atlantic b) driven by surface winds that cause pile up of water, creating pressure differences that leads to further motion deeper down in the ocean c) around high pressure ­­ rotate clockwise 22) Describe Ekman transport and the Ekman spiral a) Ekman spiral caused by Coriolis Effect b) it is the change in direction of fluid with depth c) 90 degree net transport of water to the right of surface layer d) creates coastal upwelling 23) How do ocean pressures, wind strength/direction, and the direction of the transport of water change during El Nino? What effect does this have? a) normal conditions: off the west coast of Peru, southerly winds promote upwelling of cold, nutrient­rich water that’s great for fishing economies. high pressure over eastern Pacific and low pressure around Indonesia produce easterly trade winds along Equator, causing cooler water to prevail by South America and warmer water to prevail by Indonesia (when the winds are particularly strong we call this La Nina and we have particularly cooler waters by Peru) b) every two to five years El Nino occurs → decrease in pressure over the eastern Pacific and increase in pressure in western Pacific ­ trade winds weaken or reverse direction and we have warm water by south america instead of cold water ­ BAD 24) What is the Northern Atlantic Oscillation? a) counterpart of southern oscillation b) reversal of pressure ­ Icelandic low and Bermuda high ­ strengthens or weakens westerlies depending on pressure gradient c) strong westerlies (if Bermuda high rises and Icelandic low lowers in winter) promote strong cyclonic storms on a more northerly track into Europe ­ positive phase 25) What is the Pacific Decadal Oscillation? a) changes in surface ocean temperatures ­ influences winter weather along west coast of North America b) every 20­30 years Chapter 8 Lectures: “Air Masses” and “Fronts” and “Cyclogenesis” 1) What is an air mass? ● A large body of air whose properties of temperature and humidity are fairly similar in any horizontal direction at a given altitude.