AOSC 200: Weather and Climateанаdiscussion Quiz 2 Review Answers

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.

2) What are the two main surface categories for air mass source? ● Continental ● Maritime

3) What are the three main location categories for air mass source? ● Arctic region ● Polar region ● Tropical region

4) Which air mass do we sometimes call “The Siberian Express?” a) cP and cA

5) Be able to list the characteristics of different air masses. Which ones tend to affect North America and where would they come from/hit us (be specific)? a) figure 8.2 b) continental polar and continental arctic: i) originate over cold land of ice and snow in arctic, northern Canada, Alaska ii) stable and usually dry ­ fair weather iii) huge shallow high pressure area as it moves towards us iv) can create upper­level temp inversion v) wintertime c) maritime polar: i) ocean water modifies cold air mass and turns it into maritime polar ­ added warmth and moisture ii) hits west and east coast of USA iii) wintertime d) maritime tropical: i) subtropical east pacific ocean ii) very warm and moist iii) wintertime e) continental tropical: i) hot and dry ii) source: summer in northern mexico/adjacent southwestern USA iii) basically no rain f) FIGURE 8.14

6) What is the dry line? a) A boundary that separates warm, dry air from warm, moist air. It usually represents a zone of ​ ​ ​ ​ instability along which thunderstorms form.

7) What is the process behind Lake Effect Snow and where do we see this in the USA? a) Polar or arctic air blows over warm water and pick up moisture and drops snow on the downwind side of lake b) Snow can fall in distinct bands

8) Can air masses be modified? a) Yes, by lifting and heat exchange with the surface

9) A front is a transition between density, temperature, or both? a) A front is a transition between two air masses of different densities b) Since density differences are most often caused by temperature differences, fronts usually separate air masses with contrasting temperatures c) Often separate air masses by different humidities as well.

10) What is the frontal zone? a) Upward extension of a front

11) Be able to draw/identify all the types of fronts. Know the air masses associated with each front.

12) What is a stationary front? a) No movement b) Alternating red and blue line c) Weather: clear to partly cloudy, with much colder air lying on its eastern side d) Neither air mass is strong enough to overtake the other so it doesn’t move

13) Why does a warm air mass flow over a cold air mass when they meet? a) differing densities

14) How do the weather and clouds differ between cold fronts and warm fronts? a) cold front: there is a rain band along the cold front and we have stormy weather and heavier rain, usually associated with cumulonimbus clouds b) warm front: light precipitation compared to cold fronts, usually associated with stratus­type clouds

15) How do temperatures, pressures, and wind directions change before, during, and after a warm front passes through? How about for a cold front? a) warm front: i) before: temperatures cool to cold but slowly warming, pressure usually falling, winds from south or southeast ii) during: temperatures rising steadily, pressures leveling off, winds are variable iii) after: temperatures are warmer and then steady, pressure slightly rises then falls, wins are south or southwest b) cold front: i) before: moderate or warm temperatures, pressures steadily falling, winds from south or southwest ii) during: sudden drop in temperatures, pressure goes to a minimum and then rises sharply, wind are gusty and shifting direction iii) after: temperatures steadily dropping, pressure rising steadily, wind from west or northwest c) Figure 8.14!!!!!

16) What are occluded fronts and how do they happen? Describe the difference between warm type occlusion and cold type occlusion a) when the cold front catches up with the warm front and overtakes it b) cold­type: air behind the occluded front is colder than air ahead of it, cold front lifts warm front and warm air off the ground, weather sequence is similar to that of warm front BEFORE passing through ­ high clouds become low clouds and precip ahead of front line, but AS it passes through it acts like a cold front c) warm­type: air behind the occluded front is warmer than the air ahead of it, this happens on the west coast sometimes when the continental polar air is colder than the maritime polar air coming in ­ so the air ahead of the warm front is actually colder than the air behind the cold front, cold front cannot lift up the air in front of the warm front, weather similar to a warm front d) figure 8.23/8.22 and the second paragraph of page 243 (“Contrast Fig. 8.22 and 8.23…”)

17) What is a midlatitude cyclone? Are they the same thing as hurricanes? a) NOT the same thing as hurricanes. Hurricanes have very specific mechanisms of formation and this is not it b) extratropical cyclone c) low pressure system with fronts swirling around it ­­ Katie’s nonscientific definition

18) Where do midlatitude cyclones usually form? a) right around the jet stream/polar front

19) For a cold front, where would you expect the clouds to be? a) on top of it ­ also where precip is

20) For a warm front where would you expect the clouds to be? a) in front of it ­ also where precip is

21) Comma clouds: what do they represent? What is the dry slot? a) a mid­latitude cyclone b) the dry slot is a zone of dry and relatively cloud­free air that wraps eastward or northeastward into the southern and eastern parts of a low pressure system

22) In what direction do cyclones rotate? What type of pressure system is this indicative of? a) counterclockwise ­ low pressure

23) What are the different stages of cyclogenesis? Be able to describe at each stage what each front is doing a) figure 8.25

24) What do you need for cyclogenesis? a) Differences in temperature b) Strong jet stream c) Surface boundary (mountain, coastline near warm ocean)­­something that deforms stationary front

25) In what regions do cyclones occur? What are their characteristics? ● some areas have a propensity for cyclogenesis, it doesn’t mean that cyclones can’t form in other areas though ● Named from source regions ● Alberta Clippers ○ Form on lee side (dry) of Canadian rockies (eastern), moves fast ○ If hits Great Lakes, cP air mass could transition to Lake Effect snow ○ Can be mP like ○ Fast and moving and somewhat dry ● Colorado Low ○ Form on lee side of Rockies. In the right spot for very cold polar air to interact with warm, moist Gulf air. ○ Can have a mix of precipitation. ○ Thunderstorms along the southern edge of the front, lots of snow NW of the center of low pressure ○ Can sometimes form near OK panhandle or in TX ● Gulf Low ○ Form along southern coast ○ Cold land and warm ocean means good probability of precipitation ● Hatteras Low (Nor’easter) ○ Form along eastern coast ○ Warm gulf stream water provides warm air and moisture that interacts with cold air on land ○ If the pressure of a Hatteras Low drops by 24mb in 24 hours, it’s considered a “bomb” ○ Can produce hurricane strength winds, flooding, heavy snow. ○ Can last for days!!!

26) How does the jetstream affect cyclogenesis? ● Surface high strengthened by upper level convergence ● Surface high pressure directed to southeast by jetstream ● Surface low strengthened by upper level divergence ● Surface low pressure directed northeast by jet stream

27) What is zonal flow? What is meridional flow? (in terms of jet stream movement) ● zonal is when it doesn’t meander north/south ● West to east flow, jet stream wanders N/S a lot as it moves from west to east