exam #3 Flashcards
Define UHI, why is it a problem? why is it largely a nighttime phenomenon?
UHI: urban heat island
urban areas can be up to 5 degrees warmer, dust dome of airbone pollution gets trapped.
the air warms during the day but due to UHI, there isn’t an escape of LW cooling at night
summary of causes of UHI
- increased absorption of sw radiation due to increased surface area and reflection
- increased lw radiation form sky due to air pollution
- decreased lw radiation loss due to canyon geometry and restricted sky view factor (dust dome and building don’t allow for view of sky)
- anthropogenic heat source due to building and traffic heat loss
- decreased evapotranspiration since construction materials increase impermeability and the water is filtered away -> less evaporation -> less heat exchange
- increased heat storage since the construction materials increase thermal admittance (glass, concrete, asphalt)
- decreased total turbulent heat transport due to canyon geometry -> reduction of wind speed means less displacement of heat
which 3 causes of UHI are highlighted?
- decreased lw radiation loss due to canyon geometry and restricted sky view factor (dust dome and building don’t allow for view of sky)
- decreased evapotranspiration since construction materials increase impermeability and the water is filtered away -> less evaporation -> less heat exchange
- increased heat storage since the construction materials increase thermal admittance (glass, concrete, asphalt)
which important factor limits radiative cooling at night in urban areas
restricted sky view
- much of the lw emitted is absorbed and re-emitted to the surface
define air pressure and wind. describe instruments used to measure each
air pressure: weight of the atmosphere described as force per unit area. key to understanding wind. use a barometer to measure atmospheric pressure: aneroid barometer or electronic sensors
wind: generally horizontal motion of air across earth’s surface. anemometer: measures win speed. wind vane: determines wind direction.
explain the four driving forces within the atmosphere
they determine the speed and direction of winds.
- gravitational force
- pressure gradient force: air driven from high barometric pressure to low
- coriolis effect: makes wind travelling in a straight path to appear to be deflected in relation to the earths rotating surface
- friction effect: friction between air and surface slows wind
explain several types of local and regional winds: surface winds, sea breeze, mountain valley winds
surface winds: coriolis force not perpendicular to pressure gradient force. wind crosses isobars at an angle.
sea breeze: diagram during the day, warm land and cool ocean -> low pressure on land to high pressure on ocean and creates loft sympathetic response. during the night, cool land and warmer ocean means H P on land and L on ocean, mirrored sympathetic loft response
mountain valley winds: diagram during the day, warm air rises up the slopes of the mountain = valley wind. L P on mountain and H P in valley. at night, cold air flows down mountain = mountain wind. H P on slope, L P on valley
warm, humid air is associated with low/high pressure and cold, dry air is associated with low/high pressure
warm, humid air: low pressure
cold, dry air: high pressure
which way does an easterly wind blow?
E to W
what’s an isobar? if they’re close together what does that mean?
lines of equal pressure on weather maps. closer together = greater the pressure gradient force and faster the air movement from a high-pressure area to low pressure
Why is pressure constant at surface but not at loft, how do you generate a wind at a loft/what comes of that? diagram
a) identical pressure at the beginning. expected at night
b) sun rises and heats different ground surfaces differently. air in A is warmed and it expands so the column rises and more air is above A so there is more pressure. a pressure gradient is created/
c) air moves across the gradient in the loft which creates a sympathetic response at the surface which causes pressure to rise in B and fall in A
which way to apparent forces deflect in each hemisphere. what is the coriolis force dependent on?
northern: right
souther: left
dependent on latitude. maximized at the poles due to rotational movement of the surface whereas it is zero at the equator due to earth’s rotation being translational
define geostrophic winds
balance between pressure gradient force and coriolis force
describe how thermal circulation systems occur
cool surface = high P
warm surface = low P
air flow high to low
air rises and an area of low pressure develops at the surface decreasing density. the loft mirrors what’s happening on the surface and high P occurs above.
air flow high to low in loft.
air sinks and an area of high pressure develops at the surface.
define climatology
scientific study of climate and climatic patterns and the consistent behaviour of weather
arrange the tools in paleoclimatology from most recent to oldest
ocean cores, sedimentary rocks, instrument records, tree rings, lake sediments, pollen, satellite data, documentary evidence, polar ice cores
satellite data, instrument records, documentary evidence, tree rings, polar ice cores, lake sediments, pollen, ocean cores, sedimentary rocks
why do we look at ice cores to understand the past?
we can look at the bubbles of atmosphere trapped within the ice cores to understand the concentrations of the atmosphere of that time.
define glacial and interglacial periods and how long they last
glacial periods: ice ages (100ka)
interglacial periods: ice sheets retreat (20-40ka)
when was the last glacial period? how long did it last?
pleistocene ~1800 years
list the order of the glacial and interglacial periods from latest to oldest
wisconsinan glacial
sangamonian interglacial
illinoian glacial
yarmouthian interglacial
kansan glacial
aftonian interglacial
nebraskan glacial
when was the last major warm interval? what was it called
piliocene: 3-4 million years
why do we have cycles in the eaeth/sun geometry and what does that mean for climate (12 pts)
what is the global temperature difference between glacial and interglacials?
5 degrees
when did the first major glaciation occur?
pleistocene
what is the current interglacial period and when did it begin?
holocene: 10-12000 years ago
sunspots vary in a __ year cycle
11
what is the maunder minimum? when was it from?
period when sunspot activity was very low and global temperatures were cooler (1645-1715)
whats the basis behind the normal form of climate variability that you can see
whats the geometry behind solar system physics and its effects on climate
the E received at the top of the atmosphere will vary if the motion of the Earth relative to the sun is not constant
what did milankovitch show about earth’s orbit?
three variations in the earth’s orbit that result in ~5% variation in the E received, especially at high altitudes the combined 3 effects explain the overall pattern of warming and cooling but not the speed of onset and end of glacial periods
outline the 3 cycles that are the variations in earth-sun geometry. what is their impact/how do they operate and how long is their cycle
- orbital eccentricity (stretch), 90,000 years, orbit changes from nearly circular to more elliptical, causes greater seasonality in one hemisphere and reduces it in another
- change in tilt of axis of rotation (roll), 41,000 years, orbit varies from 22 to 24.4 degrees, greater tilt means greater seasonality in both hemispheres
- procession of the equinoxes (wobble), 22,000 years, affects the timing of the aphelion and perihelion relative to the seasons, makes winters milder and summer warmers in the northern hemisphere and winters colder and summers warmer in the souther hemisphere
list potential internal changes within the earth’s system
formation of mountain barriers, volcanic eruptions, changes in ocean currents/salinities, massive calving of ice into the north atlantic, positive feedback
