Lec 14 slides and reading (pt 4) Flashcards
The environmental variable most important to organisms is …
temperature
It follows that the single most important source of ecological variation for life on earth arises from the __________ in temperature: hot near the equator, grading toward cold at the poles
latitudinal gradient
why is it hot near the equator and grading toward cold at the poles
This pattern arises from the uneven distribution of radiant electromagnetic energy that is continuously blasted at the earth from the sun
The sun is far enough from the earth that we can consider the incoming photon flux as a uniform stream of parallel rays
Making that assumption, the density of photons is ________ at the equatorial regions, where the surface of the earth is essentially ________ (90°) to the vector of the incoming photons.
highest; perpendicular
why is seasonal variation in climate is immensely important to organisms
It arises because the earth’s axis is tilted at about 23.5° off the vertical
As it makes its annual revolution, therefore, different parts of the earth experience the sun as being directly overhead at noon
At the spring and autumn equinoxes, the sun is directly above the equator. At the northern hemisphere’s summer solstice, it is directly over 23.5°N, and at the winter solstice, it is directly over 23.5°S
The annual shifts in angle are gradual, but their effects on daylength and on heat input are profound
The latitudinal lines around the earth at 23.5°N and 23.5°S are called the …
Tropic of Cancer and the Tropic of Capricorn
The “_________” (i.e., the line of latitude closest to the sun) oscillates between the two tropic lines, making one cycle per year
solar equator
How, then, does the incoming solar light energy transfer so much heat to the earth?
That transfer happens when light hits surfaces other than air: solid surfaces, especially dark ones, or water
When photons hit those surfaces, they are absorbed and reradiated at longer, infrared (IR) wavelengths
Light is converted to heat. IR radiation, unlike light, is absorbed by the atmosphere
Therefore, solar energy heats the earth’s surface, and then the surface heats the air near the surface
Therefore, solar input paradoxically heats the air at the bottom of the atmosphere, not the air at the top that is closest to the sun. And this heating is strongest near the equator
Packets of hotter, low-density water are more _____ than the colder water above them, so they are propelled upward and the colder water sinks, in the process called ________
buoyant ; convection
explain flow of air shown by red/blue arrows outside the globe in the climate circulation diagram
Photon flux from the sun is concentrated at the equator (more precisely, the solar equator—see below), so the equatorial region of the earth’s surface heats up the most
IR radiation from the heated surface in turn heats up the near-surface atmosphere, rendering the air less dense
The reduction in density (1) causes a meteorological low pressure zone and (2) impels the heated air to rise above the solar equator
As the air rises, it tends to create a partial vacuum beneath it, and that suction causes surface air to be drawn toward the solar equator from the north and south. That new air also heats up and rises.
This sets up a continuous flow—a fountain-like column of air that rises continually, like an escalator or a conveyor belt
However, the air cannot keep rising forever; it bumps up against the top of the atmosphere, and is then pushed away from the solar equator, moving to the south and the north. This flow is shown by red/blue arrows outside the globe in the climate circulation diagram
As the air rises, it expands more because…
there is less atmosphere above it to compress it
Expansion of a gas causes it to cool. The relationship of temperature drop to altitude gain is theoretically described by the __________, which is ultimately an extension of the ideal gas law
adiabatic lapse rate
sinking air warms…
up
hadley cells
large-scale atmospheric circulation patterns that affect weather patterns and the climate
-2 continuous circulation loops
-convection cells that occur in each hemisphere, where warm air rise near equator, cools as it moves toward the poles, sinks, and then warms as it moves back toward the equator
intertropical convergence zone
the zone of rising, heated air
Intertropical is an accurate descriptive name because the solar equator moves between the 2 tropic lines over the course of a year
hadley cells are 2 circulation loops that…
not only set prevailing winds in motion, but also affect precipitation
how do hadley cells affect precip
The air that comes into the ITCZ is humid, heavily laden with water vapour
As it rises and cools, much of that water vapour condenses into liquid water clouds and falls as rain, so the equatorial tropical regions are very rainy
These are the places for tall, dripping, evergreen rainforests, teeming with life. (As you are probably aware from listening to weather reports, low-pressure weather systems are always associated with precipitation.)
By the time a packet of air has reached the upper atmosphere, it has been wrung dry of most of its moisture. When that air subsequently descends at the 30° N and S latitudes, it comes down as hot, dry, and desiccating air
These latitudes chronically experience high-pressure weather systems, with the sun beating down relentlessly out of a cloudless sky. These are the places for sparsely vegetated deserts
As that dry air returns toward the ITCZ, it gradually picks up moisture from the ocean and the wetter tropical regions, setting up the next cycl
the wettest and driest places on earth both have their weather delivered by…
the hadley cell circulation
hadley cells are continuous loops but not…
closed loops
ferrell cells
Hadley cells are continuous loops but not closed loops
When the masses of dry air descend at 30°N and 30°S, nothing predestines that air to head back toward the intertropical convergence
In fact, it is pushed indiscriminately both northward and southward
The flows that move toward the poles initiate a second pair of “conveyor belts,” the Ferrell or mid-latitude cells
ferell cells and flow
The Ferrell cells are not as strong or consistent as the Hadley cells, but they are driven by the same processes
As the dry air in the Ferrell cells moves across the earth’s surface toward the pole, it also picks up moisture, and finally tends to RISE, creating another pair of rainy and snowy low-pressure zones around 60°N and 60°S
As that rising air reaches the upper atmosphere, it is shoved toward the north and south by the continuous upward flow from beneath (just as happens at the ITCZ)
The high-level flows toward the equator close the Ferrell loops; the flows toward the poles set up a third pair of circulation loops, the polar cells
The polar cells are the weakest and most diffuse of the three
prevailing winds
At different places on the earth’s surface, winds tend to blow from characteristic directions and with greater/lesser force and reliability
These wind patterns are critical influences on organisms and ecosystems, partly because they redistribute heat, but mostly because they redistribute water (as vapour) from oceans to continents
hadley cells and wind
between 0° and 30°N, the Hadley cells push air from north to south
ferell cells and wind
between 30°N and 60°N, the Ferrell cells push air in the opposite direction
polar cells and wind
between 60°N and the North Pole, the polar cells impart a flow to the south
coriolis effect
-the deflection of circulating air and other objects caused by the Earth’s rotation
our westerlies arise because the air being pushed straight northward by the Ferrell cell is passing over the surface of a spinning sphere
That action produces a twist of the wind vectors with respect to the earth’s surface—the Coriolis effect, which is sometimes called a pseudo force
coriolis effect wind direction
the wind direction in this latitudinal range acquires a westerly component caused by the Coriolis effect
ferell circulation wind direction
southerly component caused by the Ferrell circulation
coriolis effect and winds near equator
Coriolis effect induces the opposite twist in the latitudinal belts between the equator and 30 deg N or 30 deg S
Here the air is moving toward the equator, so air packets fall behind their apparent target rather than getting ahead
Therefore, these zones are subject to prevailing easterlies. Those winds were so important to maritime commerce in the sailing era that they became known as the trade winds
The prevailing winds are strongest at the latitudes in the middles of the atmospheric cells, roughly at 15° and 45°
There, the air is primarily being pushed horizontally across the earth’s surface, producing consistent winds. At the latitudes where air packets are mainly going upward (0° and 60°) or coming down (30°), there is little horizontal wind, and it is very fluky
Sailors justifiably feared these areas because they could get becalmed for weeks, and these dangerous zones acquired special names
The windless equatorial area became the “doldrums,” and the windless areas at 30° N and S became the “horse latitudes.”
The prevailing winds are strongest at the latitudes in the of _____the atmospheric cells, roughly at ________
middles ; 15° and 45°
At the latitudes where air packets are mainly going upward (0° and 60°) or coming down (30°), there is _____horizontal wind, and it is very fluky
little
The windless equatorial area became the “_____,” and the windless areas at 30° N and S became the “____________.”
doldrums; horse latitudes
Sailors encountered the opposite problem—way too much wind!—around 45° S, where the prevailing westerlies grew so fierce that they became known as the …
Roaring Forties
why are the roaring forties wind so powerful
there are no significant land masses in the vast southern oceans
