EE107 Lab 1
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Boston University *
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107
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Dec 6, 2023
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Laboratory # 1: Global Energy Budget and Earth System
This lab is designed to give a feeling and basic understanding a System, the Global Energy Budget, the
driving force for our climate and weather, by looking the Albedo of different surfaces. Within the lab you
will go outside and use an Infra-Red Thermometer to measure different temperatures on different
surfaces and explore the relationship between Sun, Clouds and surfaces. The second part is designed to
understand reservoirs and residence time.
Background for Global Energy Budget
When sunlight enters the Earth
system, most of it passes through
the atmosphere and reaches the
surface. Some is then reflected
back to space and the remainder
is absorbed, heating the ground.
This heating is uneven, however,
and can vary a great deal over a
small area. These variations help
produce distinct microclimates,
that is places with different
temperature,
humidity,
and
sunlight within a small area. In
this lab, we will study local
variations in surface heating from
sunlight. Below is a brief overview
of some of the many factors that influence the temperature of a surface. For a more thorough
explanations, please do an internet search or ask questions on the bulletin board.
Sunlight:
Sunlight provides the energy that warms Earth's surface. Anything that reduces sun exposure
will lower temperature. That might include shading, reflection, and the angle at which the sun's rays
strike the ground.
Albedo:
The percentage of sunlight reflected from a surface is called its albedo. The energy in sunlight
remaining after reflection is absorbed by the surface. All else being equal, the greater the albedo, the
cooler the surface because less sunlight is absorbed. In general, darker surfaces, like asphalt, have low
albedos and thus, under the same sun exposure, heat up more than reflective surfaces such as snow,
grass, or concrete because they reflect less and absorb more of the available sunlight.
Evaporation:
When water is available, evaporation absorbs large amounts of energy and reduces
heating. Cooling by evaporation is one of the fundamental ways that plants and animals, including
humans, shed excess heat. When no water is available, all sunlight energy absorbed is used in heating
the surface and it can become quite hot. Which is hotter: bare sand or nearby grass? Grass roots send
soil water to the leaves where it evaporates and cools the plant.
Surface Material Properties:
One of the most important properties that affect temperature is a
material's specific heat capacity, which is ratio of energy added to temperature increase. Water has the
Figure 1. The Earth's annual and global mean energy balance. (taken from
http://www.atmo.arizona.edu/students/courselinks/fall12/atmo336/lectures/sec3/
energybudget2.html)
highest specific heat of any common substance in nature, meaning that it takes a lot of energy to heat it
up compared other surfaces like concrete, soil, forest or anything else. This explains, in part, why lake
and ocean surfaces heat up much more slowly than the nearby land areas during sunny days.
Part 1: Observation
For all the Labs you are a part if a team working together or exchanging data obtained independently
therefore Record the names of the members of your team and exchange contact information in case it is
needed.
Team Members in your group:
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_________________________________
Outside Exercise
There are Infrared Thermometers available. For your measurements. You will need to go outside to do
your measurements, be as careful and precise as possible for your work exchange and discuss you
approach and data with your team members.
Time__
12:50pm
_______ Date __
Sep.25
________ Sky Conditions _
Cloudy
_________________ Location
BU Beach
________________
Survey your area visually. Imagine walking around the area in bare feet.
Which surfaces would you prefer to walk on?
Grass or soil area because they were wet therefore, they
would be the coolest on bare feet
____________________________________________________________________________________
Which do you think would be coolest?
Grassy shaded area because grass has lower solar reflectance
_____________________________________________________________________________________
Which would you avoid because you imagine they would be too hot?
Asphalt because it was exposed to
direct sunlight and the darker surface has less albedo making it hotter
_____________________________________________________________________________________
If the area received a light rain, how do you think that would affect the surface temperature?
Surface Temperature would be cooler because when water is available, evaporation absorbs large
amounts of energy and reducing heating
_____________________________________________________________________________________
_____________________________________________________________________________________
Use the infrared (IR) thermometer to record temperatures. When using the IR thermometer, put the
instrument CLOSE to the surface being measured, maybe an inch or couple of centimeters away.
Ambient Air Temperature
Air temperature as reported by meteorological services around the world is recorded in a white, shaded
box called a Stevenson screen, with open airflow and a thermometer mounted at two meters above the
surface, hence sometimes called 2m-temperature. As we do not have a standard thermometer for
measuring air temperature, we will use a proxy that should give a fairly reliable result. Measure the
SHADED side of a tree trunk at around head height. The trunk should have been in the shade for an hour
or more to ensure that it approximates the ambient air temperature. Deep shade is best. Be sure to put
the instrument CLOSE to the tree trunk, like a couple of centimeters or an inch, when taking the
measurement, not 2 or 3 meters away.
3
. _16.1 C
Temperature on shaded side of a tree at head height. Deep shade is best. Blocked from the
wind is best. We will assume this is a close approximation of ambient air temperature.
Temperature Profile to determine Heat Flow near the Surface
In nature, heat flows from areas of higher temperature toward areas of lower temperature. We will
explore the direction of heat flow near the surface on a sunny day. In an open, sunlit area of bare dry
soil, measure the temperature using the IR thermometer at the following places. For the below-ground
measurements, use the digging tool to expose the soil at the listed depths and then use the IR
thermometer to measure the temperature in the hole. Be sure to place the IR thermometer CLOSE, but
not touching, the soil.
4. _
18.5 C
________ bare, dry soil in direct sunlight
5. _
19.0 C
________ about 1 cm (1/2 inch) below the soil surface (same or adjacent location as 4)
6. _
17.9 C
________ about 7 cm (3 inches) below the soil surface (same or adjacent location as 4)
Albedo, Surface Characteristics, and Surface Temperature
Now measure the temperature of several different surfaces that have been exposed directly to sunlight
for at least several minutes. Do not take these measurements in a shaded area.
7.
16.7 C
_______ sunlit side of tree trunk
8.
15.6 C
________ shaded grassy area
9. __
16.3 C
______ sunlit grassy area
10. __
16.5 C
______ shaded concrete
11. __
18.8 C
______ sunlit concrete
12. _
20.2 C
_______ sunlit asphalt
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Effect of Evaporation on Temperature
For this measurement, we will measure the temperature of an open surface exposed to sunlight, then
mist it with water, wait until the water evaporates away and then measure the temperature again.
13. _
18.5 C
_______ concrete in sunlight before wetting
14.
_16.6 C_______
concrete after water has evaporated
15. _
17.1 C
_______ tree trunk in sunlight before wetting
16. _
14.8 C
_______ tree trunk after water has evaporated
Clouds and Greenhouse Warming
Clouds are an important part element of greenhouse warming. For these measurements point your IR
thermometer at blue sky and clouds, but DO NOT POINT DIRECTLY AT THE SUN!!!!! or you will destroy
the instrument. Do your best with these measurements, it will not be possible to get clean
measurements of all items below, but you should be able to get reasonable enough measurements to
show the general relationships.
17. _
11.2 C
_______ large patch of blue sky overhead
18. _
10.3 C
_______ base of large area of cumulus clouds as high overhead as possible
19. _
N/A_______
thin high clouds (if available, just put N/A if no thin clouds)
Other
Feel free to play around with the instrument. There are lots of interesting variations in temperature in
the environment. Try measuring your skin at different places. Where is it hotter and cooler?
I measured two different places on my body. I first measured my forearm that read as 30 degrees Celsius
and then I measured my forehead which has been covered by a hat and that measurement read 28.9
degrees Celsius. I concluded that because both parts of my body were covered by something that the
initial
reading for both
was similar, but figured my forearm was warmer because it was fully covered
and
my
forehead
only
partial.
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
________________________________________________________________________
Discussion
Answer the following questions based on your measurements and the background information given at
the beginning of this lab. Some of the answers will be speculative so do not be afraid to use your
imagination, in other words - guess.
Sun and Shade.
20. How many degrees warmer was the sunlight area than the shaded area of the: a)
tree trunk 0.6-
degree difference
__ b) grass _
0.7 degree difference
_____, and c) concrete
2.3 degree difference
___________?
21. Which surface had the greatest difference in temperature between sunny and shaded areas?
_
Concrete
_____ Speculate: Why you think that surface was heated the most by direct sunlight
? I think
concrete was heated the most by sunlight because it has a higher solar reflectance therefore a lower
albedo causing it to absorb more available sunlight.
22. Speculate: Why you think there was a difference in the amount of warming by sunlight for the
different surfaces. What physical characteristics of the surfaces could be responsible for the difference?
Use reason and creativity in answering.
Grass is physically cooler than concrete and there are many
physical and thermal reasonings. Concrete and asphalt are both physically darker surfaces and contain
thermal mass that makes surrounding areas warmer than grass would. Concrete and Asphalt also have a
higher solar reflectance than grass. Less heat is reflected off grass making the warming of grass
significantly lower than that of concrete or asphalt. Also, the process of grass through photosynthesis
helps with the process of keeping it cool.
Temperature Profile
23. In nature, heat flows from warmer areas toward colder areas. Based on your measurements in 3 and
4, where is the higher temperature - at the surface (#4) or the air above the surface (#3)?
At the surface
________________ based on this result, which direction is heat flowing - from the surface upward into
the air, or from the air downward to the surface?
Upward into the air
_____________ Remember, heat
flows from warmer areas toward cooler areas.
24. Based on your answer above, during the day, does the ground heat the air or does the air heat the
ground?
Ground
heats
the
air
through
conduction
______________________________________________________________________________
25. Based on your measurements in #4, #5, and #6, where is the higher temperature - at the surface or
the soil below the surface? _
At the surface
__________ based on this result, which direction is heat
flowing - from the surface downward into the soil, or from the soil upward toward the surface
downward
into the soil
_____________? Remember, heat flows from warmer areas toward cooler areas.
26. Assume that, at night, the bare soil surface temperature falls to 20ºC (68ºF) and the temperatures
below the surface that you measured in #5 and #6 remain the same. Under these conditions at night,
which direction will heat flow - from the surface downward into the soil, or from the soil upward to the
surface?
Downward into the soil
_____________ Explain your answer, why is heat flowing that direction
at night?
Heat is still flowing downward into the soil because the soil tested has a larger percentage of
water therefore the soil below the surface is cooler than the surface soil
Albedo
27.Which surface was hotter, concrete or asphalt?
Asphalt_______________________________
Which was darker?
Asphalt_______________________________________________________
28. Do you think darker or lighter surfaces will be hotter in general?
Darker________________
Why?
Darker surfaces are normally hotter because they absorb all the wavelengths of light and converts them
to warmth versus lighter surfaces, darker surfaces also hold low albedos.
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Effect of Evaporation
29. How many degrees did wetting cool the concrete?
1.9 C_____________
How many degrees did
wetting cool the tree trunk?
2.3 C
______________ What caused the temperature to drop?
When
wetting the tree the process of Transpiration occurs as well as evaporation to reduce heat.
____________________ (Do not say "it got wet," state the physical process that caused the cooling)
30. Did concrete or the tree trunk cool more when wet?
Tree Trunk
____
Why do you think there was a
difference? ________________
31. Compare your measurements of the sunlit, open grass (#9) and bare, dry soil (#4) areas, which was
hotter? _________ Both are exposed to the same amount of sunlight, and grass has a lower albedo than
bare soil, so why do you think there was a difference in temperature?
Urban Heat Island
32. Which surface was hotter, grass or asphalt? ________________ Why do you think it was the hottest?
33. Ever hear of an "urban heat island?" The phrase refers to the observation that urban (city) areas are
almost always hotter than the surrounding rural (country) areas. Based on your measurements and
answers above, give two reasons that urban areas might be hotter than rural areas.
First Reason: __
Urban areas have more concrete and buildings the re-emit heat from the sun
______________________________________________________________________
Second Reason: _Ubran areas are paved and have less vegation than rural areas menaing there is less
room
for
evaprotation,
and
_____________________________________________________________________
Application
34. There was a lot of variation in the surface temperature measurements. Under what conditions would
you expect all of your measurements to be approximately the same?
35. Compare your surface temperature measurements to your initial beliefs given in #2 above. Did the
measurements prove you right for the coolest and hottest surfaces? ______________
If not, what were the differences?
36. Many plants and animals cannot tolerate uncontrolled temperature fluctuations caused by direct
sunlight exposure. Based on the various measurements you took in this exercise, suggest at least three
(3) ways that plants and animals might reduce their surface heating due to direct sunlight. (HINT: which
measurements had the lowest temperatures?).
Sky
37. Which was warmer, cloud or clear sky?
Sky
_____________ Clouds can have an important effect
Earth's surface temperature. Based on your measurements, do you think the surface would be warmer
at night under clouds or clear sky? _
Clouds
______________ Explain your reasoning:
Clouds have the
effect of trapping sunlight therefore, I think at night when there is no sun the clouds would trap the heat
from the sun and therefore could still warm the surface at night
38. Clouds have a major effect on planetary temperatures by influencing the amount of sunlight
absorbed and reflected by the planet and through an analog with the so-called greenhouse effect. The
greenhouse effect traps heat in a planet's atmosphere. From the surface, the greater the greenhouse
effect, the warmer the sky appears. Based on this information and your measurements, do you think
that more clouds would increase or decrease the planetary greenhouse effect?
______________________ Explain your reasoning:
39. What was the difference in degrees between the air temperature (#3) and the cloud base
temperature (#18)? ________________. Under dry conditions, rising air cools at about 10ºC per
kilometer (5.5ºF per 1000 ft). Based on this information, how high would the surface air have to rise to
match the cloud base temperature that you measured? _____________________ (HINT: subtract cloud
temperature from surface air temperature (#3) and divide by either 10ºC or 5.5ºF, depending on the
units you are using.)
Part 2: Steady State Systems and Perturbations – a Virtual Experiment
In this second part, you will study systems that are in a steady state and examine what happens to a
system when you disturb that steady state. Your system will include a bucket of water with a faucet that
can fill the bucket with water and a spigot/hole that allows you to drain the bucket. This bucket is
analogous to a lake, which is one of a network of
reservoirs
of water in the hydrologic cycle. In the
hydrologic cycle, the water reservoirs
(ex: lakes, oceans, atmosphere) have various sizes and store water
for variable lengths of time.
Processes
such as precipitation and river discharge can transfer water into a
Lake Reservoir, and river runoff and groundwater seepage can transfer water out of it. We refer to these
transfer processes as
inputs
and
outputs
for these reservoirs. Your bucket
system
has only one reservoir
(the bucket), only one input (the faucet), and one output (the spigot), but in the hydrologic cycle, there
are many reservoirs and processes that transfer water between reservoirs. For any reservoir, we refer to
it as a
steady state system
when the quantity of material in the reservoir does not change with time, and
the rate of input into the reservoir is exactly the same as the rate of output.
Figure 2 Example of your Virtual Bucket System.
The Steady State Bucket (a virtual experiment in Excel)
You are provided with an Excel Spreadsheet on Blackboard (
EE107_Lab1_Mass_Balance_Worksheet
)
what will allow you to run three sets of systems “Experiments” simulating the changes in the volume of
water in a bucket over time as you change the rate at which water flows in and out. The bucket is a
reservoir
that has an
input
of water flowing into it from a faucet, at a known rate called
“Input Rate”
.
The bucket also has a hole in the bottom, which allows water to drain out at a given rate called
“Output
Rate”
. These three components comprise our
system
. The equation that governs this system is:
dV/dt = I-O
Where V = volume of water in the system, I = input rate and O = output rate, and dV/dt = the rate of
change of water volume with time.
Each Experiment is set up in the spreadsheet so that you can edit the variables (input rate, output rate,
the initial volume of water in a bucket). You can then click the
“Plot Experiment”
button and a plot will
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be generated simulating the change in the volume of water in the bucket with the time given your input
and output rates. You will then change these variables to determine how your system responds.
*** You will need to
Enable
Macros
when you open the Excel Sheet ***
Experiment 1: Constant Input and Output Rates
This Experiment includes a bucket with a faucet with a
constant input rate
that you can control and a
valve at the bottom of a bucket with a
constant output rate
that you can control.
1) Before you begin the experiment:
a) Make a prediction (hypothesis)
about what will happen to the system if the input rate is equal to the
output rate. How do you think the initial volume of the water in the bucket will affect how the system
evolves? Be specific.
Will the volume of the reservoir change? If so, how? Explain your reasoning.
b) Make a prediction (hypothesis)
about what will happen to the system if the input rate is greater than
the output rate. What if the output rate is greater than the input? Explain your reasoning.
2) Using the setup for Experiment one, edit the values in the yellow cells so that:
Input rate
= 1 m
3
/min
Initial Volume = 1 m
3
Output rate
= 1 m
3
/min
And then click “
Plot Experiment 1”.
What happens to the volume of water in the bucker reservoir? Did it
match your predictions?
3) Change the
initial volume
to a value greater than 1 m
3
, but keep the input and output rate equal to 1
m
3
/min, and then click “
Plot Experiment 1”
to run the experiment again. How did the volume of water in
the system change with time? Did it match your predictions?
4) Now change your variables so that the
input rate
to a value greater than the
output rate
. How did the
volume of water in the system change with time? Be specific. Did your observations match your
predictions?
5) Now change your variables so that the
output rate
to a value greater than the
input rate
. How did the
volume of water in the system change with time? Be specific. Did it match your predictions?
6) How does the magnitude of the difference between the input and output rates affect the rate at
which the volume of water in the bucket changes?
Experiment #2: Output Rate changes as a function of water volume
This Experiment includes a bucket with a faucet with a
constant input rate
that you can control and a
hole at the bottom of a bucket with a
variable
output rate
that is a function of the volume of water in the
bucket. Like in the real world, the rate at which water flows out of the bucket is faster if the bucket is full,
and slower if the bucket is nearly empty (this is the same phenomenon that you observe when coffee or
water from a large jug dispenses quickly when it is full but trickles out slowly when it is almost empty). In
this Experiment, the rate of outflow is set to be equal to a percentage of the volume of the bucket (ex:
10%). Changing this percentage is equivalent to changing the size of the hole.
1) Before you begin the experiment:
a) Make a prediction (hypothesis)
about what will happen to the system if the input rate is
not
equal to
the output rate. How do you think the initial volume of the water in the bucket will affect how the
system evolves? Be specific.
Will the volume of the reservoir change? If so, how? Explain your reasoning.
b) Make a prediction (hypothesis)
about what differences you would expect to see if you compared the
evolution of two systems (buckets) with different size holes (different outflow rates) but with the same
input rate. Explain your reasoning.
2) Using the setup for Experiment 2, edit the values in the yellow cells so that:
Input rate
= 1 m
3
/min
Initial Volume = 1 m
3
.
Output rate
= 10% of the total volume
And then click “
Plot Experiment 2
”. What happens to the volume of water in the bucker reservoir? Did it
match your predictions?
3) Try changing the experiment variables so that the initial volume is larger than 1m^3 and click “
Plot
Experiment 2”
to redraw the plot. How does the system evolve? How is it similar and different to the
experiment in question 2 above?
4) Next, you will try changing the
output rate
, which is determined as a
percentage
of the total volume:
a) Try increasing the output rate to a value greater than 10%. How did the volume of water in the system
change with time? Be specific.
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b) Try changing the output rate so that it is less than 10%. How to the volume of water in the system
change with time? Be specific. How does it compare to the system with the output rate greater than
10%?
Experiment #3: Perturbing a Steady State System
In this Experiment, you will begin with a system with an
initial input rate
and output flow rate, allow it
to achieve a steady state, and then you will perturb the system by
changing the input rate
. The
output
rate will adjust accordingly
to the new input rate. This experiment is analogous to how the volume of
water in a lake may evolve when a new input of water from a rainstorm occurs. In this experiment, the
change in input rate occurs at a time of
80 minutes
.
1) Before you begin: Make a prediction
(hypothesis) about what will happen to the volume of water in
the system when you increase the input rate
at time= 80 min? What do you think will happen if you
decrease the input rate
at time = 80 min? Be specific.
2) Using the setup for Experiment 3, edit the values in the yellow cells so that:
Initial Input rate = 1 m
3
/min
Initial Volume = 1 m
3
Output rate
= 10% of the total volume
Now edit the variable for
Perturbed Input Rate
to be a value greater than 1 m^3. Click “
Plot Experiment
3
”. What happens to the volume of water In the bucker reservoir? Did it match your predictions?
3) Now try running the experiment but change the
Initial Input rate
and the
Perturbed Input Rate
so
that the Perturbed Input rate
is less than
the Initial Input rate. What happens to the volume of water In
the bucker reservoir? Did it match your predictions?
4) We can define a new quantity called the “
residence time
” (
τ
) for water in the virtual bucket. This is
the length of time that an average water molecule spends in the bucket. It is formally defined as:
τ
(
s
)
=
Reservoir volume
(
❑
❑
)
Output rate
(
❑
❑
❑
)
Calculate the residence time for water in the virtual bucket: Show your work and include units.
a)
At time = 60 minutes in experiment 3.
b)
At time = 140 minutes in experiment 3 with increased input rate (question 2).