Table 5.1 Our eyes are remote sensors that are sensitive to light with wavelengths
between approximately 0.39-0.78 microns. A color represents a range of wavelengths.
Color
Wavelength (m)
Violet
0.390-0.455
Blue
0.455-0.492
Green
0.492-0.577
Yellow
0.577-0.597
Orange
0.597-0.622
Red
0.622-0.780
Figure 5.1 Automated Surface Observing System (ASOS) makes continuous observations
of the atmosphere using both direct and indirect methods.
Figure 5.2 A standard instrument shelter, known as the Stevenson Screen, houses and
protects temperature, pressure, and relative humidity instruments. The front door is open
to show the interior. The shelter is a white, wooden box with louvered sides and stands 4
feet above the ground (Credit: NOAA Photo Library, NOAA Central Library). (I may
be able to get a better photo)
Laser
Receiver
Transmitted light
Observed light
Mirror temperature above dew point
Laser
Receiver
Transmitted light
Observed light
Mirror temperature at dew point
Figure 5.3 Scattered light from a beam is used to measure dew point temperatures. When
dew forms, less light is received by the receiver because the dew drops scatter light into
all directions, just like clouds. (Draw dew drops on chilled mirror.)
Figure 5.4 The wind vane (left) and cup anememeter (right) are used to measure wind
direction and wind speed. (Maybe we want to label these on the photo, which was
taken from a NOAA web page.)
Figure 5.5 The vertical distribution of temperature, humidity, pressure, and winds are
obtained with an instrument called a rawinsonde. The small instrument box is located
near the bottom of the photograph. A parachute is in the center of the string between the
balloon and the instrument package, and opens when the balloon bursts. Measurements
are transmitted back to the surface for analysis.
Figure 5.6 A sounding is a plot of temperature (black line to the right) and dew point
(black line to the left) in the vertical Stuve. In the Stuve thermodynamic diagram,
temperature is represented on the x-axis and pressure on the y-axis. The straight greenlines that slope upward from right to left are the dry adiabats. The dry adiabatic lines
represent a decrease in temperature of 10C for each kilometer--the dry adiabatic lapse
rate. The dashed slightly curved lines represent the wet adiabats. These lines represent
the moist adiabatic lapse rate experienced by a rising saturated air parcel. The dotted
orange lines represent lines of constant mixing ratio. (We will want to make the
temperature and dew point temperatures lines different colors.)
Figure 5.7 The angle of the reflected and refracted ray depend on the angle of incidence,
and are measured with respect to the normal, an imaginary line drawn perpendicular to
the air-water interface.
Specular Reflection
Diffuse Reflection
Figure 5.8 In specular reflection the reflected rays of light (blue arrows) remain in the
same relative position as the incident rays, producing a mirror image. In diffuse
reflection the light rays are scattered in all directions.
Figure 5.9 Sun glint is an example of specular reflection off water. [NOAA photo
library-I can get others taken by students.]
Figure5.10 The critical angle occurs when light travels from one medium into another
that has a lower index of refraction, such as from water into air. At the critical angle the
refracted ray travels along the surface of the water. An angle of incidence that is greater
than the critical angle will be totally reflected and will not enter the air.
Star appears higher in the sky
then its true position.
Star's true position
Ligt ray refracts as
it passes through the
atmosphere.
Figure 5.11 Because of refraction of star light by the atmosphere, stars are not where they
appear to be!
Figure 5.12 When the sun is near the horizon, the sunlight travels through more
atmosphere, and all the blue light is scattered back to space and only the red, orange and
yellow are visible to the observer. (Need a diagram similar to Ahren's hardcover
figure 4.8, or use the above but get rid of the moon and put people on the earth. this figure explains why the moon is orange during a total lunar eclipse.)
Figure 5.13 During a sunset or sunrise, the sky is red and yellow, as all the blue light is
scattered away from the observer.
Figure 5.14 The bottom of thick clouds appear gray because little light exits the base
since most of the sunlight is scattered out the sides and tops of the cloud (Include a line
figure like Ahrens 15.1, to accompany this, maybe as part of this figure.)
Cloud scatters some
light back towards the
ceilometer
Transmitted
light
Figure 5.15 A ceilometer uses light scattered by clouds to determine the height of the
cloud base.
Figure 5.16 Weather satellites typically fly in geostationary or low Earth orbits. (change
850km up to 850 km high)
Figure 5.17 A visible image of North America from the GOES satellite.
Figure 5.18 A infrared image of North America from the GOES satellite. (Compare
with Figure 5.17, which was observed at the same time) Interpreting Satellite Images
Figure 5.19 Combining visible and infrared satellite images is a useful way to identify
clouds based on their brightness in each image.
Figure 5.20 A water vapor image of North America made from a GOES satellite.
Light areas are more humid than dark regions. Bright white regions indicate high clouds.
(Compare with Figures 5.18 and 5.17).
Figure 5.21 Weather radars send out a narrow beam radio wave that is scattered
off precipitation.
Some of the scattered energy returns to the weather radar and
forecasters interpret it to locate regions of precipitation and intensity. The purple lines
represent the transmitted pulse while the blue lines represent the received signal. (Edit so
the cloud and precipitation are more off to the horizon).
Figure 5.22 An example of a radar image. Colors represent the amount of energy
scattered back to the radar site. High reflectivities are colored red and indicate high
precipitation rates.
Figure 5.23 A summary of the radar observations made across the United States.
Compare this with satellite figures (Figure 5.17 through 5.20)
Figure 5.24 The frequency of sound waves change when the source, or the
observer, are moving. If the source and observer are converging, the frequency is higher;
if they are diverging, the frequency is lower. (Use an ambulance or police car in place of
the train).
Figure 5.25 A Doppler radar measures the relative direction of precipitation
particles that move toward or away from the radar. (Combine figures 5.24 and 5.23,
replacing the train with falling rain drops.
Figure 5.26 A radar display in Doppler mode (also known as velocity mode) of a
thunderstorm that spawned a tornado and caused destruction in Oklahoma City, OK in
May, 1999. Greens represent motion towards the radar and the reds indicate motion away
from the radar. Chapter 11 will describe how radars can be used to identify regions of a
thunderstorm that might develop into a tornado.
Sunlight reflects off the tree.
Some of the reflected light
propagates towards the observer,
some towards the ground where
it is refracted.
The refracted light results in an inferior
mirage, which appears to the observer
as a reflection on the ground.
Figure 5.27 A mirage is a distorted image of an object that results from refraction. An
inferior mirage, where the refracted image appears below the object’s true position,
occurs because light is refracted in a strong temperature gradient. (Include temperature
profile as in Ahrens figure 15.14, might also want to include a photo and adjust
objects in line drawing to represent photo.)
Light from the sailboat
is refracted because of a
surface temperature inversion.
Because of refraction, the boat
appears to be above the horizon.
Horizon
Boat is below the horizon.
Figure 5.28 A superior mirage occurs when air is refracted through a temperature
inversion. (Include temperature profile as in Ahrens figure 15.15. We could combine
this with figure 5.12, to make a four panel figure.)
o
22
o
22
Figure5.29 A ring around the sun is called a halo as is due to refraction of sunlight by ice
crystals. (Might need another figure of a halo. The small figure explains the sundogs,
perhaps we can do something similar for the halo picture-see Ahrens figure 15.17.
Need permission for © 1997 Gregory Thompson http://www.inclouds.com/)
light refracts through
a side of the crystal
Direction of original ray
22
Cross-sectional view

Refracted rays through ice crystal
gives the appearance of a halo around the sun.
Figure 5.30 Diagram explaining how light is refracted through a crystal to form a 22degree halo.
Figure 5.31 Prism with separation of colors. (See Ahrens figure 15.19 for an example.)
Figure 5.32 To see a rainbow the sun must be at your back and you should be looking at
water drops suspended in the air.
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o
o
54.5
Figure 5.33 Dispersion causes the different wavelengths of light to separate as they pass
through the raindrop. As the light leaves the drop at different angles, the light spreads out
so that colors from a specific section of the rainbow come from a particular raindrop.
secondary
rainbow
sunlight
primary
rainbow
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40
54.5
42
Figure 5.34 Colors of the rainbow arise from drops at different altitudes in the sky.
Distinct sections of a rainbow are prodcued by different drops suspended in the
atmosphere. When viewing a rainbow, the sun must always be behind you. (Can we
combine this with a photo of a rainbow? I like incorporating the colors as in the
bottom figure.)