# Make discussion paragraph about meteorology

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1. Post either asks a question related to the corresponding module or shares/describes something interesting (any sources are cited) and weather related. The post is thoughtful, well written, and is of substantial meaning to the discussion as a whole. The post doesn’t just regurgitate course material, but expresses your understanding and reflection of the material.2. Reply to someone else’s post, either answering their question, or building on the information provided in the original post.

In first part, you must ask one question about the module. Once, you finish first part, and give the first part to me I will give back some’s discussion to write the second part.

Each discussion should be more than 50 words

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Meteorology 10
Terrence J. Mullens
Chapter 9
Meteorology 10
Terrence J. Mullens
Chapter 9
Steps to making a Weather Forecast:
Make a “Diagnosis”
Get Weather Data
Make a “Prognosis”
Plug the data into a Weather Model (Computer)
Interpret the Model’s Solution (Human)
To find out what might happen, we need to
know what is currently happening.
Weather Data can be accessed at a variety of
locations:
The National Weather Service
The World Meteorological Organization
Mesowest
System…
Helps Forecasters Organize/Utilize all that data!
Computer Models: Computers feed all of the
data collected into a set of equations. The
solutions of those equations are a forecast.
Computer models split the Earth’s surface and
atmosphere into a grid, and then forecast the
weather for each cell in that grid.
These models are unable to perfectly represent the
atmosphere… it is too complex.
Instead, they are excellent approximations that take the
most important aspects of the atmosphere into account.
The Computer Model uses the current weather
conditions (aka Initial Conditions) to make a
forecast for each cell in the grid for a short time
out (such as 5 minutes)…
The results are then fed back into the equations to
make a forecast for the next five minutes…
And then the next five minutes…
And then the next five minutes…
And then the next five minutes…
…Until we have a forecast for our desired time.
High Resolution: Each grid box is VERY SMALL
(such as a few kilometers)… A forecast is made
for a VERY SMALL change in time (such as five
minutes).
Very Accurate… but takes FOREVER to do.
Low Resolution: Larger Grid Boxes (such as a
few hundred kilometers)… Larger change in
time (such as an hour).
Quick Forecast… but not as Accurate.
Low Resolution
High Resolution
Weather Forecasts aren’t just made at the
surface… they are also made at several key
layers above the surface…
Key Layers:
Surface: Surface Conditions (Temperature,
Humidity, Wind, etc.)
850 mb level: Moisture, Temperature, Low-Level Jet
500 mb: Ridges, Troughs, “Spin” of the air.
300 mb: Jet Stream
A “Prog” is the prognosis
of the weather.
Essentially, the forecast for
24 hours from now.
A 24 Hour Prog is the
prognosis of the weather
24 hours from now.
Each Weather Model has a different:
Resolution
Set of Equations (and how they are used)
Set of Assumptions and Approximations
Most common Weather Models:
North American Model (NAM)
Global Forecasting System (GFS)
European Model (ECMWF)
Private Weather Models
Forecasters run the same forecast model many
times… but with slightly different “initial
conditions.”
The model results form an “Ensemble.”
If each of the ensemble runs have similar results,
confidence with the forecast becomes high…
If each of the runs have very different results,
confidence with the forecast becomes low.
High Confidence
Low Confidence
Displays progs for a
single location
(rather than over a
large area).
Includes multiple
progs: 3 hour, 6
hour, etc…
Includes progs
from different
models.
Meteorology 10
Terrence J. Mullens
Chapter 9
Weather Models use Approximations and make
Assumptions.
Each weather model has strengths and
weaknesses.
Human Forecasters need to consider these
strengths and weaknesses.
…Next Time!
Persistence Forecast: Current Conditions will Persist.
Example: It’s 72°F right now… it will stay 72°F an hour from
now.
Easy to make, pretty accurate in the short term… but
become less accurate over time.
Trend Forecast: Conditions will change based on an
observed Trend:
Example: It was 68°F on Saturday, 70°F on Sunday… so it will
be 72°F today.
Easy to make, pretty accurate… but trends don’t last.
The Front
moved 800
Miles in the last
24 hours… it will
move another
800 Miles in the
next 24 hours.
Analog Forecast: Weather Repeats Itself. It predicts
future weather based on previous weather events.
Example: The last El Nino created a lot of rain… So this El
Nino will also create a lot of rain.
Analog forecasts are tricky… No two weather set-ups are
identical… no matter how similar they look.
Climatological Forecast: Predicting future weather
based on the Average Conditions for that Day.
Example: The average temperature for June 5th is 81°F. So
the high temperature for this June 5th will be 81°F.
Yesterday’s temperature: 68°F
Today’s temperature: 71°F
Tomorrow’s Climatological Average: 82°F
Let’s make a temperature forecast for San Jose
for tomorrow:
Persistence: 71°F (Today’s temperature will be
tomorrow’s temperature)
Trend: 74°F (3 degrees of warmth)
Climatological: 82°F
Many weather forecasts include some kind of
probability:
For Example: There is a 60% chance of Rain.
The National Weather Service (NWS) split probabilities
into five Categories:
No Chance: 0% chance.
Precipitation not mentioned.
Slight Chance: 10-20%.
“Cloudy with a Slight Chance of Precipitation”
Chance: 30-50%
“Cloudy with a Chance of Precipitation”
Likely: 60-70%
“Cloudy with Precipitation Likely”
Categorical: 80-100%
“Cloudy with Precipitation”
Rain and Showers don’t mean the same thing in
a weather forecast!
Showers = Off-and-On, Hit-or-Miss
Rain
Showers
A Halo Around the Sun
could mean that rain is
on the way.
Cirrostratus Clouds
(which cause the halo)
mid-latitude cyclone.
Red Sky at Night, Sailor’s Delight…
Red Sky at Morning, Sailor’s Warning…
Short-term forecasts
are pretty accurate.
However… they
aren’t perfect
Errors in Short-term
forecast become
amplified further in
the forecast period.
Atmospheric Optics
Thanks to Dr. Craig Clements and Mr. Henry Bartholomew for contributions to this
lecture
Part 1 – A detailed
Energy Budget
Earth’s Energy Budget
• 70% is absorbed by the Earth/Atmosphere
• 51% by the Ground
• 19% by the Atmosphere/Clouds
• 30% is either Reflected/Scattered
• 20% is Reflected by clouds
• 4% is Reflected by the Ground
• And the remaining 6% is scattered…
Earth’s Energy Budget
This is what scattering causes…
This is called a “Blue Flash”
And This…
Part 2 – Scattering
Visible Light
• A beam of visible light emitted from the sun
actually consists of every color of visible light.
• Color is determined by wavelength:
Scattering of Light
Scattering occurs
when an object sends
out light in all
different directions.
Cloud Droplets that
are large enough
(around 10µm in
diameter) can
effectively scatter all
wavelengths of
or less equally.
Why are clouds white?
Many cloud droplets
are small, and thus
scatter mainly white
light.
Most clouds (even
small ones) are thick
enough to scatter
most sunlight. They
are also poor
absorbers of sunlight,
but…
Why are the base of clouds dark?
Less light reaches the
base of a cloud (due to
the albedo effect).
If there are large droplets
in a cloud (like rain
drops), they absorb light
rather than scattering it…
making the cloud look
much darker!
Why is the Sky Blue?
Billions of tiny air molecules scatter shorter wavelengths of light more effectively than
longer wavelengths, and so the blue/purple colors get scattered best… thus the sky is
blue.
Why is the sky Orange/Red at
Sunrise/Sunset?
Sunlight goes through more atmosphere when it is lower on the horizon, and thus more
scattering occurs. Because shorter wavelengths are scattered more effectively, by the time the
light reaches the surface, those wavelengths have been scattered away completely; the
remaining light is longer wavelengths (such as red/orange/yellow).
Part 3: Refraction and
Mirages
The behavior of light as it enters and leaves a more-dense substance, such as
water. This is called REFRACTION.
Fig. 15-11, p. 421
Fig. 15-12, p. 422
The Mirage
Inferior mirage
The road in the photo appears wet because blue skylight is bending up into the camera
as the light passes through air of different densities.
Fig. 15-15, p. 424
Inferior mirage
The road in the photo appears wet because blue skylight is bending up into the camera
as the light passes through air of different densities.
Fig. 15-16, p. 424
Superior Mirage
The formation of a superior mirage. When cold air lies close to the surface with warm
air aloft, light from distant mountains is refracted toward the normal as it enters the
cold air. This causes an observer on the ground to see mountains higher and closer
than they really are.
Fig. 15-17, p. 425
Part 4 – Rainbows
How rainbows might form…
Refraction and dispersion of light through a glass prism.
Certain objects
(such as prisms)
can cause white
light to separate
into its individual
wavelengths
(colors). This is
called dispersion.
Each color is
refracted slightly
different, and
thus they
disperse from
white light.
Fig. 15-21, p. 427
Rainbows
Sunlight internally reflected and dispersed by a raindrop.
(a)The light ray is internally reflected only when it strikes
the backside of the drop at an angle greater than the
48° (this is called the critical angle).
(b) Refraction of the light as it enters the drop causes the
point of reflection (on the back of the drop) to be
different for each color.
Hence, the colors are separated from each other when
the light emerges from the raindrop.
48°
Fig. 15-27, p. 430
When you observe a rainbow, the sun is always to your back.
Fig. 15-26, p. 429
Double Rainbow
Higher order Rainbows!
Part 5 – Halos
Halos
• Halos: Occur when thin, cirrus clouds are present.
Light is refracted through column-type ice crystals.
There are two types of halos
• 22° Halos form from tiny ice crystals
• 46° Halos form the same way, but from slightly larger ice
crystals
A 22° halo around the sun, produced by the refraction
of sunlight through ice crystals.
Fig. 15-18, p. 425
The formation of a 22° and a 46° halo with column-type ice
crystals.
Fig. 15-19, p. 426
Halo with an upper tangent arc
Fig. 15-20, p. 427
Platelike ice crystals falling with their flat surfaces parallel to the earth produce
sundogs.
Fig. 15-22, p. 427
The bright areas on each side of the sun are sundogs.
Fig. 15-23, p. 428
A brilliant red sun pillar extending upward above the sun, produced by the
reflection of sunlight off ice crystals.
Fig. 15-24, p. 428
Optical phenomena that form when cirriform ice crystal clouds
are present.
Fig. 15-25, p. 429
Review
• Reflection of light
• When visible light hits a particle and reflects at the same
angle it hit the particle with
• Scattering of light
• When visible light hits a particle and is sent out in all
directions from the particle (and often in all colors)
• Refraction of light
• When visible light enters a different medium at an angle,
it changes speed and bends.
• Dispersion of light
• When individual wavelengths of visible light refract at
slightly different angles… white light is split up into
colors.

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