Meteorology: every day weather
Dr. Anne Clouser
National Earth Sciences Committee
Meteorology: Everyday Weather
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Everyday Weather: is the first topic in the BDivision Science Olympiad Meteorology Event.
Topics: rotate annually so a middle school
participant may receive a comprehensive
course of instruction in meteorology during the
three-year cycle.
Sequence:
1. Everyday Weather (2007)
2. Severe Storms (2008)
3. Climate (2009)
topics to be covered
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The modern atmosphere: structure and composition
Water: its states and properties as they relate to weather
Clouds and precipitation: types, and how they are formed
Heat transport: the energy budget, insolation, albedo, convection,
radiation, etc.
Atmospheric circulation: Coriolis effect, planetary wind belts, jet
streams, local wind patterns (Chinook winds, mountain and sea
breezes), and the three cell model of circulation
Air Masses: origin, temperature, density, moisture content, and
stability
Highs, lows, and fronts (warm, cold, occluded & stationary)
Surface Weather Stations: how to read and interpret them
Modern weather technology: satellite imagery, isobars and isotherms,
surface weather maps showing isobars fronts and radar data,
meteograms, stuve diagrams, and doppler imagery.
Weather instrumentation: barometers, thermometers, anemometers,
sling psychrometers, rain gauges, radiosondes, rawinsondes, and the
Beaufort scale
Atmospheric phenomena: sundogs, rainbows, aurora, virga, etc.
THE MODERN ATMOSPHERE
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ITS COMPOSITION
There are permanent gasses
(nitrogen and oxygen)
There are variable gasses (carbon
dioxide, methane, water vapor,
ozone, particulates
The composition of the atmosphere
has not been constant but has
changed through time.
We used to be the stuff of stars
(helium and hydrogen) but
outgassing, comets, UV radiation
and photosynthesis have changed
us.
http://www.uwsp.edu/gEo/faculty/ritter/geog101/textbook
/atmosphere/atmospheric_structure.html
http://www.physicalgeography.net/fundamentals/7a.html
http://www.visionlearning.com/library/module_viewer.php
?mid=107&l=&c3=
http://www.globalchange.umich.edu/globalchange1/curre
nt/lectures/samson/evolution_atm/index.html#evolution
THE MODERN ATMOSPHERE
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IT’S STRUCTURE
Layers are defined by
temperature, altitude, and unique
characteristics
There are layers where
temperature rises with altitude or
falls with altitude (our natural
instinct).
Between these layers there are
pauses where temperature is
constant with altitude change.
Each layer has unique
characteristics like 90% of the
ozone is in the stratosphere and
gasses stratify by molecular
weight in the thermosphere
Thickness of these layers varies
with latitude.
http://www.uwsp.edu/gEo/faculty/ritter/geog101/textb
ook/atmosphere/atmospheric_structure.html
http://www.albany.edu/faculty/rgk/atm101/structur.ht
m
water: its states and properties
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Water is unique in that it can
exist in three states on the
face our planet liquid, solid,
and gas
Water absorbs or releases
huge amounts of latent heat
as it changes states. This is
unique. It buffers our
environment with this
capacity.
Water is most dense at 4oC so
ice floats otherwise the
oceans would freeze from the
bottom up. No life on earth.
Water is the universal solvent
http://www.uwsp.edu/geo/faculty/ritter/geog101/text
book/atmospheric_moisture/phase_changes.html
http://en.wikipedia.org/wiki/Latent_heat
PRECIPITATION
• When cloud particles
become too heavy to
remain suspended in
the air, they fall to the
earth as precipitation.
Precipitation occurs in
a variety of forms;
hail, rain, freezing
rain, sleet or snow.
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http://ga.water.usgs.gov/edu/watercycleprecipitation
.html
http://www.laits.utexas.edu/kimmel/container.html?p
recip_types.html&2
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/p
rcp/home.rxml
PRECIPITATION
PRECIPITATION: RAIN
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Rainfall: Rain develops when
growing cloud droplets become
too heavy to remain in the cloud
and as a result, fall toward the
surface as rain.
Rain can also begin as ice crystals
that collect each other to form
large snowflakes. As the falling
snow passes through the freezing
level into warmer air, the flakes
melt and collapse into rain drops.
The picture below shows heavy
rain falling over the Grand
Canyon.
http://homepage.ntlworld.com/booty.weather/metinf
o/precipform.htm
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http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/p
rcp/rnhl.rxml
http://www.infoplease.com/ce6/weather/A0840995.h
tml
http://www.aolsvc.worldbook.aol.com/wb/Article?id=
ar458340
http://www.ess.uci.edu/~yu/class/ess5/Chapter.7.pr
ecipitation.all.pdf#search=%22hail%20formation%2
0by%20coalescence%22
PRECIPITATION: HAIL
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Hail: Hail is a large frozen raindrop produced
by intense thunderstorms, where snow and
rain can coexist in the central updraft.
As the snowflakes fall, liquid water freezes
onto them forming ice pellets that will continue
to grow as more and more droplets are
accumulated.
Upon reaching the bottom of the cloud, some
of the ice pellets are carried by the updraft
back up to the top of the storm. As the ice
pellets once again fall through the cloud,
another layer of ice is added and the hail
stone grows even larger.
Typically the stronger the updraft, the more
times a hail stone repeats this cycle and
consequently, the larger it grows. Once the
hail stone becomes too heavy to be supported
by the updraft, it falls out of the cloud toward
the surface.
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http://www.classzone.com/books/earth_scienc
e/terc/content/visualizations/es1805/es1805pa
ge01.cfm?chapter_no=visualization
http://www.mcwar.org/articles/hail.pdf#search
=%22hail%20formation%20by%20coalescenc
e%22
http://www.islandnet.com/~see/weather/alman
ac/arc2002/alm02jul.htm
http://beta.nssl.noaa.gov/primer/hail/hail_basic
s.html
PRECIPITATION: FREEZING RAIN
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FREEZING RAIN: The diagram below shows a
typical temperature profile for freezing rain with
the red line indicating the atmosphere's
temperature at any given altitude.
The vertical line in the center of the diagram is
the freezing line. Temperatures to the left of this
line are below freezing, while temperatures to
the right are above freezing. Freezing rain
develops as falling snow encounters a layer of
warm air deep enough for the snow to
completely melt and become rain.
As the rain continues to fall, it passes through a
thin layer of cold air just above the surface and
cools to a temperature below freezing. However,
the drops themselves do not freeze, a
phenomena called supercooling (or forming
"supercooled drops").
When the supercooled drops strike the frozen
ground (power lines, or tree branches), they
instantly freeze, forming a thin film of ice, hence
freezing rain.
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http://twister.sbs.ohiostate.edu/g520/ch7_1.ppt#16
http://www.islandnet.com/~see/weather/el
ements/icestorm.htm
http://ww2010.atmos.uiuc.edu/(Gh)/guide
s/mtr/cld/prcp/zr/prcs/ice.rxml
PRECIPITATION: SLEET
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SLEET: Sleet is less prevalent than
freezing rain and is defined as frozen
raindrops that bounce on impact with the
ground or other objects.
The diagram at the right shows a typical
temperature profile for sleet with the red
line indicating the atmosphere's
temperature at any given altitude.
The vertical line in the center of the
diagram is the freezing line.
Temperatures to the left of this line are
below freezing, while temperatures to the
right are above freezing.
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http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/p
rcp/slt.rxml
http://www.weatherquestions.com/What_causes_ice
_pellets.htm
http://www.geography.hunter.cuny.edu/~tbw/wc.note
s/5.cond.precip/sleet_formation.htm
PRECIPITATION: SNOW
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SNOW: Snowflakes are simply aggregates of ice
crystals that collect to each other as they fall
toward the surface.
The diagram below shows a typical temperature
profile for snow with the red line indicating the
atmosphere's temperature at any given altitude.
The vertical line in the center of the diagram is the
freezing line. Temperatures to the left of this line
are below freezing, while temperatures to the right
are above freezing.
Since the snowflakes do not pass through a layer
of air warm enough to cause them to melt, they
remain in tact and reach the ground as snow.
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http://ww2010.atmos.uiuc.edu/(Gh)/guides/
mtr/cld/prcp/snow.rxml
http://www.geography.hunter.cuny.edu/~tbw/
wc.notes/5.cond.precip/sleet_formation.htm
http://web.syr.edu/~wrt405/normal/snow.htm
l
http://express.howstuffworks.com/wqsnowstorm.htm
http://library.thinkquest.org/C003603/english
/snowstorms/index.shtml
CLOUDS: FORMATION
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FORMATION: Clouds are formed when air
containing water vapor is cooled below a critical
temperature called the dew point and the resulting
moisture condenses into droplets on microscopic
dust particles (condensation nuclei) in the
atmosphere.
Expansional cooling: The air is normally cooled
by expansion during its upward movement. As a
parcel of air rises it is cooled by expansion and
makes clouds
Upward flow of air in the atmosphere may be
caused by convection resulting from intense solar
heating of the ground, again expansional cooling.
by a cold wedge of air (cold front) near the ground
causing a mass of warm air to be forced aloft,
frontal lifting or convergence.
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by a mountain range at an angle to the wind,
orographic uplift. Again expansional cooling
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Frictional turbulence: Clouds are occasionally
produced by a reduction of pressure aloft or by the
mixing of warmer and cooler air currents.
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http://www.infoplease.com/ce6/weather/A0
857399.html
http://www.physicalgeography.net/fundame
ntals/8e.html
http://www.auf.asn.au/meteorology/section
3.html
http://www.bbc.co.uk/weather/weatherwise
/factfiles/basics/clouds_formation.shtml
CLOUDS: CLASSIFICATION
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Cirrus: high clouds that do not obscure the sun or
moon but often create halos. High cloud forms
include cirrus, detached clouds of delicate and
fibrous appearance, generally white in color, often
resembling tufts or featherlike plumes, and
composed entirely of ice crystals; cirrocumulus
(mackerel sky), composed of small white flakes or
very small globular masses, arranged in groups,
lines, or ripples; and cirrostratus, a thin whitish veil,
sometimes giving the entire sky a milky
appearance, which does not blur the outline of the
sun or moon but frequently produces a halo.
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Alto: intermediate clouds. Intermediate clouds
include altocumulus, patchy layer of flattened
globular masses arranged in groups, lines, or
waves, with individual clouds sometimes so close
together that their edges join; and altostratus,
resembling thick cirrostratus without halo
phenomena, like a gray veil, through which the sun
or the moon shows vaguely or is sometimes
completely hidden.
CLOUDS: CLASSIFICATION
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Stratus: low clouds. Low clouds include
stratocumulus, a cloud layer or patches composed
of fairly large globular masses or flakes, soft and
gray with darker parts, arranged in groups, lines, or
rolls, often with the rolls so close together that their
edges join; stratus, a uniform layer resembling fog
but not resting on the ground; and nimbostratus, a
nearly uniform, dark grey layer, amorphous in
character and usually producing continuous rain or
snow.
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Cumulus: clouds with vertical development. A
thick, detached cloud, generally associated with fair
weather, usually with a horizontal base and a domeshaped upper surface that frequently resembles a
head of cauliflower and shows strong contrasts of
light and shadow when the sun illuminates it from
the side, and cumulonimbus, the thunderstorm
cloud, heavy masses of great vertical development
whose summits rise in the form of mountains or
towers, the upper parts having a fibrous texture,
often spreading out in the shape of an anvil, and
sometimes reaching the stratosphere.
Cumulonimbus generally produces showers of rain,
snow, hailstorms, or thunderstorms.
unique cloud types: know what they mean
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Nacreous clouds: These rare clouds, sometimes
called mother-of-pearl clouds, are 15 - 25km (9 16 miles) high in the stratosphere and well above
tropospheric clouds. They are iridescent clouds.
They occur mostly but not exclusively in polar
regions and in winter at high latitudes.
They shine brightly in high altitude sunlight up to
two hours after ground level sunset or before
dawn. Their unbelievably bright iridescent colours
and slow movement relative to any lower clouds
make them an unmistakable and unforgettable
sight.
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Mammatus clouds: these clouds are formed by
down pouchings of cold air. Mammatus typically
develop on the underside of a thunderstorm's anvil
and can be a remarkable sight, especially when
sunlight is reflected off of them.
unique cloud types: know what they mean
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Noctilucent clouds: Clouds at extremely high
altitude, about 85 km, that literally (as the name
suggests) shine at night. They form in the cold,
summer polar mesopause and are believed to
be ice crystals. Because of their high altitude, in
a very dry part of the atmosphere, noctilucent
clouds are rather an enigma and are being
studied by a number of people around the world.
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Lenticular clouds: Altocumulus standing
lenticularus result from strong wind flow over
rugged terrain. Jet stream winds whipping over the
Rockies produce up-and-down wavelike patterns
on the lee side of the range. Lenticular clouds,
which occur at mid-levels of the troposphere form
at the peaks of these waves.
These eerie, elliptical cloud formations, which can
also resemble stacks of pancakes, often foretell
changes in the weather, and indicate high winds
aloft.
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unique cloud types: know what they mean
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Wave clouds: Kelvin-Helmholtz wave clouds are
formed when there are two parallel layers of air
that are usually moving at different speeds and in
opposite directions. The upper layer of air usually
moves faster than the lower layer because there
is less friction. In order for us to see this shear
layer, there must be enough water vapor in the
air for a cloud to form. Even if clouds are not
present to reveal the shear layer, pilots need to
be aware of invisible atmospheric phenomenon.
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Cap clouds: A mountain top is sometimes capped
by a more or less smooth cloud. This cap cloud is
related to lenticularis, but forms directly over the
mountaintop as opposed to lenticularis, that may
form at middle altitudes above the mountain. A
cap cloud is formed when humid air is forced to
flow over the mountain, condensing into a cloud.
heat transport and energy budget
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Absorption and re-emission of
radiation at the earth's surface is
only one part of an intricate web of
heat transfer in the earth's
planetary domain. Equally
important are selective absorption
and emission of radiation from
molecules in the atmosphere. If the
earth did not have an atmosphere,
surface temperatures would be too
cold to sustain life. If too many
gases which absorb and emit
infrared radiation were present in
the atmosphere, surface
temperatures would be too hot to
sustain life.
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http://okfirst.ocs.ou.edu/train/meteorology/EnergyBudget2.
html
http://marine.rutgers.edu/mrs/education/class/yuri/erb.html
#dosh
Insolation: intensity and duration
The amount of insolation received at the Earth’s surface is a function
of the intensity and duration of the radiation. Intensity and
duration are directly impacted by latitude as illustrated by the
graph below.
earth’s energy budget
• Earth’s Energy Budget: Earth’s external
heat engine is energy provided by the sun
• Average global surface temperature = 15°C
• This temperature represents the balance
between Incoming solar radiation
(insolation) the whole electromagnetic
spectrum and outgoing terrestrial radiation
(infrared radiation or long wave)
earth’s energy budget
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Three atmospheric processes modify the solar radiation
passing through our atmosphere destined to the Earth's
surface.
The process of scattering occurs when small particles
and gas molecules diffuse part of the incoming solar
radiation in random directions without any alteration to
the wavelength of the electromagnetic energy. Scattering
does, however, reduce the amount of incoming radiation
reaching the Earth's surface. A significant proportion of
scattered shortwave solar radiation is redirected back to
space.
The amount of scattering that takes place is dependent
on two factors: wavelength of the incoming radiation and
the size of the scattering particle or gas molecule.
In the Earth's atmosphere, the presence of a large
number of particles with a size of about 0.5 microns
results in shorter wavelengths being preferentially
scattered. This factor also causes our sky to look blue
because this color corresponds to those wavelengths
that are best diffused. If scattering did not occur in our
atmosphere the daylight sky would be black.
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http://www.physicalgeography.net/fundame
ntals/7f.html
earth’s energy budget
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Absorption: If intercepted, some
gases and particles in the atmosphere
have the ability to absorb incoming
insolation . Absorption is defined as
a process in which solar radiation is
retained by a substance and converted
into heat energy. The creation of heat
energy also causes the substance to
emit its own radiation. In general, the
absorption of solar radiation by
substances in the Earth's atmosphere
results in temperatures that get no
higher than 1800° Celsius. Bodies with
temperatures at this level or lower
would emit their radiation in the
longwave band. Further, this emission
of radiation is in all directions so a
sizable proportion of this energy is lost
to space.
earth’s energy budget
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Reflection: The final process in the
atmosphere that modifies incoming
solar radiation is reflection. Reflection
is a process where sunlight is
redirected by 180° after it strikes an
atmospheric particle. This redirection
causes a 100 % loss of the insolation.
Most of the reflection in our
atmosphere occurs in clouds when
light is intercepted by particles of
liquid and frozen water. The reflectivity
of a cloud can range from 40 to 90 %.
earth’s energy budget: albedo
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Sunlight reaching the Earth's surface
unmodified by any of the above
atmospheric processes is termed direct
solar radiation. Solar radiation that
reaches the Earth's surface after it was
altered by the process of scattering is called
diffused solar radiation. Not all of the
direct and diffused radiation available at the
Earth's surface is used to do work
(photosynthesis, creation of sensible heat,
evaporation, etc.). As in the atmosphere,
some of the radiation received at the
Earth's surface is redirected back to space
by reflection. The image to the right
describes the spatial pattern of surface
reflectivity as measured for the year 1987
The reflectivity or albedo of the Earth's
surface varies with the type of material that
covers it. For example, fresh snow can
reflect up to 95 % of the insolation that
reaches it surface. Some other surface type
reflectivities are:
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Dry sand 35 to 45 %
Broadleaf deciduous forest 5 to 10 %
Needle leaf coniferous forest 10 to 20 %
Grass type vegetation 15 to 25 %
Reflectivity of the surface is often
described by the term surface albedo.
The Earth's average albedo, reflectance
from both the atmosphere and the
surface, is about 30 %.
ATMOSPHERIC CIRCULATION: PLANETARY WINDS AND CORIOLIS
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In the three cell model, the equator
is the warmest location on the Earth
and acts as a zone of thermal lows
known as the Intertropical
convergence zone (ITCZ).
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The ITCZ draws in surface air from
the subtropics and as it reaches the
equator, it rises into the upper
atmosphere by convergence and
convection. It attains a maximum
vertical altitude of about 14
kilometers (top of the troposphere),
then begins flowing horizontally to
the North and South Poles.
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Coriolis force causes the
deflection of this moving air, and by
about 30° of latitude the air begins to
flow zonally from west to east.
ATMOSPHERIC CIRCULATION: PLANETARY WINDS AND CORIOLIS
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This zonal flow is known as the
subtropical jet stream. The zonal
flow also causes the
accumulation of air in the upper
atmosphere as it is no longer
flowing meridionally.
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To compensate for this
accumulation, some of the air in
the upper atmosphere sinks back
to the surface creating the
subtropical high pressure zone.
From this zone, the surface air
travels in two directions. A portion
of the air moves back toward the
equator completing the circulation
system known as the Hadley cell.
This moving air is also deflected
by the Coriolis effect to create the
Northeast Trades (right
deflection) and Southeast Trades
(left deflection).
ATMOSPHERIC CIRCULATION: PLANETARY WINDS AND CORIOLIS
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The surface air moving towards the poles
from the subtropical high zone is also
deflected by Coriolis acceleration producing
the Westerlies.
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Between the latitudes of 30 to 60° North and
South, upper air winds blow generally
towards the poles. Once again, Coriolis force
deflects this wind to cause it to flow west to
east forming the polar jet stream at roughly
60° North and South.
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On the Earth's surface at 60° North and
South latitude, the subtropical Westerlies
collide with cold air traveling from the poles.
This collision results in frontal uplift and the
creation of the subpolar lows or midlatitude cyclones.
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A small portion of this lifted air is sent back
into the Ferrel cell after it reaches the top of
the troposphere. Most of this lifted air is
directed to the polar vortex where it moves
downward to create the polar high.
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http://www.physicalgeography.net/funda
mentals/7p.html
Air masses
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Air masses tend to be homogeneous
in nature. The two critical properties of
any air mass are:
– 1. Temperature
– 2. Moisture
The point of origin of an air mass will
determine temperature and moisture
content. Combined these properties
produce the weather we experience
daily.
http://www.ecn.ac.uk/Education/
air_masses.htm
http://okfirst.ocs.ou.edu/train/m
eteorology/AirMasses.html
Air masses
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An air mass is a huge volume of air that covers hundreds of
thousands of square kilometers that is relatively uniform horizontally
and vertically in both temperature and humidity
The characteristics of an air mass are determined by the surface over
which they form so they are either continental or maritime indicated
with a lower case m or c
Then they are classed as Arctic, Polar, Tropical or Equitorial (A, P, T, or
E)
And finally they have a lower case k or w at the end to indicate
whether they are warmer or colder than the land over which they are
moving.
Note that arctic and polar are difficult to distinguish as are tropical and
equatorial.
Air masses are driven by the prevailing winds. Hot air originates near
the equator and cold near the poles and the middle latitudes where we
live is the mixing zone and we have spectacular weather as warm and
cold air masses work their way across us.
highs lows and fronts
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High pressure system is an
anticyclone
Highs generally have good weather
and when seen from above surface
winds surrounding a high blow in a
clockwise direction and outward
from the high
Lows and highs track with the
prevailing winds from west to east
across the US
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Low pressure system is a cyclone
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Lows tend to have cloudy bad
weather and when seen from above
surface winds surrounding a low
blow in a counter clockwise
direction and inward to the low.
Lows and highs track with the
prevailing winds from west to east
across the US
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High Altitude Divergence
High Altitude Convergence
Rising Cloudy Air
Sinking Clear Air
Surface Convergence
Surface Divergence
H
L
highs lows and fronts
• As air masses collide carrying their
characteristics of temperature and
moisture they create fronts, warm,
cold, stationary and occluded.
Each have unique vertical
characteristics with characteristic
weather patterns.
Warm fronts
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Warm fronts tend to move slowly
They carry broad bands of clouds that
begin high and drop lower with time.
They tend to be associated with light
and prolonged rains and warming
temperatures
A warm front is defined as the
transition zone where a warm air mass
is replacing a cold air mass. Warm
fronts generally move from southwest
to northeast and the air behind a warm
front is warmer and more moist than
the air ahead of it. When a warm front
passes through, the air becomes
noticeably warmer and more humid
than it was before.
Symbolically, a warm front is
represented by a solid line with
semicircles pointing towards the colder
air and in the direction of movement.
cold fronts
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A cold front is defined as the transition zone where
a cold air mass is replacing a warmer air mass.
Cold fronts generally move from northwest to
southeast. The air behind a cold front is noticeably
colder and drier than the air ahead of it. When a
cold front passes through, temperatures can drop
more than 15 degrees within the first hour.
Cold fronts tend to be associated with vertical
clouds and rains of short duration but often with
intensity.
There is typically a noticeable temperature change
from one side of a cold front to the other. In the
map of surface temperatures right, the station east
of the front reported a temperature of 55 degrees
Fahrenheit while a short distance behind the front,
the temperature decreased to 38 degrees. An
abrupt temperature change over a short distance
is a good indicator that a front is located
somewhere in between.
Symbolically, a cold front is represented by a solid
line with triangles along the front pointing towards
the warmer air and in the direction of movement.
On colored weather maps, a cold front is drawn
with a solid blue line.
Stationary fronts
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When a warm or cold front stops moving, it
becomes a stationary front. Once this
boundary resumes its forward motion, it
once again becomes a warm front or cold
front. A stationary front is represented by
alternating blue and red lines with blue
triangles pointing towards the warmer air
and red semicircles pointing towards the
colder air.
A noticeable temperature change and/or
shift in wind direction is commonly observed
when crossing from one side of a stationary
front to the other
Occluded fronts
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A developing cyclone typically has a preceding warm
front (the leading edge of a warm moist air mass) and a
faster moving cold front (the leading edge of a colder
drier air mass wrapping around the storm). North of the
warm front is a mass of cooler air that was in place
before the storm even entered the region.
As the storm intensifies, the cold front rotates around
the storm and catches the warm front. This forms an
occluded front, which is the boundary that separates the
new cold air mass (to the west) from the older cool air
mass already in place north of the warm front.
Symbolically, an occluded front is represented by a solid
line with alternating triangles and circles pointing the
direction the front is moving. On colored weather maps,
an occluded front is drawn with a solid purple line.
Changes in temperature, dew point temperature, and
wind direction can occur with the passage of an
occluded front.
A noticeable wind shift also occurred across the
occluded front. East of the front, winds were reported
from the east-southeast while behind the front, winds
were from the west-southwest.
Warm or cold occluded fronts
• Cold occlusion
• A colder air mass
advances on a cold air
mass and occludes
warmer air.
• Warm occlusion
• A warmer air mass
advances on a cold air
mass and occludes
warmer air.
Surface weather stations: what
does it all mean????
surface weather stations: precipitaton
•
A weather symbol is plotted if at the time of observation, there is either precipitation
occurring or a condition causing reduced visibility.
Below is a list of the most common weather symbols:
surface weather stations: wind
•
•
•
•
Wind is plotted in increments of
5 knots (kts), with the outer end
of the symbol pointing toward
the direction from which the
wind is blowing.
The wind speed is determined
by adding up the total of flags,
lines, and half-lines, each of
which have the following
individual values: flag: 50 kts,
Line: 10 kts, Half-Line: 5 kts.
Wind is always reported as the
direction from which it is
coming.
If there is only a circle depicted
over the station with no wind
symbol present, the wind is
calm. Below are some sample
wind symbols:
surface weather stations: pressure and trend
•
PRESSURE
Sea-level pressure is
plotted in tenths of
millibars (mb), with
the leading 10 or 9
omitted. For reference,
1013 mb is equivalent
to 29.92 inches of
mercury. Below are
some sample
conversions between
plotted and complete
sea-level pressure
values:
410: 1041.0 mb
103: 1010.3 mb
987: 998.7 mb
872: 987.2 mb
•
PRESSURE TREND
The pressure trend has two components, a number
and symbol, to indicate how the sea-level pressure has
changed during the past three hours. The number
provides the 3-hour change in tenths of millibars, while
the symbol provides a graphic illustration of how this
change occurred. Below are the meanings of the
pressure trend symbols:
surface weather stations: sky cover
• The amount that the
circle at the center
of the station plot is
filled in reflects the
approximate amount
that the sky is
covered with
clouds. To the right
are the common
cloud cover
depictions
weather technology: early
instrumentation
•
•
•
•
Thermometer
Device used to measure temperature.
Temperature
Temperature is defined as the measure of
the average speed of atoms and
molecules. The higher the temperature the
faster they move
•
•
Barometer
Instrument that measures atmospheric
pressure.
Atmospheric PressureWeight of the
atmosphere on a surface. At sea-level, the
average atmospheric pressure is 1013.25
millibars. Pressure is measured by a device
•
• .
called a barometer.
weather technology: early instrumentation
•
•
•
Anemometer used to measure wind speed. These
instruments commonly employee three methods to
measure this phenomenon:
1) speed of rotation,
2) pressure plate to measure force of wind 3) a heated
wire that measures heat loss from wind
•
http://www.arm.ac.uk/annrep/annrep2000/node13.html
•
Sling Psychrometer Psychrometer that uses a
rotating handle and a whirling motion to ventilate its
wet-bulb thermometer.
Wet-Bulb Thermometer has a moisten wick on its
reservoir bulb. When ventilated this thermometer
records a temperature that is modified by the cooling
effects of evaporation. This measurement and the
temperature reading from a dry-bulb thermometer are
then used to determine the air's relative humidity or
dew point from a psychrometric table.
•
•
http://www.geography.hunter.cuny.edu/~tbw/wc.notes/4.moisture
.atm.stability/psychrometer.htm
weather technology: early instrumentation
•
Rain gauge - This type of rain gauge counts water
droplets of known volume as they pass an optical
sensor. Rain from the main collector funnels directly
into a small reservoir chamber, which maintains a
critical water level within the system. As the level
increases, excess water flows out through a
horizontal pipe, so that drops form from a precision
tube. This tube produces drops of a specific, predetermined volume. By equating the volume of
water passing the sensor in a given time with the
collecting area, researchers can estimate the
rainfall rate.
• Remote access weather stations…new
technology combined with old
instrumentation reporting weather
remotely around the united states.
Acronym is RAWS
weather technology:
radiosondes and rawinsondes
• Before the use of
satellites we used
radiosondes and
rawinsondes to collect
important information
about our atmosphere.
These instruments are
still used today and
provide valuable
information about
atmospheric conditions.
•
•
http://www.aos.wisc.edu/~hopkins/wx-inst/wxi-raob.htm
http://www.geo.mtu.edu/department/classes/ge406/cmriley/
•
http://www.meso.com/windpersonal/glenn/171/Stuve2a.htm
•
•
•
The radiosonde is a balloon-borne
instrument platform with radio
transmitting capabilities.
The radiosonde contains instruments
capable of making direct in-situ
measurements of air temperature,
humidity and pressure with height,
typically to altitudes of approximately
30 km.
A rawinsonde (or radio wind sonde) is
a radiosonde package with an
attached radar reflector that permits
radio-direction finding equipment to
determine the wind direction and wind
speed at various altitudes during the
ascent of the package.
weather technology: radiosonde
weather technology: rawinsonde
•
• Rawinsonde
tracking unit
•
http://www.csun.edu/~hmc
60533/CSUN_103/weather
_exercises/soundings/smo
g_and_inversions/Underst
anding%20Stuve_v3.htm
Stuve Diagrams are one type of thermodynamic diagram used to
represent or plot atmospheric data as recorded by weather balloons in
their ascent through the atmosphere. The data the balloons record are
called soundings.
weather technology: rawinsonde
•
In North America prior to release
the balloon is usually filled with
hydrogen (though helium can be
used as a substitute) gas. The
ascent rate can be controlled by
the amount of gas the balloon is
filled with. Weather balloons may
reach altitudes of 40 km (25 miles)
or more, limited by diminishing
pressures causing the balloon to
expand to such a degree (typically
by a 100:1 factor) that it
disintegrates. The instrument
package is usually lost. Above that
altitude sounding rockets may
be used. After sounding rockets,
satellites are used for even
higher altitudes.
weather technology: satellites and radar
imagery
• With the advent of satellites and radar vast
amounts of weather data may be observed
. . . It is learning what it all means and
what it can do for us that is important.
• Lets look at some of the types of data
collected by these satellites.
weather technology: radar fronts and data
•
There is a tremendous amount of information on maps like these and they make excellent material for test
questions. For instance, what type of front is about to enter the state of Arkansas? What is the current
wind direction and speed for the surface weather station in central New Mexico? Students need to know
their state maps!
weather technology: infrared imagery
•
•
•
These images come from satellites which remain above a fixed point on the Earth (i.e. they are "geostationary"). The infrared image shows the invisible
infrared radiation emitted directly by cloud tops and land or ocean surfaces. The warmer an object is, the more intensely it emits radiation, thus allowing
us to determine its temperature. These intensities can be converted into greyscale tones, with cooler temperatures showing as lighter tones and warmer
as darker.
Lighter areas of cloud show where the cloud tops are cooler and therefore where weather features like fronts and shower clouds are. The advantage of
infrared images is that they can be recorded 24 hours a day. However, low cloud, having similar temperatures to the underlying surface, are less easily
discernable. Coast-lines and lines of latitude and longitude have been added to the images and they have been altered to northern polar stereographic
projection.
The infrared images are updated every hour. It usually takes about 20 minutes for these images to be processed and be updated on the website. The
time shown on the image is in UTC.
weather technology: water vapor imagery
•
•
•
These images come from satellites which remain above a fixed point on the Earth
(geostationary). The infrared image shows the invisible infrared radiation emitted directly
by cloud tops and land or ocean surfaces. The warmer an object is, the more intensely it
emits radiation, thus allowing us to determine its temperature. These intensities can be
converted into grayscale tones, with cooler temperatures showing as lighter tones and
warmer as darker.
The advantage of infrared images is that they can be recorded 24 hours a day. However,
low clouds, having similar temperatures to the underlying surface, are less easily
discernable
The infrared images are updated every hour. The time shown on the image is in UTC.
weather technology: visible light imagery
•
These images come from satellites which remain above a fixed point on the Earth
(geostationary). The visible image record visible light from the sun reflected back to the
satellite by cloud tops and land and sea surfaces. They are equivalent to a black and white
photograph from space. They are better able to show low cloud than infrared images.
However, visible pictures can only be made during daylight hours. The visible images are
updated hourly and the time shown on the image is in UTC.
weather technology: meteograms
•
Meteograms give vast amounts of information about a given areas weather
over a 24 hour period. Great thinking questions can be drawn from this
material
Atmospheric phenomena: crepuscular rays
• Solar rays are also known as sunrays or cloud rays. In folklore the
effect is called "the sun drawing water". Solar rays can be seen
when sunlight passes past sharply defined clouds (like cumulus
clouds) when the atmosphere is slightly dusty or hazy. Light is
scattered by the aerosols and the light paths past the clouds
become visible. In fact, it is often the shadow rays near the clouds
which are remarkable, rather than the light solar rays themselves.
Solar rays are all parallel to each other, but perspective causes the
apparent divergence from the sun.
Atmospheric phenomena: pracipitato
•
Pracipitato - A precipitation curtain that reaches to ground, often
seen under storm clouds. Dark fall streaks are rain and light fall
streaks are snow or ice.
Atmospheric phenomena: virga
• Virga - A fallstreak of precipitation, which evaporates in midair before reaching ground.
Atmospheric phenomena: red flash
• Red Flash - The red flash of the setting sun is similar to the
green flash, albeit that the red flash appears on the lower edge
of the solar disk. The red flash appears as a momentary small
seclusion of the lower red rim of the solar disk, while the sun
moves through small inversions in the atmosphere. It requires
a telescope to be seen clearly.
Atmospheric phenomena: green flash
• Green flash is the phenomenon that the last bit of the sun colors
green when the sun sets below the horizon. The effect is due to
atmospheric refraction of light. When the sun sets, the green rim is
the last to disappear. The actual green flash, a green flame above
the point where the sun set below horizon a few seconds after
sunset, is extremely rare. However, the green rim can frequently be
seen, even if the sun is well above the horizon, as well as small
green flashes due to inversions in the atmosphere.
Atmospheric phenomena: primary
rainbow
• Primary Rainbow - The primary
rainbow must be the most wellknown atmospheric optical
phenomenon to people.
However, it is actually
relatively uncommon to see in
relation to natural weather. It is
caused by light being refracted
and internally reflected by
spherical raindrops over an
angle of 138 deg. Due to the
refraction the coloured arc is
produced, having a radius of
42 degrees.
Atmospheric phenomena: halo
• Halo - A halo around
the sun or moon with a
radius of 20 degrees,
caused by refraction of
light by randomly
oriented pyramidal ice
crystals. On the photo
at the left, it is very
faintly visible between
the very bright 22degrees halo and the
faint 18-degrees halo.
On the photos, look to
the upper right of the
sun; there, it is most
pronounced.
Atmospheric phenomena: light pilar
•
Light Pillar - A light pillar can
sometimes be seen above the sun
when it is setting or rising. It is
caused by reflection of light off the
base of horizontally aligned plate
ice crystals in the atmosphere. The
extend of the pillar is usually only a
few degrees. More rarely, it is as
much as 20 degrees or more. Light
pillars are possible above and
below the sun or moon; however,
for earth-bound observers, the
upper light pillar is most common,
while the lower pillar is more likely
when you are in an airplane flying
above a cloud of ice crystals. The
upper and lower light pillars at the
sun can be present together with
the parhelic circle and then form a
giant cross in the sky, which was
considered a much feared omen by
ancient and medieval folklore.
Atmospheric phenomena: aurora
•
The sun gives off high-energy charged
particles (also called ions) that travel
out into space at speeds of 300 to
1200 kilometers per second. A cloud of
such particles is called a plasma. The
stream of plasma coming from the sun
is known as the solar wind. As the
solar wind interacts with the edge of
the earth's magnetic field, some of the
particles are trapped by it and they
follow the lines of magnetic force down
into the ionosphere, the section of the
earth's atmosphere that extends from
about 60 to 600 kilometers above the
earth's surface. When the particles
collide with the gases in the
ionosphere they start to glow,
producing the spectacle that we know
as the auroras, northern and southern.
The array of colours consists of red,
green, blue and violet.
•
•
http://www.geo.mtu.edu/weather/aurora/
http://virtual.finland.fi/finfo/english/aurora_borealis.h
tml
glossary
• This is the link to one of the best
glossaries on the internet as far as science
is concerned and almost all weather
materials are covered.
• Use it often and well for all your Science
Olympiad needs!
• http://www.physicalgeography.net/glossary
.html