Meteorology: every day weather

         Dr. Anne Clouser
National Earth Sciences Committee
    Meteorology: Everyday Weather
•    Everyday Weather: is the first topic in the B-
     Division 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
•   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
•   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.
    •   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
•   Layers are defined by
    temperature, altitude, and unique
•   There are layers where
    temperature rises with altitude or
    falls with altitude (our natural
•   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.
    water: its states and properties
•   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
•   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

• 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.        •
•   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                           rcp/rnhl.rxml
    rain falling over the Grand                             tml
    Canyon.                                             •
•       ar458340
    o/precipform.htm                                    •
               PRECIPITATION: HAIL
•   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
•   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           ge01.cfm?chapter_no=visualization
    times a hail stone repeats this cycle and          •
    consequently, the larger it grows. Once the            =%22hail%20formation%20by%20coalescenc
    hail stone becomes too heavy to be supported
    by the updraft, it falls out of the cloud toward       ac/arc2002/alm02jul.htm
    the surface.                                       •
•   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       ements/icestorm.htm
    freezing rain.                                        •
•   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.

•   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.

•   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
•   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       857399.html
    causing a mass of warm air to be forced aloft,        •
    frontal lifting or convergence.                           entals/8e.html
•   by a mountain range at an angle to the wind,              3.html
    orographic uplift. Again expansional cooling          •

•   Frictional turbulence: Clouds are occasionally
    produced by a reduction of pressure aloft or by the
    mixing of warmer and cooler air currents.
•   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.

•   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.
•   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

•   Cumulus: clouds with vertical development. A
    thick, detached cloud, generally associated with fair
    weather, usually with a horizontal base and a dome-
    shaped 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
•   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

•   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

•   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.

•   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
           unique cloud types: know what they mean

•   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.

•   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
•   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.                          •
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
•   Three atmospheric processes modify the solar radiation
    passing through our atmosphere destined to the Earth's
•   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
•   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.
            earth’s energy budget
•   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
•   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
•   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      •   Dry sand 35 to 45 %
    by reflection. The image to the right            •   Broadleaf deciduous forest 5 to 10 %
    describes the spatial pattern of surface         •   Needle leaf coniferous forest 10 to 20 %
    reflectivity as measured for the year 1987       •   Grass type vegetation 15 to 25 %
•   The reflectivity or albedo of the Earth's        •   Reflectivity of the surface is often
    surface varies with the type of material that        described by the term surface albedo.
    covers it. For example, fresh snow can               The Earth's average albedo, reflectance
    reflect up to 95 % of the insolation that            from both the atmosphere and the
    reaches it surface. Some other surface type          surface, is about 30 %.
    reflectivities are:
•   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).

•   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.

•    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.

•   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.

•   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).

•   The surface air moving towards the poles
    from the subtropical high zone is also
    deflected by Coriolis acceleration producing
    the Westerlies.

•   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.

•   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 mid-
    latitude cyclones.

•   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.

Air masses
     •   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

                         Air masses
•   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
•   Note that arctic and polar are difficult to distinguish as are tropical and
•   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
•   High pressure system is an           •   Low pressure system is a cyclone
    anticyclone                          •   Lows tend to have cloudy bad
•   Highs generally have good weather        weather and when seen from above
    and when seen from above surface         surface winds surrounding a low
    winds surrounding a high blow in a       blow in a counter clockwise
    clockwise direction and outward          direction and inward to the low.
    from the high                        •   Lows and highs track with the
•   Lows and highs track with the            prevailing winds from west to east
    prevailing winds from west to east       across the US
    across the US

                                                      High Altitude Divergence
            High Altitude Convergence
                                                         Rising Cloudy Air
                Sinking Clear Air

                                                       Surface Convergence
               Surface Divergence

     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
•   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
•   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
•   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
•   Cold fronts tend to be associated with vertical
    clouds and rains of short duration but often with
•   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
•   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
•   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           • Warm occlusion
• A colder air mass        • A warmer air mass
  advances on a cold air     advances on a cold air
  mass and occludes          mass and occludes
  warmer air.                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
•   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                  •   PRESSURE TREND

    Sea-level pressure is         The pressure trend has two components, a number
                                  and symbol, to indicate how the sea-level pressure has
    plotted in tenths of          changed during the past three hours. The number
    millibars (mb), with          provides the 3-hour change in tenths of millibars, while
    the leading 10 or 9           the symbol provides a graphic illustration of how this
    omitted. For reference,       change occurred. Below are the meanings of the
    1013 mb is equivalent         pressure trend symbols:
    to 29.92 inches of
    mercury. Below are
    some sample
    conversions between
    plotted and complete
    sea-level pressure

    410: 1041.0 mb
    103: 1010.3 mb
    987: 998.7 mb
    872: 987.2 mb
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
          weather technology: early
•   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
•   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

•   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.
                     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, pre-determined 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                                            •   The radiosonde is a balloon-borne
                                                                   instrument platform with radio
  satellites we used                                               transmitting capabilities.
  radiosondes and                                              •   The radiosonde contains instruments
  rawinsondes to collect                                           capable of making direct in-situ
                                                                   measurements of air temperature,
  important information                                            humidity and pressure with height,
  about our atmosphere.                                            typically to altitudes of approximately
  These instruments are                                            30 km.
  still used today and                                         •   A rawinsonde (or radio wind sonde) is
                                                                   a radiosonde package with an
  provide valuable                                                 attached radar reflector that permits
  information about                                                radio-direction finding equipment to
  atmospheric conditions.                                          determine the wind direction and wind
•          speed at various altitudes during the
                                                                   ascent of the package.
weather technology: radiosonde
          weather technology: rawinsonde
                               •   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.

• Rawinsonde
  tracking unit
    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
• 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
•   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
•   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
   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 mid-
  air 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
• Primary Rainbow - The
  primary rainbow must be the
  most well-known 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 22-
                    degrees halo and the
                    faint 18-degrees halo.
                    On the photos, look to
                    the upper right of the
                    sun; there, it is most
         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.
• 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!

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