Meteorology: every day weather

Dr. Anne ClouserNational 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 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• 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.ph

p?mid=107&l=&c3=

• http://www.globalchange.umich.edu/globalchange1/current/lectures/samson/evolution_atm/index.html#evolution

THE MODERN ATMOSPHERE• 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/textbook/atmosphere/atmospheric_structure.html

• http://www.albany.edu/faculty/rgk/atm101/structur.htm

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 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/textbook/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.

• http://ga.water.usgs.gov/edu/watercycleprecipitation.html

• http://www.laits.utexas.edu/kimmel/container.html?precip_types.html&2

• http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/prcp/home.rxml

PRECIPITATION

PRECIPITATION: RAIN

• 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/metinfo/precipform.htm

• http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/prcp/rnhl.rxml

• http://www.infoplease.com/ce6/weather/A0840995.html

• http://www.aolsvc.worldbook.aol.com/wb/Article?id=ar458340

• http://www.ess.uci.edu/~yu/class/ess5/Chapter.7.precipitation.all.pdf#search=%22hail%20formation%20by%20coalescence%22

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 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.

• http://www.classzone.com/books/earth_science/terc/content/visualizations/es1805/es1805page01.cfm?chapter_no=visualization

• http://www.mcwar.org/articles/hail.pdf#search=%22hail%20formation%20by%20coalescence%22

• http://www.islandnet.com/~see/weather/almanac/arc2002/alm02jul.htm

• http://beta.nssl.noaa.gov/primer/hail/hail_basics.html

PRECIPITATION: FREEZING RAIN• 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.

• http://twister.sbs.ohio-state.edu/g520/ch7_1.ppt#16

• http://www.islandnet.com/~see/weather/elements/icestorm.htm

• http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/prcp/zr/prcs/ice.rxml

PRECIPITATION: SLEET• 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.

• http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/prcp/slt.rxml

• http://www.weatherquestions.com/What_causes_ice_pellets.htm

• http://www.geography.hunter.cuny.edu/~tbw/wc.notes/5.cond.precip/sleet_formation.htm

PRECIPITATION: SNOW• 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.

• 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.html

• http://express.howstuffworks.com/wq-snowstorm.htm

• http://library.thinkquest.org/C003603/english/snowstorms/index.shtml

CLOUDS: FORMATION• 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.

• by a mountain range at an angle to the wind, 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.

• http://www.infoplease.com/ce6/weather/A0857399.html

• http://www.physicalgeography.net/fundamentals/8e.html

• http://www.auf.asn.au/meteorology/section3.html

• http://www.bbc.co.uk/weather/weatherwise/factfiles/basics/clouds_formation.shtml

CLOUDS: CLASSIFICATION• 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.

CLOUDS: CLASSIFICATION• 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.

• 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 sight.

• 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 aloft.

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. • 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• 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.

• http://www.physicalgeography.net/fundamentals/7f.html

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 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:

• 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

• 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.

ATMOSPHERIC CIRCULATION: PLANETARY WINDS AND CORIOLIS

• 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).

ATMOSPHERIC CIRCULATION: PLANETARY WINDS AND CORIOLIS

• 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.

• http://www.physicalgeography.net/fundamentals/7p.html

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 daily.

• http://www.ecn.ac.uk/Education/air_masses.htm

• http://okfirst.ocs.ou.edu/train/meteorology/AirMasses.html

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 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• 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

• Low pressure system is a cyclone • 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

H

Surface Divergence

Sinking Clear Air

High Altitude Convergence

HH

Surface Divergence

Sinking Clear Air

High Altitude Convergence

Surface Convergence

L

Rising Cloudy Air

High Altitude Divergence

Surface Convergence

L

Rising Cloudy Air

High Altitude 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 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• 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• 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• 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 mb103: 1010.3 mb987: 998.7 mb872: 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, 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 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/wind-personal/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• 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

• http://www.csun.edu/~hmc60533/CSUN_103/weather_exercises/soundings/smog_and_inversions/Understanding%20Stuve_v3.htm

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 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 rainbow

• 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 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.html

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