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 schoolparticipant may receive a comprehensivecourse of instruction in meteorology during thethree-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, jetstreams, local wind patterns (Chinook winds, mountain and seabreezes), and the three cell model of circulation
•Air Masses: origin, temperature, density, moisture content, andstability
•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 theBeaufort scale
•Atmospheric phenomena: sundogs, rainbows, aurora, virga, etc.
THE MODERN ATMOSPHERE
•ITS COMPOSITION
•There are permanent gasses(nitrogen and oxygen)
•There are variable gasses (carbondioxide, methane, water vapor,ozone, particulates
•The composition of the atmospherehas not been constant but haschanged through time.
•We used to be the stuff of stars(helium and hydrogen) butoutgassing, comets, UV radiationand photosynthesis have changedus.
THE MODERN ATMOSPHERE
•IT’S STRUCTURE
•Layers are defined bytemperature, altitude, and uniquecharacteristics
•There are layers wheretemperature rises with altitude orfalls with altitude (our naturalinstinct).
•Between these layers there arepauses where temperature isconstant with altitude change.
•Each layer has uniquecharacteristics like 90% of theozone is in the stratosphere andgasses stratify by molecularweight in the thermosphere
•Thickness of these layers varieswith latitude.
water: its states and properties
•Water is unique in that it canexist in three states on theface our planet liquid, solid,and gas
•Water absorbs or releaseshuge amounts of latent heatas it changes states. This isunique. It buffers ourenvironment with thiscapacity.
•Water is most dense at 4oC soice floats otherwise theoceans would freeze from thebottom up. No life on earth.
•Water is the universal solvent
![phase_change[1]](data/images/img5.png)
PRECIPITATION
•When cloud particlesbecome too heavy toremain suspended inthe air, they fall to theearth as precipitation.Precipitation occurs ina variety of forms;hail, rain, freezingrain, sleet or snow.
PRECIPITATION
PRECIPITATION: RAIN
•Rainfall: Rain develops whengrowing cloud droplets becometoo heavy to remain in the cloudand as a result, fall toward thesurface as rain.
•Rain can also begin as ice crystalsthat collect each other to formlarge snowflakes. As the fallingsnow passes through the freezinglevel into warmer air, the flakesmelt and collapse into rain drops.
•The picture below shows heavyrain falling over the GrandCanyon.
PRECIPITATION: HAIL
•Hail: Hail is a large frozen raindrop producedby intense thunderstorms, where snow andrain can coexist in the central updraft.
•As the snowflakes fall, liquid water freezesonto them forming ice pellets that will continueto grow as more and more droplets areaccumulated.
•Upon reaching the bottom of the cloud, someof the ice pellets are carried by the updraftback up to the top of the storm. As the icepellets once again fall through the cloud,another layer of ice is added and the hailstone grows even larger.
•Typically the stronger the updraft, the moretimes a hail stone repeats this cycle andconsequently, the larger it grows. Once thehail stone becomes too heavy to be supportedby the updraft, it falls out of the cloud towardthe surface.
PRECIPITATION: FREEZING RAIN
•FREEZING RAIN: The diagram below shows atypical temperature profile for freezing rain withthe red line indicating the atmosphere'stemperature at any given altitude.
•The vertical line in the center of the diagram isthe freezing line. Temperatures to the left of thisline are below freezing, while temperatures tothe right are above freezing. Freezing raindevelops as falling snow encounters a layer ofwarm air deep enough for the snow tocompletely melt and become rain.
•As the rain continues to fall, it passes through athin layer of cold air just above the surface andcools to a temperature below freezing. However,the drops themselves do not freeze, aphenomena called supercooling (or forming"supercooled drops").
• When the supercooled drops strike the frozenground (power lines, or tree branches), theyinstantly freeze, forming a thin film of ice, hencefreezing rain.
PRECIPITATION: SLEET
•SLEET: Sleet is less prevalent thanfreezing rain and is defined as frozenraindrops that bounce on impact with theground or other objects.
•The diagram at the right shows a typicaltemperature profile for sleet with the redline indicating the atmosphere'stemperature at any given altitude.
•The vertical line in the center of thediagram is the freezing line.
•Temperatures to the left of this line arebelow freezing, while temperatures to theright are above freezing.
PRECIPITATION: SNOW
•SNOW: Snowflakes are simply aggregates of icecrystals that collect to each other as they falltoward the surface.
•The diagram below shows a typical temperatureprofile for snow with the red line indicating theatmosphere's temperature at any given altitude.The vertical line in the center of the diagram is thefreezing line. Temperatures to the left of this lineare below freezing, while temperatures to the rightare above freezing.
•Since the snowflakes do not pass through a layerof air warm enough to cause them to melt, theyremain in tact and reach the ground as snow.
CLOUDS: FORMATION
•FORMATION: Clouds are formed when aircontaining water vapor is cooled below a criticaltemperature called the dew point and the resultingmoisture condenses into droplets on microscopicdust particles (condensation nuclei) in theatmosphere.
•Expansional cooling: The air is normally cooledby expansion during its upward movement. As aparcel of air rises it is cooled by expansion andmakes clouds
•Upward flow of air in the atmosphere may becaused by convection resulting from intense solarheating of the ground, again expansional cooling.
•by a cold wedge of air (cold front) near the groundcausing 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 occasionallyproduced by a reduction of pressure aloft or by themixing of warmer and cooler air currents.
CLOUDS: CLASSIFICATION
•Cirrus: high clouds that do not obscure the sun ormoon but often create halos. High cloud formsinclude cirrus, detached clouds of delicate andfibrous appearance, generally white in color, oftenresembling tufts or featherlike plumes, andcomposed entirely of ice crystals; cirrocumulus(mackerel sky), composed of small white flakes orvery small globular masses, arranged in groups,lines, or ripples; and cirrostratus, a thin whitish veil,sometimes giving the entire sky a milkyappearance, which does not blur the outline of thesun or moon but frequently produces a halo.
•Alto: intermediate clouds. Intermediate cloudsinclude altocumulus, patchy layer of flattenedglobular masses arranged in groups, lines, orwaves, with individual clouds sometimes so closetogether that their edges join; and altostratus,resembling thick cirrostratus without halophenomena, like a gray veil, through which the sunor the moon shows vaguely or is sometimescompletely hidden.
CLOUDS: CLASSIFICATION
•Stratus: low clouds. Low clouds includestratocumulus, a cloud layer or patches composedof fairly large globular masses or flakes, soft andgray with darker parts, arranged in groups, lines, orrolls, often with the rolls so close together that theiredges join; stratus, a uniform layer resembling fogbut not resting on the ground; and nimbostratus, anearly uniform, dark grey layer, amorphous incharacter and usually producing continuous rain orsnow.
•Cumulus: clouds with vertical development. Athick, detached cloud, generally associated with fairweather, usually with a horizontal base and a dome-shaped upper surface that frequently resembles ahead of cauliflower and shows strong contrasts oflight and shadow when the sun illuminates it fromthe side, and cumulonimbus, the thunderstormcloud, heavy masses of great vertical developmentwhose summits rise in the form of mountains ortowers, the upper parts having a fibrous texture,often spreading out in the shape of an anvil, andsometimes 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, sometimescalled mother-of-pearl clouds, are 15 - 25km (9 -16 miles) high in the stratosphere and well abovetropospheric clouds. They are iridescent clouds.They occur mostly but not exclusively in polarregions and in winter at high latitudes.They shine brightly in high altitude sunlight up totwo hours after ground level sunset or beforedawn. Their unbelievably bright iridescent coloursand slow movement relative to any lower cloudsmake them an unmistakable and unforgettablesight.
•Mammatus clouds: these clouds are formed bydown pouchings of cold air. Mammatus typicallydevelop on the underside of a thunderstorm's anviland can be a remarkable sight, especially whensunlight is reflected off of them.
unique cloud types: know what they mean
•Noctilucent clouds: Clouds at extremely highaltitude, about 85 km, that literally (as the namesuggests) shine at night. They form in the cold,summer polar mesopause and are believed tobe ice crystals. Because of their high altitude, ina very dry part of the atmosphere, noctilucentclouds are rather an enigma and are beingstudied by a number of people around the world.
•Lenticular clouds: Altocumulus standinglenticularus result from strong wind flow overrugged terrain. Jet stream winds whipping over theRockies produce up-and-down wavelike patternson the lee side of the range. Lenticular clouds,which occur at mid-levels of the troposphere format the peaks of these waves.
•These eerie, elliptical cloud formations, which canalso resemble stacks of pancakes, often foretellchanges in the weather, and indicate high windsaloft.
unique cloud types: know what they mean
•Wave clouds: Kelvin-Helmholtz wave clouds areformed when there are two parallel layers of airthat are usually moving at different speeds and inopposite directions. The upper layer of air usuallymoves faster than the lower layer because thereis less friction. In order for us to see this shearlayer, there must be enough water vapor in theair for a cloud to form. Even if clouds are notpresent to reveal the shear layer, pilots need tobe aware of invisible atmospheric phenomenon.
•Cap clouds: A mountain top is sometimes cappedby a more or less smooth cloud. This cap cloud isrelated to lenticularis, but forms directly over themountaintop as opposed to lenticularis, that mayform at middle altitudes above the mountain. Acap cloud is formed when humid air is forced toflow over the mountain, condensing into a cloud.
heat transport and energy budget
•Absorption and re-emission ofradiation at the earth's surface isonly one part of an intricate web ofheat transfer in the earth'splanetary domain. Equallyimportant are selective absorptionand emission of radiation frommolecules in the atmosphere. If theearth did not have an atmosphere,surface temperatures would be toocold to sustain life. If too manygases which absorb and emitinfrared radiation were present inthe atmosphere, surfacetemperatures would be too hot tosustain life.
•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 functionof the intensity and duration of the radiation. Intensity andduration are directly impacted by latitude as illustrated by thegraph below.
earth’s energy budget
•Earth’s Energy Budget: Earth’s externalheat engine is energy provided by the sun
•Average global surface temperature = 15°C
•This temperature represents the balancebetween Incoming solar radiation(insolation) the whole electromagneticspectrum and outgoing terrestrial radiation(infrared radiation or long wave)
earth’s energy budget
•Three atmospheric processes modify the solar radiationpassing through our atmosphere destined to the Earth'ssurface.
•The process of scattering occurs when small particlesand gas molecules diffuse part of the incoming solarradiation in random directions without any alteration tothe wavelength of the electromagnetic energy. Scatteringdoes, however, reduce the amount of incoming radiationreaching the Earth's surface. A significant proportion ofscattered shortwave solar radiation is redirected back tospace.
•The amount of scattering that takes place is dependenton two factors: wavelength of the incoming radiation andthe size of the scattering particle or gas molecule.
• In the Earth's atmosphere, the presence of a largenumber of particles with a size of about 0.5 micronsresults in shorter wavelengths being preferentiallyscattered. This factor also causes our sky to look bluebecause this color corresponds to those wavelengthsthat are best diffused. If scattering did not occur in ouratmosphere the daylight sky would be black.
earth’s energy budget
•Absorption: If intercepted, somegases and particles in the atmospherehave the ability to absorb incominginsolation . Absorption is defined asa process in which solar radiation isretained by a substance and convertedinto heat energy. The creation of heatenergy also causes the substance toemit its own radiation. In general, theabsorption of solar radiation bysubstances in the Earth's atmosphereresults in temperatures that get nohigher than 1800° Celsius. Bodies withtemperatures at this level or lowerwould emit their radiation in thelongwave band. Further, this emissionof radiation is in all directions so asizable proportion of this energy is lostto space.
earth’s energy budget
•Reflection: The final process in theatmosphere that modifies incomingsolar radiation is reflection. Reflectionis a process where sunlight isredirected by 180° after it strikes anatmospheric particle. This redirectioncauses a 100 % loss of the insolation.Most of the reflection in ouratmosphere occurs in clouds whenlight is intercepted by particles ofliquid and frozen water. Thereflectivity of a cloud can range from40 to 90 %.
earth’s energy budget: albedo
•Sunlight reaching the Earth's surfaceunmodified by any of the aboveatmospheric processes is termed directsolar radiation. Solar radiation thatreaches the Earth's surface after it wasaltered by the process of scattering is calleddiffused solar radiation. Not all of thedirect and diffused radiation available at theEarth's surface is used to do work(photosynthesis, creation of sensible heat,evaporation, etc.). As in the atmosphere,some of the radiation received at theEarth's surface is redirected back to spaceby reflection. The image to the rightdescribes the spatial pattern of surfacereflectivity as measured for the year 1987
•The reflectivity or albedo of the Earth'ssurface varies with the type of material thatcovers it. For example, fresh snow canreflect up to 95 % of the insolation thatreaches it surface. Some other surface typereflectivities 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 oftendescribed by the term surface albedo.The Earth's average albedo, reflectancefrom both the atmosphere and thesurface, is about 30 %.
ATMOSPHERIC CIRCULATION: PLANETARY WINDS AND CORIOLIS
•In the three cell model, the equatoris the warmest location on the Earthand acts as a zone of thermal lowsknown as the Intertropicalconvergence zone (ITCZ).
•The ITCZ draws in surface air fromthe subtropics and as it reaches theequator, it rises into the upperatmosphere by convergence andconvection. It attains a maximumvertical altitude of about 14kilometers (top of the troposphere),then begins flowing horizontally tothe North and South Poles.
• Coriolis force causes thedeflection of this moving air, and byabout 30° of latitude the air begins toflow zonally from west to east.
ATMOSPHERIC CIRCULATION: PLANETARY WINDS AND CORIOLIS
•This zonal flow is known as thesubtropical jet stream. The zonalflow also causes theaccumulation of air in the upperatmosphere as it is no longerflowing meridionally.
•To compensate for thisaccumulation, some of the air inthe upper atmosphere sinks backto the surface creating thesubtropical high pressure zone.From this zone, the surface airtravels in two directions. A portionof the air moves back toward theequator completing the circulationsystem known as the Hadley cell.This moving air is also deflectedby the Coriolis effect to create theNortheast Trades (rightdeflection) and Southeast Trades(left deflection).
ATMOSPHERIC CIRCULATION: PLANETARY WINDS AND CORIOLIS
•The surface air moving towards the polesfrom the subtropical high zone is alsodeflected by Coriolis acceleration producingthe Westerlies.
•Between the latitudes of 30 to 60° North andSouth, upper air winds blow generallytowards the poles. Once again, Coriolis forcedeflects this wind to cause it to flow west toeast forming the polar jet stream at roughly60° North and South.
•On the Earth's surface at 60° North andSouth latitude, the subtropical Westerliescollide with cold air traveling from the poles.This collision results in frontal uplift and thecreation of the subpolar lows or mid-latitude cyclones.
Air masses
•Air masses tend to be homogeneousin nature. The two critical properties ofany air mass are:
–1. Temperature
–2. Moisture
•The point of origin of an air mass willdetermine temperature and moisturecontent. Combined these propertiesproduce the weather we experiencedaily.
Air masses
•An air mass is a huge volume of air that covers hundreds ofthousands of square kilometers that is relatively uniform horizontallyand vertically in both temperature and humidity
•The characteristics of an air mass are determined by the surface overwhich they form so they are either continental or maritime indicatedwith 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 indicatewhether they are warmer or colder than the land over which they aremoving.
•Note that arctic and polar are difficult to distinguish as are tropical andequatorial.
•Air masses are driven by the prevailing winds. Hot air originates nearthe equator and cold near the poles and the middle latitudes where welive is the mixing zone and we have spectacular weather as warm andcold air masses work their way across us.
highs lows and fronts
•High pressure system is ananticyclone
•Highs generally have good weatherand when seen from above surfacewinds surrounding a high blow in aclockwise direction and outwardfrom the high
•Lows and highs track with theprevailing winds from west to eastacross the US
•Low pressure system is a cyclone
•Lows tend to have cloudy badweather and when seen from abovesurface winds surrounding a lowblow in a counter clockwisedirection and inward to the low.
•Lows and highs track with theprevailing winds from west to eastacross the US
highs lows and fronts
•As air masses collide carrying theircharacteristics of temperature andmoisture they create fronts, warm,cold, stationary and occluded.Each have unique verticalcharacteristics with characteristicweather patterns.
Warm fronts
•Warm fronts tend to move slowly
•They carry broad bands of clouds thatbegin high and drop lower with time.
•They tend to be associated with lightand prolonged rains and warmingtemperatures
•A warm front is defined as thetransition zone where a warm air massis replacing a cold air mass. Warmfronts generally move from southwestto northeast and the air behind a warmfront is warmer and more moist thanthe air ahead of it. When a warm frontpasses through, the air becomesnoticeably warmer and more humidthan it was before.
•Symbolically, a warm front isrepresented by a solid line withsemicircles pointing towards the colderair and in the direction of movement.
cold fronts
•A cold front is defined as the transition zonewhere a cold air mass is replacing a warmer airmass. Cold fronts generally move from northwestto southeast. The air behind a cold front isnoticeably colder and drier than the air ahead of it.When a cold front passes through, temperaturescan drop more than 15 degrees within the firsthour.
•Cold fronts tend to be associated with verticalclouds and rains of short duration but often withintensity.
•There is typically a noticeable temperature changefrom one side of a cold front to the other. In themap of surface temperatures right, the station eastof the front reported a temperature of 55 degreesFahrenheit while a short distance behind the front,the temperature decreased to 38 degrees. Anabrupt temperature change over a short distanceis a good indicator that a front is locatedsomewhere in between.
•Symbolically, a cold front is represented by a solidline with triangles along the front pointing towardsthe warmer air and in the direction of movement.On colored weather maps, a cold front is drawnwith a solid blue line.
Stationary fronts
•When a warm or cold front stops moving, itbecomes a stationary front. Once thisboundary resumes its forward motion, itonce again becomes a warm front or coldfront. A stationary front is represented byalternating blue and red lines with bluetriangles pointing towards the warmer airand red semicircles pointing towards thecolder air.
•A noticeable temperature change and/orshift in wind direction is commonly observedwhen crossing from one side of a stationaryfront to the other
Occluded fronts
•A developing cyclone typically has a preceding warmfront (the leading edge of a warm moist air mass) and afaster moving cold front (the leading edge of a colderdrier air mass wrapping around the storm). North of thewarm front is a mass of cooler air that was in placebefore the storm even entered the region.
•As the storm intensifies, the cold front rotates aroundthe storm and catches the warm front. This forms anoccluded front, which is the boundary that separates thenew cold air mass (to the west) from the older cool airmass already in place north of the warm front.Symbolically, an occluded front is represented by a solidline with alternating triangles and circles pointing thedirection the front is moving. On colored weather maps,an occluded front is drawn with a solid purple line.
•Changes in temperature, dew point temperature, andwind direction can occur with the passage of anoccluded front.
•A noticeable wind shift also occurred across theoccluded front. East of the front, winds were reportedfrom the east-southeast while behind the front, windswere from the west-southwest.
Warm or cold occluded fronts
•Cold occlusion
•A colder air massadvances on a cold airmass and occludeswarmer air.
•Warm occlusion
•A warmer air massadvances on a cold airmass and occludeswarmer air.
Surface weather stations: whatdoes it all mean????
surface weather stations: precipitaton
•A weather symbol is plotted if at the time of observation, there is either precipitationoccurring 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 of5 knots (kts), with the outer endof the symbol pointing towardthe direction from which thewind is blowing.
•The wind speed is determinedby adding up the total of flags,lines, and half-lines, each ofwhich have the followingindividual values: flag: 50 kts,Line: 10 kts, Half-Line: 5 kts.
•Wind is always reported as thedirection from which it iscoming.
•If there is only a circle depictedover the station with no windsymbol present, the wind iscalm. Below are some samplewind symbols:
surface weather stations: pressure and trend
•PRESSURESea-level pressure isplotted in tenths ofmillibars (mb), withthe leading 10 or 9omitted. For reference,1013 mb is equivalentto 29.92 inches ofmercury. Below aresome sampleconversions betweenplotted and completesea-level pressurevalues:410: 1041.0 mb103: 1010.3 mb987: 998.7 mb872: 987.2 mb
•PRESSURE TRENDThe pressure trend has two components, a numberand symbol, to indicate how the sea-level pressure haschanged during the past three hours. The numberprovides the 3-hour change in tenths of millibars, whilethe symbol provides a graphic illustration of how thischange occurred. Below are the meanings of thepressure trend symbols:
surface weather stations: sky cover
•The amount that thecircle at the centerof the station plot isfilled in reflects theapproximate amountthat the sky iscovered withclouds. To the rightare the commoncloud coverdepictions
weather technology: earlyinstrumentation
•Thermometer
•Temperature
• Temperature is defined as the measure ofthe average speed of atoms andmolecules. The higher the temperature thefaster they move
•.
•Barometer
•Atmospheric PressureWeight of theatmosphere on a surface. At sea-level, theaverage atmospheric pressure is 1013.25millibars. Pressure is measured by a devicecalled a barometer.
weather technology: early instrumentation
•Anemometer used to measure wind speed. Theseinstruments commonly employee three methods tomeasure this phenomenon:
•1) speed of rotation,
•2) pressure plate to measure force of wind 3) a heatedwire that measures heat loss from wind
•Sling Psychrometer Psychrometer that uses arotating handle and a whirling motion to ventilate itswet-bulb thermometer.
•Wet-Bulb Thermometer has a moisten wick on itsreservoir bulb. When ventilated this thermometerrecords a temperature that is modified by the coolingeffects of evaporation. This measurement and thetemperature reading from a dry-bulb thermometer arethen used to determine the air's relative humidity ordew point from a psychrometric table.
weather technology: early instrumentation
•Rain gauge - This type of rain gauge counts waterdroplets of known volume as they pass an opticalsensor. Rain from the main collector funnelsdirectly into a small reservoir chamber, whichmaintains a critical water level within the system.As the level increases, excess water flows outthrough a horizontal pipe, so that drops form from aprecision tube. This tube produces drops of aspecific, pre-determined volume. By equating thevolume of water passing the sensor in a given timewith the collecting area, researchers can estimatethe rainfall rate.
•Remote access weather stations…newtechnology combined with oldinstrumentation reporting weatherremotely around the united states.Acronym is RAWS
weather technology:radiosondes and rawinsondes
•Before the use ofsatellites we usedradiosondes andrawinsondes to collectimportant informationabout our atmosphere.These instruments arestill used today andprovide valuableinformation aboutatmospheric conditions.
•The radiosonde is a balloon-borneinstrument platform with radiotransmitting capabilities.
•The radiosonde contains instrumentscapable of making direct in-situmeasurements of air temperature,humidity and pressure with height,typically to altitudes of approximately30 km.
•A rawinsonde (or radio wind sonde) isa radiosonde package with anattached radar reflector that permitsradio-direction finding equipment todetermine the wind direction and windspeed at various altitudes during theascent of the package.
weather technology: radiosonde
weather technology: rawinsonde
•Stuve Diagrams are one type of thermodynamic diagram used torepresent or plot atmospheric data as recorded by weather balloons intheir ascent through the atmosphere. The data the balloons record arecalled soundings.
•Rawinsondetracking unit
weather technology: rawinsonde
•In North America prior to releasethe balloon is usually filled withhydrogen (though helium can beused as a substitute) gas. Theascent rate can be controlled bythe amount of gas the balloon isfilled with. Weather balloons mayreach altitudes of 40 km (25 miles)or more, limited by diminishingpressures causing the balloon toexpand to such a degree (typicallyby a 100:1 factor) that itdisintegrates. The instrumentpackage is usually lost. Above thataltitude sounding rockets maybe used. After sounding rockets,satellites are used for evenhigher altitudes.
weather technology: satellites and radarimagery
•With the advent of satellites and radar vastamounts of weather data may be observed. . . It is learning what it all means andwhat it can do for us that is important.
•Lets look at some of the types of datacollected 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 testquestions. For instance, what type of front is about to enter the state of Arkansas? What is the currentwind direction and speed for the surface weather station in central New Mexico? Students need to knowtheir 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 invisibleinfrared radiation emitted directly by cloud tops and land or ocean surfaces. The warmer an object is, the more intensely it emits radiation, thus allowingus to determine its temperature. These intensities can be converted into greyscale tones, with cooler temperatures showing as lighter tones and warmeras 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 ofinfrared images is that they can be recorded 24 hours a day. However, low cloud, having similar temperatures to the underlying surface, are less easilydiscernable. Coast-lines and lines of latitude and longitude have been added to the images and they have been altered to northern polar stereographicprojection.
•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. Thetime 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 directlyby cloud tops and land or ocean surfaces. The warmer an object is, the more intensely itemits radiation, thus allowing us to determine its temperature. These intensities can beconverted into grayscale tones, with cooler temperatures showing as lighter tones andwarmer 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 easilydiscernable
•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 thesatellite by cloud tops and land and sea surfaces. They are equivalent to a black and whitephotograph 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 areupdated hourly and the time shown on the image is in UTC.
weather technology: meteograms
•Meteograms give vast amounts of information about a given areas weatherover a 24 hour period. Great thinking questions can be drawn from thismaterial
Atmospheric phenomena: crepuscular rays
•Solar rays are also known as sunrays or cloud rays. In folklore theeffect is called "the sun drawing water". Solar rays can be seenwhen sunlight passes past sharply defined clouds (like cumulusclouds) when the atmosphere is slightly dusty or hazy. Light isscattered by the aerosols and the light paths past the cloudsbecome visible. In fact, it is often the shadow rays near the cloudswhich are remarkable, rather than the light solar rays themselves.Solar rays are all parallel to each other, but perspective causes theapparent divergence from the sun.
Atmospheric phenomena: pracipitato
•Pracipitato - A precipitation curtain that reaches to ground, oftenseen under storm clouds. Dark fall streaks are rain and light fallstreaks 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 thegreen flash, albeit that the red flash appears on the lower edgeof the solar disk. The red flash appears as a momentary smallseclusion of the lower red rim of the solar disk, while the sunmoves through small inversions in the atmosphere. It requiresa telescope to be seen clearly.
Atmospheric phenomena: green flash
•Green flash is the phenomenon that the last bit of the sun colorsgreen when the sun sets below the horizon. The effect is due toatmospheric refraction of light. When the sun sets, the green rim isthe last to disappear. The actual green flash, a green flame abovethe point where the sun set below horizon a few seconds aftersunset, is extremely rare. However, the green rim can frequently beseen, even if the sun is well above the horizon, as well as smallgreen flashes due to inversions in the atmosphere.
Atmospheric phenomena: primaryrainbow
•Primary Rainbow - Theprimary rainbow must be themost well-known atmosphericoptical phenomenon to people.However, it is actuallyrelatively uncommon to see inrelation to natural weather. It iscaused by light being refractedand internally reflected byspherical raindrops over anangle of 138 deg. Due to therefraction the coloured arc isproduced, having a radius of42 degrees.
Atmospheric phenomena: halo
•Halo - A halo aroundthe sun or moon with aradius of 20 degrees,caused by refraction oflight by randomlyoriented pyramidal icecrystals. On the photoat the left, it is veryfaintly visible betweenthe very bright 22-degrees halo and thefaint 18-degrees halo.On the photos, look tothe upper right of thesun; there, it is mostpronounced.
Atmospheric phenomena: light pilar
•Light Pillar - A light pillar cansometimes be seen above the sunwhen it is setting or rising. It iscaused by reflection of light off thebase of horizontally aligned plateice crystals in the atmosphere. Theextend of the pillar is usually only afew degrees. More rarely, it is asmuch as 20 degrees or more. Lightpillars are possible above andbelow the sun or moon; however,for earth-bound observers, theupper light pillar is most common,while the lower pillar is more likelywhen you are in an airplane flyingabove a cloud of ice crystals. Theupper and lower light pillars at thesun can be present together withthe parhelic circle and then form agiant cross in the sky, which wasconsidered a much feared omen byancient and medieval folklore.
Atmospheric phenomena: aurora
•The sun gives off high-energy chargedparticles (also called ions) that travelout into space at speeds of 300 to1200 kilometers per second. A cloudof such particles is called a plasma.The stream of plasma coming from thesun is known as the solar wind. As thesolar wind interacts with the edge ofthe earth's magnetic field, some of theparticles are trapped by it and theyfollow the lines of magnetic force downinto the ionosphere, the section of theearth's atmosphere that extends fromabout 60 to 600 kilometers above theearth's surface. When the particlescollide with the gases in theionosphere they start to glow,producing the spectacle that we knowas the auroras, northern and southern.The array of colours consists of red,green, blue and violet.
glossary
•This is the link to one of the bestglossaries on the internet as far as scienceis concerned and almost all weathermaterials are covered.
•Use it often and well for all your ScienceOlympiad needs!