Difference between revisions of "AY Honors/Weather - Advanced/Answer Key"

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[[Image:BAROGRAM.JPG|thumb|Barogram of a heavy storm over northern Germany 2005]]
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[[Image:IntertropicalConvergenceZone-EO.jpg|right|300px|thumb|The thunderstorms of the Intertropical Convergence Zone form a line across the eastern Pacific Ocean.]]
  
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A '''barograph''' is a recording loser who has nothing to do but sit on his couch and find the radius of his nose [[aneroid barometer]]. It produces a paper or foil chart called a '''barogram''' that records the [[barometric pressure]] over [[time]].
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The '''Intertropical Convergence Zone''' '''(ITCZ)''', also known as the '''Intertropical Front''', '''[[Monsoon trough]]''', '''Doldrums''' or the '''Equatorial Convergence Zone''', is a belt of [[low pressure area|low pressure]] girdling [[Earth]] at the [[equator]]. It is formed by the vertical ascent of warm, moist air from the latitudes above and below the equator.
  
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Barographs use one or more aneroid cells acting through a gear or lever train to drive a recording arm that has at its extreme end either a scribe or a pen. A scribe records on smoked foil while a pen records on paper. The recording material is mounted on a [[cylinder (geometry)|cylindrical]] drum which is rotated slowly by [[clockwork]]. Commonly, the drum makes one revolution per [[day]], per [[week]], or per [[month]] and the rotation rate can often be selected by the user.
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The air is drawn into the intertropical convergence zone by the action of the [[Hadley cell]], a [[scale (spatial)|macroscale]] [[earth's atmosphere|atmospheric]] feature which is part of the Earth's heat and moisture distribution system. It is transported aloft by the [[convection|convective]] activity of [[thunderstorm]]s; regions in the intertropical convergence zone receive [[precipitation (meteorology)|precipitation]] more than 200 days in a year.
  
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Because the amount of movement that can be generated by a single aneroid is minuscule, up to seven aneroids (so called Vidie-cans) are often stacked "in series" to amplify their motion. It was invented in 1843 by the Frenchman [[Lucien Vidie]] (1805-1866).
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[[Image:ITCZ january-july.png|right|300px|thumb|Position of the ITCZ in July (red) and in January (blue).]]
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==Position==
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The location of the intertropical convergence zone varies over time. Over land, it moves back and forth across the equator  following the sun's [[zenith]] point.  Over the oceans, where the convergence zone is better defined, the seasonal cycle is more subtle, as the convection is constrained by the distribution of ocean temperatures.  
  
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As atmospheric pressure responds in a predictable manner to changes in altitude, barographs may be used to record elevation changes during an aircraft flight. Barographs were required by the [[Federation Aeronautique Internationale|FAI]] to record certain tasks and record attempts associated with [[sailplanes]]. A continuously varying trace indicated that the sailplane had not landed during a task, while measurements from a calibrated trace could be used to establish the completion of altitude tasks or the setting of records. Examples of FAI approved sailplane barographs included the Replogle mechanical drum barograph and the EW electronic barograph (which may be used in conjunction with [[Global Positioning System|GPS]]). Mechanical barographs are not commonly used for flight documentation now, having been displaced by [[International Gliding Commission#GNSS Flight Recorders|GNSS Flight Recorders]].
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Sometimes, a double ITCZ forms, with one located north and another south of the equator. When this occurs, a narrow ridge of high pressure forms between the two convergence zones, one of which is usually stronger than the other.  
  
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Nowadays, mechanical recording barographs have commonly been superseded by electronic weather instruments that use [[computer]] methods to record the barometric pressure. These are not only less expensive than mechanical barographs but they may also offer both greater recording length and the ability to perform further [[data analysis]] on the captured data including automated use of the data to forecast the weather.
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==Effects on weather==
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[[Image:Omega-500-july-era40-1979.png|thumb|right|Vertical velocity at 500 hPa, July average. Ascent (negative values) is a tracer for the ITCZ and is concentrated close to the solar equator; descent (positive values) is more diffuse.]]
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Variation in the location of the intertropical convergence zone drastically affects rainfall in many equatorial [[nation]]s, resulting in the wet and dry seasons of the tropics rather than the cold and warm seasons of higher latitudes. Longer term changes in the intertropical convergence zone can result in severe droughts or flooding in nearby areas.
  
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==Three Day Barograph==
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Within the ITCZ the average winds are slight, unlike the zones north and south of the equator where the [[trade wind]]s feed in. Early sailors named this belt of calm '''the doldrums''' because of the inactivity and stagnation they found themselves in after days of no wind.[http://www.randomhouse.com/wotd/index.pperl?date=19971016] To find oneself becalmed in this region in a hot and muggy climate could mean death in an era when wind was the only major motive force.
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[[Image:Barograph.JPG|thumb|Three day barograph of the type used by the [http://www.msc.ec.gc.ca/ Meteorological Service of Canada]]]
 
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On the of the crapytop helloright of the picture of the three day barograph can be seen a silver knurled knob. This is to adjust the barograph so that it correctly reflects the station pressure. Barely visible below the knob is a small silver plunger. This is pressed every three hours to leave a time mark on the paper.
 
  
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The line between two of these marks is called the 'characteristic of barometric tendency' and is used by [[weather forecast]]ers. The observer would first note if the pressure was lower or higher than three hours prior. Next, a code number would be chosen that best represents the three hour trace. There are nine possible choices (0 to 8) and no single code has preference over another. In the case of the graph on the barograph, one of two codes could be picked. An 8 (steady then decreasing) or 6 (decreasing then steady). The observer should pick the 6 because it represents the last part of the trace and is thus most representative of the pressure change.  
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==Role in tropical cyclone formation==
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[[Tropical cyclogenesis]] depends upon low-level vorticity as one of its six requirements, and the ITCZ/monsoon trough fills this role as it is a zone of wind change and speed, otherwise known as horizontal [[wind shear]]. As the ITCZ migrates more than 500 km from the equator during the respective hemisphere's summer season, increasing [[coriolis force]] allows the formation of [[tropical cyclones]] within this zone more possible. In the north Atlantic and the northeastern Pacific oceans, [[tropical wave]]s move along the axis of the ITCZ causing an increase in thunderstorm activity, and under weak vertical [[wind shear]], these clusters of thunderstorms can become [[tropical cyclones]].
  
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In the bottom centre is the aneroid (large circular silver object). As the pressure increases the aneroid is pushed down causing the arm to move up and leave a trace on the paper. As the pressure decreases the spring lifts the aneroid and the arm moves down.
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==See also==
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*[[Horse latitudes]]
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*[[Monsoon trough]]
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*[[Tropical cyclogenesis]]
  
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After three days the drum to which the graph is attached is removed. At this point the clockwork motor is wound and if necessary corrections can be made to increase or decrease the speed and new chart is attached.
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==References==
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*[http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=4028 Short NASA article with high resolution photo]
  
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==Images of barographs==
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[[Category:Tropical meteorology]]
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{{Commons|Barograph}}
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[[Category:Atmospheric dynamics]]
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{| align=center
 
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| [[Image:Barograph 02.jpg|thumb|center|150px|[[Sailplane]] barograph in its case]]
 
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| [[Image:Barograph 03.jpg|thumb|center|180px|Capsule pile and linkage. This barograph can be seen to have five aneroid capsules stacked in series.]]
 
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| [[Image:Barograph 01.jpg|thumb|center|180px|A stationary barograph without its case]]
 
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|}
 
  
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{{Met_inst}}
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[[de:Innertropische Konvergenzzone]]
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[[es:Zona de convergencia intertropical]]
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[[Category:Meteorological instrumentation and equipment]]
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[[fr:Zone de convergence intertropicale]]
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[[ja:熱帯収束帯]]
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[[cs:Barograf]]
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[[nl:Intertropische convergentiezone]]
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[[de:Barograph]]
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[[no:Den intertropiske konvergenssonen]]
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[[pl:Barograf]]
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[[nn:Den intertropiske konvergenssona]]
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[[sv:Barograf]]
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[[pl:Tropikalna strefa konwergencji]]
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[[simple:Doldrums]]
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[[fi:Pasaatituulten kohtaamisvyöhyke]]
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[[sv:Intertropiska konvergenszonen]]

Revision as of 04:05, 22 March 2007

The thunderstorms of the Intertropical Convergence Zone form a line across the eastern Pacific Ocean.

The Intertropical Convergence Zone (ITCZ), also known as the Intertropical Front, Monsoon trough, Doldrums or the Equatorial Convergence Zone, is a belt of low pressure girdling Earth at the equator. It is formed by the vertical ascent of warm, moist air from the latitudes above and below the equator.

The air is drawn into the intertropical convergence zone by the action of the Hadley cell, a macroscale atmospheric feature which is part of the Earth's heat and moisture distribution system. It is transported aloft by the convective activity of thunderstorms; regions in the intertropical convergence zone receive precipitation more than 200 days in a year.

Position of the ITCZ in July (red) and in January (blue).

Position

The location of the intertropical convergence zone varies over time. Over land, it moves back and forth across the equator following the sun's zenith point. Over the oceans, where the convergence zone is better defined, the seasonal cycle is more subtle, as the convection is constrained by the distribution of ocean temperatures.

Sometimes, a double ITCZ forms, with one located north and another south of the equator. When this occurs, a narrow ridge of high pressure forms between the two convergence zones, one of which is usually stronger than the other.

Effects on weather

Vertical velocity at 500 hPa, July average. Ascent (negative values) is a tracer for the ITCZ and is concentrated close to the solar equator; descent (positive values) is more diffuse.

Variation in the location of the intertropical convergence zone drastically affects rainfall in many equatorial nations, resulting in the wet and dry seasons of the tropics rather than the cold and warm seasons of higher latitudes. Longer term changes in the intertropical convergence zone can result in severe droughts or flooding in nearby areas.

Within the ITCZ the average winds are slight, unlike the zones north and south of the equator where the trade winds feed in. Early sailors named this belt of calm the doldrums because of the inactivity and stagnation they found themselves in after days of no wind.[1] To find oneself becalmed in this region in a hot and muggy climate could mean death in an era when wind was the only major motive force.

Role in tropical cyclone formation

Tropical cyclogenesis depends upon low-level vorticity as one of its six requirements, and the ITCZ/monsoon trough fills this role as it is a zone of wind change and speed, otherwise known as horizontal wind shear. As the ITCZ migrates more than 500 km from the equator during the respective hemisphere's summer season, increasing coriolis force allows the formation of tropical cyclones within this zone more possible. In the north Atlantic and the northeastern Pacific oceans, tropical waves move along the axis of the ITCZ causing an increase in thunderstorm activity, and under weak vertical wind shear, these clusters of thunderstorms can become tropical cyclones.

See also

References

de:Innertropische Konvergenzzone es:Zona de convergencia intertropical fr:Zone de convergence intertropicale ja:熱帯収束帯 nl:Intertropische convergentiezone no:Den intertropiske konvergenssonen nn:Den intertropiske konvergenssona pl:Tropikalna strefa konwergencji simple:Doldrums fi:Pasaatituulten kohtaamisvyöhyke sv:Intertropiska konvergenszonen

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