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

Revision as of 15:21, 18 May 2006

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 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.

The location of the intertropical convergence zone varies over time, as it moves back and forth across the equator in a semiannual pattern, following the sun's zenith point. There is also a diurnal cycle, with cumulus developing around midday and building to thunderstorms in mid to late afternoon.

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 low spirits they found themselves in after days of no wind. To find oneself becalmed in this region in a hot and muggy climate could mean death in the era when wind was the only motive force.

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, and usually, one or the other of the zones is stronger than the other.

References

Short NASA article with high resolution photo

de:Innertropische Konvergenzzone es:Zona de convergencia intertropical fr:Zone de convergence intertropicale nl:Doldrum no:Den intertropiske konvergenssonen nn:Den intertropiske konvergenssonen pl:Tropikalna strefa konwergencji simple:Doldrums fi:Pasaatituulten kohtaamisvyöhyke sv:Intertropiska konvergenszonen

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-[[Image:BAROGRAM.JPG|thumb|Barogram of a heavy storm over northern Germany 2005]]
+[[Image:IntertropicalConvergenceZone-EO.jpg|right|300px|thumb|The thunderstorms of the Intertropical Convergence Zone form a line across the eastern Pacific Ocean.]]
-[[Image:Barograph.JPG|thumb|Three day barograph of the type used by the [http://www.msc.ec.gc.ca/ Meteorological Service of Canada]]]
-A '''barograph''' is a recording [[aneroid barometer]]. It produces a paper or foil chart called a '''barogram''' that records the [[barometric pressure]] over [[time]].
+The '''Intertropical Convergence Zone''' '''(ITCZ)''', also known as the '''Intertropical Front''' 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.
-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.
+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.
-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).
+The location of the intertropical convergence zone varies over time, as it moves back and forth across the equator in a semiannual pattern, following the sun's [[zenith]] point. There is also a [[diel|diurnal]] cycle, with [[cumulus cloud|cumulus]] developing around midday and building to thunderstorms in mid to late afternoon.
-Flight Recording: 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 are required by the [[Federation Aeronautique Internationale|FAI]] to record certain tasks and record attempts associated with [[sailplanes]]. A continuously varying trace indicates that the sailplane has not landed during a task, while measurements from a calibrated trace may be used to establish the completion of altitude tasks or the setting of records.  Examples of FAI approved sailplane barographs include the Replogle mechanical drum barograph and the EW electronic barograph (which may be used in conjunction with [[GPS]]).  For more information about approved barograph measurement devices, goto the Soaring Society of America at [http://www.SSA.org SSA].
+[[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.]]
-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.
+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.
-==Three Day Barograph==
+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 low spirits they found themselves in after days of no wind. To find oneself becalmed in this region in a hot and muggy climate could mean death in the era when wind was the only motive force.
-On the top right 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.
-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.
+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, and usually, one or the other of the zones is stronger than the other.
-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.
+==References==
+*[http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=4028 Short NASA article with high resolution photo]
-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.
-==Images of barographs==
+[[category:Tropical meteorology]]
-{| align=center
+[[category:Atmospheric dynamics]]
-| [[Image:MUGGIANU_Jean-Marie_IMAG0003.jpg|thumb|center|150px|[[Sailplane]] barograph in its case]]
-| [[Image:MUGGIANU_Jean-Marie_IMAG0002-1.jpg|thumb|center|180px|Capsule pile and linkage. This barograph can be seen to have five aneroid capsules stacked in series.]]
-| [[Image:MUGGIANU_Jean-Marie_IMAG0010.jpg|thumb|center|180px|A stationary barograph without its case]]
-|}
-{{Met_inst}}
+[[de:Innertropische Konvergenzzone]]
+[[es:Zona de convergencia intertropical]]
-{{Commons|Barograph}}
+[[fr:Zone de convergence intertropicale]]
+[[nl:Doldrum]]
-[[Category:Measuring instruments]]
+[[no:Den intertropiske konvergenssonen]]
-[[Category:Meteorological instrumentation and equipment]]
+[[nn:Den intertropiske konvergenssonen]]
+[[pl:Tropikalna strefa konwergencji]]
+[[simple:Doldrums]]
-[[cs:Barograf]]
+[[fi:Pasaatituulten kohtaamisvyöhyke]]
-[[de:Barograph]]
+[[sv:Intertropiska konvergenszonen]]