Isentropic Lab 21 February 2006

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Isentropic Lab21 February 2006

• Team 3
• Pounder, Bard

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Isentropic Analysis

• Based on our analysis of the isentropic and
  isobaric plots, there is rising motion in the
  coastal states along the Gulf of Mexico and
  sinking motion within the Central Plains and
  Midwest.
• This is evidenced first by the wind gradient
  showing wind flowing towards low pressure from
  the Gulf of Mexico, and the clouds which are
  visible on the satellite image. The sinking
  motion is made obvious by the clear skies over
  Kansas and extending eastward to Virginia. While
  the winds are not perpendicular to the pressure
  gradient, the pressure gradient itself is very
  tight.
• The second piece of evidence for the regions of
  rising and sinking motion are the isobaric plots
  showing areas of warm and cold air advection.
  These regions are the same as the regions in the
  isentropic plots. Warm air advection is shown on
  the isobaric plots over the coastal states along
  the Gulf of Mexico, and cold air advection is
  shown over the Central Plains and Midwest
  regions.
• Finally, while the rising and sinking motion may
  or may not cause the formation of clouds and
  clear skies, respectively, this problem can be
  examined by analyzing the moisture profile of the
  areas to see the effects of moisture transport.
  There is clearly a heavy moisture plume over the
  Gulf of Mexico, while over the Central Plains,
  the relative humidity does not exceed 60.
• To summarize, southerly winds from the Gulf of
  Mexico transport moisture, provide warm air
  advection, and blow towards lower pressure, which
  result in rising motion and cloud formation over
  the Deep South. Conversely, northwesterly winds
  provide cold air advection into a region of low
  moisture and higher pressure, resulting in
  sinking motion and clear skies.

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Cold Air Advection
Warm Air Advection
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850mb verical motion

• Air on the 285K surface is rising from the
  surface up to 850mb, about 1.5km, and continuing
  to ascend to about the 600mb surface, about 2.5km
  more.  Air is falling on this surface starting
  around 500mb down to 850mb, about 3.5km, and
  reach the surface about 1km below the 850mb
  surface.  Up to the 295K surface, air is rising
  off the ground to 850mb, and it rises farther up
  to about 500mb, about 3.5K more over southern
  Ontario.  Air is descending from 400mb down to
  850, about 4.5km, across Central Canada and the
  Northern US Plains.  That air will meet the
  ground about 1km below 850mb.

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Insentropic surface with RH

• Very little precipitation is expected with this
  system.  One major factor is the lack of moisture
  transport from the Gulf of Mexico.  Southerly
  winds are very weak across the Northern Gulf but
  are very strong coming out of Texas.  So the air
  that's rising across the Ohio and Mid-Mississippi
  River valleys are basically land-derived, so it's
  quite dry.  The moist air across the deep south
  doesn't get very high into the atmosphere it
  gets deflected eastward well south of Tennessee. 
  Moisture in the middle troposphere is located
  above the Central and Eastern Great Lakes area,
  but the air is relatively drier towards the
  surface.  So it looks as if precipitation in this
  area will be minimal when it reaches the surface
  due to evaporation.

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Montgomery streamfunction vs. 850mb map

• The isentropic map and the 850mb map show a
  couple similarities.  Wind is shown to flow along
  the Montgomery Stream Function contours on the
  isentropic map.  Likewise, wind generally follows
  the height contours on the pressure map.  On both
  maps, the magnitudes of the wind shown are
  comparably proportionate.  The flow around the
  the Southeastern ridge match, and the trough over
  the Great Lakes and Central Plains is at least
  somewhat apparent.  However, on the isentropic
  map, features like high and low pressure regions
  as well as frontal zones are lost, where as on
  the 850mb map they jump off the page.  The
  isentropic map do not depict advection patterns
  very well either.  Also the isentropic map shows
  the direction of the geostrophic winds and how
  they follow the direction of air parcels.  On the
  850mb map, it shows the wind in two-dimentional
  motion, and it's a  very simplified version of a
  combination of physical processes.