Vertical structure of the atmosphere Introduction to

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Vertical structure of the atmosphere

• Introduction to Meteorology
• Leila Carvalho

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Where is the upper boundary of the atmosphere?
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Well

• There is no definite answer to this question.
  What happens is that air becomes thinner at
  higher altitudes.
• At an altitude of 16 km (10mi) the density of the
  air is only about 10 of that at the sea level
  and at 50km is only about 1 of that at the sea
  level
• At 100km (60mi) 99.99997 of the atmosphere is
  below this height
• Most of the action or the weather that
  affects surface occurs below 12km, the region
  we call troposphere ( Greek "tropos" for
  "turning" or "mixing)

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How can we explain these differences in density ?
The ME mass of the Earth 5.981024
kg Ggravitational constant6.67x10-11 Nm2kg2

• Answer GRAVITY FORCE!

FG Gravitational force
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Now we can define atmospheric pressure
Definition is defined as the force per unit area
exerted against a surface by the weight of the
air molecules above that surface. Unities
millibar (USA) or hPa (hectopascals used in
scientific publications 100N/m2)
P2
P1 gt P2
P1
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The basics to understand winds is to keep in mind
that
Wind is air in movement Air always move from high
to low pressure regions That is why we plot maps
with lines with same pressure at surface
(isobars) to localize where regions with high
and low pressure exist
High pressure (H)
Low pressure (L)
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Training concepts Arrows represent winds and
colors temperature (F). Try to identify patterns
of sea level pressure (relatively high and low
pressure systems)
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These are surface analysis for Jan 05/2011
solid yellow lines isobars (lines with the same
sea level pressure)
H- High pressure systems
DBZ- radar reflectivity related to precipitation
L Low pressure systems
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Vertical structure of the atmosphere
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First intriguing question

• Why does temperature decrease with height in the
  troposphere and not the other way around??

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The reason is

• The atmosphere is relatively transparent to most
  types of radiant energy emitted by the Sun
  which means that the direct sun radiation (mostly
  VIS and UV) does not contribute to the warming
• The solar radiation does warm the Earth surface
  (it is absorbed by the earth)
• The emanating energy (or radiation) from the
  earth surface warms the atmosphere (and I am sure
  you remember why!)

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BECAUSE OF GREENHOUSE GASES!!!
CO2, CH4, H20
IR - heat
UV, VIS
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Second intriguing question

• Why does temperature increases in the
  stratosphere??

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YES, OF COURSE YOU KNOW THE ANSWER BECAUSE OF
THE OZONE LAYER!!!!
NASA
O2
http//www.ccpo.odu.edu/SEES/ozone/oz_class.htm
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Third intriguing question why now temperature
decreases in the mesosphere to values even below
the upper troposphere?
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Well

• The explanation is that the heat at the base of
  the mesosphere comes from absorption of the solar
  radiation near the base. This heat is dispersed
  upward by vertical air motions.

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Fourth and most intriguing question why now
temperature increases again in the thermosphere?
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Other intriguing facts about the thermosphere

• Temperature in the thermosphere increases with
  altitude to values in excess of 1500oC!

• However, remember temperature is a measure of
  kinetic energy, which is a measure of the speed
  at which its molecules move.

Consider the small balls as molecules with random
movement within each box . In which situation
molecules would have large speed and why?
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After all, can one freeze or fry in the
thermosphere??

• The amount of heat contained in the air reflects
  not only its temperature but ALSO ITS MASS AND
  SPECIFIC HEAT (the amount of heat necessary to
  change its temperature by a certain amount).
• Because there are so few gases molecules in this
  layer, the air cannot have a high heat content no
  matter what its temperature is.
• In fact, the atmosphere is so sparse in the upper
  thermosphere that a gas molecule will normally
  move as much as several kilometers before
  colliding with another.
• Thus, an ordinary thermometer in this part of the
  atmosphere would have little contact with the
  surrounding air.
• Under this circumstances, the concept of
  temperature loses meaning and cannot be
  associated with the everyday terms of hot and
  cold. You will certainly freeze to death in
  the thermosphere!

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ionosphere

• The layers defined before were defined according
  to temperature profiles
• The ionosphere, as the name suggest, is defined
  based on its electrical properties.
• This layer extends from the upper mesosphere into
  the thermosphere and contains large numbers of
  electrically charged particles (ions)
• Ions are formed when electrically neutral atoms
  or molecules lose one or more electrons and
  become positively charged ions, or gain one or
  more electrons and become negatively charged
  ions.

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More curiosities about the ionosphere

• In the Ionosphere, atoms and molecules lose
  electrons as they are bombarded by solar
  radiation (UV) and shorter X-Ray
• Opposing process called recombination begins to
  take place in which a free electron is "captured"
  by a positive ion if it moves close enough to it.
  
• As the gas density increases at lower altitudes,
  the recombination process accelerates since the
  gas molecules and ions are closer together. The
  point of balance between these two processes
  determines the degree of ionization present at
  any given time.

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• The ionization depends primarily on the Sun and
  its activity. The amount of ionization in the
  ionosphere varies greatly with the amount of
  radiation received from the sun.
• Thus there is a diurnal (time of day) effect and
  a seasonal effect. The local winter hemisphere
  receives less solar radiation.
• The activity of the sun is associated with the
  sunspot cycle (11 yrs), with more radiation
  occurring with more sunspots. There are
  disturbances such as solar flares and the
  associated release of charged particles into the
  solar wind which reaches the Earth and interacts
  with its geomagnetic field.

Sunspots
Solar Flares
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Solar Wind

• The sun is our main source of light, but it also
  gives off particles, consisting mostly of
  electrons and protons.
• Sunlight takes about eight minutes to travel from
  the sun to the Earth (the speed of light is
  constant and 300,000 kilometers per second).
• The solar particles make up what we call the
  solar wind that blows outward from the sun from
  about 250 kilometers per second up to 2,500
  kilometers per second. Thus, it takes the solar
  wind particles from 17 hours to 7 days to travel
  the 150 million kilometers to Earth.

Earth magnetic field
Picture VIS from satellite SOHO
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More on the ionosphere

• The inosphere is important also for reflecting AM
  radio waves back toward Earth, increasing the
  distance at which broadcasts can be received.

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• The ionosphere is divided into several sublayers
  D, E, F
• The D-layer exists only during the daylight hours
  and absorbs AM radio waves (ionization by the
  sun)
• During the night it disappears and the E-layer
  weakens as their free electrons recombine with
  positive charged ions
• The radio waves are then able to reach the
  F-layer which reflects radio waves rather than
  absorbing them and redirects the transmission
  back to Earth, overcoming the effect of Earths
  curvature.

This is why perhaps you have listened to AM radio
at night and happened to pick up a distant radio
station that disappeared in the next day
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• The ionosphere is also responsible for the
  Aurora Borealis (NH) (northern lights) or
  Australis SH
• They occur because in the ionosphere sub-atomic
  particles from the sun are captured by Earths
  magnetic field (the field that makes the compass
  needles point to north)
• Particles are accelerated and they excite in the
  atmosphere (electrons of the atoms jump to great
  orbital distances from their nuclei)
• When they fall back to lower orbits, radiation is
  emitted
• Auroras emit light much like a neon lamp

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An interplanetary shock wave (generated by a
coronal mass ejection from the giant sunspot
9393) passed NASA's ACE spacecraft at 0030 UT on
March 31st (730 pm EST on March 30th) and struck
Earth's magnetosphere about 30 minutes later. The
leading edge of the shock front was dense (150
protons/cc) and strongly magnetized -- traits
that can (and did!) give rise to powerful
geomagnetic disturbances. Sky watchers spotted
Northern Lights as far south as Mexico.
http//spaceweather.com/aurora/gallery_31mar01.htm
l
South Dakota , 2001
Sacramento CA, 2001
Alaska, 2001
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Monitoring the space1) NOAA /Space Weather
Prediction Center http//www.swpc.noaa.gov/NOAAs
cales/ Watch a video that warns us about
possible solar storms and repercussions to
communication http//www.digitaljournal.com/arti
cle/272022 Monitoring space weather 2)
http//spaceweather.com/
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Conclusions-1

• The density of the air decreases exponentially
  with height due to the pull of the gravity
• Air pressure is the force per unit area exerted
  against a surface by the weight of the air
  molecules above that surface. It is given in
  unities of 100 N/m2 (1 hPa hecto Pascal),
  equivalent to 1 mb
• Pressure also decreases exponentially with height
• Temperature decreases with height in the
  troposphere because of the decrease of the
  density of greenhouse gases
• Temperature increases in the Stratosphere due to
  the presence of ozone

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Conclusions-2

• In the Thermosphere the mean free path or the
  average distance covered by a particle between
  successive impacts is very large and that results
  in high speed and kinetic energy (high
  temperatures)
• The Ionosphere extends from the upper mesosphere
  into the thermosphere and contains large numbers
  of electrically charged particles (ions). Very
  important for radio communication