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METEOROLOGY
GEL-1370
Grading Scheme
• Assignment – 30 points
• Exam – 1 – 30 points
• Exam – 2 – 30 points
• Final Exam – 40 points
Lowest one unit of 30 points will be dropped
Turning-in Assignment is a MUST!! – If not, one
of the tests will not be counted towards the final
course grade
Pop Quizzes as a bonus will be periodically given
Historical Developments - Meteorology
• ‘Meteorology’ comes from the Greek Word
‘Meteoros’ meaning ‘high in the air’
• STUDY OF THE ATMOSPHERE AND ITS
PHENOMENA
• Greek Philosopher Aristotle (340 BC) wrote a book
on natural philosophy entitled “Meteorologica” –
first attempt to explain atmospheric phenomena in a
philosophical and speculative manner
• Aristotle’s student, Theophrastus, compiled a book
on weather forecasting – ‘Book of Signs”
Historical Developments – contd.
• Meteorological Parameters: Air temperature,
pressure, humidity, wind speed and direction
• During 1500s, Italian Physicist and Astronomer,
Galileo: Invented a cruse water thermometer
• 1643: Evangelista Torricelli, student of Galileo,
invented Hg barometer to measure air pressure
• A few years later, Blaise Pascal and Rene
Descartes (French): Atmospheric pressure
decreases with increasing altitude
• 1667: Robert Hooks (British): Invented a Plate
Anemometer for measuring wind speed
Historical Developments – contd.
• 1719: Gabriel Fahrenheit (German), developed a temperature
scale
• 1742: Anders Celsius (Swedish), developed centigrade scale
• 1780: Horace deSaussure (Swiss), invented hair hygrometer to
measure humidity
• 1787: Jacques Charles (French), discovered the relationship
between temperature and volume of air
• 1835: Gaspard Coriolis (French) demonstrated the effect that
the earth’s rotation has on atmospheric motion
• 1840s: Ideas about winds and storms were partially understood
• 1843: Invention of Telegraph
• 1869: Isobars (lines of equal pressure) were placed on weather
maps
• Ca. 1920: Concepts of air masses and weather fronts were
formulated in Norway.
Historical Developments – contd.
• 1940s: Upper-air balloon observations of T, P,
Humidity yielded 3-D view of the atmosphere and
military aircrafts discovered existence of jet streams
• 1950s: High-speed computers to solve mathematical
equations to describe the atmospheric behavior
• 1960: First weather satellite, Tiros I was launched –
Space Age Meteorology
• Princeton, NJ (Geophysical Fluid Dynamics
Program): Numerical methods to predict weather
• Mid-1990s: Conventional radars were replaced by
Doppler radars to peer into severe thunderstorms and
unveil their winds
•
Chapter One
The Earth’s Atmosphere
Grading
• Assignment – 30 points
• Exam – 1 – 30 points
• Exam – 2 – 30 points
• Final Exam – 40 points
Lowest one unit of 30 points will be dropped
Turning-in Assignment is a MUST!! – If not, one
of the tests will not be counted towards the final
course grade
Pop Quizzes as a bonus will be periodically given
Some Basic Questions – Why Meteorology??
• If we approach near a fire place, we feel hotter – if
we move to a hill resort (towards the sun) why we
feel cooler (not hotter)?
• What is the role of atmosphere in ‘Greenhouse Effect’
and ‘acid rain’
• Why hurricanes is confined to certain regions –
lessons from (St.) Andrew?
• Why thunderstorm in the Gulf Coast is much stronger
than the Midwest?
• What would happen to this planet if there were no
atmosphere??
How Weather Affects our Lives?
• Our lives center around the weather – type of clothing we wear,
plants we grow, our comforts in the form of heating/cooling our
homes, etc.
• Wind chill makes us feel lot colder than what it is
• Health is affected – Arthritis pain is likely to occur when rising
humidity with falling pressure; our mood swings (hot, dry wind
vs cool breeze); incidence of heart attacks shows statistical peak
after the passage of warm fronts when rain and wind are
common
• Cold summer of 1992 – saved billions of $ to people
• Bitter cold winter of 1986-1987 in Europe: several hundred
people died
• Huge Ice storm in Jan 1998 in Northern New England and
Canada – millions of people without power
How weather affects our lives – contd.
• 1999: Heat waves in US caused 250 deaths
• 1995: >500 people died due to high humidity and heat
waves in Illinois
• People are killed by Tornadoes
• 10 yrs ago, 55 people died due to Andrews in FL (30
billion $ loss)
• Fog can affect the visibility
• Weather Channel, NOAA Weather Radio Station
CHAPTER – 1
THE EARTH’S ATMOSPHERE
*ATMOSPHERE: LIFE-GIVING BLANKET OF AIR
HORIZONTAL LONG-DISTANCE MOVEMENT IS EASY – WE CAN’T DO
MORE THAN 8 KM FROM EARTH’S SURFACE - SUFFOCATION
SURVIVING WITHOUT FOOD OR WATER FOR A FEW DAYS POSSIBLE – NOT
WITHOUT AIR
IF THERE IS NO ATMOSPHERE, THERE WON’T BE ANY LAKE OR OCEANS
: ATMOSPHERE SERVES AS A BUFFER FOR EARTH’S CLIMATE – FROM
UNBEARINGLY HOT DURING DAY AND UMIMAGINABLY COLD AT NIGHT
AIR PROTECTS FROM SCORCHING SUN – AIR MOLECULES TRAVEL FROM
ONE CONTINENT TO ANOTHER IN LESS THAN A WEEK TIME SCALE
Introduction-contd.
• Our planet is driven by the solar energy – a
small portion of the outgoing solar radiation
is intercepted by the Earth- Sun is at 150
million km away from us (93 million miles)
• Average temp of earth ~15°C (59 °F)
• Temperature fluctuation: -85 °C to 50 °C (121 °F to 122 °F)
Introduction-contd.
• Composition of the Atmosphere (Permanent
Gases)
• Gas
Symbol
% (volume) dry air
–
–
–
–
–
–
–
Nitrogen
Oxygen
Argon
Neon
Helium
Hydrogen
Xenon
N2
O2
Ar
Ne
He
H2
Xe
78.08
20.95
0.93
0.0018
0.0005
0.00006
0.000009
Composition of the Atmosphere Near
the Earth’s surface-contd.
Gas & particles Symbol % (volume)
ppm
Water vapor
H2O
0 to 4
Carbon dioxide CO2
0.037
368
Methane
CH4
0.00017
1.7
Nitrous Oxide N2O
0.00003
0.3
Ozone
O3
0.000004
0.04
Particles (dust, soot, etc) 0.000001 0.01-0.15
Chlorofluorocarbons (CFCs) 0.00000002 0.0002
Atmospheric composition-contd.
• 99% of the atmosphere lies within 30 km from surface
of the earth
– Atmosphere protects us from
• UV Radiation from Space
• Impact of high energy particles from Cosmos
• Extreme temperature fluctuations
• Water vapor varies from place to place – up to 4% warm
tropical locations to <1% in colder arctic areas
• Condensation (vapor into liquid) and evaporation (liquid
becoming vapor)
• Importance of Water vapor in the atmosphere:
– Releases large amounts of latent heat (source of atmospheric
energy for thunderstorms and hurricanes)
– Water vapor is a ‘greenhouse gas’ (absorbs outgoing energy)
Importance of CO2
• 0.037%
• Sources: Burning of fossil fuel, deforestation, volcanic eruption, decay
of vegetation, exhalation of animal life
• Ocean is a huge reservoir – Phytoplankton uptake (source and
Sink; Fe expt; atmospheric transport of dust)
• Oceans hold X 50 times the atmospheric CO2
• Before Industrial revolution, CO2 level at 280 ppm and it is now ~370 ppm
(1.5 ppm/yr; ~32% increase) and expected to reach 500 ppm by end of this
century [Freight train won’t stop; US consumption of 1/3 vs population of
5%]
• Increase in CO2 will result in global warming – 1 to 3.5°C – Flooding in
certain areas and drought in other regions; global sea level change; global
air currents that guide the major storm systems could shift
Measurements of CO2 (ppm) at Mauna Loa
Observatory
Other Greenhouse gases
• Methane: Increases by 0.5%/year; Sources include: Paddy
fields (breakdown of plant material by certain bacteria), wet
oxygen-poor soil, biological activity of termites and biochemical
reactions in the stomachs of cow
• Nitrous Oxides: Increases by 0.25%/year; Sources include:
release from industrial activity followed by chemical reactions,
formation in the soil by microbial activity
• Chloroflurorocarbons (CFCs): Increases with time;
Sources include: solvents for cleaning electronic microcircuits;
propellants for the blowing of plastic-foam insulation, etc – Play a
part in destroying Ozone molecule in the stratosphere Implications
Ozone (O3)
• The Primary ingradient of photochemical smog
(chemical reaction of pollutants in big cities with
sunlight)
• ~92% found in stratosphere (11-50 km) – formed when
O combines with O2 – abundance < 0.002% by volume
• Shields plants, animals and humans from sun’s harmful
UV rays- offers protective shield – CFCs release ozone
destroying Cl – Ozone conc. has been decreasing over
parts of the Northern and Southern Hemisphere –
Ozone hole in Antarctica during September & October
Aerosols
• Smoke from Forest fires, salt particles from seawater spray, aeolian dust, fine ash particles and
gases derived from volcanic eruptions –aerosols
– Act as surfaces for nuclei condensation
• Pollutants: Derived from automobiles: CO,
hydrocarbons, NO2, sulfur-containing fuels (coal
and oil) releases SO2 --- lead to acid rain; NO2
reacts with hydrocarbon in the presence of light
to produce ozone
Early Atmosphere
• Earth’s first atmosphere is believed to contain mainly H
and He (with traces of NH3 and CH4) – Earth’s hot
surface led to the escape of these gases
• Later, escaped gases from volcanic eruptions & steam
vents, surrounded the Earth – Mostly water vapor and
CO2 formed the second atmosphere --- CO2 reached the
ocean and eventually got locked in carbonate rocks --Slowly but steadily, the N2 content of the atmosphere
increased
• Energetic cosmic rays split H2O molecule in O and H –
escape of H lead to increase in Oxygen – Plant growth
led to the increase in Oxygen levels
Vertical Structure of the Atmosphere
• Classification based on: Temperature, composition or
electrical properties
• Air Density: number of air molecules/volume
• Atmospheric Pressure: Force/area of surface
• Total weight of air 5,600 trillion tons
• Units of pressure: 1 Atmosphere = 1.01325 bars =
1013.25 millibars (mb) = 101326 Pascal = 1013.25
hectopascal = 29.92 in. Hg = 760 mm Hg = 14.7 lb/inch
Air pressure and density decrease with increasing altitude
Atmospheric pressure rapidly decreases with height
Layers of atmosphere
• Earth’s surface to 11 km – temp decreases – sunlight warms the
earth’s surface and the surface warms the air above it
• Lapse Rate (LR) = Rate of decrease of temp. with height; in the
lower atmosphere, LR ~ 6.5°C/km; colder air leads to higher LR
and warmer air to lower LR; LR fluctuates from day to day &
season to season;
• Isothermal Zone: At Tropopause, Stratopause and Mesopause, the
Lapse Rate is zero
• Temperature Inversion: Occasional increase of temp. with height
known as Temp. Inversion;
• Troposphere: From earth’s surface to where the air stops
becoming colder with height; up to 11 km from earth’s surface;
controls all the weather; the layer is well mixed by
ascending/descending air masses
Temperature-based classification of atmosphere
Atmospheric layers – contd.
• Stratosphere: From the top of tropopause to until the
temperature remains constant (~50 km);
• Tropopause height varies – higher in the equatorial region &
decreases poleward; tropopause is higher in summer and lower in
winter at all latitudes;
• In some regions, tropopause breaks, leading to stratospheretroposphere air mixing (mainly during spring/summer months
and in mid latitudes – Stratosphere-Troposphere Exchange; these
breaks also mark the position of jet streams (wind speeds >100
knots)
• At ~20 km from earth, air temperature increases with height –
Temperature Inversion – This inversion reduces the vertical
movement of air masses within the stratosphere (temp at ~30 km
from earth is ~-46°C); this reason
Atmospheric layers – contd.
• Inversion in the stratosphere is due to heating of
stratosphere from the absorption of UV rays by O3;
absence of O3 ---- air would become colder with height
• Mesosphere: Extremely thin air, low pressure and density;
average temp. ~-90°C;
• Thermosphere: Hot layer above Mesosphere; very few
atoms and molecules in air; Range of an air molecule ~
1km (compare with < 10-6 cm in earth’s surface)
• At the top of thermosphere (>500 km from earth’s
surface), particles can escape to space – Water Loss
Possible?? (this region called Exosphere- upper limit of
our atmosphere)
Composition-based Atmospheric Layering
Homosphere: A well-mixed layer in terms of
composition; below the thermosphere, the
composition of air (78% N2 and 21% O2) remains
constant by turbulent mixing
Heterosphere: Complete stirring in the thermosphere is
not possible due to few atoms/molecules; diffusion is
dominant; heavier atoms at the bottom & lighter atoms
at the top – heterogeneity in introduced
Ionosphere: Region within the upper atmosphere where
large concentrations of ions and free electrons exist
Layers of atmosphere
Ionosphere
Simplified surface weather map
Weather Map
• Weight of air in the column varies and hence
atmospheric pressure
• L: Marks the center of the middle-latitude storm
• H: Regions of high atmospheric pressure, anticyclones
• Coriolis Force: Earth’s rotation causes the wind to
deflect toward the right in the Northern Hemisphere.
This deflection causes the winds to blow clockwise and
outward from the center of the highs &
counterclockwise and inward toward the center of the
low
• Front: A boundary that separates the warm and cool air
appears as a heavy, dark line on the map.
Weather Map – contd.
• Weather front is to the west of Chicago – when
westerty winds push the front eastward, areas
in outskirts of Chicago will observe the
approaching front as a line of thunderstorms –
heavy showers with thunder and lightning and
gusty winds are expected