Download METEOROLOGY

METEOROLOGY
GEL-1370
Grading Scheme
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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
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‘Meteorology’ comes from the Greek Word ‘Meteoros’ meaning ‘high in the air’
• STUDY OF THE ATMOSPHERE AND ITS PHENOMENA
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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.
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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.
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1940s: Upper-air balloon observations of T, P, Humidity yielded 3-D view of the atmosphere
and military aircrafts discovered existence of jet streams
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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
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Chapter One
The Earth’s Atmosphere
Grading
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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??
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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
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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.
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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)
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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.
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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)
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Average temp of earth ~15°C (59 °F)
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Temperature fluctuation: -85 °C to 50 °C (-121 °F to 122 °F)
Introduction-contd.
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Composition of the Atmosphere (Permanent Gases)
Gas Symbol
% (volume) dry air
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Nitrogen N2
Oxygen O2
Argon
Neon
Helium
Hydrogen
Xenon
78.08
20.95
Ar
Ne
He
H2
Xe
0.93
0.0018
0.0005
0.00006
0.000009
Composition of the Atmosphere Near the Earth’s surfacecontd.
Gas & particles
Symbol
% (volume) ppm
Water vapor H2O
0 to 4
Carbon dioxide
CO2
0.037
368
Methane
CH4
0.00017
Nitrous Oxide N2O
0.00003
0.3
Ozone
O3
0.000004
0.04
Particles (dust, soot, etc)
0.000001
0.01-0.15
1.7
Chlorofluorocarbons (CFCs) 0.00000002 0.0002
Atmospheric composition-contd.
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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
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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)
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Oceans hold X 50 times the atmospheric CO2
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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%]
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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
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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
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Nitrous Oxides: Increases by 0.25%/year; Sources include: release from industrial activity followed
by chemical reactions, formation in the soil by microbial activity
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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)
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The Primary ingradient of photochemical smog (chemical reaction of pollutants in big cities
with sunlight)
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~92% found in stratosphere (11-50 km) – formed when O combines with O2 – abundance <
0.002% by volume
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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
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Smoke from Forest fires, salt particles from sea-water spray, aeolian dust, fine ash
particles and gases derived from volcanic eruptions –aerosols
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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
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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
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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;
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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.
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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 stratosphere-troposphere air mixing (mainly during
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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.
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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
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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.
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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
CHAPTER SUMMARY