ฟิ สิ กส์บรรยากาศ
หลักสู ตรเจ้าหน้าที่เทคนิคข่าวอากาศ
หมวดวิชาที่ ๑ ทฤษฏีอุตุนิยมวิทยา
ฟิ สิ กส์บรรยากาศ
Atmospheric Physics
(Lecture 12 hrs)
Evaluation
1. Class Attention
10 points
2. Home Work 15 questions 30 points
3. Multiple choice 60 question 60 points
Total 100 points
Earth Rotation and Revolution
Earth rotation
the North Pole the rotation appears to move in a
counter- clockwise, the South Pole the Earth’s
rotation appears clockwise.
daily cycles of day and night
• apparent movement of the Sun across the horizon
• takes exactly twenty-four hours
•
Earth revolution
• responsible for the Earth’s seasons(1 year)
• Earth is farthest from the Sun on July 4, or aphelion (152.1 million km)
• On January 3, perihelion, the Earth is closest to the Sun (147.3 million km)
TEMPERATE
TROPIC
POLAR
Atmospheric Processes
Interactions - Atmosphere and Ocean
Energy Heat Transfer
Energy is transferred between the earth's
surface and the atmosphere via conduction,
convection, and radiation.
Conduction is the process by which heat energy is
transmitted through contact with neighboring
molecules.
Convection transmits heat by transporting groups of
molecules from place to place within a substance.
Convection occurs in fluids such as water and air, which
move freely.
Radiation is the transfer of heat energy without the
involvement of a physical substance in the transmission.
Radiation can transmit heat through a vacuum.
Energy Interactions with the Atmosphere
and at the Surface
Solar and Terrestrial Radiation
Solar radiation
emr emitted from sun which passes through the
atmosphere and is reflected in varying degrees
by Earth's surface and atmosphere
detectable only during daylight
Sun's visible surface (photosphere) has temperature - 6000K
energy radiated from gamma to radio waves
99% of sun's radiation fall between 0.2 - 5.6um; 80% - 0.4 - 1.5um
(visible and reflected infrared, atmosphere quite transparent to
incoming solar radiation
maximum radiation occurs 0.48um (visible)
Terrestrial radiation
energy emitted from the Earth and atmosphere
detectable both day and night
Earth's ambient temperature - 300K
Earth radiates 160,000 times less than the sun
essentially all energy is radiated at (invisible)
thermal infrared wavelengths between 4-25um
maximum emission occurs at 9.7um
Radiation-Matter Interactions
Albedo
• Fraction of total radiation reflected by an
object (surface).
• Varies according to:




Cloud cover.
Particles in air.
Angle of sun’s rays.
Types of surface.
Radiation Balance
Incoming solar radiation = Outgoing longwave radiation
100 = 35 (reflected - albedo) + 65 (terrestrial emitted
Global Solar Radiation Budget
•
•
•
•
Reflected 31%
Absorbed by atmosphere 20%
Absorbed by Earth’s surface 49%
Earth’s climate is controlled by a Greenhouse
Effect
• Gases in the atmosphere control this effect
– H2Ovapor, CO2, O3, CH4, N2O
– The percent of IR radiation absorbed varies with l
– An Atmospheric Window is a range of l over which
little or no radiation is absorbed
– A visible window extends 0.3-0.9mm and major IR 813 mm, the peak IR emission of the planet is at 10mm
Greenhouse Gases
• CO2 is stored in four reservoirs: three that are
active and one inactive reservoir including
–
–
–
–
the atmosphere,
the oceans,
the terrestrial system
Earth’s crust
• Most CO2 is stored in the oceans while the
smallest amount is found in the atmosphere.
• Short-wavelength incoming radiation is not
blocked by CO2, but re-radiated longwavelength energy is, and this warms the
atmosphere causing the greenhouse effect
Absorptivity is very low or near zero in atmospheric window
Sensible heat is heat energy transferred between the
surface and air when there is a difference in temperature
between them. A change in temperature over distance is
called a "temperature gradient".
Latent Heat is heat energy is added to water it will
change states or phase as it does not raise the
temperature of molecules.
อุณหภูมิ (Temperature)
• อุณหภูมิ หมายถึง การบอกระดับความร้อนหรื อความเย็น หน่วยเป็ นองศา
• สสารต่างๆมีอุณหภูมิต่างกัน ได้รับพลังงานความร้อนไม่เท่ากัน
โครงสร้างทางโมเลกุลแตกต่างกัน เมื่อให้ความร้อนจานวนเท่ากัน
สสารสองชนิดที่มีปริ มาตรเท่าๆกัน อาจมีอุณหภูมิไม่เท่ากัน
• อุณหภูมิมีผลกระทบต่อประสิ ทธิ ภาพของอากาศยาน และเป็ นสาเหตุให้เกิด
ปรากฏการณ์ทางอุตุนิยมวิทยา
Air temperature is a measure of the heat content of the
air as a measure of the average speed or kinetic energy
level of molecules.
The temperature of our atmosphere is controlled by a
complex set of interactions between the biosphere,
lithosphere and atmosphere.
The air temperature at a particular place by examining
radiation and energy exchanges between the earth
and air above.
Controls over air temperature at a place
-Radiation transfers
-Sensible heat transfer
-Location with respect to water bodies
(Continentality)
- Air mass movement
Average Earth surface temperatures. Blue indicates
lowest temperatures (polar regions), red indicates
highest temperatures (around the equator). The data
used for this diagram were collected between January
1985 and December 1992.
Temperature measurement using modern scientific
thermometers and temperature scales :Fahrenheit's
scale is still in use in the USA, with the Celsius scale
in use in the rest of the world and the Kelvin scale.
In the International System of Units (SI) is the kelvin
(Symbol: K). The kelvin and Celsius scales are, by
international agreement .
Absolute zero is defined as being precisely 0 K and
−273.15 °C. Absolute zero is where all kinetic motion in
the particles comprising matter ceases and they are at
complete rest
Absolute humidity is the weight of water vapor per unit
volume of air, usually measured in units of grams of
water vapor per cubic meter of air. Absolute humidity is
not often used to express the moisture content of air
because it is sensitive to changes in both the
temperature of the air and atmospheric pressure.
Specific humidity is measured as the weight of water
vapor in the air per unit weight of air, which includes the
weight of water vapor. The units of measurement are
grams of water vapor per kilogram of air.
mixing ratio is the weight of water vapor per unit weight
of dry air. Because the atmosphere is made up of so
little moisture by volume, the mixing ratio is virtually the
same as the specific humidity.
Vapor pressure is the partial pressure created by
water vapor. Vapor pressure, like atmospheric
pressure, is measured in millibars and is relatively
insensitive to volumetric expansion or temperature.
The saturation vapor pressure is simply the
pressure that water vapor creates when the air is
fully saturated.
Dew point temperature is the temperature at which
condensation takes place and is used as a measure of
moisture content. The dew point temperature depends
on the amount of moisture in the air, the more moisture
in the air, the higher the dew point temperature.
Relative humidity is the ratio of the amount of water
vapor in the air to its saturation point. Often relative
humidity is defined as the amount of water vapor in the
air to "how much it can hold" at a given temperature.
The air must be at or near its saturation point for
condensation to take place. Air can become
saturated in two ways,
1) add water to the air by evaporation thus
bringing it to saturation given its present
temperature,
2) cool the air to its dew point temperature.
Cooling the air is the most common way for
condensation to occur and create clouds.
Air can be cooled through contact with a cold
surface or by uplift.
Clausius–Clapeyron relation
Mean Distribution of Water Vapor
Atmospheric stability
Adiabatic - A process in which heat is neither
added nor subtracted from the system.
Adiabatic Cooling. Also called Expansional
Cooling.
Adiabatic Warming.
we have to do is get the parcel of air lifted
- Orographic Lifting
- Convergence and Divergence
- Surface Boundaries
- Convection
Orographic Lifting
- Air is forced upward by topography
- Adiabatic Warming (Leeward Side)
Adiabatic Cooling
(Windward Side)
- it is usually wetter on the windward side than
on the leeward side.
Convergence and Divergence
Convergence at the surface (Low Pressure), air rises
Divergence Aloft
Surface Boundaries
Warm and Cold Fronts
Outflow Boundaries (Thunderstorms)
Dry Line
Convection
Lift by heating surface (diabatic)
Parcels of warm air rise from the surface and
mix with the ambient air.
Responsible for cumuliform clouds.
Cloud Formation
When the parcel cools to the point when
the parcel mixing ratio and the
saturation mixing ratio are equal, RH
will be 100% and a cloud will form.
Cloud Condensation Nuclei
The atmosphere has plenty of CCN:
Dust
Salt Spray from Oceans
Volcanoes
Sulfate Particles from Phytoplankton
Forest Fires
Trees
Anthropogenic Origins
Atmospheric Stability
Basic concept – when the temperature of
the air parcel is greater than the
temperature of the surrounding
environment, then it will rise, and when the
temperature of the air parcel is less than
the surrounding environment, then it will
sink.
Atmospheric stability is the resistance of the
atmosphere to vertical motion. The distribution of
temperature vertically in the troposphere influences
vertical motion. A large decrease of temperature with
height indicates an unstable condition which
promotes up and down currents. A small decrease
with height indicates a stable condition which inhibits
vertical motion. Where the temperature increases
with height, through an inversion, the atmosphere is
extremely stable.
To determine stability conditions, temperature
lapse rates are compared to dry- or moistadiabatic lapse rates. Between stable and
unstable lapse rates we may have a
conditionally unstable saturated. During
condensation in saturated air, heat is released
which warms the air and may produce instability;
during evaporation, heat is absorbed and may
increase stability.
Temperature Inversions
A temperature inversion exists when the
temperature of the environmental air
increases with height, which is the
opposite (i.e. the inverse) of the pattern we
normally observe in the troposphere.
A temperature inversion is an extremely
stable situation.
Dry Adiabatic Lapse Rate (DALR)
Meteorologists normally assume that
unsaturated air parcels (i.e. air outside
clouds) change temperature in an
adiabatic process as they rise or sink.
The Dry Adiabatic Lapse Rate (DALR) is
the rate at which an unsaturated air parcel
cools as it rises.
DALR
Since the temperature is a function of the
internal energy, when the internal energy
decreases, then the temperature
decreases.
Thus, the rising parcel expands and
cools.
This process is called adiabatic cooling.
Environmental Lapse Rate
The Environmental Lapse Rate (ELR) is
the rate at which the measured
temperature of the air in the environment
outside the air parcel decreases with
height.
We send up balloons with instrument
packages called radiosondes to measure
the temperature at different levels above
the Earth’s surface.
Stable: A temperature lapse rate less than the
dry adiabatic rate of 3°c per 1,000 feet for an
unsaturated parcel is considered stable, because
vertical motion is damped.
Unstable: A lapse rate greater than dry-adiabatic (a
superadiabatic lapse rate) favors vertical motion and
is unstable. Since it is unstable, the air tends to adjust
itself through mixing and overturning to a more stable
condition.
Neutral: In the absence of saturation, an
atmospheric layer is neutrally stable if its lapse
rate is the same as the dry-adiabatic rate.
Subsidence is the gradual lowering of a layer of air over
a broad area. When it begins at high levels in the
troposphere, the air, which has little initial moisture,
becomes increasingly warmer with resulting lower
relative humidity as it approaches the surface. If some
mechanism is present by which this warm, dry air can
reach the surface, a very serious fire situation can result.
Atmospheric Boundary Layer Structure
Stull defines the atmospheric boundary layer as ``the part
of the troposphere that is directly influenced by the
presence of the earths surface, and responds to surface
forcings with a time scale of about an hour or less.'' Figure
3 illustrates a typical daytime evolution of the atmospheric
boundary layer in high pressure conditions over land. The
solar heating causes thermal plumes to rise, transporting
moisture, heat and aerosols. The plumes rise and expand
adiabatically until a thermodynamic equilibrium is reached
at the top of the atmospheric boundary layer. The moisture
transferred by the thermal plumes forms convective
clouds.
ฟิ สิ กส์บรรยากาศ