General description

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Transcript General description

Structure of atmosphere
Meteorological/Environmental parameters
Meteorological phenomena
Scopes of studies
Climatology and Meteorology are branches of
similar areas of study.
Climatology is focused on averages of weather and
climatic conditions over a long period of time.
Meteorology focuses more on current weather
conditions such as humidity, air pressure, and
temperatures and forecasting the short-term
weather conditions to come.
http://en.wikipedia.org/wiki/Earth's_atmosphere
Ozone maximum
Refer to:
1. Layers of the Atmosphere (National Weather Service
JetStream – Online School for Weather,
www.srh.noaa.gov/srh/jetstream/atmos/layers.htm#ion)
2. E. Aguado and J.E. Burt, Chapter 1 of Understanding Weather
and Climate
Troposphere 對流層
• The troposphere ranges form the earth surface to 8-16 km
(mean 11 km) height.
• We are living in this region, even travelling in a plane.
• Almost all weather occurs in this region.
• Air concentration drops with height.
• Temperature drops with height from 17°C (62°F) to -51°C (-60°F),
because air is mainly warmed by radiation from the surface.
• Decreasing temperature with height causes convection of air.
• The upper transition boundary is called the tropopause.
Stratosphere 同溫層;平流層
• The stratosphere ranges from 20 – 50 km height.
• It holds 19% of the atmosphere's gases but very little water vapor.
The temperature increases from -57 to -2oC with increasing height.
• The upper regions receives more intense UV radiation. More UV is
absorbed by oxygen causing a higher temperature. Less UV
radiation reaches the lower boundary, where a lower temperature
is resulted.
• A balance between cooling effect with height and UV heating is
reached near the bottom of this layer, resulting in a constant temp
range.
• Ozone reaches the max. concentration.
• The increase of temperature with height results in a calm layer
with slow gas movement.
• The upper boundary is called the stratopause.
Mesosphere
•The mesosphere extends from the stratopause to 85 km
above the surface.
•It is believed that the absorption of solar radiation at the
bottom provides most of the heat of this layer. Heat is
dispersed upward by vertical air motion.
•On average, temperature decreases from -15°C to -120°C
from bottom to top of the layer.
•The top boundary is called the mesopause.
•The gases in this layer are thick enough to slow down
meteorites (流星) hurtling into the atmosphere, where they
burn up, leaving fiery trails in the night sky.
Thermosphere
•The Thermosphere extends from the mesopause to 690 km
above the earth.
•Higher energy ultraviolet and x-ray radiation from the sun are
absorbed by gas molecules which concentrations are very low.
•Temperature of the ionized species could be as high as
2000°C.
•However, despite the high temperature, this layer is still very
cold to our skin because of the extremely thin air.
Earth-atmosphere energy balance
Spectra of solar radiation and terrestrial radiation
http://www.stvincent.ac.uk/Resources/Weather/Meteosat/System/imaging.html
Earth-atmosphere energy balance
Why is the sky blue (Scattering of light)?
http://www.phys.ufl.edu/~avery/course/3
400/atmosphere?N=A
Why are sunsets red (scattering of light)?
http://www.weatherquestions.com/Why_
are_sunsets_red.htm
Earth-Atmosphere energy balance
http://www.srh.noaa.gov/srh/jetstream/atmos/energy_balance.htm
A stable
temperature
is reached.
Wind chill
effect
http://atschool.eduweb.co.uk/kingworc/departments/geography/not
tingham/atmosphere/pages/solarradiationalevel.html
Causing internal movements of fluid systems (water in ocean
and air) to keep a steady state of the globe.
Circulation of ocean streams
Atmospheric circulation
“Greenhouse effect”: A greenhouse is designed to admit both long and short wavelength radiation,
and is opaque to the re-irradiated long wavelength radiation. It also precludes heat loss due to
convection.
The latter effect does not exactly occurs in the atmosphere (not a true greenhouse effect).
Moreover, if there is no greenhouse effect, the mean temp of the earth would be -18oC, and
oscillate widely from day to night.
Earth surface temperature distribution
North
America
South
America
Europe
Asia
Africa
Australia
Antarctica
Ice point: 0°C or 32°F
(in this case °C = °F – 32)
Catching a fever: 40°C or 104°F
(°C = (°F-32)x a factor smaller than 1, i.e. 5/9)
°C = (°F-32) x 5/9
°F = °Cx9/5 + 32
Temperature
Description
Very Cold 嚴 寒
Temperature (oC)
<= 7 oC
Cold 寒 冷
Cool 清 涼
Mild 和 暖
Warm 溫 暖
8 - 12 oC
13 - 17 oC
18 - 22 oC
23 - 27 oC
Hot 炎 熱
Very Hot 酷 熱
28 - 32 oC
>= 33 oC
Measurements of temperature
Recording the volume change of mercury of
alcohol. Disadvantage is not ready for autorecording.
Mercury thermometer
Measurement range:
10C - 100C
Alcohol thermometer
Range: 30C - 60C
Electronic thermometer is needed
•
•
•
•
For automatic recording 電腦網絡傳送)
For the convenience of data transfer (through internet/wireless
technology, recording in computer and server)
Remote sensing
More accurate
Platinum thermometer
Radiosonde telemetry
Atmospheric pressure and Wind
Pressure = weight of air / area
in
or
or
or
Pa = N/m²
hPa = 100 Pa
atm (atmospheric pressure)
bar
1 standard atmospheric pressure
= 1.013 x 105 Pa
= 1013 hPa (hectopascal)
= 1 bar = 1000 mbar
Barometer (氣壓計)
In Barometer, there is a
pressure sensor:
Pressure changes
electrical capacitance
Height dependence of pressure
Sea level pressure ~ P(0) = 1000
mb (1 atm)
Pressure drops with height (h):
P(h) = P(0) e-h/H
where H is a constant
http://gb.weather.gov.hk/education/packag
e/pack01_severe_wx/severewx.html
http://www.marinewaypoints.com/marine/wind.shtml
Beaufort
No.
Description
Wind Speed
(km / hr)
Effects Land
0
Calm
<2
Still, calm air, smoke will rise vertically.
1
Light Air
2-
Rising smoke drifts, wind vane is inactive.
2
Light Breeze
-12
Leaves rustle, can feel wind on your face, wind vanes
begin to move.
3
Gentle Breeze
13 -
Leaves and small twigs move, light weight flags extend.
4
Moderate Breeze
- 30
Small branches move, raises dust, leaves and paper.
5
Fresh Breeze
31 - 40
6
Strong Breeze
41 -
Large tree branches move, telephone wires begin to
"whistle", umbrellas are difficult to keep under control.
7
Moderate Gale
62 -
Large trees sway, becoming difficult to walk.
8
Gale
63 -
Twigs and small branches are broken from trees, walking
is difficult.
9
Strong Gale
- 87
Slight damage occurs to buildings, shingles are blown off
of roofs.
10
Storm
88 -
Trees are broken or uprooted, building damage is
considerable.
11
Violent Storm
- 117
Extensive widespread damage.
12
Hurricane
118+
Extreme destruction, devastation.
Small trees sway.
Weather Map Wind Symbols (1 knot = 1.85 km / hr)
Composition of the atmosphere
Permanent gases
Constituent
percentage
Nitrogen
78.08
Oxygen
20.95
Argon
0.93
Ne, He, Kr, Xe,H2
Remainder
Variable gases: Though the contents are rare, but is important
to meteorological phenomena, and have great influence to
comfort.
Constituent
percentage
Water vapor
0.25
CO2
0.038
Ozone
0.01
Measurement of wind speed and direction
wind vane (風向計)
wind cup
(風杯)
anemometer (風速計)
Turbo Meter
• A turbine rotates freely at a
speed directly proportional to the wind speed.
• The resulting signal is processed and displayed.
Relative Humidity
Description
Very Dry
Dry
Humid
Relative Humidity ( % )
0 - 40 %
40 - 70 %
85 - 95 %
Very Humid
95 - 100 %
Relative humidity
Water evaporate Vapor compense water
(of sea)
(cloud,
(Rain, dew)
fog)
Relative humidity = content of
water vapor in air relative
to the saturated value
Relative humidity in %
= amount of vapor/maximum quantity of
water at that temperature
Average relative humidity in HK ~ 70-80%
In winter : ~30-40%
When red signal of rainstorm is in force:
RH ~ 100%
Rain fall
黃色暴雨警告信號
紅色暴雨警告信號
黑色暴雨警告信號
In broad area of Hong
Kong, a rainfall of 30
mm/h is recorded
In broad area of Hong
Kong, a rainfall of 50
mm/h is recorded
In broad area of Hong
Kong, a rainfall of 70
mm/h is recorded
Rain gauge : as simple
as a cylindrical
container + a ruler
Make your own rain gauge
http://www.fi.edu/weather/todo/r-gauge.html
With two flip-flop buckets,
each with a conducting
contact for counting the
time of switching cycles.
Rainfall (in mm/hr) =
volume / area of the
entrance / time of
measurement