Transcript Atmosphere. Clouds.

Lecture 25
Atmosphere. Weather.
Chapter 13.1  13.7
• Structure of the Atmosphere
• Clouds
• Winds
The Atmosphere
The atmosphere is the gaseous envelope of the Earth.
The atmosphere was formed over a long time.
Initially gases came out of the Earth’s interiors with
volcano eruptions.
Later oxygen from photosynthesis accumulated there.
The atmosphere is responsible for: the blue sky color,
appearance of the rainbow, our protection from the
ultraviolet and X-ray radiation of the Sun, etc.
Composition and Structure
The chemical composition of the atmosphere includes :
78.08% of N
20.95% of O
0.03% of CO2
0.93% of Ar and ~0.001% of other noble gases
0  4% water vapor
The densest and lowest part of the atmosphere is called
troposphere (0  11 km).
The next layer (11  50 km) is called stratosphere.
The ozone (O3) layer within the stratosphere absorbs the
solar ultraviolet (UV) radiation, but it is being damaged by
chlorofluorocarbons (CFC, CCl2F2).
Upper Layers
The layer above stratosphere is called mesosphere.
It is located between 50 and 80 km above the sea level.
The uppermost layer is called thermosphere (ionosphere)
and spans from 80 to ~600 km.
The temperature there is high (~2000 K), but the density
is extremely low.
Ionosphere is responsible for absorption of the most
energetic particles from space, reflecting radio waves,
and hosting aurorae.
Water Vapor in the Atmosphere
Water vapor are water molecules that escaped from a body
of water (sea, ocean, lake, etc.).
The amount of water vapor in the air is referred to as
humidity.
Water vapor is continually added to air and removed by
condensation to form clouds, fog, rain, and snow.
The air is saturated when it cannot take more water vapor
(moisture).
The amount of moisture that air can take rises with
temperature.
Clouds
The vapor condenses to a liquid when air is cooled past the
saturation point.
Dew forms due to the ground temperature drop at night.
Fog forms when large areas of cool land or water come in
contact with air.
Clouds form due to air cooling by expansion as it rises.
A normal cooling rate of air is 0.65oC for each 100 m of rise.
There are several cloud types which form at different
altitudes.
Precipitation
Precipitation refers to any type of atmospheric condensate
falling on the surface.
Rain occurs when a cloud is suddenly cooled.
Small water droplets stick to one another forming large
ones (up to ~2 mm in diameter), which are too heavy to
stay within the cloud.
Sleet consists of raindrops frozen on the way to the ground.
Hail is formed by vertical motion of droplets, which freeze
at higher altitude and pick up more water on the way down.
Largest hailstones found: size 5.5 inches, weight 1.5 lbs.
Weather and Insolation
Weather refers to the temperature, humidity, air pressure,
cloudiness, and rain(snow)fall.
The study of weather is called meteorology.
Climate is a summary of weather conditions over long
periods of time.
Insolation (incoming solar radiation) is the solar energy
that arrives at the upper atmosphere.
Part of the insolation is reflected back to space (~30%),
~20% is absorbed in the atmosphere, and ~50% comes to
the surface and becomes heat.
Heating the atmosphere from the ground is called the
greenhouse effect.
Winds
Winds are horizontal movements of air caused by pressure
differences in the atmosphere.
The pressure differences are due to temperature differences.
The higher the differences, the stronger the winds.
This type of air movements is called convection currents.
Another type of air movements are due to the Coriolis effect.
It is due to Earth rotation and makes wind paths curved.
Circulation in the Atmosphere
The air is heated near the equator, rises and flows toward
the poles, where it cools down and returns back as winds.
Due to rotation, the north and south wind are deflected
by the Coriolis effect.
This leads to westward drift in the middle of each
hemisphere and a eastward drift in the tropics.
The westward winds contain zones of high-speed winds
called jet streams (up to 500 km/h).