1. Introduction to weather and climate:
The Atmosphere is a mixture of gas molecules, microscopically small suspended particles
of solid and liquid, and falling precipitation.
The Meteorology is the study of atmosphere and the processes (such as cloud formation,
lighting and wind movement) that cause what we refer to as the “weather”.
Weather is distinct from climate in that the former deals with short-term phenomena and
the latter with long-term patterns. Climate is what you expect but weather is what you
Climatologist and meteorologist study the same thing but in different scale. Climatologist
wants to know the variability of the weather elements: the average temperature of the
month, the highest rainfall… frequencies of occurrence of weather events- such as hailing
or lighting- are the aspect of climates.
2. The Atmosphere:
a. Thickness of the atmosphere:
Most of the atmosphere is contained within a relatively shallow envelope
surrounding the oceans and continents. Because of the shallowness of the
atmosphere, its motions over large areas are primary horizontally. However, the
vertical motions also determine the atmospheric behavior.
b. Composition of the atmosphere:
Molecules in the atmosphere can be exchanged with the Earth’s surface
through physical processes (volcanic eruptions) or biological processes (plant and
animal respiration). Molecules can also be destroyed or produced by internal
processes (chemical reactions between gases).
The concentration of the gas exists in a steady rate: the gas concentration
of the input rate (from the earth to the atmosphere)= the output rate.
Residence time:--- the time that the gas molecules stay in the
atmosphere before being removed.
---- = mass of the substance ( kg)/ the rate at which the
substance enters and exits the atmosphere (kg/year) Atmospheric gases:
----- Permanent gases:
form a constant proportion of the atmospheric mass
account for 99.999% of the atmosphere
occur nearly constant proportion throughout the atmospheres
lowest 80km, which is the homosphere.
The homosphere contains mostly nitrogen (in N form). and
oxygen, with small amount of the insert gases, such as neon,
argon. The process of add and removing N is very slowly so
it has a very long residence time- 42 million years.2N has
really little effect on most meteorological or climatological
Second most dominant gas, oxygen (O ), in form of paired
atom, called diatomic oxygen. The residence time is
extremely long as well.
------ Variable gases:
gases whose distribution in the atmosphere varies in both time
Above the homosphere is the heterosphere, where lighter
gases( hydrogen, helium) become increasingly dominant with
Heterosphere contains no truly permanent gases.
Water vapor’s concentration decreases rapidly with altitude
and most atmospheric water vapor is found in the lowest 5km
of the atmosphere. Water is constantly being cycled between
the planet and the atmosphere in what is called the
hydrologic cycle. Water vapor has a short residence time- 10
days. Water vapor is not in form of liquid (rainfall) so it’s
similar to 2 or O2but it is different in term of its easiness to
change into liquid or solid forms both at Earth’s surface and
in the atmosphere.
Carbon dioxide-CO , 2s supplied to the atmosphere through
plant and animal respiration, the decay of organic material, volcanic eruption and natural anthropogenic (human-
produced) combustion. CO is 2emoved from the atmosphere
through photosynthesis, has residence time of about 150
CO 2ike water vapor, effectively absorbs radiation emitted by
CO 2s greatest amount in the early spring and lowest in late
Ozone :is the part of the upper atmosphere called the
stratosphere is vital to life on Earth because it absorbs the UV
rays from the Sun.
Methane: CH has4been increasing, due to rice cultivation,
biomass burning and fossil fuel extraction; residence time of
10 years and is an extremely effective absorber of thermal
radiation emitted by Earth’s surface( >> CH leads4to
Aerosols: small solid particles and liquid droplets( not cloud
droplets and precipitation), life span of few days or several
weeks; affects: urban smog( dust storm), cloud droplets.
c. Vertical structure of the atmosphere:
> Is the amount of mass of the substance(kg) contained in a unit of
volume(m ) 3
> One characteristic of gas is that no limit to the amount of mass
that can fill in a given volume.
> Density decreases as altitude increases.-> the greatest density
is at the lower level
> Mean free path: one way to think about density is in term of the
average distance a molecule travels before colliding with another.
- the lowest of the four temperature layers
- temperature decreases with height
- contains 80% of the atmosphere’s mass
- The depth of the troposphere varies depend on the average