Download Introduction to meteorology

INTRODUCTION TO
METEOROLOGY
UNDERSTANDING THE BASICS
HOW TO THINK LIKE A METEOROLOGIST:
• The atmosphere is a fluid, we see everything as a fluid (with changing density)
• The atmosphere is made up of a mix of different gases, particles and aerosols
• The atmosphere is only kept by Earth as an “envelope” due to the Earth’s gravitational pull
BASIC ASTRONOMY – WHAT CAUSES CHANGES IN
ENERGY?
•
For the majority of the Earth’s surface, energy varies on daily (diurnal) and seasonal (annual) timescales (and this is
dependent on the Earth’s orbit)
•
Solar activity such as sunspots and solar wind (solar wind increases in magnitude at times of high sunspot activity)
•
Energy received at different points on the Earth is not consistent. As we move from the equator to the poles, the quantity of
energy decreases due to 1. the distance it has to travel because of the earth’s curvature and 2. the amount of atmosphere is
has to travel through. Because of this, more energy is lost.
•
Axis on which the Earth rotates is tilted at an angle (thought to have happened when moon
was formed, when something large hit the Earth). During Summer, we are tilted towards the
sun, and during Winter we are tilted away. Without this tilt, it would be perpetually the
same temperature in one spot all year round. Also, the precession of the Earth’s axis makes
a difference. Like a spinning top, the Earth is slowing, and as it does, the axis traces a cone shape.
This tilt angle varies between 22 and 25 degrees.
•
In addition, the Earth’s orbit around the sun is elliptical. This changes over 100s of 1000s of years.
•
Orbital eccentricity - As the Earth is additionally effected by other planets’ gravitation pulls, the
Earth also moves on a saw-tooth type movement around the sun. When there is an alignment of
planets (extremely rare), this can cause very high tides.
•
Milankovitch cycles/orbital forcing account for up to 60% of the variation of energy on the Earth.
•
Bathymetry – gravitational pull of the moon, even though it doesn’t cause a difference in solar energy, it
creates kinetic energy under the ocean.
•
All these processes are irrelevant to humans and would happen anyway. Combinations of these cycles overlapping may cause
a glaciation/an interglacial
COMPOSITION OF THE ATMOSPHERE
GAS
PERCENT*
Nitrogen
78.08
Oxygen
20.95
Argon
0.93
Neon
0.0018
Helium
0.0005
Hydrogen
0.00006
Xenon
0.000009
* = Percent by volume dry air
** = Percent by volume
GAS & PARTICLES PERCENT**
ppm
Water vapour
0 to 4
Carbon dioxide
0.036
365
Methane
0.00017
1.7
Nitrous oxide
0.00003
0.3
Ozone
0.000004
0.04
Particles
0.000001 0.01-0.15
Chloroflourocarbons 0.00000002
0.0002
• Carbon dioxide on the rise
From Ahrens C. D, 2000
ATMOSPHERIC LAYERS
• Troposphere – closest to the Earth. Between 22-23km. Contains 75% of
atmosphere’s ‘molecular and gaseous’ mass. Wider at equator than
poles. Temperature and pressure drop as you go higher up (as we climb,
fewer air molecules above us because of gravity holding molecules to
the surface. Temperature drops because you need more moving
particles to generate heat). Atmospheric turbulence and weather
conditions mostly occur here.
• Stratosphere – Around 28km (ends 50km from Earth). Upper portion
taken up by the ozone layer, which reacts with solar rays and creates
more heat). Volcanic eruptions also eject material (such as dust and
sulphur dioxide) high into the stratosphere.
• Mesosphere – (ends 100km from Earth). Decrease in temperature
again. Pressure is very low here. Thick, and slows down meteors which
have entered the atmosphere and they turn up.
• Thermosphere – (ends 400km from Earth) Extremely hot – few
molecules which exist in this layer gain lots of energy from the sun.
(Atmospheric density is extremely low) If we could feel it however, it is
unlikely these few particles would hit us and it would therefore feel very
cold. Gases in this layer are stratified. (within the Ionosphere)
• And after leaving the thermosphere, you reach the exosphere where
you are receiving direct sunlight and it would be extremely hot.
ATMOSPHERIC PAUSES (AND
WHAT HAPPENS AT EACH ONE)
• Maximum changes appear at these pauses between the different
sections.
• Tropopause – Considered to be a “thermal layer” or “cold trap” as
water vapour cannot rise past this point without becoming ice and
freezing and trapping itself. If the Earth didn’t have this, the Earth
would have no water. (Equatorial tropopause contains the coldest
temperature)
• Stratopause - Temperature decreases with increasing altitude.
• Mesopause – Temperature stops decreasing with increasing altitude.
However, at this point the atmosphere is at it’s lowest temperature.
• Thermopause – The atmospheric boundary of the Earth. Due to the
increased presence of heavier gases below this, it is an insulator. Exact
altitude of this pause varies due to different factors.
IMPORTANT EQUATIONS
• DENSITY = MASS/VOLUME
• Density tells us how much matter is in a given space or volume
• PRESSURE = FORCE/AREA
• Each time an air molecule bounces against an object it gives it a minuscule push. This tiny pushing force,
divided by the area on which it pushes is called pressure.
• Hectopascals (hPa)
GLOSSARY
• Coronal Mass Ejection (CME) – huge cloud of plasma and the magnetic field ejected from the sun,
which, when directed at the Earth, can cause Geomagnetic storms.
• Geomagnetic storm – Described as a large disturbance in the Earth’s magnetosphere
• Van Allen belts – Belts of radiation which is full of highly charged electrons and protons, protecting
Earth from heavy solar activity and radiation. It is thought that the belts were made by solar winds and
particles from cosmic rays, but both of the (surviving) Van Allen belts were made by different processes
(as there is an outer and an inner one). The inner one consists of more protons, and the outer one more
electrons.
• Hectopascals (hPa) – How we measure and discuss air pressure (previously called millibars mb, same
measurement – everyone uses this except America)