Course: Introduction to Atmospheric sciencesATOC210 by GyuWon LEE

1
General introduction
Objective - Conceptual understanding of weather
and climate systems and their evolution.
Expectation - Ability to understand
the general features of weather from
meteorological information (measurements, model
outputs, forecasts) - Ability to
realize the impacts of the weather and to utilize
the weather information for your daily life.
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
2
Winds
Wind direction and speed NW 20 kts (10m/s)
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
3
Winds
Pressure gradient force Coriolis
force Centripetal force Frictional
force Gravitational force
Geostrophic winds straight-line flow aloft
Surface winds
Hydrostatic balance (equilibrium)
Gradient winds Curved winds around lows and
highs aloft
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
4
Winds
Constant pressure chart (upper level map)
Constant height chart (Sea-level or surface map)
Solid line contour lines Dashed line isotherm
Solid line isobars
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
5
Winds
Sea and land breeze
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
6
Models three-cell model
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
7
Mean distributions of winds and pressure January
vs. July
January (Winter)
July (Summer)
- Summer and winter monsoon (thermal
lows/highs) - The zone of maximum surface heating
shifts seasonally the pressure systems, wind
belts, and ITCZ shift toward the north in July.
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
8
Precipitation patterns
Temporal and spatial variation
From NASA
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
9
Jet streams
1. Strong temperature gradient 2. Conservation of
angular momentum
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
10
Types of stability
Causes of instability 1) cooling of the air
aloft - winds brings in colder air (cold
advection) - clouds (or the air) emitting
infrared radiation to space (radiational
cooling) 2) warming of the surface air
- daytime solar heating of the surface. - an
influx of warm air brought in by the wind
(warm advection) - air moving over a warm
surface. 3) mixing or lifting of a layer of
air.
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
11
Air stability vs. cloud development
Vertical extension of clouds
Animation
(Ref) Dew point temperature decreases 2
C/1000m. When the air saturates and condensation
continues to occur, the dew point temperature
decreases at the moist adiabatic rate.
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
12
Air stability vs. cloud development
Orographic uplift, cloud development, and the
formation of a rain shadow
Rocky Mountains
moist pacific flow
Chinook (Foehn) winds
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
13
Types of air masses
Air masses of North America
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
14
Types of fronts
Identification of fronts
1. Sharp temperature changes 2. Change in the
airs moisture 3. Shifts in wind direction 4.
Pressure and pressure change 5. Clouds and
precipitation patterns
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
15
Consequence cloud and precipitation patterns
Cold front
- Showers with gusty winds are prevalent when the
warmer air is moist and unstable - Anvil with Ci,
Cs - Squall line ahead of a fast moving front -
Move faster (15 25knots) and are steeply sloped
( 1 50)
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
16
Consequence cloud and precipitation patterns
Warm front

• - Wide spread rain ahead of the sfc front
  (overrunning)
• - Ci, Cs, As, Ns - The wind veers with
  altitude
• Frontal inversion in the region of the upper
  level front
• - Move slower (10knots) and are gently sloped (
  1 200)

Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
17
Where do mid-latitude cyclones tend to form?
Cyclogenesis
lee cyclogenesis
northeasters
Over warm ocean
Anticyclones during winter
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
18
Developing mid-latitude cyclone
1. Upper level support 2. Jet stream
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
19
Steps in weather forecasts
Surface stations, ships, aircrafts, sounding,
satellites, weather radars
Data acquisition
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
20
Forecasting methods

• Numerical weather prediction by solving
  mathematical equations that approximates the most
  important aspects of the atmosphere
• Persistence forecast the future weather will be
  the same as present weather
• (example snow today, snow tomorrow)
• Steady-state, or trend method surface weather
  systems tend to move in the same direction and at
  approximately the same speed as they have been
  moving.
• Analogue method existing features on a weather
  chart (or a series of charts) may strongly
  resemble features that produced certain weather
  conditions sometimes in the past.
• Probability forecast (precipitation) a
  numerical estimate that any point in your
  forecast area will get measurable precipitation
  during the forecast period.
• Ensemble forecast A forecasting technique that
  entails running several forecast models (or
  different versions of a single model), each
  beginning with slightly different weather
  information. The forecaster's level of confidence
  is based on how well the models agree (or
  disagree) at the end of some specified time.
• (ex the less agreement among the progs, the less
  predictable the weather)

Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
21
Limits of numerical weather forecasts
The Butterfly Effect sensitivity to initial
conditions
Chaos theory
The initial conditions were 0.506127, and 0.506
(truncated).
The flapping of a single butterfly's wing today
produces a tiny change in the state of the
atmosphere. Over a period of time, what the
atmosphere actually does diverges from what it
would have done. So, in a month's time, a tornado
that would have devastated the Indonesian coast
doesn't happen. Or maybe one that wasn't going to
happen, does. (Ian Stewart, Does God Play Dice?
The Mathematics of Chaos, pg. 141)
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
22
Types of thunderstorms
Life cycle of an ordinary thunderstorms (air-mass
tstm)
Cumulus stage
Growing cumulus, No precipitation, no lightning,
thunder Updraft only
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
23
Outcomes
Flash flood floods that rises rapidly with
little or no advance warning
Lightning a discharge of electricity which
occurs in thunderstorms Thunder sound due to
rapidly expanding gases along the channel of a
lightning discharge.
Tornado - a rapidly rotating column of air that
blows around a small area of intense low
pressure with a circulation that reaches the
ground. - counterclockwise or clockwise
(rare) rotation
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
24
How hurricanes form?
Conditions 1) light winds 2) a deep layer of
high humidity (extending up through the
troposphere) 3) Over tropical oceans with
surface temperature greater than 26.5 C over a
vast area (no friction) 4) The Coriolis force
must not be too small (5 to 20 degree
latitude) 5) Trigger
Convergence on the eastern side of a tropical
wave along the ITCZ
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
25
Structure of hurricanes
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
26
Hurricanes vs. mid-latitude cyclones
Hurricanes Energy from latent heat Warm core
cyclone, weakens with height Central clear eye,
sinking air Strongest winds at surface Circular
isobars, stronger pressure gradients, no fronts
Mid-Latitude Storms Energy from temperature
contrast Cold core low, strengthens with height
Centres of rising cloudy air Winds strongest
aloft Isobars have kinks, weaker pressure
gradients, fronts
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
27
ENSO El Nino/Southern Oscillation
La Nina
A condition in the tropical Pacific whereby the
reversal of surface air pressure at opposite ends
of the Pacific Ocean induces westerly winds, a
strengthening of the equatorial countercurrent,
and extensive ocean warming.
El Nino
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
28
Climate change Past (and future?)
- Through much of earths history the global
average temperature was probably 8 C - 15C
warmer than now and ice-free. - Warm periods
interrupted by periods of glaciation about 700
mya (million years ago), 300 mya, and 2 mya
(Pleistocene, or Ice Age). - Within the Ice Age,
there are interglacial periods (warmer periods)
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
29
Climate change driving factors
- There is no single cause that can explain all
of the changes. - The climate system is very
complicated with many interactions and feedbacks,
some positive and some negative. - A positive
feedback will tend to amplify small changes in
the system whereas a negative feedback will tend
to diminish small changes.

• Water vapour temperature rise feedback
  (positive)
• Small increase in temperature ?
• Increased evaporation from oceans ?
• Increased concentration of water vapour (a
  greenhouse gas) in atmosphere ?
• Increased surface temperature

Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
30
Climate change driving factors
Snow albedo feedback (positive) Small increase
in temperature ? Decrease in snow cover
? Decrease in albedo ? Increase in surface
temperature
Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE
31

• Movie Time
• An example of weather forecasting on 28 Sept 05
• (The weather network)
• How much can you understand contents
  conceptually?
• Can you make your own forecast with given
  information?

Course Introduction to Atmospheric
sciences(ATOC210) by GyuWon LEE