Air Pressure, Clouds and
Weather
Laura Schofield, Ipswich Public Schools
Tina Ciarametaro, Ipswich Public Schools
University of MA, Amherst STEMS
Jan. 26, 2013
Today’s Driving Questions:
1) What are basis characteristics of the atmosphere?
2) What is the horizontal and vertical movement of air in a “High” and
“Low?”
3) How do clouds form and what can they tell us?
4) How are temperature, pressure and clouds related?
5) Applying concepts to real-time data
Today’s Schedule
1) Highs and Lows (PowerPoint & Application)
Short Break
2) Clouds (PowerPoint & Application)
Short Break
3) WeatherCycler (Application)
Short Break
4) Real Time Data (Application and Resources
Earth’s Atmosphere
• Ocean of air **3-dimensional
• We live on the bottom of this
“ocean”
• Air moves horizontally and
vertically
Air Mass
Body of air that
covers thousands of
kilometers2
Horizontally
homogenous in
temperature and
humidity
Characteristics
determined by type of
surface over which
the air mass resides
or travels
Air Mass
Tropical: “warm”
Polar: “cold”
and
Continental: “dry”
Maritime: “humid”
Continental tropical (cT)
Maritime tropical (mT)
Maritime polar (mP)
Continental polar (cP)
Arctic (A)
Weather vs. Climate
State of atmosphere at a
specific time and place,
variables include:
• Temperature
• Humidity
• Cloudiness
• Precipitation
• Wind (speed & direction)
• Weather, of a given location,
averaged over a period of
time
• Includes extremes in weather
behavior observed during the
same time period
• How the weather behaves
over relatively long periods of
time
“Weather tells you what to wear on any given day;
climate tells you what wardrobe to have.”
H = “highs” or high pressure system
L = “lows” or low pressure system
Highs vs. Lows
High or “H,” symbol on a weather map, the center
of a high pressure system - where air pressure is
relatively high compared to the *air pressure in
surrounding area
Low or “L” signifies the center of low pressure
system - where *air pressure is relatively low
compared to surrounding air
*air pressure is calibrated to sea level measurements
Air Pressure
Weight of a column of air above
a per unit area
Highs are associated with fair weather
Lows are associated with stormy weather
Horizontal Movement at surface in
Highs (anticyclone)
• Air near the center of Highs
flows outward toward lower
pressure.
• Earth’s rotation makes this
air spiral outward
• In the northern hemisphere
and as seen from above this
air moves outward and
clockwise
Anticyclones
Anticyclones
Anticyclones
Anticyclones
Anticyclones
Anticyclones
Anticyclones
Anticyclones
Vertical Movement in a High
• Air sinks from above
with Highs and replaces
outward spiraling air
• Sinking air in Highs
warms due to
compression
• Clouds, if present,
vaporize and skies tend
to clear
Horizontal movement of air at surface in Lows
(cyclone)
• Air flows toward the center
of a low
• Earth’s rotation makes this
air spiral inward
• In the northern hemisphere
and as seen from above this
air moves inward and
counter clockwise
Cyclones
Cyclones
Cyclones
Cyclones
Cyclones
Cyclones
Cyclones
Cyclones
Vertical Movement in a Low
• Air spiraling into low
produces an upward
motion
• Rising air expands and
cools
• Clouds form and
precipitation can
develop
Activity: Highs and Lows
Modeling vertical and horizontal air movements using your hands.
Clouds are Evidence
of motion & conditions of the air in which they exist
Cloud Appreciation Society
Clouds are:
• Is a visible suspension of
minute water droplets
and/or ice crystals in
the atmosphere above
Earth’s surface
• Fog is a cloud in contact
with Earth’s surface
• Clouds form as a result
of condensation or
deposition of water
vapor in ascending air
Global Water Cycle
The end circulation of a fixed amount of water among Earth’s
ocean, atmosphere and terrestrial reservoirs.
Movement of
between Earth’s
surface and the atmosphere
• Evaporation – Process of liquid water molecules absorbing
heat energy and changing to water vapor
• Condensation – Process of water vapor releasing heat energy
to the atmosphere and changing to liquid water
• Transpiration – Process by which water is taken up by roots of
plants and released as water vapor through tiny leaf pores
• Sublimation – Process of ice absorbing heat energy and
changing directly to water vapor
• Deposition - Process of water vapor releasing heat energy to
atmosphere and changing directly to ice
• Precipitation – when water, in liquid or solid form falls from
clouds
Water Vapor in the atmosphere
• All air contains water vapor, although the amount can
vary greatly
• Amount of water vapor air can hold has a limit which is
dictated by air temperature
• Warmer air can “hold” more water vapor than cold air
Saturation – air can’t “hold” any more water vapor
Unsaturated air can become saturated by
a) More water vapor evaporating or
b) Cooling the air temperature****
Most clouds are made by the cooling
of air, as air moves upward
• Boundary between
two air masses of
different densities
Also called an air
front
• Fronts are mapped
where the
boundary touches
Earth’s surface
Fronts
Stationary front
Fronts
Warm front
Fronts
Cold front
Most clouds are made when air cools
as it moves upward
• Air Front
• Moving up the
slopes of a
mountain or hill
• Air near ground
heats up causing
less dense air to
rise
• Where surface
winds converge (L)
or Low
Clouds Sky watcher Chart
Strong vertical
motions, updrafts
Long, flat clouds indicate more
horizontal air motion
Shapes, numbers, sizes and motion of clouds gives us
clues to what the invisible air is doing.
Activity: Clouds, Air Pressure and
Temperature
How to make a cloud appear and disappear?
Putting it all together
Current Weather Studies 1A
General info about isobars:
An isobar is a line passing through locations having the
same air pressure
By U.S. conventions, isobars are drawn at 4-mb
intervals (e.g., 996 mb, 1000 mb, 1004 mb)
In Europe the convention is to use 5-mb intervals
CWS 1A - Drawing Isobars
A) Draw an isobar so that air pressure readings greater than the isobar’s
value are always on one side of the isobar and lower values are on the
other side
B) Assume a uniform pressure change between neighboring stations. E.g.
a 1012-mb isobar would be drawn between 1010 and 1013 about
2/3s the way to 1010.
C) Adjacent isobars tend to have similar shapes. Isobars will generally
align with the curves of its neighboring isobars because the horizontal
changes in air pressure from place to place are usually gradual
D) Draw isobar until it reaches boundary of map or “closes” to form a
loop
E) Isobars never stop or end within a data field, they never fork, or cross
one another
F) Isobars CANNOT be skipped if their values fall within the range of air
pressures reported on the map
CWS 1B – Air Pressure & Wind Direction
• Wind direction is identified by the direction
from which it is coming…
”I want to know where my air is coming
from…down from the arctic or from the south.”
• Air moves from higher pressure area to lower
pressure area
Real Time Data Resources
• AMS Datastreme Atmosphere
– Unanalyzed (“Pressures”) with the analyzed (“Isobars &
Pressures”) surface pressure maps
– Weather maps and maps showing water vapor
• Blue Hill Observatory in Milton, MA
• National Weather Service www.weather.gov
Supplies and other resources
•
•
•
Thermometers, American Meteorological Society
The WeatherCycler, The Weather School
Textbook, Weather Studies by Joseph M. Moran
• Improve teachers’ competence and confidence
• Provide materials that are standards-based and
scientifically accurate
o Transformed by teachers into discipline- and
age-appropriate lessons
• Offer FREE graduate credits (SUNY Brockport)
• Create a structure for peer-training
• Training impacts felt in schools and communities
• Create pathway for continued communication
between trained teachers, scientists, and
mentors
Project Atmosphere
Maury Project
DataStreme Atmosphere
DataStreme Ocean
DataStreme Earth’s Climate System (ECS)
AMS DataStreme Atmosphere