Transcript Atmospheric Measurements - University of Wisconsin–Madison

Atmospheric Measurements
Nick Bassill
January 28th 2009
What types of atmospheric
variables are measured?
What types of atmospheric
variables are measured?
Some examples:
• Temperature
• Moisture content (often in terms of relative humidity or dewpoint)
• Atmospheric pressure
• Wind (both speed and direction)
• Visibility
• Cloud cover
• Types of weather (rain, snow, fog, etc.)
Measuring Temperature
•
•
Measuring instrument: the thermometer
Commonly measured in units of Fahrenheit
(F) or Celsius (C)
• For ˚F, 32˚ represents the freezing point,
while 212˚ is the boiling point
• For ˚C, 0˚ represents the freezing point and
100˚ represents the boiling point
• For converting between the two,
• ˚C=˚F*5/9-32˚, or ˚F=˚C*9/5+32˚
• Records (http://en.wikipedia.org/wiki/Temperature):
Lowest temperature recorded on Earth: -128.2˚F
Highest temperature recorded on Earth: 136.4˚F
http://en.wikipedia.org/wiki/File:Galileo_Thermometer_closeup.jpg
Measuring Moisture
• Measuring instrument: the hygrometer
• Often given by the “dewpoint” or the “relative humidity”
• Relative humidity is defined as the ratio of the amount
of water vapor currently in the atmosphere to the
maximum amount possible (this is most often given as
a percentage)
• The dewpoint is the temperature at which the
atmosphere would achieve 100% relative humidity
• When the atmosphere is warmer, it can hold more
water vapor
Measuring Atmospheric Pressure
• Measuring instrument: the barometer
• Commonly given in inches of mercury, hectoPascals
(hPa or mb)
• Stations above sea level normally report lower
pressures than those at sea level (due to their height)
• Therefore, normally pressures are converted to “sealevel” pressures, to make comparisons from location to
location easier
• Conventionally, “low” pressures are associated with
active weather, while “high” pressures are associated
with sunny weather
The Stevenson Screen
• The Stevenson screen is
a commonly used
enclosure for these
measuring devices
• It is a box with slits in the
side to allow for air
movement
• It is frequently situated
roughly 6 feet (2 meters)
above the ground
http://en.wikipedia.org/wiki/S
tevenson_screen
Measuring the Wind
• Measuring instrument: the
anemometer
• Wind has both velocity (speed)
and direction components
• Wind speeds is often recorded in
miles/hours (mph) or
meters/second
• Aside from compass directions,
wind direction can be measured
in degrees (where 0˚ is North, 90˚
is East, etc.)
http://en.wikipedia.org/wiki/File:Prop
_vane_anemometer.jpg
Measurements Above The Surface
• In order to measure these
quantities above the Earth’s
surface, a “radiosonde” is used
• These weather balloons are
conventionally released twice a
day in the United States
• These observations help us
understand what is occurring in
the atmosphere
http://personalpages.manchest
er.ac.uk/staff/geraint.Vaughan/
UFAM/radiosonde_launch.jpg
Station Models
These display virtually all the relevant current weather observations for a given
weather station
http://weather.cod.edu/notes/stnmodel.html
Meanings
Wind Speeds
An Example
From
Tuesday
Morning:
http://www.ral.ucar.e
du/weather/surface/
Observations about Observations
• Conventionally, only temperature, dewpoint,
wind speed and direction, cloud cover, pressure,
current weather, and visibility (if less than 10
miles) are shown
• However, much of the planet goes unobserved
• Large differences in temperature, dewpoint, etc.
can exist from location to location
• This is why we must do contour analysis in order
to “fill in” the missing data