Chapter 5
- Meteorological
observations can be done in 2 ways:
- Direct
Methods- measure properties of the air that are in contact with the
instrument being used. Ex: Thermometer
- Indirect
Methods- do not come into physical contact, obtain data from afar. Can be both active and passive.
- Direct
Methods measure:
- Temperature-
Mercury Thermometer, Resistance Thermometer
- Humidity-
Dew Point Hygrometer, Psychrometer (measures relative humidity)
- Pressure-
Mercury Barometer, Aneroid Barometer
- Wind-
has both speed and direction. Anemometers
measure wind speed and Wind Vanes measure wind direction. Cup Anemometer, Propellers, and Windsocks
measure wind speed.
- Precipitation-
Rain Gauge
- Radiosondes
are instrument packages carried aloft by a helium-filled “weather balloon”
that measure vertical profiles of air temperature, relative humidity, and
pressure from the ground up to 30 kilometers.
- Rawinsondes
measure wind speed and direction, along with temperature and humidity, by
tracking the position of the balloon
- Indirect
Methods types are:
- Active
sensors- emit energy into the atmosphere and then measure the energy that
returns.
- Passive
sensors- measure radiation emitted by the atmosphere, the Earth’s
surface, or the Sun.
- Reflection
is when rays are turned back in the direction in which they came.
- Refraction
is when transmitted rays change direction due to spatial variations in
properties of the medium.
- Scattering
is when light rays change direction when they encounter small particles,
such as aerosols. --- Causes sunrises and sunsets to look red.
- Cloud
Ceiling is the height of the lowest widespread cloud base.
- Ceilometer
is used to measure cloud ceiling and is an active remote sensing
instrument.
- Weather
Satellites fly around the Earth in two basic orbits:
- GEO-Geostationary
Earth Orbit—orbits the Earth as fast as the Earth spins and hovers over a
single point above the Earth at an altitude of 36,000 kilometers. Must be located over the Equator
- LEO-Low
Earth Orbit—orbit the Earth at an altitude of 850 kilometers. Travels from pole to pole.
- Satellite
instruments measure electromagnetic energy that the Earth and the
atmosphere reflect, scatter, transmit, and emit and the most common
weather satellite images are the visible, infrared, and water vapor.
- Radiometers
are passive remote sensing instruments classified by two types:
- Visible-
measures the amount of visible light from the Sun that is reflected or
scattered back to space by the Earth’s surface or by clouds. Differences in albedo of clouds, land,
water, etc. allow distinguishing of different features.
- Infrared
(IR)- measures the amount of radiation, or heat, emitted by the surface
or clouds. Cold objects appear
white, while hot objects appear black.
The advantage of this is that it gives information during both day
and night.
- Radar
(Radio Detection and Ranging)- actively senses radiowaves scattered by
large water and ice particles and converts them into information about
precipitation.
- Doppler
Radar can measure the location and intensity of precipitation, as well as
the speed of the wind in precipitating regions.
- The
Doppler Effect refers to the change in the frequency of a wave pattern
caused by the relative motion of the wave emitter and the observer of the
wave. (i.e. the pitch becomes higher as the sound approaches you, and then
the pitch goes down as the source of the sound moves away)
- Wind
Profilers are Doppler radars pointed skyward and can determine the wind
speed even when precipitation is not present by measuring the change in
the frequency of the returning radar beam.
Atmospheric Optics
- Light
can be reflected, bent (refracted), scattered, and diffracted, with its
colors being dispersed, which can create optical effects in the sky.
- A
Mirage is an image formed by the refraction of light by layers of air with
different temperatures.
- A Halo
is a whitish ring that encircles but does not touch the Sun or Moon and is
caused by the refraction of light by ice crystals.
- When
sunlight passes through a triangular glass prism, it separates into colors
of the rainbow. This is due to
different colors, defined by their wavelength, refracting at different
amounts with blue and violet refracting the most and red refracting the
least. This separation of colors is
called Dispersion.
- Sundogs
are an optical effect caused by refraction and dispersion where it appears
that shiny, colored regions are on either side of the Sun.
- A
Rainbow is a single, bright, colored arc, which is a result of reflection,
refraction, and dispersion of light in raindrops.
- Diffraction
occurs when light is bent around small objects.