Transcript Lecture 5 - University of California, Irvine

Lecture 6
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Observational network
Direct measurements (in situ= in place)
Indirect measurements, remote sensing
Application of satellite observations to
study the tropical atmosphere
ASOS (automated surface observing
system)
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Cloud height
Visibility
Precipitation
Pressure
Temperature
Dew point
Wind direction and speed
Rainfall accumulation
The station model for weather obs.
Observations, data assimilation
• The “point” observations are fed into a
comprehensive numerical weather
prediction model that “adjusts” the
observations to correct for errors, fill in
gaps etc to produce gridded fields that are
dynamically consistent.
• Analysis products are observations that
have been “fed” through a model to check
for errors, adjust for consistency etc
Direct measurements of upper-air
variables
• Radiosondes are instrument packages
carried aloft by helium filled balloons
• measure vertical profiles of temperature,
humidity, pressure. Velocity may be
inferred by tracking; in that case called
rawinsonde
• Rawinsonde measurements are made at
weather stations worldwide, at least twice
per day
Reflection -- Refraction
Index of refraction:
Speed of light in
Vacuum divided
by speed of light
in substance
Scattering
• Radiation can be absorbed, reflected or
transmitted. Also, scattered = when light
changes direction after interacting with a
particle.
• Rayleigh scattering: when the particles
are small compared to the wavelength
(e.g., molecules)
• Geometric (Mie) scattering: when
particles are large (e.g., drops).
Scattering (cont’ued)
• Rayleigh scattering: same amount of
energy scattered both forward and
backward
• Geometric scattering: more energy
scattered forward
Indirect methods of observing the
atmosphere
• Passive sensors: measure radiation
emitted by the Earth System or by the sun
• Active sensors emit radiation into the
atmosphere and then measure the
returning radiation.
• How does radiation interact with the
atmosphere. Reflection/refraction
Note the atm window, the visible channel (both “see” the surface), water vapor
channel measures total column water vapor (sees the atm higher up)
Multiple scattering
Repeated scattering of light. Causes
whitish light because light of all colors is
scattered toward the eye.
Both high and low clouds in sunshine look
white due to scattering.
Bottom appears
grey– little light
Top appears
white
because of
scattering
Multiple scattering and climate change
Human activities have lead to increased
amount of aerosols. Lead to different
clouds (smaller and more numerous
droplets) increased scattering. Also,
increased concentration of aerosols
increases scattering.
• Cooling effect
• It may be hiding some of the warming due
increased greenhouse gases
Satellite observations – GEO, LEO
Geostationary Earth Orbit
Low Earth Orbit
Satellite observations
• GEO: GOES E & W series of satellites.
Always above the same point over the
equator. Continuous view of the tropics
and midlatitudes. High latitudes not seen.
• LEO flies from pole to pole. Flies over
tropics and midlatitudes twice per day.
Passive measurements (radiometers)
• Visible channel, near 0.6 micron
• IR channel, in atm window 10-12 micron
• Water vapor channel (6.5—6.9)
Visible detects albedo (of surface or cloud)
IR detects emission temperature of object
radiating (either surface or cloud top)
Wvc detects the total column of H2O (g).
Visible image
Infrared image
Visible/IR satellite images of clouds
Water vapor channel
Upper to
middle
troposphere
Other satellite measurements (active)
• Surface vector wind (scatterometer),
example: QuikScat
• Atmospheric composition, Aura
• Surface characteristic of land, Terra
• Ocean properties, Aqua
• Rainfall, TRMM
Satellites are the primary means of global-scale obs, grouped by orbit
The global satellite observation system: geostationary (35800 km), polar orbiting
(850 km), R&D (orbit between certain latitudes at a few 100 km)
Satellite based precipitation radar: Tropical Rainfall Measurement Mission
(TRMM) launched in 1997. With a 250 km swath it can only observe each
location once or twice per day.
Provides precip measurements where most of it falls (tropics). GEWEX
IR water vapor from GOES
Visible
Combine measurements from many satellites
POES soundings
(each color a
different satellite)
Water vapor and
cloud track
winds
Vertical structure
(soundings)
Satellite derived mid-upper level wind (track water vapor features in upper
troposphere and cloud elements in lower troposphere). Limitation: height determ
Low level wind
Soundings from GPS radio occultation
Observing tropical clouds and rain
• The A train consists of a number of satellites that follow
each other in succession so that they are approximately
viewing the same scene at the same time
• Polar orbiters
• CloudSat is the first mm wavelength cloud radar in space
– more than 1000 time more sensitive than weather radars
– Collects data about the vertical structure of clouds, including
liquid water and ice and how clouds affect solar & terrestrial
radiation
• Particle concentrations, cloud liquid water, precip rate
CloudSat, CALIPSO, Aqua pass almost at the same time
3D
structure
CloudSat profile
GOES image
TS Ernesto
Aqua IR image
CloudSat
profile
(reflectivity)
Vertical structure of
hurricanes from
CloudSat. 3D
structure by
combining with OLR
(Gordon)
With the radar can
distinguish
between cirrus
and deep
convection
Scatterometry from space: surface wind (2D)
QuikScat has proven incredibly useful for tropical meteorology as well as for
oceanography
Satellite images of the shallow
ITCZ (20 Sept 2000)
VS
IR