RADIOSONDES and TOTAL PRECIPITABLE WATER VAPOR

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RADIOSONDES and TOTAL PRECIPITABLE WATER VAPOR
VAISALA RS80 RADIOSONDE Intercomparison with
the AERI FTIR SPECTROMETER and sunphotometers.
A radiosonde is an instrument package carried by
a balloon that ascends to altitudes of 20 to 30
kilometers. It measures temperature, humidity,
and pressure in the atmosphere and broadcasts the
information back to a ground station. The Global
Positioning System is used to record the
trajectory during ascent to determine wind speed
and direction.
From http//www.aero.org/publications/crosslink/su
mmer2000/02.html
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Launch that Balloon
ALSO . http//www.youtube.com/watch?vB2Q07yBN
7PQ
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RS 80 RADIOSONDE
From http//nsidc.org/data/docs/daac/radiosondes_i
nstrument.gd.html
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Capacitance
Diagram of a parallel-plate capacitor
Dielectric material
The capacitor's capacitance (C) is a measure of
the amount of charge (Q) stored on each plate for
a given potential difference or voltage (V) which
appears between the plates
http//en.wikipedia.org/wiki/Capacitor
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Capacitors
Applications Energy storage, power
conditioning, filtering, decoupling, noise
filters, snubbers, signal processing, sensing,
pulsed power weapons.
http//en.wikipedia.org/wiki/Capacitor
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Capacitors as Sensors
Most capacitors are designed to maintain a fixed
physical structure. However, various factors can
change the structure of the capacitor the
resulting change in capacitance can be used to
sense those factors. Changing the dielectric
the effects of varying the physical and/or
electrical characteristics of the dielectric can
also be of use. Capacitors with an exposed and
porous dielectric can be used to measure humidity
in air. Changing the distance between the
plates Capacitors are used to accurately measure
the fuel level in airplanes. Capacitors with a
flexible plate can be used to measure strain or
pressure. Capacitors are used as the sensor in
condenser microphones, where one plate is moved
by air pressure, relative to the fixed position
of the other plate. Some accelerometers use MEMS
capacitors etched on a chip to measure the
magnitude and direction of the acceleration
vector. They are used to detect changes in
acceleration, eg. as tilt sensors or to detect
free fall, as sensors triggering airbag
deployment, and in many other applications. Some
fingerprint sensors use capacitors. Additionally,
a user can adjust the pitch of a theremin musical
instrument by moving his hand since this changes
the effective capacitance between the user's hand
and the antenna. Changing the effective area of
the plates capacitive touch switches
http//en.wikipedia.org/wiki/Capacitor
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RS 80 RADIOSONDE
Pressure Sensor (BAROCAP) (incorporated in the
Vaisala RS 80 Radiosondes) Type Capacitive
Aneroid Measuring Range 1060 hPa (mb) to 3 hPa
(mb) Resolution 0.1 hPa Accuracy 0.5 hPa
repeated calibration method, standard deviation
of differences The pressure sensor is a small
aneroid capsule with capacitive transducer plates
inside. The external diameter of the capsule is
35.5 mm and the weight of the complete assembly
only 5 g.
Pressure sensor (BAROCAP) Transducer plates are
supported by membranes made of special steel
alloy. The supporting rods of the plates are
fixed to the membranes with hermetic
glass-to-metal seals. The inverted construction
is used to obtain maximum sensitivity at low
pressure....The transducer electronics senses the
capacitance between the plates only, with no
influence of stray capacitances between the
transducer plates and the membranes, which are
grounded.
From http//nsidc.org/data/docs/daac/radiosondes_i
nstrument.gd.html
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RS 80 RADIOSONDE
Temperature Sensor (THERMOCAP) Sensor type
Capacitive bead Measuring range 60 degrees C to
-90 degrees C Resolution 0.1 degree C Accuracy
/- 0.2 degrees C Lag less than 2.5 s (6m/s flow
at 1000 hPa) The temperature sensor is based on
dielectric ceramic materials, the temperature
dependence of which can be accurately controlled
with selection of materials and processing
parameters. Metal electrodes are formed on both
sides of a tiny ceramic chip (0.5 X 0.5 mm,
thickness 0.2 mm). The capacitance between the
electrodes is a function of temperature. To
ensure complete moisture protection the sensor is
hermetically sealed in a small glass capsule (2.5
X diameter 1.5 mm) with two connecting leads
(diameter 0.4 mm). To avoid uncontrolled stray
capacitances which could be caused, for instance,
by water droplets on the glass capsule, an
electrically grounded thin film aluminum coating
is deposited on the sensor capsule and leads.
This coating also has excellent radiation
properties for minimizing the radiation error
(max 2 degrees C at 10 mb and 45 degrees solar
elevation) of the observation. An insulation
layer on the leads prevents short circuits.
From http//nsidc.org/data/docs/daac/radiosondes_i
nstrument.gd.html
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RS 80 RADIOSONDE
Humidity Sensor (HUMICAP) Sensor type Thin
film capacitor Measuring range 0 RH to
100 RH Resolution 1 RH Lag 1 s
(6m/s flow at 1000 hPa, 20 degrees
C) Accuracy /- 2 RH
repeated calibration method, standard deviation
of differences The humidity sensor is a thin
film capacitor with a polymer dielectric. The
polymer is about 1 micron thick. The sensor
capacitance is dependent on the water absorption
in the sensor's dielectrical material. The sensor
is fabricated using thin film technology similar
to that generally used in microelectronics. The
sensor is small (4 X 4 X 0.2 mm), hence its
thermal mass is also small and the sensor very
closely and quickly follows the ambient air
temperature. This is obviously necessary for
obtaining true relative humidity values in the
atmosphere. Other attractive features of the
sensor are fast response, good linearity, low
hysteresis and small temperature coefficient. The
sensor operates reliably in low temperatures to
at least the -60 degree C level.
From http//nsidc.org/data/docs/daac/radiosondes_i
nstrument.gd.html
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Total Precipitable Water Vapor in Words
Total precipitable water is the amount of water
that can be obtained from the surface to the
"top" of the atmosphere if all of the water and
water vapor were condensed to a liquid phase.
The tropics, which are warm and very humid,
typically have high total precipitable water
because there is so much water vapor in the air.
Concentrated areas of precipitable water vapor
are usually indicative of clouds and
precipitation. The frequency on the satellite
based Advanced Microwave Sounding Unit AMSU can
be set to measure the amount of water vapor in
the atmosphere. By integrating this data over a
volume, the total precipitable water can be
calculated.
Adapted from http//sos.noaa.gov/datasets/Atmosphe
re/precipitablewater.html
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Example of Total Precipitable Water Vapor
Source http//sos.noaa.gov/datasets/Atmosphere/p
recipitablewater.html
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Turner et al Radiosonde analysis
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More on the Precipitable Water Vapor
The total atmospheric water vapor contained in a
vertical column of unit cross-sectional area
extending between any two specified levels,
commonly expressed in terms of the height to
which that water substance would stand if
completely condensed and collected in a vessel of
the same unit cross section.
From http//amsglossary.allenpress.com/glossary/se
arch?idprecipitable-water1
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More on the Precipitable Water Vapor
The total precipitable water is that
contained in a column of unit cross section
extending all of the way from the earth's surface
to the top of the atmosphere. Mathematically,
if x(p) is the mixing ratio at the pressure
level, p, then the precipitable water vapor, W,
contained in a layer bounded by pressures p1 and
p2 is given by where g is the acceleration
of gravity.
From http//amsglossary.allenpress.com/glossary/se
arch?idprecipitable-water1
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Turner et al mixing ratio example
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PROJECT IDEA

• Gather radiosonde data from a variety of sites
  (not just the skew T log P graphs, but the actual
  data).
• Calculate the total precipitable water vapor from
  the sounding and compare it with the sounding
  value.
• Calculate the water vapor mixing ratio and plot
  it versus altitude.
• Compare your results for different representative
  sites around the world, dry, wet, low altitude,
  high altitude, and during different seasons.

http//weather.uwyo.edu/upperair/sounding.html
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More on the Precipitable Water Vapor
In actual rainstorms, particularly thunderstorms,
amounts of rain very often exceed the total
precipitable water vapor of the overlying
atmosphere. This results from the action of
convergence that brings into the rainstorm the
water vapor from a surrounding area that is often
quite large. Nevertheless, there is general
correlation between precipitation amounts in
given storms and the precipitable water vapor of
the air masses involved in those storms.
From http//amsglossary.allenpress.com/glossary/se
arch?idprecipitable-water1
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FTIR Data from the SGP Oklahoma Dry and Moist
Conditions
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Sunphotometer Can Get Total Precipitable Water
Vapor
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PROJECT IDEA

• Two Channel Sunphotometer (870 nm and 940 nm)
• 870 nm channel provides aerosol optical depth.
• 940 nm channel provides water vapor column and
  aerosol optical depth.
• Additional 660 nm channel could be used to
  improve the aerosol optical depth by spectral
  extrapolation between 660 nm and 870 nm to 940
  nm.
• Do sunphotometer measurements each day at around
  4 pm local.
• Compare water vapor from sun photometer with
  total precipitable water vapor from the
  radiosonde launched by the NWS in Reno each day.

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Sunphotometer Aerosol Optical Depth from Geronimo
Creek Texas
http//www.sunandsky.org/Sun_and_Sky_Data.html
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Sunphotometer Column Water Vapor from Geronimo
Creek Texas
http//www.sunandsky.org/Sun_and_Sky_Data.html