RADIOSONDES and TOTAL PRECIPITABLE WATER VAPOR

VAISALA RS80 RADIOSONDE Intercomparison with theAERI 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/summer2000/02.html

Launch that Balloon …

ALSO …. http://www.youtube.com/watch?v=B2Q07yBN7PQ

Picture from http://www.artfromthesoul.com/BalloonRelease.html

RS 80 RADIOSONDE

From http://nsidc.org/data/docs/daac/radiosondes_instrument.gd.html

CapacitanceDiagram 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

Capacitors

http://en.wikipedia.org/wiki/Capacitor

Applications: Energy storage, power conditioning, filtering, decoupling, noise filters, snubbers, signal processing, sensing, pulsed power & weapons.

Capacitors as Sensors

http://en.wikipedia.org/wiki/Capacitor

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

RS 80 RADIOSONDE

From http://nsidc.org/data/docs/daac/radiosondes_instrument.gd.html

Pressure Sensor (BAROCAP)(incorporated in the Vaisala RS 80 Radiosondes)Type: Capacitive AneroidMeasuring Range: 1060 hPa (mb) to 3 hPa (mb)Resolution: 0.1 hPaAccuracy*: 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_instrument.gd.html

RS 80 RADIOSONDE

Temperature Sensor (THERMOCAP)Sensor type: Capacitive beadMeasuring range: +60 degrees C to -90 degrees CResolution: 0.1 degree CAccuracy*: +/- 0.2 degrees CLag: 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_instrument.gd.html

RS 80 RADIOSONDE

Humidity Sensor (HUMICAP) Sensor type: Thin film capacitor Measuring range: 0 % RH to 100 % RHResolution: 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.

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/Atmosphere/precipitablewater.html

Example of Total Precipitable Water Vapor

Source: http://sos.noaa.gov/datasets/Atmosphere/precipitablewater.html

Turner et al Radiosonde

analysis

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/search?id=precipitable-water1

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/search?id=precipitable-water1

x =

0.622 ep−e

e=RH ×es(T )

Turner et al mixing ratio example

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

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/search?id=precipitable-water1

FTIR Data from the SGP Oklahoma: Dry and Moist Conditions

Sunphotometer Can Get Total Precipitable Water Vapor

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.

Sunphotometer Aerosol Optical Depth from Geronimo Creek Texas

http://www.sunandsky.org/Sun_and_Sky_Data.html

Sunphotometer Column Water Vapor from Geronimo Creek Texas

http://www.sunandsky.org/Sun_and_Sky_Data.html