GCOS Upper Air Workshop, 22 May 2006 GCOS Upper Air Workshop, 22 May 2006 Holger Vömel Holger Vömel Cooperative Institute for Research in Environmental Cooperative Institute for Research in Environmental Sciences Sciences University of Colorado University of Colorado Water vapor observations in Water vapor observations in the upper troposphere and the upper troposphere and lower stratosphere lower stratosphere
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GCOS Upper Air Workshop, 22 May 2006 Holger Vömel Cooperative Institute for Research in Environmental Sciences University of Colorado Water vapor observations.
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GCOS Upper Air Workshop, 22 May 2006GCOS Upper Air Workshop, 22 May 2006
Holger VömelHolger Vömel
Cooperative Institute for Research in Environmental SciencesCooperative Institute for Research in Environmental Sciences
University of ColoradoUniversity of Colorado
Water vapor observations in the upper Water vapor observations in the upper troposphere and lower stratospheretroposphere and lower stratosphere
• Measurement based on simple physicsMeasurement based on simple physics• Measurement not calibrated for water Measurement not calibrated for water
vapor, but rather for temperaturevapor, but rather for temperature(assume vapor pressure equation is correct)(assume vapor pressure equation is correct)
• Extremely large dynamic rangeExtremely large dynamic range
• Long history for technologyLong history for technology
CFH LimitationsCFH Limitations
• Instrument may fail completely in “thick” liquid Instrument may fail completely in “thick” liquid clouds or highly ice-supersaturated airclouds or highly ice-supersaturated air
• High costHigh cost• Availability of cryogenAvailability of cryogen• Instrument needs minor preparationInstrument needs minor preparation• Data product needs understanding of instrumentData product needs understanding of instrument
Snow White frostpoint hygrometerSnow White frostpoint hygrometer
• Peltier coolingPeltier cooling
• Vertical Range: surface to < tropopauseVertical Range: surface to < tropopause
• Measurement based on simple physicsMeasurement based on simple physics
• Measurement not calibrated for water Measurement not calibrated for water vapor, but rather for temperaturevapor, but rather for temperature
• Large dynamic rangeLarge dynamic range
• Simple operationSimple operation
Snow White LimitationsSnow White Limitations
• Highly sensitive to cloud contaminationHighly sensitive to cloud contamination• Occasional unexplained failureOccasional unexplained failure• Moderate costModerate cost• Limited to below tropopauseLimited to below tropopause• Limited to RH Limited to RH ≥≥ 3-6% 3-6%• Data product needs understanding of instrumentData product needs understanding of instrument
• Vertical Range: upper troposphere to Vertical Range: upper troposphere to stratosphere stratosphere (0.5 to 500 ppmv) (0.5 to 500 ppmv)
• Calibrated against reference frost point Calibrated against reference frost point
• Uncertainty: 9% MRUncertainty: 9% MR
• Night time (descent) onlyNight time (descent) only
• Weight: ~ 1 kgWeight: ~ 1 kg
• Currently interfaced Vaisala RS80Currently interfaced Vaisala RS80
• 45 soundings45 soundings
FLASH - Lyman-FLASH - Lyman-αα
FLASH - Lyman-FLASH - Lyman-αα
FLASH AdvantagesFLASH Advantages
• Calibrated against frost point standardCalibrated against frost point standard
• High measurement precisionHigh measurement precision
• Very fast sensorVery fast sensor
• Largely insensitive to cloudsLargely insensitive to clouds
• Large dynamic range (low mixing ratios)Large dynamic range (low mixing ratios)
FLASH LimitationsFLASH Limitations
• Instrument measures properly on descentInstrument measures properly on descent• Can only measure during night timeCan only measure during night time• Full moon limits data rangeFull moon limits data range• High costHigh cost• Measurement range : 0.5 to 500 ppmvMeasurement range : 0.5 to 500 ppmv• Currently can’t check calibration in the fieldCurrently can’t check calibration in the field
MayComm TDLMayComm TDL
• Tunable Diode LaserTunable Diode Laser
• Vertical Range: mid troposphere to Vertical Range: mid troposphere to stratosphere stratosphere
• Calibrated against reference frost point Calibrated against reference frost point
• Uncertainty: 5% MRUncertainty: 5% MR or 0.5 ppmv or 0.5 ppmv
• High measurement precisionHigh measurement precision
• Very fast sensorVery fast sensor
• Insensitive to cloudsInsensitive to clouds
• Large dynamic range (low mixing ratios)Large dynamic range (low mixing ratios)
• Easy to useEasy to use
MayComm TDL LimitationsMayComm TDL Limitations
• Prototype onlyPrototype only• High costHigh cost• No lower troposphere No lower troposphere
(Can extend to surface with second path)(Can extend to surface with second path)• No stable interface/telemetry system yetNo stable interface/telemetry system yet
• Very large solar radiation sensitivityVery large solar radiation sensitivity• Good measurements need third party correctionsGood measurements need third party corrections• Very hard to trace calibration changes Very hard to trace calibration changes • Very hard to trace sensor changesVery hard to trace sensor changes