Measurement of Total Water with a Tunable Diode Laser Hygrometer: Inlet Analysis, Calibration Procedure, and Ice Water Content Determination

2007 ◽  
Vol 24 (3) ◽  
pp. 463-475 ◽  
Author(s):  
Sean M. Davis ◽  
A. Gannet Hallar ◽  
Linnea M. Avallone ◽  
William Engblom
Keyword(s):  
Particle Size ◽  
Water Vapor ◽  
Water Content ◽  
Diode Laser ◽  
Tunable Diode Laser ◽  
Calibration Data ◽  
Total Water ◽  
Wide Range ◽  
Ice Water Content ◽  
Ice Water

Abstract The University of Colorado closed-path tunable diode laser hygrometer (CLH), a new instrument for the in situ measurement of enhanced total water (eTW, the sum of water vapor and condensed water enhanced by a subisokinetic inlet), has recently been flown aboard the NASA DC-8 and WB-57F aircrafts. The CLH has the sensitivity necessary to quantify the ice water content (IWC) of extremely thin subvisual cirrus clouds (∼0.1 mg m−3), while still providing measurements over a large range of conditions typical of upper-tropospheric cirrus (up to 1 g m−3). A key feature of the CLH is its subisokinetic inlet system, which is described in detail in this paper. The enhancement and evaporation of ice particles that results from the heated subisokinetic inlet is described both analytically and based on computational fluid dynamical simulations of the flow around the aircraft. Laboratory mixtures of water vapor with an accuracy of 2%–10% (2σ) were used to calibrate the CLH over a wide range of water vapor mixing ratios (∼50–50 000 ppm) and pressures (∼100–1000 mb). The water vapor retrieval algorithm, which is based on the CLH instrument properties as well as on the spectroscopic properties of the water absorption line, accurately fits the calibration data to within the uncertainty of the calibration mixtures and instrument signal-to-noise ratio. A method for calculating cirrus IWC from the CLH enhanced total water measurement is presented. In this method, the particle enhancement factor is determined from an independent particle size distribution measurement and the size-dependent CLH inlet efficiency. It is shown that despite the potentially large uncertainty in particle size measurements, the error introduced by this method adds ∼5% error to the IWC calculation. IWC accuracy ranges from 20% at the largest IWC to 50% at small IWC (<5 mg m−3).

scholarly journals A two-channel, tunable diode laser-based hygrometer for measurement of water vapor and cirrus cloud ice water content in the upper troposphere and lower stratosphere

2015 ◽  
Vol 8 (1) ◽  
pp. 211-224 ◽  
Author(s):  
T. D. Thornberry ◽  
A. W. Rollins ◽  
R. S. Gao ◽  
L. A. Watts ◽  
S. J. Ciciora ◽  
...  
Keyword(s):  
Water Vapor ◽  
Water Content ◽  
Lower Stratosphere ◽  
Tunable Diode Laser ◽  
Cirrus Cloud ◽  
Total Water ◽  
Cloud Particle ◽  
Upper Troposphere ◽  
Ice Water Content ◽  
Ice Water

Abstract. The recently developed NOAA Water instrument is a two-channel, closed-path, tunable diode laser absorption spectrometer designed for the measurement of upper troposphere/lower stratosphere water vapor and enhanced total water (vapor + inertially enhanced condensed phase) from the NASA Global Hawk unmanned aircraft system (UAS) or other high-altitude research aircraft. The instrument utilizes wavelength-modulated spectroscopy with second harmonic detection near 2694 nm to achieve high precision with a 79 cm double-pass optical path. The detection cells are operated under constant temperature, pressure, and flow conditions to maintain a constant sensitivity to H2O independent of the ambient sampling environment. An onboard calibration system is used to perform periodic in situ calibrations to verify the stability of the instrument sensitivity during flight. For the water vapor channel, ambient air is sampled perpendicular to the flow past the aircraft in order to reject cloud particles, while the total water channel uses a heated, forward-facing inlet to sample both water vapor and cloud particles. The total water inlet operates subisokinetically, thereby inertially enhancing cloud particle number in the sample flow and affording increased cloud water content sensitivity. The NOAA Water instrument was flown for the first time during the second deployment of the Airborne Tropical TRopopause EXperiment (ATTREX) in February–March 2013 on the NASA Global Hawk UAS. The instrument demonstrated a typical in-flight precision (1 s, 1σ) of better than 0.17 parts per million (ppm, 10−6 mol mol−1), with an overall H2O vapor measurement uncertainty of 5% ± 0.23 ppm. The inertial enhancement for cirrus cloud particle sampling under ATTREX flight conditions ranged from 33 to 48 for ice particles larger than 8 μm in diameter, depending primarily on aircraft altitude. The resulting ice water content detection limit (2σ) was 0.023–0.013 ppm, corresponding to approximately 2 μg m−3, with an estimated overall uncertainty of 20%.

scholarly journals A two-channel, tunable diode laser-based hygrometer for measurement of water vapor and cirrus cloud ice water content in the upper troposphere and lower stratosphere

2014 ◽  
Vol 7 (8) ◽  
pp. 8271-8309 ◽  
Author(s):  
T. D. Thornberry ◽  
A. W. Rollins ◽  
R. S. Gao ◽  
L. A. Watts ◽  
S. J. Ciciora ◽  
...  
Keyword(s):  
Water Vapor ◽  
Water Content ◽  
Lower Stratosphere ◽  
Tunable Diode Laser ◽  
Cirrus Cloud ◽  
Total Water ◽  
Cloud Particle ◽  
Upper Troposphere ◽  
Ice Water Content ◽  
Ice Water

Abstract. The recently developed NOAA Water instrument is a two-channel, closed-path, tunable diode laser absorption spectrometer designed for the measurement of water vapor and enhanced total water (vapor + inertially enhanced condensed-phase) in the upper troposphere/lower stratosphere from the NASA Global Hawk unmanned aircraft system (UAS) or other high-altitude research aircraft. The instrument utilizes wavelength-modulated spectroscopy with second harmonic detection near 2694 nm to achieve high precision with a 79 cm double-pass optical path. The detection cells are operated under constant temperature, pressure and flow conditions to maintain a constant sensitivity to H2O independent of the ambient sampling environment. An on-board calibration system is used to perform periodic in situ calibrations to verify the stability of the instrument sensitivity during flight. For the water vapor channel, ambient air is sampled perpendicular to the flow past the aircraft in order to reject cloud particles, while the total water channel uses a heated, forward-facing inlet to sample both water vapor and cloud particles. The total water inlet operates subisokinetically, thereby inertially enhancing cloud particle number in the sample flow and affording increased cloud water content sensitivity. The NOAA Water instrument was flown for the first time during the second deployment of the Airborne Tropical TRopopause EXperiment (ATTREX) in February–March 2013 on board the Global Hawk UAS. The instrument demonstrated a typical in-flight precision (1 s, 1σ) of better than 0.17 parts per million (ppm, 10−6 mol mol−1), with an overall H2O vapor measurement uncertainty of 5% ± 0.23 ppm. The inertial enhancement for cirrus cloud particle sampling under ATTREX flight conditions ranged from 33–48 for ice particles larger than 8 μm in diameter, depending primarily on aircraft altitude. The resulting ice water content detection limit (2σ) was 0.023–0.013 ppm, corresponding to approximately 2 μg m−3, with an estimated overall uncertainty of 20%.

scholarly journals A fiber-coupled laser hygrometer for airborne total water measurement

2014 ◽  
Vol 7 (1) ◽  
pp. 215-223 ◽  
Author(s):  
S. W. Dorsi ◽  
L. E. Kalnajs ◽  
D. W. Toohey ◽  
L. M. Avallone
Keyword(s):  
Water Vapor ◽  
Water Content ◽  
Diode Laser ◽  
Near Infrared ◽  
Tunable Diode Laser ◽  
Infrared Light ◽  
Closed Path ◽  
Total Water ◽  
University Of Colorado ◽  
Condensed Water

Abstract. The second-generation University of Colorado closed-path tunable-diode laser hygrometer (CLH-2) is an instrument for the airborne in situ measurement of total water content – the sum of vapor-, liquid- and ice-phase water – in clouds. This compact instrument has been flown on the NSF/NCAR Gulfstream-V aircraft in an underwing canister. It operates autonomously and uses fiber-coupled optics to eliminate the need for a supply of dry compressed gas. In operation, sample air is ingested into a forward-facing sub-isokinetic inlet; this sampling configuration results in particle concentrations that are enhanced relative to ambient and causes greater instrument sensitivity to condensed water particles. Heaters within the inlet vaporize the ingested water particles, and the resulting augmented water vapor mixing ratio is measured by absorption of near-infrared light in a single-pass optical cell. The condensed water content is then determined by subtracting the ambient water vapor content from the total and by accounting for the inertial enhancement of particles into the sampling inlet. The CLH-2 is calibrated in the laboratory over a range of pressures and water vapor mixing ratios; the uncertainty in CLH-2 condensed water retrievals is estimated to be 14.3% to 16.1% (1-σ). A vapor-only laboratory intercomparison with the first-generation University of Colorado closed-path tunable-diode laser hygrometer (CLH) shows agreement within the 2-σ uncertainty bounds of both instruments.

scholarly journals A fiber-coupled laser hygrometer for airborne total water measurement

2013 ◽  
Vol 6 (4) ◽  
pp. 7355-7378 ◽  
Author(s):  
S. W. Dorsi ◽  
L. E. Kalnajs ◽  
D. W. Toohey ◽  
L. M. Avallone
Keyword(s):  
Water Vapor ◽  
Water Content ◽  
Diode Laser ◽  
Tunable Diode Laser ◽  
Infrared Light ◽  
Vapor Concentration ◽  
Closed Path ◽  
Total Water ◽  
University Of Colorado ◽  
Condensed Water

Abstract. The second-generation University of Colorado closed-path tunable-diode laser hygrometer (CLH-2) is an instrument for the airborne in situ measurement of total water content – the sum of vapor-, liquid- and ice-phase water – in clouds. This compact instrument has been flown on the NSF/NCAR Gulfstream-V aircraft in an underwing canister. It operates autonomously and uses fiber-coupled optics to eliminate the need for a supply of dry compressed gas. In operation, sample air is ingested into a forward-facing sub-isokinetic inlet; this sampling configuration results in particle concentrations that are enhanced relative to ambient and conveys greater instrument sensitivity to condensed water particles. Heaters within the inlet vaporize the ingested water particles, and the resulting augmented water vapor mixing ratio is measured by absorption of near-infrared light in a single-pass optical cell. The condensed water content is then determined by subtracting the ambient water vapor concentration from the total and by accounting for the inertial enhancement of particles into the sampling inlet. The CLH-2 is calibrated in the laboratory over a range of pressures and water vapor mixing ratios; the uncertainty in CLH-2 condensed water retrievals is estimated to be 14.3% to 16.1% (1-σ). A vapor-only laboratory intercomparison with the first-generation University of Colorado closed-path tunable-diode laser hygrometer (CLH) shows agreement within the 2-σ uncertainty bounds of both instruments.

Determination of the Combined Ventilation Factor and Capacitance for Ice Crystal Aggregates from Airborne Observations in a Tropical Anvil Cloud

2008 ◽  
Vol 65 (2) ◽  
pp. 376-391 ◽  
Author(s):  
Paul R. Field ◽  
J. Heymsfield ◽  
Aaron Bansemer ◽  
Cynthia H. Twohy
Keyword(s):  
Particle Size ◽  
Water Vapor ◽  
Water Content ◽  
Numerical Models ◽  
Mean Value ◽  
Ice Crystal ◽  
Ice Water Content ◽  
Water Vapor Mixing Ratio ◽  
Ice Water ◽  
Ventilation Factor

Abstract The ventilation factor and capacitance used in numerical models to represent ice crystal aggregates directly affects the growth rate of the ice crystal aggregates, and consequently the sink of atmospheric water vapor. Currently, numerical models that prognose ice water content (IWC) and water vapor mixing ratio represent the capacitance and ventilation factor of precipitation-sized particles with simplified geometries, such as hexagonal plates. The geometries of actual precipitation-sized particles are often more complex, and a test of the values being employed is needed. Aircraft observations obtained during a Lagrangian spiral descent through the sublimation zone of a tropical anvil cloud have been used to determine an estimate of combined dimensionless capacitance and ventilation factor for the nonpristine geometries exhibited by ice crystal aggregates. By combining measurements of bulk ice water content, the particle size distribution, and environmental subsaturation, the change in ice water content was modeled throughout the spiral descent and compared with observations of the change in ice water content. Uncertainties resulting from potential systematic biases in the measurements and parameterizations used in the analysis were investigated with sensitivity tests. Most of the uncertainty was related to an assumed maximum potential bias in the measurement of IWC of ±45%. The resulting combined ventilation factor and dimensionless capacitance value was 1.3 (with a range of 0.6–1.9, defined by 68% of sensitivity test trials) for a particle size–weighted mean value of (Sc)1/3(Re)1/2 = 14.9 ± 1.7, where Sc is the Schmidt number and Re is the Reynolds number. Results from commonly adopted combinations of ventilation factor relations and capacitances are compared with the observations presented here, and, finally, surrogate dimensionless capacitances are suggested that when combined with commonly used ventilation factor relations are consistent with the results presented herein.

scholarly journals A statistical analysis of the influence of deep convection on water vapor variability in the tropical upper troposphere

2009 ◽  
Vol 9 (15) ◽  
pp. 5847-5864 ◽  
Author(s):  
J. S. Wright ◽  
R. Fu ◽  
A. J. Heymsfield
Keyword(s):  
Water Vapor ◽  
Deep Convection ◽  
Tropical Rainfall Measuring Mission ◽  
Upper Troposphere ◽  
Ambient Relative Humidity ◽  
Wide Range ◽  
Ice Water Content ◽  
The Tropics ◽  
Ice Water ◽  
Tropical Upper Troposphere

Abstract. The factors that control the influence of deep convective detrainment on water vapor in the tropical upper troposphere are examined using observations from multiple satellites in conjunction with a trajectory model. Deep convection is confirmed to act primarily as a moisture source to the upper troposphere, modulated by the ambient relative humidity (RH). Convective detrainment provides strong moistening at low RH and offsets drying due to subsidence across a wide range of RH. Strong day-to-day moistening and drying takes place most frequently in relatively dry transition zones, where between 0.01% and 0.1% of Tropical Rainfall Measuring Mission Precipitation Radar observations indicate active convection. Many of these strong moistening events in the tropics can be directly attributed to detrainment from recent tropical convection, while others in the subtropics appear to be related to stratosphere-troposphere exchange. The temporal and spatial limits of the convective source are estimated to be about 36–48 h and 600–1500 km, respectively, consistent with the lifetimes of detrainment cirrus clouds. Larger amounts of detrained ice are associated with enhanced upper tropospheric moistening in both absolute and relative terms. In particular, an increase in ice water content of approximately 400% corresponds to a 10–90% increase in the likelihood of moistening and a 30–50% increase in the magnitude of moistening.

Observations and Simulations of Small-Scale Variability of Temperature, Water Vapor, and Cloud Liquid and Ice Water Content

2009 ◽  
Author(s):  
Brian H. Kahn ◽  
João Teixeira ◽  
Svetla Hristlova-Veleva ◽  
Seungwon Lee ◽  
Eric J. Fetzer
Keyword(s):  
Water Vapor ◽  
Water Content ◽  
Small Scale ◽  
Ice Water Content ◽  
Ice Water ◽  
Temperature Water

scholarly journals High ice water content at low radar reflectivity near deep convection – Part 2: Evaluation of microphysical pathways in updraft parcel simulations

2015 ◽  
Vol 15 (20) ◽  
pp. 11729-11751 ◽  
Author(s):  
A. S. Ackerman ◽  
A. M. Fridlind ◽  
A. Grandin ◽  
F. Dezitter ◽  
M. Weber ◽  
...  
Keyword(s):  
Water Vapor ◽  
Water Content ◽  
Deep Convection ◽  
Radar Reflectivity ◽  
Doppler Velocity ◽  
Diffusional Growth ◽  
Ice Particles ◽  
Ice Water Content ◽  
Water Drops ◽  
Ice Water

Abstract. The aeronautics industry has established that a threat to aircraft is posed by atmospheric conditions of substantial ice water content (IWC) where equivalent radar reflectivity (Ze) does not exceed 20–30 dBZ and supercooled water is not present; these conditions are encountered almost exclusively in the vicinity of deep convection. Part 1 (Fridlind et al., 2015) of this two-part study presents in situ measurements of such conditions sampled by Airbus in three tropical regions, commonly near 11 km and −43 °C, and concludes that the measured ice particle size distributions are broadly consistent with past literature with profiling radar measurements of Ze and mean Doppler velocity obtained within monsoonal deep convection in one of the regions sampled. In all three regions, the Airbus measurements generally indicate variable IWC that often exceeds 2 g m-3 with relatively uniform mass median area-equivalent diameter (MMDeq) of 200–300 μm. Here we use a parcel model with size-resolved microphysics to investigate microphysical pathways that could lead to such conditions. Our simulations indicate that homogeneous freezing of water drops produces a much smaller ice MMDeq than observed, and occurs only in the absence of hydrometeor gravitational collection for the conditions considered. Development of a mass mode of ice aloft that overlaps with the measurements requires a substantial source of small ice particles at temperatures of about −10 °C or warmer, which subsequently grow from water vapor. One conceivable source in our simulation framework is Hallett–Mossop ice production; another is abundant concentrations of heterogeneous ice freezing nuclei acting together with copious shattering of water drops upon freezing. Regardless of the production mechanism, the dominant mass modal diameter of vapor-grown ice is reduced as the ice-multiplication source strength increases and as competition for water vapor increases. Both mass and modal diameter are reduced by entrainment and by increasing aerosol concentrations. Weaker updrafts lead to greater mass and larger modal diameters of vapor-grown ice, the opposite of expectations regarding lofting of larger ice particles in stronger updrafts. While stronger updrafts do loft more dense ice particles produced primarily by raindrop freezing, we find that weaker updrafts allow the warm rain process to reduce competition for diffusional growth of the less dense ice expected to persist in convective outflow.

scholarly journals On the relationship of polar mesospheric cloud ice water content, particle radius and mesospheric temperature and its use in multi-dimensional models

2009 ◽  
Vol 9 (22) ◽  
pp. 8889-8901 ◽  
Author(s):  
A. W. Merkel ◽  
D. R. Marsh ◽  
A. Gettelman ◽  
E. J. Jensen
Keyword(s):  
Particle Size ◽  
Water Content ◽  
Computational Cost ◽  
Cloud Microphysics ◽  
Effective Radius ◽  
Local Temperature ◽  
Decadal Scale ◽  
Ice Water Content ◽  
Ice Water ◽  
The Relationship

Abstract. The distribution of ice layers in the polar summer mesosphere (called polar mesospheric clouds or PMCs) is sensitive to background atmospheric conditions and therefore affected by global-scale dynamics. To investigate this coupling it is necessary to simulate the global distribution of PMCs within a 3-dimensional (3-D) model that couples large-scale dynamics with cloud microphysics. However, modeling PMC microphysics within 3-D global chemistry climate models (GCCM) is a challenge due to the high computational cost associated with particle following (Lagrangian) or sectional microphysical calculations. By characterizing the relationship between the PMC effective radius, ice water content (iwc), and local temperature (T) from an ensemble of simulations from the sectional microphysical model, the Community Aerosol and Radiation Model for Atmospheres (CARMA), we determined that these variables can be described by a robust empirical formula. The characterized relationship allows an estimate of an altitude distribution of PMC effective radius in terms of local temperature and iwc. For our purposes we use this formula to predict an effective radius as part of a bulk parameterization of PMC microphysics in a 3-D GCCM to simulate growth, sublimation and sedimentation of ice particles without keeping track of the time history of each ice particle size or particle size bin. This allows cost effective decadal scale PMC simulations in a 3-D GCCM to be performed. This approach produces realistic PMC simulations including estimates of the optical properties of PMCs. We validate the relationship with PMC data from the Solar Occultation for Ice Experiment (SOFIE).

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