Design and Sampling Characteristics of a New Airborne Aerosol Inlet for Aerosol Measurements in Clouds

Craig, Lucas; Schanot, Allen; Moharreri, Arash; Rogers, D. C.; Dhaniyala, Suresh

doi:10.1175/jtech-d-12-00168.1

Cited by 16 publications

(24 citation statements)

References 23 publications

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“…The sample flow was extracted from the flow-through tube at an angle of ∼ 80 • , ensuring that only particles smaller than a cut size will be sampled. The sampling efficiency of such a cross-flow sampling inlet is largely determined by the size of the flow-constricting nozzle (Craig et al, 2013b). Using 3-D CFD simulations, the appropriate size of the flowconstricting nozzle required for a 2 µm sampling cut size was determined.…”

Section: Base-iimentioning

confidence: 99%

“…Enhancement values greater than 1 are usually indicative of shatter artifacts in CN measurements (Craig et al, 2013b). To facilitate a direct comparison of the performance of the two BASE designs, the BASE CN enhancement values were normalized using CN enhancements from the SMAI as a reference sampler.…”

Section: Cn Measurements In Warm Cloudsmentioning

confidence: 99%

“…experienced by the two inlets. The SMAI (Craig et al, 2013a) was chosen as a reference sampler because it was previously shown to be minimally affected by shatter artifacts during in-cloud sampling (Craig et al, 2013b). Also, for both PLOWS and ICE-T campaigns, the operation and location of the SMAI was identical relative to the BASE, making it an optimal reference sampler.…”

Section: Cn Measurements In Warm Cloudsmentioning

confidence: 99%

“…In general, breakup mechanisms and characteristics of shatter particles depend on a number of factors including the shape of crystals, the crystal structure, and the angle of each individual impaction event. From past observations (Craig et al, 2013b;Weber et al, 1998), the general expectations are that the impaction of ice and snow particles on the sampler will result in the generation of fewer shatter particles that are, on average, larger in size than shatter particles generated from the breakup of liquid droplets. This expectation was confirmed with observations made with BASE-II, where smaller enhancement values are observed at lower temperatures in general (Fig.…”

Section: Performance In Cold Cloudsmentioning

confidence: 99%

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Aircraft testing of the new Blunt-body Aerosol Sampler (BASE)

et al. 2014

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Abstract. There is limited understanding of the role of aerosols in the formation and modification of clouds, partly due to inadequate data on such systems. Aircraft-based aerosol measurements in the presence of cloud particles have proven to be challenging because of the problem of cloud droplet/ice particle shatter and the generation of secondary artifact particles that contaminate aerosol samples. Recently, the design of a new aircraft inlet, called the Blunt-body Aerosol Sampler (BASE), which enables sampling of interstitial aerosol particles, was introduced. Numerical modeling results and laboratory test data suggested that the BASE inlet should sample interstitial particles with minimal shatter particle contamination. Here, the sampling performance of the inlet is established from aircraft-based measurements. Initial aircraft test results obtained during the PLOWS (Profiling of Winter Storms) campaign indicated two problems with the original BASE design: separated flows around the BASE at high altitudes and a significant shatter problem when sampling in drizzle. The test data were used to improve the accuracy of flow and particle trajectory modeling around the inlet, and the results from the improved flow model were used to guide design modifications of the BASE to overcome the problems identified in its initial deployment. The performance of the modified BASE was tested during the ICE-T (Ice in Clouds Experiment -Tropics) campaign, and the inlet was seen to provide near shatter-free measurements in a wide range of cloud conditions. The initial aircraft test results, design modifications, and the performance characteristics of the BASE relative to another interstitial inlet, the submicron aerosol inlet (SMAI), are presented.

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Section: Base-iimentioning

confidence: 99%

Section: Cn Measurements In Warm Cloudsmentioning

confidence: 99%

Section: Cn Measurements In Warm Cloudsmentioning

confidence: 99%

Section: Performance In Cold Cloudsmentioning

confidence: 99%

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Aircraft testing of the new Blunt-body Aerosol Sampler (BASE)

et al. 2014

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“…Observations from Craig et al (2013b) and Weber et al (1998) showed that enhancements of aerosol concentrations were greater in warm liquid clouds than in cold ice clouds. Observations from Craig et al (2013b) and Weber et al (1998) showed that enhancements of aerosol concentrations were greater in warm liquid clouds than in cold ice clouds.…”

Section: Introductionmentioning

confidence: 99%

Aircraft-Based Aerosol Sampling in Clouds: Performance Characterization of Flow-Restriction Aerosol Inlets

Craig

Moharreri

Rogers³

et al. 2014

Journal of Atmospheric and Oceanic Technology

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Interaction of liquid cloud droplets and ice particles with aircraft aerosol inlets can result in the generation of a large number of secondary particles and contaminate aerosol measurements. Recent studies have shown that a sampler designed with a perpendicular subsampling tube located within a flow-through conduit (i.e., a flow-restriction inlet) was best suited for in-cloud sampling. Analysis of field data obtained from different flow-restriction inlets shows that their critical cloud droplet breakup diameters are strongly dependent on design details and operating conditions. Using computational fluid dynamics (CFD) simulations, in-cloud sampling performance of a selected inlet can be predicted reasonably accurately for known operating conditions. To understand the relation between inlet design parameters and its sampling performance, however, CFD calculations are impractical. Here, using a simple, representative one-dimensional velocity profile and a validated empirical droplet breakup criteria, a parametric study is conducted to understand the relationship between different inlet design features and operating conditions on its critical breakup diameters. The results of this study suggest that an optimal inlet for in-cloud aerosol sampling should have a combination of a restriction nozzle at the aft end of the flow-through conduit to minimize wall-impaction shatter artifacts and a blunt leading edge to minimize shatter artifact generation from the aerodynamic breakup of cloud droplets. Inlets for in-cloud aerosol sampling from aircraft will, therefore, differ significantly in design from those used for clear-air aerosol sampling.

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Low‐altitude summer/winter microphysics, dynamics, and CCN spectra of northeastern Caribbean small cumuli, and comparisons with stratus

Hudson

Noble

2014

JGR Atmospheres

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Low-altitude cloud microphysics and cloud condensation nuclei (CCN) spectra are presented and analyzed from two cumulus cloud aircraft field campaigns, Ice in Clouds Experiment-Tropical (ICE-T) and Rain in Cumulus over the Ocean (RICO), in the same eastern Caribbean location at opposite seasons. These are further compared with two previously analyzed stratus cloud aircraft campaigns off the central California coast, Physics of Stratocumulus Tops (POST) and Marine Stratus/Stratocumulus Experiment (MASE). Multiple regression analysis predictions of cloud droplet concentrations (N c ) based on CCN spectra, N CCN (S) where S is supersaturation, compared much better with measured N c than single N CCN -N c regressions in both cumulus projects. The addition of vertical velocity (W) to the single and multiple regressions showed small improvements. For RICO the multiple regression correlations were also superior to previous adiabatic model predictions of N c also based on N CCN (S) and mean W. More adiabatic cloud parcels with considerably higher N c , liquid water contents, and W showed only slightly better correlations than flight-averaged N c of all low clouds. Results show the value of more extensive CCN spectra and the relative unimportance of W variations for determining N c , in these Caribbean cumuli. The fact that flight-averaged N c of all low cloud data was almost as well correlated with N CCN (S) as were N c of more adiabatic cloud parcels indicates that entrainment did not significantly perturb CCN-N c relationships. As should be expected higher cloud S were determined for the cumulus clouds than for the stratus clouds. Suppression of cloud S by higher N CCN that had previously been observed in stratus was observed in ICE-T but not in RICO where the N CCN range may have been too low for cloud S suppression. But ICE-T and POST even showed this S suppression over the same limited N CCN range as RICO (< 200 cm À3 ).

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Design and Sampling Characteristics of a New Airborne Aerosol Inlet for Aerosol Measurements in Clouds

Cited by 16 publications

References 23 publications

Aircraft testing of the new Blunt-body Aerosol Sampler (BASE)

Aircraft testing of the new Blunt-body Aerosol Sampler (BASE)

Aircraft-Based Aerosol Sampling in Clouds: Performance Characterization of Flow-Restriction Aerosol Inlets

Low‐altitude summer/winter microphysics, dynamics, and CCN spectra of northeastern Caribbean small cumuli, and comparisons with stratus

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