Search Results
You are looking at 1 - 10 of 14 items for
- Author or Editor: D. Baumgardner x
- Refine by Access: All Content x
Abstract
Distortion of airflow around aircraft bodies can affect measurements made from these airborne platforms. In particular, particle sizes and concentrations can be in error, and ice crystals incorrectly classified as a result of flow field distortion. The magnitude of distortion has been evaluated for airflow around wingtip-mounted particle measuring probes on a Beechcraft King Air. The flow field in front of the probes was measured with a five-hole pressure probe during wind tunnel and airborne tests. Results from these tests show significant flow distortion and partially explain the preferred orientation of ice crystals which has been observed in previous measurements.
Abstract
Distortion of airflow around aircraft bodies can affect measurements made from these airborne platforms. In particular, particle sizes and concentrations can be in error, and ice crystals incorrectly classified as a result of flow field distortion. The magnitude of distortion has been evaluated for airflow around wingtip-mounted particle measuring probes on a Beechcraft King Air. The flow field in front of the probes was measured with a five-hole pressure probe during wind tunnel and airborne tests. Results from these tests show significant flow distortion and partially explain the preferred orientation of ice crystals which has been observed in previous measurements.
Abstract
A validation method of measurements from the forward-scattering spectrometer probe (FSSP) allowing preliminary analysis and verification of rough data is presented. It is based on the comparison of observed spectral distributions from undiluted cloudy air with theoretical adiabatic ones. The latter are obtained using an ascending adiabatic cloud-parcel model and the corresponding cloud-base conditions. A two-step approach is used to correct observed spectral distributions and is illustrated with data collected during the 1985 Joint Hawaii Warm Rain Project (JHWRP). The procedure provides an alternate way of obtaining the response matrix for an FSSP and can be used to validate the laboratory-derived response matrix. The results obtained (spectral characteristics and liquid water contents) agree well with the ones calculated from the laboratory characterization, which was made after the experiment, taking into account the laser beam nonuniformities.
Abstract
A validation method of measurements from the forward-scattering spectrometer probe (FSSP) allowing preliminary analysis and verification of rough data is presented. It is based on the comparison of observed spectral distributions from undiluted cloudy air with theoretical adiabatic ones. The latter are obtained using an ascending adiabatic cloud-parcel model and the corresponding cloud-base conditions. A two-step approach is used to correct observed spectral distributions and is illustrated with data collected during the 1985 Joint Hawaii Warm Rain Project (JHWRP). The procedure provides an alternate way of obtaining the response matrix for an FSSP and can be used to validate the laboratory-derived response matrix. The results obtained (spectral characteristics and liquid water contents) agree well with the ones calculated from the laboratory characterization, which was made after the experiment, taking into account the laser beam nonuniformities.
Abstract
The forward-scattering spectrometer probe (FSSP) is an optical particle counter widely used for the measurement of cloud droplet size distributions and concentration. Previous studies have identified operational limitations of these probes and a number of techniques have been developed to minimize the impact of these limitations on the measurements. The majority of effort has been focused on accounting for droplets missed by the FSSP as a result of droplet coincidence and electronic dead time. This note reviews the algorithms that have been developed to account for these losses, describes how and when to apply them to previously acquired measurements, and recommends methods to improve the quality of future measurements.
Abstract
The forward-scattering spectrometer probe (FSSP) is an optical particle counter widely used for the measurement of cloud droplet size distributions and concentration. Previous studies have identified operational limitations of these probes and a number of techniques have been developed to minimize the impact of these limitations on the measurements. The majority of effort has been focused on accounting for droplets missed by the FSSP as a result of droplet coincidence and electronic dead time. This note reviews the algorithms that have been developed to account for these losses, describes how and when to apply them to previously acquired measurements, and recommends methods to improve the quality of future measurements.
Abstract
Wet wind tunnel tests have been Performed on several versions of the CSIRO probe designed for the airborne measurement of liquid water content. Four different controller units and 17 different Probe sensors (including half-size and shielded versions) were tested. Even with tests conducted under extreme conditions, differences in response for all units were always less than 15%, except for the shielded units which needed to be operated at least 60°C better than the unshielded ones to yield the same output. Probe measurements with the unshielded sensors were typically within 5% and always within 10% of the tunnel values which were determined from icing cylinder measurements. The short length probes performed equally as well as the standard length ones and have certain operational advantages, such as Water robustness and the ability to operate at higher liquid water contents for a given supply voltage. Changing airspeed from 15 to 100 m s−1 and ambient temperature from −28°C to +10°C produced no measurable effect on any probe response, whereas grossly overdamping the probes via incorrect offset voltages could reduce the apparent output sensitivity by as much as 50%.
Abstract
Wet wind tunnel tests have been Performed on several versions of the CSIRO probe designed for the airborne measurement of liquid water content. Four different controller units and 17 different Probe sensors (including half-size and shielded versions) were tested. Even with tests conducted under extreme conditions, differences in response for all units were always less than 15%, except for the shielded units which needed to be operated at least 60°C better than the unshielded ones to yield the same output. Probe measurements with the unshielded sensors were typically within 5% and always within 10% of the tunnel values which were determined from icing cylinder measurements. The short length probes performed equally as well as the standard length ones and have certain operational advantages, such as Water robustness and the ability to operate at higher liquid water contents for a given supply voltage. Changing airspeed from 15 to 100 m s−1 and ambient temperature from −28°C to +10°C produced no measurable effect on any probe response, whereas grossly overdamping the probes via incorrect offset voltages could reduce the apparent output sensitivity by as much as 50%.
Abstract
Wind profilers are radars that operate in the VHF and UHF hands and are designed for detecting the weak echoes reflected by the optically clear atmosphere. An unexpected application of wind profilers has been the revival of an old method of estimating drop size distributions in rain from the Doppler spectrum of the received signal. Originally attempted with radars operating at microwave frequency, the method showed early promise but was seriously limited in application because of the crucial sensitivity of the estimated drop sizes to the vertical air velocity, a quantity generally unknown and, at that time, unmeasurable. Profilers have solved this problem through their ability to measure, under appropriate conditions, both air motions and drop motions. This paper compares the drop sizes measured by a UHF profiler at two altitudes in a shower with those measured simultaneously by an instrumented airplane. The agreement is satisfactory, lending support to this new application of wind profilers.
Abstract
Wind profilers are radars that operate in the VHF and UHF hands and are designed for detecting the weak echoes reflected by the optically clear atmosphere. An unexpected application of wind profilers has been the revival of an old method of estimating drop size distributions in rain from the Doppler spectrum of the received signal. Originally attempted with radars operating at microwave frequency, the method showed early promise but was seriously limited in application because of the crucial sensitivity of the estimated drop sizes to the vertical air velocity, a quantity generally unknown and, at that time, unmeasurable. Profilers have solved this problem through their ability to measure, under appropriate conditions, both air motions and drop motions. This paper compares the drop sizes measured by a UHF profiler at two altitudes in a shower with those measured simultaneously by an instrumented airplane. The agreement is satisfactory, lending support to this new application of wind profilers.
Abstract
Understanding the formation and evolution of ice in clouds requires detailed information on the size, shape, mass, and optical properties of individual cloud hydrometeors and their bulk properties over a broad range of atmospheric conditions. Since the 1960s, instrumentation and research aircraft have evolved, providing increasingly more accurate and larger quantities of data about cloud particle properties. In this chapter, the current status of electrical powered, in situ measurement systems are reviewed with respect to their strengths and weaknesses and their limitations and uncertainties are documented. There remain many outstanding challenges. These are summarized and accompanied by recommendations for moving forward through new developments that fill the remaining information gaps. Closing these gaps will remove the obstacles that continue to hinder our understanding of cloud processes in general and the evolution of ice in particular.
Abstract
Understanding the formation and evolution of ice in clouds requires detailed information on the size, shape, mass, and optical properties of individual cloud hydrometeors and their bulk properties over a broad range of atmospheric conditions. Since the 1960s, instrumentation and research aircraft have evolved, providing increasingly more accurate and larger quantities of data about cloud particle properties. In this chapter, the current status of electrical powered, in situ measurement systems are reviewed with respect to their strengths and weaknesses and their limitations and uncertainties are documented. There remain many outstanding challenges. These are summarized and accompanied by recommendations for moving forward through new developments that fill the remaining information gaps. Closing these gaps will remove the obstacles that continue to hinder our understanding of cloud processes in general and the evolution of ice in particular.
Abstract
This study compares cirrus-cloud properties and, in particular, particle effective radius retrieved by a Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)-like method with two similar methods using Moderate-Resolution Imaging Spectroradiometer (MODIS), MODIS Airborne Simulator (MAS), and Geostationary Operational Environmental Satellite imagery. The CALIPSO-like method uses lidar measurements coupled with the split-window technique that uses the infrared spectral information contained at the 8.65-, 11.15-, and 12.05-μm bands to infer the microphysical properties of cirrus clouds. The two other methods, using passive remote sensing at visible and infrared wavelengths, are the operational MODIS cloud products (using 20 spectral bands from visible to infrared, referred to by its archival product identifier MOD06 for MODIS Terra) and MODIS retrievals performed by the Clouds and the Earth’s Radiant Energy System (CERES) team at Langley Research Center (LaRC) in support of CERES algorithms (using 0.65-, 3.75-, 10.8-, and 12.05-μm bands); the two algorithms will be referred to as the MOD06 and LaRC methods, respectively. The three techniques are compared at two different latitudes. The midlatitude ice-clouds study uses 16 days of observations at the Palaiseau ground-based site in France [Site Instrumental de Recherche par Télédétection Atmosphérique (SIRTA)], including a ground-based 532-nm lidar and the MODIS overpasses on the Terra platform. The tropical ice-clouds study uses 14 different flight legs of observations collected in Florida during the intensive field experiment known as the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL-FACE), including the airborne cloud-physics lidar and the MAS. The comparison of the three methods gives consistent results for the particle effective radius and the optical thickness but discrepancies in cloud detection and altitudes. The study confirms the value of an active remote sensing method (CALIPSO like) for the study of subvisible ice clouds, in both the midlatitudes and Tropics. Nevertheless, this method is not reliable in optically very thick tropical ice clouds, because of their particular microphysical properties.
Abstract
This study compares cirrus-cloud properties and, in particular, particle effective radius retrieved by a Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)-like method with two similar methods using Moderate-Resolution Imaging Spectroradiometer (MODIS), MODIS Airborne Simulator (MAS), and Geostationary Operational Environmental Satellite imagery. The CALIPSO-like method uses lidar measurements coupled with the split-window technique that uses the infrared spectral information contained at the 8.65-, 11.15-, and 12.05-μm bands to infer the microphysical properties of cirrus clouds. The two other methods, using passive remote sensing at visible and infrared wavelengths, are the operational MODIS cloud products (using 20 spectral bands from visible to infrared, referred to by its archival product identifier MOD06 for MODIS Terra) and MODIS retrievals performed by the Clouds and the Earth’s Radiant Energy System (CERES) team at Langley Research Center (LaRC) in support of CERES algorithms (using 0.65-, 3.75-, 10.8-, and 12.05-μm bands); the two algorithms will be referred to as the MOD06 and LaRC methods, respectively. The three techniques are compared at two different latitudes. The midlatitude ice-clouds study uses 16 days of observations at the Palaiseau ground-based site in France [Site Instrumental de Recherche par Télédétection Atmosphérique (SIRTA)], including a ground-based 532-nm lidar and the MODIS overpasses on the Terra platform. The tropical ice-clouds study uses 14 different flight legs of observations collected in Florida during the intensive field experiment known as the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL-FACE), including the airborne cloud-physics lidar and the MAS. The comparison of the three methods gives consistent results for the particle effective radius and the optical thickness but discrepancies in cloud detection and altitudes. The study confirms the value of an active remote sensing method (CALIPSO like) for the study of subvisible ice clouds, in both the midlatitudes and Tropics. Nevertheless, this method is not reliable in optically very thick tropical ice clouds, because of their particular microphysical properties.
Abstract
Based on both in-flight measurements and a fluid dynamics model, airflow in the National Center for Atmospheric Research (NCAR) Community Aerosol Inlet (CAI) is similar to fully developed pipe flow. Distortions of the velocity field were pronounced when suction to inlet tubes was shut off, but conditions were otherwise insensitive to all flight parameters but airspeed. The principal value of the multiuser CAI system for NCAR's C-130 is that it decelerates air with no curves until the velocity has been reduced to 10 m s−1. It then supplies uniformly modified air (after turbulent losses) to all users, enabling valid closure experiments.
Chemical data from both the First Aerosol Characterization Experiment (ACE-1) and the Second Community Aerosol Inlet Evaluation Program (CAINE-II) clearly indicate that while passing efficiency for submicron aerosol is acceptable, very little of the sea salt mode mass is transmitted by the CAI to instruments inside the aircraft. Comparisons between chemical samples from an external total aerosol sampler and samplers behind the CAI indicate that 70%–90% of the sea salt mass is unable to pass the CAI. The 50% cut size is about 3 μm, but the precise details of the efficiency curve are obscured by the difficulty of measuring a reference ambient aerosol distribution. The loss of particle mass becomes very significant above 3 μm, but the size cut is not sharp. These conclusions are supported by calculated particle transmission efficiencies for the CAI.
Abstract
Based on both in-flight measurements and a fluid dynamics model, airflow in the National Center for Atmospheric Research (NCAR) Community Aerosol Inlet (CAI) is similar to fully developed pipe flow. Distortions of the velocity field were pronounced when suction to inlet tubes was shut off, but conditions were otherwise insensitive to all flight parameters but airspeed. The principal value of the multiuser CAI system for NCAR's C-130 is that it decelerates air with no curves until the velocity has been reduced to 10 m s−1. It then supplies uniformly modified air (after turbulent losses) to all users, enabling valid closure experiments.
Chemical data from both the First Aerosol Characterization Experiment (ACE-1) and the Second Community Aerosol Inlet Evaluation Program (CAINE-II) clearly indicate that while passing efficiency for submicron aerosol is acceptable, very little of the sea salt mode mass is transmitted by the CAI to instruments inside the aircraft. Comparisons between chemical samples from an external total aerosol sampler and samplers behind the CAI indicate that 70%–90% of the sea salt mass is unable to pass the CAI. The 50% cut size is about 3 μm, but the precise details of the efficiency curve are obscured by the difficulty of measuring a reference ambient aerosol distribution. The loss of particle mass becomes very significant above 3 μm, but the size cut is not sharp. These conclusions are supported by calculated particle transmission efficiencies for the CAI.
No abstract available.
No abstract available.
Abstract
A focused cavity aerosol spectrometer aboard a NASA ER-2 high-altitude aircraft provided high-resolution measurements of the size of the stratospheric particles in the 0.06–2.0-µm-diameter range in flights following the eruption of Mount Pinatubo in 1991. Effects of anisokinetic sampling and evaporation in the sampling system were accounted for by means adapted and specifically developed for this instrument. Calibrations with monodisperse aerosol particles provided the instrument's response matrix, which upon inversion during data reduction yielded the particle size distributions. The resultant dataset is internally consistent and generally shows agreement to within a factor of 2 with comparable measurements simultaneously obtained by a condensation nuclei counter, a forward-scattering spectrometer probe, and aerosol particle impactors, as well as with nearby extinction profiles obtained by satellite measurements and with lidar measurements of backscatter.
Abstract
A focused cavity aerosol spectrometer aboard a NASA ER-2 high-altitude aircraft provided high-resolution measurements of the size of the stratospheric particles in the 0.06–2.0-µm-diameter range in flights following the eruption of Mount Pinatubo in 1991. Effects of anisokinetic sampling and evaporation in the sampling system were accounted for by means adapted and specifically developed for this instrument. Calibrations with monodisperse aerosol particles provided the instrument's response matrix, which upon inversion during data reduction yielded the particle size distributions. The resultant dataset is internally consistent and generally shows agreement to within a factor of 2 with comparable measurements simultaneously obtained by a condensation nuclei counter, a forward-scattering spectrometer probe, and aerosol particle impactors, as well as with nearby extinction profiles obtained by satellite measurements and with lidar measurements of backscatter.
