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- Author or Editor: R.G. Knollenberg x
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Abstract
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Abstract
An experiment was conducted with the NCAR Sabreliner to measure the ice water content (IWC) and the total ice budget within its contrail. Particle size distributions were measured with an optical-array particle size spectrormeter. The experiment was performed in a region of the atmosphere void of natural ice crystals (cirrus) but estimated to be above ice saturation and favorable to ice crystal growth.
The IWC measured was found to be in excess of 0.1 gm m−3 near the contrail axis with average values of a few hundredths of a gram throughout the contrail. The measured water mass within the contrail was found to be four orders of magnitude greater than that computed as a combustion product. Average crystal sizes of nearly 0.5 mm allow for a transfer of moisture at generation level to much lower levels before re-evaporation. Because of the magnitude of the measured effect and its believed frequent occurrence, the overall effect of sub-tropopause jet traffic is likely to lower the water abundance at the most traveled levels.
The total number of ice crystals produced is similar to the number of droplets expected in the initial liquid water contrail. All ice crystals appear to be produced through the freezing of droplets.
The rate of diffusional spreading of the contrail corresponds to an eddy diffusivity of 1.5× 105cmsec−1. No turbulence was detected and the diffusion appears isotropic after the rapid dissipation of the initial vertically organized turbulent wake.
Abstract
An experiment was conducted with the NCAR Sabreliner to measure the ice water content (IWC) and the total ice budget within its contrail. Particle size distributions were measured with an optical-array particle size spectrormeter. The experiment was performed in a region of the atmosphere void of natural ice crystals (cirrus) but estimated to be above ice saturation and favorable to ice crystal growth.
The IWC measured was found to be in excess of 0.1 gm m−3 near the contrail axis with average values of a few hundredths of a gram throughout the contrail. The measured water mass within the contrail was found to be four orders of magnitude greater than that computed as a combustion product. Average crystal sizes of nearly 0.5 mm allow for a transfer of moisture at generation level to much lower levels before re-evaporation. Because of the magnitude of the measured effect and its believed frequent occurrence, the overall effect of sub-tropopause jet traffic is likely to lower the water abundance at the most traveled levels.
The total number of ice crystals produced is similar to the number of droplets expected in the initial liquid water contrail. All ice crystals appear to be produced through the freezing of droplets.
The rate of diffusional spreading of the contrail corresponds to an eddy diffusivity of 1.5× 105cmsec−1. No turbulence was detected and the diffusion appears isotropic after the rapid dissipation of the initial vertically organized turbulent wake.
Abstract
Particle size spectra were measured during 20 hr of sampling in cirrus generating cells (uncinus, stratus, spissatus, thunderstorm anvil) and the particle concentration, mean crystal length, ice water content, reflectivity factor, and precipitation rate were calculated from these spectra. Average values of the physical properties in the generating cells were:
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Ice crystal concentration: 10,000–25,000m−3
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Mean crystal length: 0.6–1.0 mm
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Particle habit: bullet, rosette, column (75%)-plate (25%)
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Ice crystal density. 0.6–0.9 gm m−3
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Ice water content. 0.15–0.25 gm −3
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Reflectivity factor: 5.0–20.0 mm6−3
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Precipitation rate. 0.5–0.7 mm hr−1
Growth was found to be downward, reaching a maximum ice water content just below the base of the generating cell. The maximum ice water contents (not including the thunderstorm anvil) were found in cirrus uncinus. Liquid water was not found throughout the cirrus sampling by measurement with the Johnson-Williams hot wire liquid water meter; however, we believe that liquid water is present as a transient phase.
Abstract
Particle size spectra were measured during 20 hr of sampling in cirrus generating cells (uncinus, stratus, spissatus, thunderstorm anvil) and the particle concentration, mean crystal length, ice water content, reflectivity factor, and precipitation rate were calculated from these spectra. Average values of the physical properties in the generating cells were:
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Ice crystal concentration: 10,000–25,000m−3
-
Mean crystal length: 0.6–1.0 mm
-
Particle habit: bullet, rosette, column (75%)-plate (25%)
-
Ice crystal density. 0.6–0.9 gm m−3
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Ice water content. 0.15–0.25 gm −3
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Reflectivity factor: 5.0–20.0 mm6−3
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Precipitation rate. 0.5–0.7 mm hr−1
Growth was found to be downward, reaching a maximum ice water content just below the base of the generating cell. The maximum ice water contents (not including the thunderstorm anvil) were found in cirrus uncinus. Liquid water was not found throughout the cirrus sampling by measurement with the Johnson-Williams hot wire liquid water meter; however, we believe that liquid water is present as a transient phase.
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.
