Backscattersonde: a new instrument for atmospheric aerosol research

Rosen, James M.; Kjome, Norman T.

doi:10.1364/ao.30.001552

Cited by 108 publications

(81 citation statements)

References 12 publications

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“…It has specifications comparable to the Wyoming backscatter sonde by Rosen and Kjome (1991) but implements high-power light emitting diodes (LEDs) in place of the flashlamp. COBALD is much lighter (500 g including batteries) than the Rosen and Kjome sonde (6 kg).…”

Section: Cobald Particle Backscatter Sondementioning

confidence: 99%

“…Laboratory experiments have shown α < 0.1 (Pratte et al, 2006;Magee et al, 2006), which has been interpreted as colliding water molecules being trapped in a precursor state (Sadtchenko et al, 2004) on the ice surface and desorbing before being incorporated into the lattice. This inability of the surface to bind the water molecules has been related to surface disorder, which begins to develop on the topmost layers of ice at temperatures above 180 K, and thus ice surfaces are potentially disordered under all conditions prevailing atmospheric conditions.…”

Section: Comparison Of Measured and Modeled Relative Humiditymentioning

confidence: 99%

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Balloon-borne match measurements of midlatitude cirrus clouds

et al. 2014

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Abstract.Observations of high supersaturations with respect to ice inside cirrus clouds with high ice water content (> 0.01 g kg −1 ) and high crystal number densities (> 1 cm −3 ) are challenging our understanding of cloud microphysics and of climate feedback processes in the upper troposphere. However, single measurements of a cloudy air mass provide only a snapshot from which the persistence of ice supersaturation cannot be judged. We introduce here the "cirrus match technique" to obtain information about the evolution of clouds and their saturation ratio. The aim of these coordinated balloon soundings is to analyze the same air mass twice. To this end the standard radiosonde equipment is complemented by a frost point hygrometer, "SnowWhite", and a particle backscatter detector, "COBALD" (Compact Optical Backscatter AerosoL Detector). Extensive trajectory calculations based on regional weather model COSMO (Consortium for Small-Scale Modeling) forecasts are performed for flight planning, and COSMO analyses are used as a basis for comprehensive microphysical box modeling (with grid scale of 2 and 7 km, respectively). Here we present the results of matching a cirrus cloud to within 2-15 km, realized on 8 June 2010 over Payerne, Switzerland, and a location 120 km downstream close to Zurich. A thick cirrus cloud was detected over both measurement sites. We show that in order to quantitatively reproduce the measured particle backscatter ratios, the smallscale temperature fluctuations not resolved by COSMO must be superimposed on the trajectories. The stochastic nature of the fluctuations is captured by ensemble calculations. Possibilities for further improvements in the agreement with the measured backscatter data are investigated by assuming a very slow mass accommodation of water on ice, the presence of heterogeneous ice nuclei, or a wide span of (spheroidal) particle shapes. However, the resulting improvements from these microphysical refinements are moderate and comparable in magnitude with changes caused by assuming different regimes of temperature fluctuations for clear-sky or cloudysky conditions, highlighting the importance of proper treatment of subscale fluctuations. The model yields good agreement with the measured backscatter over both sites and reproduces the measured saturation ratios with respect to ice over Payerne. Conversely, the 30 % in-cloud supersaturation measured in a massive 4 km thick cloud layer over Zurich cannot be reproduced, irrespective of the choice of meteorological or microphysical model parameters. The measured supersaturation can only be explained by either resorting to an unknown physical process, which prevents the ice particles from consuming the excess humidity, or -much more likely -by a measurement error, such as a contamination of the sensor housing of the SnowWhite hygrometer by a precipitation drop from a mixed-phase cloud just below the cirrus layer or from some very slight rain in the boundary layer. This uncertainty calls for in-flight checks or calibrations of hygrom...

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Section: Cobald Particle Backscatter Sondementioning

confidence: 99%

Section: Comparison Of Measured and Modeled Relative Humiditymentioning

confidence: 99%

Balloon-borne match measurements of midlatitude cirrus clouds

et al. 2014

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“…It is based on similar principles as the Wyoming backscatter sonde of Rosen and Kjome (1991), which has been used extensively in field studies (e.g., Larsen et al, 1994;Rosen et al, 1997;Beyerle et al, 2001). COBALD uses two high power (250 mW) LEDs at wavelengths centred at 455 nm (blue) and 870 nm (infrared).…”

Section: Backscatter Sonde Cobaldmentioning

confidence: 99%

Particle backscatter and relative humidity measured across cirrus clouds and comparison with microphysical cirrus modelling

et al. 2012

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Abstract. Advanced measurement and modelling techniques are employed to estimate the partitioning of atmospheric water between the gas phase and the condensed phase in and around cirrus clouds, and thus to identify in-cloud and outof-cloud supersaturations with respect to ice. In November 2008 the newly developed balloon-borne backscatter sonde COBALD (Compact Optical Backscatter and AerosoL Detector) was flown 14 times together with a CFH (Cryogenic Frost point Hygrometer) from Lindenberg, Germany (52 • N, 14 • E). The case discussed here in detail shows two cirrus layers with in-cloud relative humidities with respect to ice between 50 % and 130 %. Global operational analysis data of ECMWF (roughly 1 • × 1 • horizontal and 1 km vertical resolution, 6-hourly stored fields) fail to represent ice water contents and relative humidities. Conversely, regional COSMO-7 forecasts (6.6 km × 6.6 km, 5-min stored fields) capture the measured humidities and cloud positions remarkably well. The main difference between ECMWF and COSMO data is the resolution of small-scale vertical features responsible for cirrus formation. Nevertheless, ice water contents in COSMO-7 are still off by factors 2-10, likely reflecting limitations in COSMO's ice phase bulk scheme. Significant improvements can be achieved by comprehensive size-resolved microphysical and optical modelling along backward trajectories based on COSMO-7 wind and temperature fields, which allow accurate computation of humidities, homogeneous ice nucleation, resulting ice particle size distributions and backscatter ratios at the COBALD wavelengths. However, only by superimposing small-scale temperature fluctuations, which remain unresolved by the numerical weather prediction models, can we obtain a satisfying agreement with the observations and reconcile the measured in-cloud nonequilibrium humidities with conventional ice cloud microphysics. Conversely, the model-data comparison provides no evidence that additional changes to ice-cloud microphysics -such as heterogeneous nucleation or changing the water vapour accommodation coefficient on ice -are required.

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“…The backscattersonde has been described by Rosen and Kjome [1991] and has been in routine use for several years [Rosen et al, 1997a, b]. Briefly, the instrument measures the locally backscattered light at two wavelengths (nominally 940 and 490 nm) on the rising and/or descending balloon.…”

Section: Backscattersondementioning

confidence: 99%

Springtime aerosol layers in the free troposphere over Australia: Mildura Aerosol Tropospheric Experiment (MATE 98)

Rosen¹,

Young²,

Laby³

et al. 2000

J. Geophys. Res.

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Abstract. A field campaign focused primarily on free tropospheric aerosol measurements over Mildura, Australia, at 34øS (Mildura Aerosol Tropospheric Experiment (MATE 98)) was conducted in the austral spring of 1998 to test for the current presence of a seasonal aerosol layering activity observed in the 1970s and to obtain additional characteristics that would lead to a better understanding of the phenomenon. Ground-based lidar as well as balloon-borne optical particle counters and backscattersondes with ozone sensors were employed. The results indicate that large horizontal scale layers are present and show that their structure is highly correlated with excess ozone. Particle concentrations in the layers were sufficient to measurably affect aerosol optical depth. The probable source is distant biomass burning regions, but a detailed understanding of associated smoke transport and evolution as observed over Mildura is incomplete. At the time of these measurements it was believed that the enhancements were related to biomass burning, but conclusive supporting evidence for this assumption was lacking. For example, since reliable relative humidity measurements were not made, it could be argued that the layers were simply caused by particle growth in layers of higher relative humidity that might be expected with springtime moisture. In addition, for biomass burning aerosols a good correlation with certain other trace species, such as ozone and/or carbon monoxide, might be expected, but this type of supporting information was unavailable. Also, it was unknown if the layers were localized or of large scale, as would be consistent with distant biomass burning sources.Only a two-point slope of the size distribution was measured in the 1970s, but a more complete size distribution was required to assess the physical and optical properties of the aerosol for relating it to the suspected source regions and estimating its radiative impact. For example, it could not be determined if the steep slope of the size distribution indicated that the aerosols were to be associated with the tail of a much higher concentration condensation nuclei mode or rather were part of a relatively narrow accumulation mode. Since the effective particle size for scattering could not be determined reliably from the available size information, it was not clear to us that the layers had sufficient optical cross sections to appreciably affect the radiative properties of the atmosphere. MATE 98In the austral spring of 1998 the Mildura Aerosol Tropospheric Experiment (MATE 98) was conducted for the purpose of reexamining the layers over Mildura in more detail and with the expectation that substantial evidence could be found linking them to biomass burning sources. The initial goal was to observe the presence of the layers and possibly identify changes in activity and/or magnitude. A more sophisticated OPC was employed to obtain extended size distributions for optical model calculations. Some optical properties of the 17,833

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Backscattersonde: a new instrument for atmospheric aerosol research

Cited by 108 publications

References 12 publications

Balloon-borne match measurements of midlatitude cirrus clouds

Balloon-borne match measurements of midlatitude cirrus clouds

Particle backscatter and relative humidity measured across cirrus clouds and comparison with microphysical cirrus modelling

Springtime aerosol layers in the free troposphere over Australia: Mildura Aerosol Tropospheric Experiment (MATE 98)

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