Small, highly reflective ice crystals in low‐latitude cirrus

Garrett, T. J.; Gerber, H.; Baumgardner, Darrel; Twohy, Cynthia H.; Weinstock, E. M.

doi:10.1029/2003gl018153

Cited by 102 publications

(105 citation statements)

References 31 publications

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“…These small ice crystal effective dimensions have been chosen so as to maximise scattering so that differences between ice crystal shapes may become more apparent. However, such a small D e value might occur in tropical cirrus (Garrett et al 2003). The difference in D e between the two shapes is 1.18 µm and such a small difference will not affect the conclusions of this paper.…”

Section: Impact Of Ice Crystal Geometrymentioning

confidence: 78%

The impact of cirrus microphysical and macrophysical properties on upwelling far‐infrared spectra

Baran

2007

Quart J Royal Meteoro Soc

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ABSTRACT:The potential for exploiting upwelling high-resolution far-infrared measurements to obtain information on cirrus microphysical properties is evaluated assuming single-layer and multiple-layer cirrus embedded in standard midlatitude winter and tropical atmospheres. The microphysical sensitivity of two high-resolution spectral regions (606 cm −1 -333 cm −1 and 250 cm −1 -80 cm −1 ) to changes in optically thin single-layer cirrus height, and to perturbing the volume mixing ratio of water vapour of the standard midlatitude winter atmosphere by 30% is studied. It is found that there are spectral 'windows' in the far-infrared which are strongly dependent on ice crystal effective size. In particular, 'windows' existing between the wave numbers of about 365 cm −1 to 500 cm −1 and 85 cm −1 to 140 cm −1 demonstrate potential sensitivity to ice crystal effective dimension of up to about 100.0 µm and 50.0 µm, respectively. However, these same spectral windows are also shown to be strongly sensitive to assumptions about the shape of the particle size distribution function and ice crystal geometry. Moreover, sensitivity to ice crystal effective dimension is further shown to be dependent on the location of the cirrus layer within the atmosphere, especially in the spectral region 606 cm −1 -333 cm −1 . Perturbing the volume mixing ratio of water vapour by 30% has its largest impact on the cirrus layer located higher in the atmosphere. In this case the sensitivity to the smallest ice crystal effective dimension of about 8.0 µm is essentially removed and the sensitivity to the largest ice crystal effective dimension of about 100 µm is significantly reduced in the spectral region of 606 cm −1 -333 cm −1 . Therefore, in order to retrieve cirrus microphysical properties in the far-infrared, prior information on ice crystal geometry and shape of the distribution function is required. Moreover, the volume mixing ratio of water vapour should be measured to within an accuracy of better than 30%. It is further demonstrated that for selected wave numbers in the far-infrared, assuming a three-layer cloud, there is also some dependence on the vertical structure of the atmosphere as well as the vertical profile of ice crystal effective size.  Crown

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Section: Impact Of Ice Crystal Geometrymentioning

confidence: 78%

The impact of cirrus microphysical and macrophysical properties on upwelling far‐infrared spectra

Baran

2007

Quart J Royal Meteoro Soc

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“…The observation of a decreasing effective radius with altitude is in agreement with observations and model calculations in the tropics presented by Chen et al (1997), who show a decreasing effective radius with altitude. Also Garrett et al (2003) observed a decreasing effective radius with decreasing ambient temperature in the sub-tropics. They suggest that this is caused by the fact that homogeneous ice nucleation favours smaller ice crystals at colder temperatures, due to the exponential dependence of the saturation vapour pressure over ice on temperature (Kärcher and Lohmann, 2002), rather than the effect of ageing of the cirrus cloud or gravitational settling.…”

Section: Effective Radius and Ice Water Contentmentioning

confidence: 92%

Evidence for ice particles in the tropical stratosphere from in-situ measurements

et al. 2009

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Abstract. In-situ ice crystal size distribution measurements are presented within the tropical troposphere and lower stratosphere. The measurements were performed using a combination of a Forward Scattering Spectrometer Probe (FSSP-100) and a Cloud Imaging Probe (CIP), which were installed on the Russian high altitude research aircraft M55 "Geophysica" during the SCOUT-O 3 campaign in Darwin, Australia. One of the objectives of the campaign was to characterise the Hector convective system, which appears on an almost daily basis during the pre-monsoon season over the Tiwi Islands, north of Darwin. In total 90 encounters with ice clouds, between 10 and 19 km altitude were selected from the dataset and were analysed. Six of these encounters were observed in the lower stratosphere, up to 1.4 km above the local tropopause. Concurrent lidar measurements on board "Geophysica" indicate that these ice clouds were a result of overshooting convection. Large ice crystals, with a maximum dimension up to 400 µm, were observed in the stratosphere. The stratospheric ice clouds included an ice water content ranging from 7.7×10 −5 to 8.5×10 −4 g m −3 and were observed at ambient relative humidities (with respect to ice) between 75 and 157%. Three modal lognormal size distributions were fitted to the average size distributions for different potential temperature intervals, showing that the Correspondence to: S. Borrmann (stephan.borrmann@mpic.de) shape of the size distribution of the stratospheric ice clouds are similar to those observed in the upper troposphere.In the tropical troposphere the effective radius of the ice cloud particles decreases from 100 µm at about 10 km altitude, to 3 µm at the tropopause, while the ice water content decreases from 0.04 to 10 −5 g m −3 . No clear trend in the number concentration was observed with altitude, due to the thin and inhomogeneous characteristics of the observed cirrus clouds.The ice water content calculated from the observed ice crystal size distribution is compared to the ice water content derived from two hygrometer instruments. This independent measurement of the ice water content agrees within the combined uncertainty of the instruments for ice water contents exceeding 3×10 −4 g m −3 .Stratospheric residence times, calculated based on gravitational settling, and evaporation rates show that the ice crystals observed in the stratosphere over the Hector storm system had a high potential of humidifying the stratosphere locally.

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“…Yet, if present, small ice crystals are important for the radiative properties of these clouds (Garrett et al, 2003). Two recent studies by Garrett (2010, 2011) used remote sensing observations by the MODIS satellite as an independent method to constrain the frequency of thin cirrus clouds composed of small ice particles with an effective radius below 20 µm.…”

Section: Introductionmentioning

confidence: 99%

Influence of particle size and shape on the backscattering linear depolarisation ratio of small ice crystals – cloud chamber measurements in the context of contrail and cirrus microphysics

et al. 2012

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Abstract. The article presents the laser scattering and depolarisation instrument SIMONE that is installed at the large aerosol and cloud chamber facility AIDA of the Karlsruhe Institute of Technology. SIMONE uses a 488 nm cw laser to probe simulated atmospheric clouds by measuring the scattered light from the 1.8 • and 178.2 • directions. At 178.2 • , the scattered light is analysed for the linear polarisation state to deduce the particle linear depolarisation ratio δ p which is a common measurement parameter of atmospheric lidar applications. The optical setup and the mathematical formalism of the depolarisation detection concept are given. SIMONE depolarisation measurements in spheroidal hematite aerosol and supercooled liquid clouds are used to validate the instrument.SIMONE data from a series of AIDA ice nucleation experiments at temperatures between 195 and 225 K were analysed in terms of the impact of the ice particle microphysics on δ p . We found strong depolarisation values of up to 0.4 in case of small growing and sublimating ice particles with volume equivalent diameters of only a few micrometers.Modelling runs with the T-matrix method showed that the measured depolarisation ratios can be accurately reproduced assuming spheroidal and cylindrical particles with a size distribution that has been constrained by IR extinction spectroscopy. Based on the T-matrix modelling runs, we demonstrate that in case of small ice crystals the SIMONE depolarisation results are representative for the lidar depolarisation ratio which is measured at exact backscattering direction of 180 • .The relevance of our results for the interpretation of recent lidar observations in cirrus and contrails is discussed. In view of our results, the high depolarisation ratios observed by the spaceborne lidar CALIOP in the tropical upper troposphere might be a hint for the presence of small (sublimating) ice particles in the outflows of deep convective systems.

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Small, highly reflective ice crystals in low‐latitude cirrus

Cited by 102 publications

References 31 publications

The impact of cirrus microphysical and macrophysical properties on upwelling far‐infrared spectra

The impact of cirrus microphysical and macrophysical properties on upwelling far‐infrared spectra

Evidence for ice particles in the tropical stratosphere from in-situ measurements

Influence of particle size and shape on the backscattering linear depolarisation ratio of small ice crystals – cloud chamber measurements in the context of contrail and cirrus microphysics

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