LIDAR measurements of cirrus clouds in the northern and southern midlatitudes during INCA (55°N, 53°S): A comparative study

Immler, Franz; Schrems, Otto

doi:10.1029/2002gl015077

Cited by 35 publications

(31 citation statements)

References 15 publications

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“…Recent studies of cloud optical properties have shown the LR frequency distribution is centred at 25 ± 15 sr for ice clouds (Yorks et al, 2011). This value is consistent with other lidar measurements made using this technique (Giannakaki et al, 2007;Immler and Schrems, 2002). In order to have the same confidence in all cases, including thin or thick clouds, and following the literature, we decided to use a constant LR of 25 sr.…”

Section: Ohp Ground-based Lidarsupporting

confidence: 54%

A decadal cirrus clouds climatology from ground-based and spaceborne lidars above the south of France (43.9° N–5.7° E)

et al. 2013

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This study provides an analysis of cirrus cloud properties at midlatitude in the southern part of France from ground-based and spaceborne lidars. A climatology of cirrus cloud properties and their evolution over more than 12 yr is presented and compared to other mid-latitude climatological studies. Cirrus clouds occur ~37% of the total observation time and remain quasi-constant across seasons with a variation within ~5% around the mean occurrence. Similar results are obtained from CALIOP and the ground-based lidar, with a mean difference in occurrence of ~5% between both instruments. From the ground-based lidar data, a slight decrease in occurrence of ~3% per decade is observed but found statistically insignificant. Based on a clustering analysis of cirrus cloud parameters, three distinct classes have been identified and investigations concerning their origin are discussed. Properties of these different classes are analysed, showing that thin cirrus in the upper troposphere represent ~50% of cloud cover detected in summer and fall, decreasing by 15–20% for other seasons

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Section: Ohp Ground-based Lidarsupporting

confidence: 54%

A decadal cirrus clouds climatology from ground-based and spaceborne lidars above the south of France (43.9° N–5.7° E)

et al. 2013

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“…Thus it cannot be excluded that heterogeneous nucleation is much more important for cirrus formation in the northern hemisphere than anywhere else. In fact, recent lidar measurements of cirrus clouds in both northern and southern midlatitudes suggest that just this is the case (Immler and Schrems, 2002).…”

Section: Discussionmentioning

confidence: 99%

On the transition between heterogeneous and homogeneous freezing

Gierens

2003

Atmos. Chem. Phys.

111

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Abstract. Box model simulations of an uplifting and adiabatically cooling cloud of aerosol have been performed in order to study the transition between cirrus formation dominated by homogeneous nucleation of ice to that dominated by heterogeneous nucleation. The aerosol was assumed to consist of an internal mixture of sulfuric acid solution droplets with inclusions of soot. The parametrisation of DeMott et al. (1997) was used to simulate the heterogeneous nucleation of ice in such droplets with soot inclusions. The simulations show that the transition from heterogeneous to homogeneous nucleation occurs over a narrow range of soot concentration. Thus it seems to be possible to fix critical concentrations of heterogeneous ice nuclei which must be exceeded if heterogeneous freezing dominates cirrus formation. A formula has been derived that allows to compute the critical concentrations of heterogeneous ice nuclei as a function of temperature, updraft speed, ambient pressure, and supersaturation at which heterogeneous freezing occurs. Generally, homogeneous nucleation dominates in regions with updrafts stronger than 20 cm s −1 , with the exception of heavily polluted areas which could be common in the northern hemisphere due to air traffic, where updrafts of the order 1 m s −1 may be necessary to render heterogeneous nucleation unimportant. According to the present results it cannot be excluded that heterogeneous nucleation plays a more important role for cirrus formation in the northern midlatitudes than anywhere else. A possible consequence of these results is that air pollution may lead to a higher coverage of cirrus clouds, but then these clouds will be optically thinner than clouds formed by homogeneous freezing, with the exception of regions where condensation trails are frequent.

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“…Additionally, the overall system depolarization should be taken into account (Biele et al, 2000). However, the simplified procedure which we use here leads to very reasonable results, not only in so far as the dust aerosol is concerned but also cirrus are described appropriately (Immler and Schrems, 2002). It should be kept in mind that considerable bias might be connected to the depolarization measurement.…”

Section: Depolarizationmentioning

confidence: 99%

Vertical profiles, optical and microphysical properties of Saharan dust layers determined by a ship-borne lidar

Immler

Schrems

2003

Atmos. Chem. Phys.

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Abstract.A unique data set of ship-borne lidar measurements of Saharan dust layers above the Atlantic ocean has been collected aboard the research vessel Polarstern with a mobile Aerosol Raman Lidar (MARL) during the LIMPIDOcampaign in June 2000. Extended Saharan dust layers have been observed in the region between 8.5 • N and 34 • N in an altitude range between 2 and 6 km. The continental, North African origin of the probed air masses is confirmed by 8-day backward trajectories. The Saharan dust is characterized by an optical depth in the range of 0.1 and 0.3, a depolarization around 10% and high lidar ratios of 45 sr at 532 nm and 75 sr at 355 nm. The backscattering by the dust particles at the UV-wavelength is relatively weak, resulting in a negative color index. From the measured optical properties the effective radius and the refractive index of the dust particles are derived using a new approach based on Mie Theory and nonspherical scattering calculations. The low backscatter coefficient observed at 355 nm is due to significant absorption which increases with decreasing wavelength. This finding agrees very well with results from satellite and sun photometer measurements. The effective radii decrease from about 3 µm at the base to 0.6 µm at the top of the dust plumes. The non-spherical shapes of the dust particles are responsible for the high values of the lidar ratios.

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LIDAR measurements of cirrus clouds in the northern and southern midlatitudes during INCA (55°N, 53°S): A comparative study

Cited by 35 publications

References 15 publications

A decadal cirrus clouds climatology from ground-based and spaceborne lidars above the south of France (43.9° N–5.7° E)

A decadal cirrus clouds climatology from ground-based and spaceborne lidars above the south of France (43.9° N–5.7° E)

On the transition between heterogeneous and homogeneous freezing

Vertical profiles, optical and microphysical properties of Saharan dust layers determined by a ship-borne lidar

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