Observations and modelling of microphysical variability, aggregation and sedimentation in tropical anvil cirrus outflow regions

Gallagher, Martin; Connolly, Paul; Crawford, Ian; Heymsfield, A. J.; Bower, Keith; Choularton, T. W.; Allen, Grant; Flynn, Michael J.; Vaughan, G.; Hacker, Jörg

doi:10.5194/acp-12-6609-2012

Cited by 31 publications

(52 citation statements)

References 55 publications

(64 reference statements)

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“…5, 6, 7 and 14 with results from tropical/maritime storms, such as Fig. 10 in Gallagher et al (2012) or earlier observations of maritime/tropical chain aggregates (e.g., Stith et al, 2004, Fig. 13), suggest a very similar chain-aggregate structure exists in the Midwestern clouds we studied, with the exception that many of the Midwestern chain aggregates were composed of frozen droplets instead of faceted ice crystals.…”

Section: Discussionmentioning

confidence: 67%

Ice particles in the upper anvil regions of midlatitude continental thunderstorms: the case for frozen-drop aggregates

et al. 2014

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Abstract. This study examines the occurrence and morphology of frozen-drop aggregates in thunderstorm anvils from the United States Midwest and describes the environmental conditions where they are found. In situ airborne data collected in anvils using several particle imaging and sizing probes and bulk total water instrumentation during the 2012 Deep Convective Clouds and Chemistry experiment are examined for the presence of frozen-drop aggregates. Chains of frozen drops have been only rarely reported before and are hypothesized to aggregate due to electrical forces in the clouds. They were identified in nine of the anvil cases examined to date, suggesting that they are common features in these Midwestern anvils. High concentrations of individual frozen droplets occurred on the tops and edges of one particular set of anvils, while regions closer to the center and bottom of these anvils exhibited fewer frozen drops and more frozen-drop aggregates. Bulk ice water content measurements across these anvils could only be explained by contributions from both small particles (frozen droplets) and large particles (large aggregates of frozen droplets). Dual Doppler radar analysis confirmed the presence of deep and strong (> 15 m s −1 ) updrafts in the parent cloud of one of the anvils. These features contrast with previous anvil measurements in tropical/maritime anvils that evidently do not exhibit the same frequency of frozen-drop aggregates.

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Section: Discussionmentioning

confidence: 67%

Ice particles in the upper anvil regions of midlatitude continental thunderstorms: the case for frozen-drop aggregates

et al. 2014

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“…However, the small ice particles are not included in this analysis and the depolarisation of the dissipating stage is quite different to that of the mature clouds. This might be a hint for in situ nucleation of ice particles at this altitude, similar to the nucleation of new ice as observed in deep convection at the cloud edge by Gallagher et al (2012). In that case, the smaller ice particles, or a subset of them, would be recently frozen in situ while the larger crystals are leftovers from the mature stage.…”

Section: In Situ Ice Particle Nucleation In Aged Anvilmentioning

confidence: 99%

“…However, such in situ formed particles would be expected to have sizes of only up to a few tens of µm (e.g. Gallagher et al, 2012), whereas sizes in the developing stage exceed 100 µm. In the mature stage also larger particles reach the upper parts of the cloud.…”

Section: Freezing History Revealed From Depolarisation Ratiomentioning

confidence: 99%

“…As air is pushed upwards, sufficiently low temperatures and high relative humidities can be reached. Once the deep convective cloud ages and the anvil loses a large fraction of its ice water content (IWC) by sedimentation, new ice nucleation can occur, as observed by Gallagher et al (2012) in the cloud edge region. Thus, eventually not enough ice particles are left to reduce water vapour excess and suppress homogeneous freezing, as in the high updraft scenario mentioned above.…”

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confidence: 99%

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Tropical deep convective life cycle: Cb-anvil cloud microphysics from high-altitude aircraft observations

et al. 2014

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Abstract. The case study presented here focuses on the life cycle of clouds in the anvil region of a tropical deep convective system. During the SCOUT-O3 campaign from Darwin, Northern Australia, the Hector storm system has been probed by the Geophysica high-altitude aircraft. Clouds were observed by in situ particle probes, a backscatter sonde, and a miniature lidar. Additionally, aerosol number concentrations have been measured. On 30 November 2005 a double flight took place and Hector was probed throughout its life cycle in its developing, mature, and dissipating stage. The two flights were four hours apart and focused on the anvil region of Hector in altitudes between 10.5 and 18.8 km (i.e. above 350 K potential temperature). Trajectory calculations, satellite imagery, and ozone measurements have been used to ensure that the same cloud air masses have been probed in both flights.The size distributions derived from the measurements show a change not only with increasing altitude but also with the evolution of Hector. Clearly different cloud to aerosol particle ratios as well as varying ice crystal morphology have been found for the different development stages of Hector, indicating different freezing mechanisms. The development phase exhibits the smallest ice particles (up to 300 µm) with a rather uniform morphology. This is indicative for rapid glaciation during Hector's development. Sizes of ice crystals are largest in the mature stage (larger than 1.6 mm) and even exceed those of some continental tropical deep convective clouds, also in their number concentrations. The backscatter properties and particle images show a change in ice crystal shape from the developing phase to rimed and aggregated particles in the mature and dissipating stages; the specific shape of particles in the developing phase cannot be distinguished from the measurements. Although optically thin, the clouds in the dissipating stage have a large vertical extent (roughly 6 km) and persist for at least 6 h. Thus, the anvils of these high-reaching deep convective clouds have a high potential for affecting the tropical tropopause layer by modifying the humidity and radiative budget, as well as for providing favourable conditions for subvisible cirrus formation. The involved processes may also influence the amount of water vapour that ultimately reaches the stratosphere in the tropics.

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“…If the cloud is thick, reflection of solar radiation back to space can become greater than the long-wave absorption, and consequently can cause the surface of the Earth to cool (Baran, 2009). This net radiative effect depends on macroscopic cloud properties like optical thickness, ice water content, and geometric extent as well as on its microphysical parameters such as ice crystal number, size, and shape Gallagher et al, 2012;Zhang et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

Determining stages of cirrus evolution: a cloud classification scheme

et al. 2017

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Abstract. Cirrus clouds impose high uncertainties on climate prediction, as knowledge on important processes is still incomplete. For instance it remains unclear how cloud microphysical and radiative properties change as the cirrus evolves. Recent studies classify cirrus clouds into categories including in situ, orographic, convective and liquid origin clouds and investigate their specific impact. Following this line, we present a novel scheme for the classification of cirrus clouds that addresses the need to determine specific stages of cirrus evolution. Our classification scheme is based on airborne Differential Absorption and High Spectral Resolution Lidar measurements of atmospheric water vapor, aerosol depolarization, and backscatter, together with model temperature fields and simplified parameterizations of freezing onset conditions. It identifies regions of supersaturation with respect to ice (ice-supersaturated regions, ISSRs), heterogeneous and homogeneous nucleation, depositional growth, and ice sublimation and sedimentation with high spatial resolution. Thus, all relevant stages of cirrus evolution can be classified and characterized. In a case study of a gravity leewave-influenced cirrus cloud, encountered during the ML-CIRRUS flight campaign, the applicability of our classification is demonstrated. Revealing the structure of cirrus clouds, this valuable tool might help to examine the influence of evolution stages on the cloud's net radiative effect and to investigate the specific variability of optical and microphysical cloud properties in upcoming research.

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Observations and modelling of microphysical variability, aggregation and sedimentation in tropical anvil cirrus outflow regions

Cited by 31 publications

References 55 publications

Ice particles in the upper anvil regions of midlatitude continental thunderstorms: the case for frozen-drop aggregates

Ice particles in the upper anvil regions of midlatitude continental thunderstorms: the case for frozen-drop aggregates

Tropical deep convective life cycle: Cb-anvil cloud microphysics from high-altitude aircraft observations

Determining stages of cirrus evolution: a cloud classification scheme

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