Convective formation of pileus cloud near the tropopause

Abstract. Pileus clouds form where humid, vertically stratified air is mechanically displaced ahead of rising convection. This paper describes convective formation of pileus cloud in the tropopause transition layer (TTL), and explores a possible link to the formation of long-lasting cirrus at cold temperatures. The study examines in detail in-situ measurements from off the coast of Honduras during the July 2002 CRYSTAL-FACE experiment that showed an example of TTL cirrus associated with, and penetrated by, deep convection. The TTL cirrus was enriched with total water compared to its surroundings, but was composed of extremely small ice crystals with effective radii between 2 and 4 μm. Through gravity wave analysis, and intercomparison of measured and simulated cloud microphysics, it is argued that the TTL cirrus originated neither from convectively-forced gravity wave motions nor environmental mixing alone. Rather, it is hypothesized that a combination of these two processes was involved in which, first, a pulse of convection forced pileus cloud to form from TTL air; second, the pileus layer was punctured by the convective pulse and received larger ice crystals through interfacial mixing; third, the addition of this condensate inhibited evaporation of the original pileus ice crystals where a convectively forced gravity wave entered its warm phase; fourth, through successive pulses of convection, a sheet of TTL cirrus formed. While the general incidence and longevity of pileus cloud remains unknown, in-situ measurements, and satellite-based Microwave Limb Sounder retrievals, suggest that much of the tropical TTL is sufficiently humid to be susceptible to its formation. Where these clouds form and persist, there is potential for an irreversible repartition from water vapor to ice at cold temperatures.

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Modelling rain heterogeneities within an urban neighbourhood

10.5194/egusphere-egu21-7806 ◽

2021 ◽

Author(s):

Karolin S. Ferner ◽

K. Heinke Schlünzen ◽

Marita Boettcher

Keyword(s):

Wind Speed ◽

Urban Areas ◽

Climate Model ◽

Numerical Models ◽

Urban Climate ◽

Cloud Microphysics ◽

In Situ Measurements ◽

Small Scale ◽

Atmospheric Processes

Urbanisation locally modifies the regional climate: an urban climate develops. For example, the average wind speed in cities is reduced, while the gustiness is increased. Buildings induce vertical winds, which influence the falling of rain. All these processes lead to heterogeneous patterns of rain at ground and on building surfaces. The small-scale spatial rain heterogeneities may cause discomfort for people. Moreover, non-uniform wetting of buildings affects their hydrothermal performance and durability of their facades.Measuring rain heterogeneities between buildings is, however, nearly impossible. Building induced wind gusts negatively influence the representativeness of in-situ measurements, especially in densely urbanised areas. Weather radars are usually too coarse and, more importantly, require an unobstructed view over the domain and thus do not measure ground precipitation in urban areas. Consequently, researchers turn to numerical modelling in order to investigate small-scale precipitation heterogeneities between buildings.In building science, numerical models are used to investigate rain heterogeneities typically focussing on single buildings and vertical facades. Only few studies were performed for more than a single building or with inclusion of atmospheric processes such as radiation or condensation. In meteorology, increasing computational power now allows the use of small-scale obstacle-resolving models resolving atmospheric processes while covering neighbourhoods.In order to assess rain heterogeneities between buildings we extended the micro-scale and obstacle-resolving transport- and stream model MITRAS (Salim et al. 2019). The same cloud microphysics parameterisation as in its mesoscale sister model METRAS (Schl&#252;nzen et al., 2018) was applied and boundary conditions for cloud and rain water content at obstacle surfaces were introduced. MITRAS results are checked for plausibility using radar and in-situ measurements (Ferner et al., 2021). To our knowledge MITRAS is the first numerical urban climate model that includes rain and simulates corresponding processes.Model simulations were initialised for various wind speeds and mesoscale rain rates to assess their influence on the heterogeneity of falling rain in a domain of 1.9 x 1.7 km&#178; around Hamburg City Hall. We investigated how wind speed or mesoscale rain rate influence the precipitation patterns at ground and at roof level. Based on these results we assessed the height dependence of precipitation. First analyses show that higher buildings receive more rain on their roofs than lower buildings; the results will be presented in detail in our talk.Ferner, K.S., Boettcher, M., Schl&#252;nzen, K.H. (2021): Modelling the heterogeneity of rain in an urban neighbourhood. Publication in preparationSalim, M.H., Schl&#252;nzen, K.H., Grawe, D., Boettcher, M., Gierisch, A.M.U., Fock B.H. (2018): The microscale obstacle-resolving meteorological model MITRAS v2.0: model theory. Geosci. Model Dev., 11, 3427&#8211;3445, https://doi.org/10.5194/gmd-11-3427-2018.Schl&#252;nzen, K.H., Boettcher, M., Fock, B.H., Gierisch, A.M.U., Grawe, D., and Salim, M. (2018): Scientific Documentation of the Multiscale Model System M-SYS. Meteorological Institute, Universit&#228;t Hamburg. MEMI Technical Report 4

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Application of infrared remote sensing to constrain in-situ estimates of ice crystal particle size during SPartICus

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-4-3055-2011 ◽

2011 ◽

Vol 4 (3) ◽

pp. 3055-3081

Author(s):

S. J. Cooper ◽

T. J. Garrett

Keyword(s):

Remote Sensing ◽

In Situ Measurements ◽

Ice Crystals ◽

Cirrus Cloud ◽

Atmospheric Conditions ◽

Airborne Measurements ◽

Remote Sensing Technique ◽

Infrared Remote Sensing ◽

Retrieval Scheme

Abstract. In a prior paper (Cooper and Garrett, 2010), an infrared remote sensing technique was developed that quantifies the effective radius re of ice crystals in cirrus clouds. By accounting for a broad range of expected inversion uncertainties, this retrieval scheme isolates those radiometric signatures that can only occur if the cirrus has nominally "small" values of re below 20 μm. The method is applicable only for specific cloud and atmospheric conditions. However, it can be particularly useful in constraining in-situ estimates of cirrus cloud re obtained from aircraft. Recent studies suggest that airborne measurements may be compromised by the shattering of ice crystals on airborne instrument inlets, so robust, independent confirmation of these measurements is needed. Here, we expand the Cooper and Garrett (2010) retrieval scheme to identify ice clouds that are likely to have "large" values of re greater than 20 μm. Using MODIS observations, we then compare assessments of cirrus cloud re with in-situ measurements obtained during three test cases from the 2010 SpartICus campaign. In general, there is good agreement between retrievals and in-situ measurements for a "small" and "large" crystal case. For a more ambiguously "small" re case, the 2D-S cloud probe indicates values of re that are slightly larger than expected from infrared retrievals, possibly indicating a slight bias in the 2D-S results towards large particles. There is no evidence to support that an FSSP-100 with unmodified inlets produces measurements of re in cirrus that are strongly biased low, as has been claimed.

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Observing cirrus halos to constrain in-situ measurements of ice crystal size

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-1295-2007 ◽

2007 ◽

Vol 7 (1) ◽

pp. 1295-1325 ◽

Cited By ~ 2

Author(s):

T. J. Garrett ◽

M. B. Kimball ◽

G. G. Mace ◽

D. G. Baumgardner

Keyword(s):

Crystal Size ◽

In Situ Measurements ◽

Ice Crystals ◽

Ice Crystal ◽

Optical Extinction ◽

Airborne Measurements ◽

Ice Cloud ◽

Ice Crystal Size ◽

High Concentrations

Abstract. In this study, characteristic optical sizes of ice crystals in synoptic cirrus are determined using airborne measurements of ice crystal size distributions, optical extinction and water content. The measurements are compared with coincident visual observations of ice cloud optical phenomena, in particular the 22° and 46° halos. In general, the scattering profiles derived from the in-situ cloud probe measurements are consistent with the observed halo characteristics. It is argued that this implies that the measured ice crystals were small, probably with characteristic optical radii between 10 and 20 μm. There is a current contention that in-situ measurements of high concentrations of small ice crystals reflect artifacts from the shattering of large ice crystals on instrument inlets. Significant shattering cannot be entirely excluded using this approximate technique, but it is not indicated. On the basis of the in-situ measurements, a parameterization is provided that relates the optical effective radius of ice crystals to the temperature in mid-latitude synoptic cirrus.

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In situ measurements of capillary-gravity wave spectra using a scanning laser slope gauge and microwave radars

Journal of Geophysical Research Atmospheres ◽

10.1029/94jc00531 ◽

1994 ◽

Vol 99 (C6) ◽

pp. 12593 ◽

Cited By ~ 34

Author(s):

Tetsu Hara ◽

Erik J. Bock ◽

David Lyzenga

Keyword(s):

Gravity Wave ◽

In Situ Measurements ◽

Scanning Laser ◽

Wave Spectra

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In situ measurements of cloud microphysics and aerosol over coastal Antarctica during the MAC campaign

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-13049-2017 ◽

2017 ◽

Vol 17 (21) ◽

pp. 13049-13070 ◽

Cited By ~ 12

Author(s):

Sebastian J. O'Shea ◽

Thomas W. Choularton ◽

Michael Flynn ◽

Keith N. Bower ◽

Martin Gallagher ◽

...

Keyword(s):

Liquid Water ◽

Cloud Microphysics ◽

Effective Radius ◽

In Situ Measurements ◽

Weddell Sea ◽

Interquartile Range ◽

Future Climate Change ◽

Cloud Base ◽

Ice Production

Abstract. During austral summer 2015, the Microphysics of Antarctic Clouds (MAC) field campaign collected unique and detailed airborne and ground-based in situ measurements of cloud and aerosol properties over coastal Antarctica and the Weddell Sea. This paper presents the first results from the experiment and discusses the key processes important in this region, which is critical to predicting future climate change. The sampling was predominantly of stratus clouds, at temperatures between −20 and 0 °C. These clouds were dominated by supercooled liquid water droplets, which had a median concentration of 113 cm−3 and an interquartile range of 86 cm−3. Both cloud liquid water content and effective radius increased closer to cloud top. The cloud droplet effective radius increased from 4 ± 2 µm near cloud base to 8 ± 3 µm near cloud top. Cloud ice particle concentrations were highly variable with the ice tending to occur in small, isolated patches. Below approximately 1000 m, glaciated cloud regions were more common at higher temperatures; however, the clouds were still predominantly liquid throughout. When ice was present at temperatures higher than −10 °C, secondary ice production most likely through the Hallett–Mossop mechanism led to ice concentrations 1 to 3 orders of magnitude higher than the number predicted by commonly used primary ice nucleation parameterisations. The drivers of the ice crystal variability are investigated. No clear dependence on the droplet size distribution was found. The source of first ice in the clouds remains uncertain but may include contributions from biogenic particles, blowing snow or other surface ice production mechanisms. The concentration of large aerosols (diameters 0.5 to 1.6 µm) decreased with altitude and were depleted in air masses that originated over the Antarctic continent compared to those more heavily influenced by the Southern Ocean and sea ice regions. The dominant aerosol in the region was hygroscopic in nature, with the hygroscopicity parameter κ having a median value for the campaign of 0.66 (interquartile range of 0.38). This is consistent with other remote marine locations that are dominated by sea salt/sulfate.

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Evaluation of the Lidar–Radar Cloud Ice Water Content Retrievals Using Collocated in Situ Measurements

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-15-0040.1 ◽

2015 ◽

Vol 54 (10) ◽

pp. 2087-2097 ◽

Cited By ~ 6

Author(s):

Sujan Khanal ◽

Zhien Wang

Keyword(s):

Remote Sensing ◽

Water Content ◽

Cloud Microphysics ◽

In Situ Measurements ◽

Ice Water Content ◽

Flight Level ◽

The Mean ◽

Cloud Ice ◽

Ice Water

AbstractRemote sensing and in situ measurements made during the Colorado Airborne Multiphase Cloud Study, 2010–2011 (CAMPS) with instruments aboard the University of Wyoming King Air aircraft are used to evaluate lidar–radar-retrieved cloud ice water content (IWC). The collocated remote sensing and in situ measurements provide a unique dataset for evaluation studies. Near-flight-level IWC retrieval is compared with an in situ probe: the Colorado closed-path tunable diode laser hygrometer (CLH). Statistical analysis showed that the mean radar–lidar IWC is within 26% of the mean in situ measurements for pure ice clouds and within 9% for liquid-topped mixed-phase clouds. Considering their different measurement techniques and different sample volumes, the comparison shows a statistically good agreement and is close to the measurement uncertainty of the CLH, which is around 20%. It is shown that ice cloud microphysics including ice crystal shape and orientation has a significant impact on IWC retrievals. These results indicate that the vertical profile of the retrieved lidar–radar IWC can be reliably combined with the flight-level measurements made by the in situ probes to provide a more complete picture of the cloud microphysics.

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Microphysical and optical properties of precipitating drizzle and ice particles obtained from alternated lidar and in situ measurements

Annales Geophysicae ◽

10.5194/angeo-25-1487-2007 ◽

2007 ◽

Vol 25 (7) ◽

pp. 1487-1497 ◽

Cited By ~ 20

Author(s):

J.-F. Gayet ◽

I. S. Stachlewska ◽

O. Jourdan ◽

V. Shcherbakov ◽

A. Schwarzenboeck ◽

...

Keyword(s):

Optical Properties ◽

Particle Morphology ◽

In Situ Measurements ◽

Ice Crystals ◽

Cloud Formation ◽

Cloud Particle ◽

Flight Pattern ◽

Depolarisation Ratio ◽

Scattering Phase Function

Abstract. During the international ASTAR experiment (Arctic Study of Aerosols, Clouds and Radiation) carried out from Longyearbyen (Spitsbergen) from 10 May to 11 June 2004, the AWI (Alfred Wegener Institute) Polar 2 aircraft was equipped with a unique combination of remote and in situ instruments. The airborne AMALi lidar provided downward backscatter and Depolarisation ratio profiles at 532 nm wavelength. The in situ instrumental setup comprised a Polar Nephelometer, a Cloud Particle Imager (CPI) as well as a Nevzorov and standard PMS probes to measure cloud particle properties in terms of scattering characteristics, particle morphology and size, and in-cloud partitioning of ice/water content. The objective of the paper is to present the results of a case study related to observations with ice crystals precipitating down to supercooled boundary-layer stratocumulus. The flight pattern was predefined in a way that firstly the AMALi lidar probed the cloud tops to guide the in situ measurements into a particular cloud formation. Three kinds of clouds with different microphysical and optical properties have therefore been quasi-simultaneously observed: (i) water droplets stratiform-layer, (ii) drizzle-drops fallstreak and (iii) precipitating ice-crystals from a cirrus cloud above. The signatures of these clouds are clearly evidenced from the in situ measurements and from the lidar profiles in term of backscatter and Depolarisation ratio. Accordingly, typical lidar ratios, i.e., extinction-to-backscatter ratios, are derived from the measured scattering phase function combined with subsequent particle shapes and size distributions. The backscatter profiles can therefore be retrieved under favourable conditions of low optical density. From these profiles extinction values in different cloud types can be obtained and compared with the direct in situ measurements.

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The passing of long internal and external gravity wave over a step. Laboratory and in-situ measurements compared with analytical modelling

IEEE Oceanic Engineering Society. OCEANS'98. Conference Proceedings (Cat. No.98CH36259) ◽

10.1109/oceans.1998.724362 ◽

2002 ◽

Author(s):

K. Guizien ◽

C. Ramirez ◽

E. Barthelemy ◽

D. Renouard

Keyword(s):

Gravity Wave ◽

In Situ Measurements ◽

Analytical Modelling

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The Structure of Turbulence and mixed-phase Cloud Microphysics in a Highly Supercooled Altocumulus Cloud

10.5194/acp-2019-749 ◽

2019 ◽

Author(s):

Paul A. Barrett ◽

Alan Blyth ◽

Philip R. A. Brown ◽

Steven J. Abel

Keyword(s):

Cloud Microphysics ◽

In Situ Measurements ◽

Cloud Layer ◽

Mixed Phase ◽

Turbulence Spectrum ◽

Ice Cloud ◽

Cloud Properties ◽

Negative Skewness ◽

Turbulence Data

Abstract. Observations of vertically resolved turbulence and cloud microphysics in a mixed-phase altocumulus cloud are presented using in situ measurements from an instrumented aircraft. The turbulence spectrum is observed to have an increasingly negative skewness with distance below cloud top, confirming that longwave radiative cooling from the liquid layer cloud is the source of turbulence kinetic energy. Turbulence data are presented from both the liquid cloud layer and ice virga below. Vertical profiles of both bulk and microphysical liquid and ice cloud properties indicate that ice is produced within the liquid cloud layer at a temperature of −30 °C. These high resolution in situ measurements support previous remotely-sensed observations from both ground based and space borne instruments, and could be used to evaluate numerical model simulations of altocumulus clouds at all scales from eddy resolving to climate.

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