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

Abstract. During austral summer 2015 the Microphysics of Antarctic Clouds (MAC) field campaign collected 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. The sampling was predominantly of stratus cloud, 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 inter-quartile range of 86 cm−3. The concentration of large aerosols (0.5 to 1.6 μm) decreased with altitude and were depleted in airmasses 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 0.64 (interquartile range = 0.34). This is consistent with other remote marine locations that are dominated by sea salt/sulphate. Cloud ice particle concentrations were highly variable with the ice tending to occur in small isolated patches. Below ca 2000 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 Hallet-Mossop mechanism lead 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. However, higher ice concentrations were found in updrafts and downdrafts compared to quiescent regions. 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.

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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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Convective formation of pileus cloud near the tropopause

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-1185-2006 ◽

2006 ◽

Vol 6 (5) ◽

pp. 1185-1200 ◽

Cited By ~ 15

Author(s):

T. J. Garrett ◽

J. Dean-Day ◽

C. Liu ◽

B. Barnett ◽

G. Mace ◽

...

Keyword(s):

Gravity Wave ◽

Deep Convection ◽

Cloud Microphysics ◽

In Situ Measurements ◽

Ice Crystals ◽

Total Water ◽

Wave Analysis ◽

Cold Temperatures ◽

Face Experiment

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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Swell Genesis, Modelling and Measurements in West Africa

Volume 2B: Structures, Safety and Reliability ◽

10.1115/omae2013-11201 ◽

2013 ◽

Cited By ~ 2

Author(s):

Marc Prevosto ◽

Kevin Ewans ◽

George Z. Forristall ◽

Michel Olagnon

Keyword(s):

West Africa ◽

Numerical Models ◽

Austral Summer ◽

In Situ Measurements ◽

West African ◽

The South ◽

West African Coast ◽

Westerly Direction ◽

Propagation Of Waves

Swell events show a large variety of configurations when they arrive at sites off West Africa after generation and propagation of waves across the Atlantic Ocean. Within the West Africa Swell Project (WASP JIP), these different configurations have been described and discussed and the ability of numerical models to reproduce faithfully their properties has been assessed from comparisons with in-situ measurements. During the austral winter months, swells approach West African coast from the south to south-westerly direction. These swells are generated by storms in the South Atlantic mainly between 40°S and 60°S. But during austral summer, north-westerly swells are also observed coming from North Atlantic. Typical situations of superposition of these different swells are illustrated in the paper. In spite of a poor overlapping between numerical and in-situ measurements databases at the time of the WASP project, and of reduced durations of measurement campaigns, comparisons between in situ measurements and hindcast models permitted identification of the limitations of the different numerical models available. Three sites have been used for this study, one in the Gulf of Guinea with directional Waverider and Wavescan buoys, a second one off Namibia with a directional Waverider and one last instrumented with two wavestaffs off Cabinda (Angola). In addition, the existence of infra-gravity waves in shallow water measurements has been investigated.

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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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Modeling of the Russell glacier's basal conditions at seasonal time scale using the satellite observations of surface ice speed

10.5194/egusphere-egu21-4672 ◽

2021 ◽

Author(s):

Anna Derkacheva ◽

Fabien Gillet-Chaulet ◽

Jeremie Mouginot

Keyword(s):

Time Series ◽

Temporal Resolution ◽

Flow Model ◽

In Situ Measurements ◽

Satellite Observations ◽

Surface Velocity ◽

Ice Flow ◽

Surface Ice ◽

The Impact

Greenland&#8217;s future response to climate change will be determined partly by various phenomena controlling ice flow. For the land-terminating sectors, the water lubricating the glacier's base is considered as a major control on the ice motion. For instance, the seasonal modulations of water input induced by summer melt can cause glacier speed-up up to +200-300% compared to the winter mean. Thus, a comprehensive understanding of variations in the basal conditions, which are at the origin of the glacier flow fluctuations, plays a key role for the climate projections.While the in-situ measurements stay a local and hard approach to investigate the basal conditions, ice flow modeling offers the possibility to invert for them over the large area based on observations of surface glacier speed and topography. During the last decade, the number of available satellite observations has increased significantly, allowing for far more frequent measurements of the glacier speed and precise reconstruction of the seasonal fluctuations. Here, we investigate the possibility of applying this satellite-derived time-series of surface ice velocity to reconstruct the annual behavior of the basal conditions with 2 weeks temporal resolution using an ice flow model.The area of this study is Russell glacier located on the southwest coast of Greenland. A time series of surface velocity dataset was created by merging measurements from Sentinel-1&2 and Landsat-8, covering an area up to 100 km inland with 150 m/pix spatial resolution and 2-weeks temporal resolution (Derkacheva et al. 2020). The 3D Full-Stokes ice flow model Elmer/Ice is used to invert for the effective basal friction coefficient for each time step.&#160; Usage of a friction law that has been derived for hard beds (Gagliardini et al., 2007) allows to constrain the variation of the basal effective pressure. Overall, the results from the model inversions give access to the evolution of the basal ice speed, friction, effective and water pressure, floatation fraction throughout a complete year. The results are compared with in-situ measurements in terms of absolute values and show a good agreement. The impact of the flow model setup, regularization, assumptions for the ice rheology, and the impact of noise in the speed data are also examined and compared with in-situ measurements.

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A recent update on the circulation and water masses around the Filchner and Ronne ice shelves in the southern Weddell Sea

10.5194/egusphere-egu2020-10194 ◽

2020 ◽

Author(s):

Markus Janout ◽

Hartmut Hellmer ◽

Tore Hattermann ◽

Svein Osterhus ◽

Lucrecia Stulic ◽

...

Keyword(s):

Sea Ice ◽

Ocean Circulation ◽

Large Scale ◽

Austral Summer ◽

Weddell Sea ◽

Shelf Water ◽

Ice Shelf ◽

Present Context ◽

The Stability ◽

Ice Production

The Filchner and Ronne ice sheets (FRIS) compose the second largest contiguous ice sheet on the Antarctic continent. Unlike at several other Antarctic glaciers, basal melt rates at FRIS are comparatively low, as cold and dense waters presently dominate the wide southern Weddell Sea (WS) continental shelf and effectively block out any significant inflow of warmer ocean waters. We revisited the southern WS shelf in austral summer 2018 during Polarstern expedition PS111 with detailed hydrographic and tracer measurements along both the Ronne and Filchner ice fronts. The hydrography along FRIS was characterized by near-freezing high salinity shelf water (HSSW) in front of Ronne, and a striking dominance of ice shelf water (ISW) in Filchner Trough. The cold (-2.2&#176;C) and fresher (34.6) ISW was formed by the interaction of Ronne-sourced HSSW with the ice shelf base. The strong dominance of ISW in Filchner Trough indicates a recently enhanced circulation below FRIS, likely fueled by enhanced sea ice production in the southwestern WS. We view these recent observations in a multidecadal (1973-present) context, contrast the two dominant circulation modes below FRIS, and discuss the importance of sea ice formation and large-scale sea level pressure patterns for the stability of the ocean circulation and basal melt rates underneath FRIS.

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Measurements of precipitation in Dumont d'Urville, Adélie Land, East Antarctica

The Cryosphere ◽

10.5194/tc-11-1797-2017 ◽

2017 ◽

Vol 11 (4) ◽

pp. 1797-1811 ◽

Cited By ~ 28

Author(s):

Jacopo Grazioli ◽

Christophe Genthon ◽

Brice Boudevillain ◽

Claudio Duran-Alarcon ◽

Massimo Del Guasta ◽

...

Keyword(s):

Austral Summer ◽

Ground Level ◽

Blowing Snow ◽

Climatological Data ◽

Weather Forecasts ◽

First Results ◽

Terre Adélie ◽

Intensive Observation ◽

Rain Radar

Abstract. The first results of a campaign of intensive observation of precipitation in Dumont d'Urville, Antarctica, are presented. Several instruments collected data from November 2015 to February 2016 or longer, including a polarimetric radar (MXPol), a Micro Rain Radar (MRR), a weighing gauge (Pluvio2), and a Multi-Angle Snowflake Camera (MASC). These instruments collected the first ground-based measurements of precipitation in the region of Adélie Land (Terre Adélie), including precipitation microphysics. Microphysical observations during the austral summer 2015/2016 showed that, close to the ground level, aggregates are the dominant hydrometeor type, together with small ice particles (mostly originating from blowing snow), and that riming is a recurring process. Eleven percent of the measured particles were fully developed graupel, and aggregates had a mean riming degree of about 30 %. Spurious precipitation in the Pluvio2 measurements in windy conditions, leading to phantom accumulations, is observed and partly removed through synergistic use of MRR data. The yearly accumulated precipitation of snow (300 m above ground), obtained by means of a local conversion relation of MRR data, trained on the Pluvio2 measurement of the summer period, is estimated to be 815 mm of water equivalent, with a confidence interval ranging between 739.5 and 989 mm. Data obtained in previous research from satellite-borne radars, and the ERA-Interim reanalysis of the European Centre for Medium-Range Weather Forecasts (ECMWF) provide lower yearly totals: 655 mm for ERA-Interim and 679 mm for the climatological data over DDU. ERA-Interim overestimates the occurrence of low-intensity precipitation events especially in summer, but it compensates for them by underestimating the snowfall amounts carried by the most intense events. Overall, this paper provides insightful examples of the added values of precipitation monitoring in Antarctica with a synergistic use of in situ and remote sensing measurements.

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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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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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Summertime Moisture Transport to the Southern South American Altiplano: Constraints from In Situ Measurements of Water Vapor Isotopic Composition

Journal of Climate ◽

10.1175/jcli-d-14-00511.1 ◽

2015 ◽

Vol 28 (7) ◽

pp. 2635-2649 ◽

Cited By ~ 16

Author(s):

Joseph Galewsky ◽

Kimberly Samuels-Crow

Keyword(s):

Water Vapor ◽

Isotopic Composition ◽

Austral Summer ◽

Dry Season ◽

In Situ Measurements ◽

South American ◽

Moist Air ◽

Wet Season ◽

Rayleigh Distillation

Abstract Austral summer transport of water vapor to the southern South American Altiplano is investigated using in situ measurements of water vapor isotopic composition collected from 1 November 2012 to 10 February 2013 on the Chajnantor Plateau in the Chilean Andes. Onset of the wet season in December was associated with an increase in mixing ratios from an average of 1500 ppmv during the winter dry season to 5400 ppmv in early December. Water vapor isotopes δD and δ18O increased from dry season averages of −235‰ and −31‰, respectively, to wet season averages of −142‰ and −17‰, reaching as high as −70‰ and −17‰, respectively. The highest water vapor δ values were close to those measured in coastal settings, suggesting little condensation during transport to the site. About 5% of the wet season data have δ values that are lower than expected for Rayleigh distillation and are associated with high relative humidity (>75%), easterly winds, and periods of low outgoing longwave radiation over the Altiplano, consistent with moistening by deep convection. The remainder of the data have δ values that are greater than expected for Rayleigh distillation, up to 250‰ above the Rayleigh curve. These data are consistent with mixing between very dry air and moist air from the boundary layer. The data show intraseasonal variability coherently linked to the position of the Bolivian high, with moist air associated with a southward displacement in the Bolivian high. The humidity over the southern Altiplano during the wet season reflects a balance among advective drying, advective moistening with little condensation, and convective moistening.

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