Synoptic conditions and atmospheric moisture pathways associated to virga and precipitation over coastal Adélie Land in Antarctica

Jullien, Nicolas; Vignon, Étienne; Sprenger, Michael; Aemisegger, Franziska; Berne, Alexis

doi:10.5194/tc-2019-270

Cited by 5 publications

(7 citation statements)

References 29 publications

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“…Our knowledge gap regarding Antarctic rain primarily lies in the technical difficulties in measuring precipitation in the harsh meteorological conditions prevailing on the remote Antarctic continent. Insights might be gained from remotely sensed measurements at stations where radars have been deployed (e.g., Gorodetskaya et al., 2015; Grazioli et al., 2017; Jullien et al., 2020). Preliminary analyses of radar vertical profiles at DDU suggest that during rain events, the melting layer is found in the first hundreds of meters above the ground (Vignon, Besic, et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

Present and Future of Rainfall in Antarctica

Vignon

Roussel

Gorodetskaya

et al. 2021

Geophysical Research Letters

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During the austral summer 2013-2014, an Adélie penguin colony near Dumont d'Urville (DDU) station, coastal Adélie Land, Antarctica, experienced a complete reproductive failure, a so-called "zero" year. Among the main reasons for this disaster was an unusual and dramatic rainfall event that occurred on January 1, 2014, and that was responsible for the death of all chicks, whose downy plumage has little waterproofing ability (Ropert-Coudert et al., 2015). According to ice-core records in which water from rainfall and melting manifests as clear frozen layers, two occurrences of heavy liquid precipitation and/or melt could be detected in the decade preceding 2014 in coastal Adélie Land (Goursaud et al., 2017).At a distance of about 1,500 km to the South-East, the Ross Ice Shelf underwent an extensive, intense, and prolonged surface melt event in January 2016 (Nicolas et al., 2017). Such an event was caused by a strong and sustained advection of warm oceanic air. During the first days of the event, rainfall significantly preconditioned the snowpack by increasing its temperature due to latent heat release from water freezing and hence, contributed to extend the melting. Such a phenomenon has been frequently observed over Greenland (Doyle et al., 2015) but is quite rare in Antarctica.The phase of Antarctic precipitation can directly impact the surface mass balance of the ice sheet through modulation of the surface albedo (Kirchgäßbner, 2011). Liquid precipitation can also accelerate the retreat

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Section: Introductionmentioning

confidence: 99%

Present and Future of Rainfall in Antarctica

Vignon

Roussel

Gorodetskaya

et al. 2021

Geophysical Research Letters

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“…It was associated with the passage of a warm front of an extra-tropical cyclone setting at the west of DDU. This type of precipitation system is typical for DDU (Jullien et al, 2020). The accumulated precipitation at the ground during the event was 3.4 mm (Vignon et al, 2019a).…”

Section: Application Of the Methodology To Two Case Studiesmentioning

confidence: 82%

Identification of snowfall microphysical processes from vertical gradients of polarimetric radar variables

Planat¹,

Gehring²,

Vignon³

et al. 2020

Preprint

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Abstract. Polarimetric radar systems are commonly used to study the microphysics of precipitation. While they offer continuous measurements with a large spatial coverage, retrieving information about the microphysical processes that govern the evolution of snowfall from the polarimetric signal is challenging. The present study develops a new method, called Process Identification based on Vertical gradient Signs (PIVS), to spatially identify the occurrence of the main microphysical processes (aggregation and riming, crystal growth by vapor deposition, and sublimation) in snowfall from dual-polarization Doppler radar scans. We first derive an analytical framework to assess in which meteorological conditions the local vertical gradients of radar variables reliably inform about microphysical processes. In such conditions, we then identify regions dominated by (i) vapor deposition, (ii) aggregation and riming and (iii) snowflake sublimation and possibly snowflake breakup based on the sign of the local vertical gradients of the reflectivity ZH and the differential reflectivity ZDR. The method is then applied to data from two frontal snowfall events: one in coastal Adélie Land, Antarctica and one in the Taebaeck mountains in South Korea. The validity of the method is assessed by comparing its outcome with snowflake observations using a Multi-Angle Snowflake Camera and with the output of a hydrometeor classification based on polarimetric radar signal. The application of the method further makes it possible to better characterize and understand how snowfall forms, grows and decays in two different geographical and meteorological contexts. For the Antarctic case study, we show that crystal growth by vapor deposition dominates above 2500 m a.g.l., aggregation and riming prevail between 1500 and 2500 m a.g.l. and snowflake sublimation by low-level katabatic winds occurs below 1500 m a.g.l.. For the event in South Korea, aggregation and riming dominate between 4000 and 4800 m a.g.l., with local sublimation below and vapor deposition above. We infer some microphysical characteristics in terms of radar variables from statistical analysis of the method output (e.g. ZH and ZDR distribution for each process). We finally highlight the potential for extensive application to cold precipitation events in different meteorological contexts.

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“…S4) showing that the maritime air advection happens in the upper marine boundary layer, while near-surface layers are dominated by a concurrent advection of continental air. The latter vertical atmospheric structure has been observed at the Adélie Coast during the advection of moist air at upper levels in the warm sector of extratropical cyclones (Vignon et al, 2019;Jullien et al, 2020).…”

Section: A23 Lv13 -Extratropical Cyclone Activitymentioning

confidence: 79%

Exploring the coupled ocean and atmosphere system with a data science approach applied to observations from the Antarctic Circumnavigation Expedition

Landwehr¹,

Volpi

Haumann

et al. 2021

Earth Syst. Dynam.

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Abstract. The Southern Ocean is a critical component of Earth's climate system, but its remoteness makes it challenging to develop a holistic understanding of its processes from the small scale to the large scale. As a result, our knowledge of this vast region remains largely incomplete. The Antarctic Circumnavigation Expedition (ACE, austral summer 2016/2017) surveyed a large number of variables describing the state of the ocean and the atmosphere, the freshwater cycle, atmospheric chemistry, and ocean biogeochemistry and microbiology. This circumpolar cruise included visits to 12 remote islands, the marginal ice zone, and the Antarctic coast. Here, we use 111 of the observed variables to study the latitudinal gradients, seasonality, shorter-term variations, geographic setting of environmental processes, and interactions between them over the duration of 90 d. To reduce the dimensionality and complexity of the dataset and make the relations between variables interpretable we applied an unsupervised machine learning method, the sparse principal component analysis (sPCA), which describes environmental processes through 14 latent variables. To derive a robust statistical perspective on these processes and to estimate the uncertainty in the sPCA decomposition, we have developed a bootstrap approach. Our results provide a proof of concept that sPCA with uncertainty analysis is able to identify temporal patterns from diurnal to seasonal cycles, as well as geographical gradients and “hotspots” of interaction between environmental compartments. While confirming many well known processes, our analysis provides novel insights into the Southern Ocean water cycle (freshwater fluxes), trace gases (interplay between seasonality, sources, and sinks), and microbial communities (nutrient limitation and island mass effects at the largest scale ever reported). More specifically, we identify the important role of the oceanic circulations, frontal zones, and islands in shaping the nutrient availability that controls biological community composition and productivity; the fact that sea ice controls sea water salinity, dampens the wave field, and is associated with increased phytoplankton growth and net community productivity possibly due to iron fertilisation and reduced light limitation; and the clear regional patterns of aerosol characteristics that have emerged, stressing the role of the sea state, atmospheric chemical processing, and source processes near hotspots for the availability of cloud condensation nuclei and hence cloud formation. A set of key variables and their combinations, such as the difference between the air and sea surface temperature, atmospheric pressure, sea surface height, geostrophic currents, upper-ocean layer light intensity, surface wind speed and relative humidity played an important role in our analysis, highlighting the necessity for Earth system models to represent them adequately. In conclusion, our study highlights the use of sPCA to identify key ocean–atmosphere interactions across physical, chemical, and biological processes and their associated spatio-temporal scales. It thereby fills an important gap between simple correlation analyses and complex Earth system models. The sPCA processing code is available as open-access from the following link: https://renkulab.io/gitlab/ACE-ASAID/spca-decomposition (last access: 29 March 2021). As we show here, it can be used for an exploration of environmental data that is less prone to cognitive biases (and confirmation biases in particular) compared to traditional regression analysis that might be affected by the underlying research question.

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Synoptic conditions and atmospheric moisture pathways associated to virga and precipitation over coastal Adélie Land in Antarctica

Cited by 5 publications

References 29 publications

Present and Future of Rainfall in Antarctica

Present and Future of Rainfall in Antarctica

Identification of snowfall microphysical processes from vertical gradients of polarimetric radar variables

Exploring the coupled ocean and atmosphere system with a data science approach applied to observations from the Antarctic Circumnavigation Expedition

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