Remote and autonomous measurements of precipitation for the northwestern Ross Ice Shelf, Antarctica

The Antarctic Precipitation System project deployed and maintained four sites across the northwestern Ross Ice Shelf in Antarctica from November 2017 to November 2019. The goals for the project included the collection of in situ observations of precipitation in Antarctica spanning a duration of 2 years, an improvement in the understanding of precipitation events across the Ross Ice Shelf, and the ability to validate precipitation data from atmospheric numerical models. At each of the four sites the precipitation was measured with an OTT Pluvio2 precipitation gauge. Additionally, snow accumulation at the site was measured with a sonic ranging sensor and using GPS interferometric reflectivity. Supplemental observations of temperature, wind speed, particle count, particle size and speed, and images and video from a camera were collected to provide context to the precipitation measurements. The collected dataset represents some of the first year-round observations of precipitation in Antarctica at remote locations using an autonomous measurement system. The acquired observations have been quality-controlled and post-processed, and they are available for retrieval through the United States Antarctic Program Data Center (https://doi.org/10.15784/601441, Seefeldt, 2021).

Evaluation of coastal Antarctic precipitation in LMDz6 global atmospheric model using ground-based radar observations

In the current context of climate change in the poles, one of the objectives of the APRES3 (Antarctic Precipitation Remote Sensing from Surface and Space) project was to characterize the vertical structure of precipitation in order to better simulate it. Precipitation simulated by models in Antarctica is currently very widespread and it overestimates the data. Sensitivity studies have been conducted using a global climate model and compared to the observations obtained at the Dumont d’Urville coast station, obtained by a Micro Rain Radar (MRR). The LMDz/IPSL general circulation model, with zoomed configuration over Dumont d’Urville, has been considered for this study. A sensitivity study was conducted on the physical and numerical parameters of the LMDz model with the aim of estimating their contribution to the precipitation simulation. Sensitivity experiments revealed that changes in the sedimentation and sublimation parameters do not significantly impact precipitation rate. However, dissipation of the LMDz model, which is a numerical process that dissipates spatially excessive energy and keeps the model stable, impacts precipitation indirectly but very strongly. A suitable adjustment of the dissipation reduces significantly precipitation over Antarctic peripheral area, thus providing a simulated profile in better agreement with the MRR observations.

Remote and Autonomous Measurements of Precipitation for the Northwest Ross Ice Shelf, Antarctica

The Antarctic Precipitation System project deployed and maintained four sites across the northwest Ross Ice Shelf in Antarctica from November 2017 to November 2019. The goals for the project included the collection of in situ observations of precipitation in Antarctica spanning a duration of two years, an improvement in the understanding of precipitation events across the Ross Ice Shelf, and the ability to validate precipitation data from atmospheric numerical models. At each of the four sites the precipitation was measured with an OTT Pluvio2 precipitation gauge. Additionally, snow accumulation at the site was measured with a sonic ranging sensor and using GPS-Interferometry Reflectivity. Supplemental observations of temperature, wind speed, particle count, particle size and speed, and images and video from a camera, were collected to provide context to the precipitation measurements. The collected dataset represents some of the first year-round observations of precipitation in Antarctic at remote locations using an autonomous measurement system. The acquired observations have been quality controlled, post-processed, and are available for retrieval through the United States Antarctic Program Data Center (Seefeldt, 2021; doi.org/10.15784/601441).

A dedicated robust instrument for water vapor generation at low humidity for use with a laser water isotope analyzer in cold and dry polar regions

Obtaining precise continuous measurements of water vapor isotopic composition in dry places (polar or high-altitude regions) is an important challenge. The current limitation is the strong influence of humidity on the measured water isotopic composition by laser spectroscopy instruments for low humidity levels (below 3000 ppmv). This problem is addressed by determining the relationships between humidity and measured δ18O and δD of known water standards. Here, we present the development of a robust field instrument able to generate water vapor, down to 70 ppmv, at very stable humidity levels (average 1σ lower than 10 ppmv). This instrument, operated by a Raspberry interface, can be coupled to a commercial laser spectroscopy instrument. We checked the stability of the system as well as its accuracy when expressing the measured isotopic composition of water vapor on the VSMOW–SLAP (Vienna Standard Mean Ocean Water – Standard Light Antarctic Precipitation) scale. It proved to be highly stable during autonomous operation over more than 1 year at the East Antarctic Concordia and Dumont d'Urville stations.

Antarctic ice mass variations from 1979 to 2017 driven by anomalous precipitation accumulation

Antarctic ice mass balance is determined by precipitation and ice discharge, and understanding their relative contributions to contemporary Antarctic ice mass change is important to project future ice mass loss and resulting sea level rise. There has been evidence that anomalous precipitation affects Antarctic ice mass loss estimates, and thus the precipitation contribution should be understood and considered in future projections. In this study, we revisit changes in Antarctic ice mass over recent decades and examine precipitation contributions over this period. We show that accumulated (time-integrated) precipitation explains most inter-annual anomalies of Antarctic ice mass change during the GRACE period (2003–2017). From 1979 to 2017, accumulated Antarctic precipitation contributes to significant ice mass loss acceleration in the Pacific sector and deceleration in the Atlantic-Indian Sectors, forming a bi-polar spatial pattern. Principal component analysis reveals that such a bi-polar pattern is likely modulated by the Southern Annular Mode (SAM). We also find that recent ice mass loss acceleration in 2007 is related to a variation in precipitation accumulation. Overall ice discharge has accelerated at a steady rate since 1992, but has not seen a recent abrupt increase.

Brief communication: Evaluating Antarctic precipitation in ERA5 and CMIP6 against CloudSat observations

CMIP5, CMIP6, and ERA5 Antarctic precipitation is evaluated against CloudSat data. At continental and regional scales, ERA5 and the median CMIP models are biased high, with insignificant improvement from CMIP5 to CMIP6. However, there are fewer positive outliers in CMIP6. AMIP configurations perform better than the coupled ones, and, surprisingly, relative errors in areas of complex topography are higher (up to 50 %) in the five higher-resolution models. The seasonal cycle is reproduced well by the median of the CMIP models, but not by ERA5. Progress from CMIP5 to CMIP6 being limited, there is still room for improvement.

Evaluation of coastal Antarctic precipitation in MAR3.9 regional and LMDz6 global atmospheric model with ground-based radar observations

In the current context of climate change in the poles, one of the objectives of the APRES3 (Antarctic Precipitation Remote Sensing from Surface and Space) project is to characterize the vertical structure of precipitation in order to better simulate it. Nowadays, the precipitation simulated by models in Antarctica is very widespread and overestimated the data. Sensitivity studies have been conducted using two models and compared to the observations obtained at the Dumont d'Urville coast station, obtained by a Micro Rain Radar (MRR). The MAR meso-scale model specifically developed for the polar regions and the LMDz/IPSL general circulation model, with zoomed configuration over Dumont d'Urville, have been considered for this study. These models being different in resolution and physical configuration, performing an inter-comparison required numerical, dynamic and physical adjustments in LMDz. A sensitivity study was conducted on the physical and numerical parameters of the LMDz model and on the resolution of the MAR with the aim of estimating their contribution to the precipitation simulation. Sensitivity tests with MAR revealed that this model is well adjusted for precipitation modeling in polar climates, this confirming that this model is a reference in polar climate modeling. Regarding LMDz, sensitivity experiments revealed that modifications in the sedimentation and sublimation parameters do not significantly impact precipitation rate. However, dissipation of the LMDz model, which is a numerical process that dissipates spatially excessive energy and keeps the model stable, impacts precipitation indirectly but very strongly. A suitable adjustment of the dissipation reduces significantly precipitation over Antarctic peripheral area, thus providing a simulated profile in better agreement with the MRR observations.