Showing papers by "Anais Orsi published in 2019"
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TL;DR: In this paper, the authors evaluate new simulations of the polar RCM MAR forced by three reanalyses, ERA-Interim, JRA-55, and MERRA-2, for the period 1979-2015, and compare MAR results to the last outputs of the RCM RACMO2 forced by ERA-interim.
Abstract: . The Antarctic ice sheet mass balance is a major component of the sea level
budget and results from the difference of two fluxes of a similar magnitude:
ice flow discharging in the ocean and net snow accumulation on the ice sheet
surface, i.e. the surface mass balance (SMB). Separately modelling ice
dynamics and SMB is the only way to project future trends.
In addition, mass balance studies frequently use regional climate models
(RCMs) outputs as an alternative to observed fields because SMB observations
are particularly scarce on the ice sheet. Here we evaluate new simulations of
the polar RCM MAR forced by three reanalyses, ERA-Interim, JRA-55, and MERRA-2,
for the period 1979–2015, and we compare MAR results to the last outputs of
the RCM RACMO2 forced by ERA-Interim. We show that MAR and RACMO2 perform
similarly well in simulating coast-to-plateau SMB gradients, and we find no
significant differences in their simulated SMB when integrated over the ice
sheet or its major basins. More importantly, we outline and quantify missing
or underestimated processes in both RCMs. Along stake transects, we show that
both models accumulate too much snow on crests, and not enough snow in
valleys, as a result of drifting snow transport fluxes not included in MAR
and probably underestimated in RACMO2 by a factor of 3. Our results tend
to confirm that drifting snow transport and sublimation fluxes are much
larger than previous model-based estimates and need to be better resolved and
constrained in climate models. Sublimation of precipitating particles in
low-level atmospheric layers is responsible for the significantly lower
snowfall rates in MAR than in RACMO2 in katabatic channels at the ice sheet
margins. Atmospheric sublimation in MAR represents 363 Gt yr−1 over the grounded ice sheet for the year 2015, which is 16 %
of the simulated snowfall loaded at the ground. This estimate is consistent
with a recent study based on precipitation radar observations and is more
than twice as much as simulated in RACMO2 because of different time
residence of precipitating particles in the atmosphere. The remaining spatial
differences in snowfall between MAR and RACMO2 are attributed to differences
in advection of precipitation with snowfall particles being likely advected too
far inland in MAR.
177 citations
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TL;DR: During the second half of the twentieth century, the proportion of 18O18O in O2 decreased, which implies that tropospheric O3 increased by less than 40 per cent during that time, corroborate model predictions of global-scale increases in surface pollution and vegetative stress caused by increasing anthropogenic emissions of O3 precursors.
Abstract: Tropospheric ozone (O3) is a key component of air pollution and an important anthropogenic greenhouse gas1. During the twentieth century, the proliferation of the internal combustion engine, rapid industrialization and land-use change led to a global-scale increase in O3 concentrations2,3; however, the magnitude of this increase is uncertain. Atmospheric chemistry models typically predict4–7 an increase in the tropospheric O3 burden of between 25 and 50 per cent since 1900, whereas direct measurements made in the late nineteenth century indicate that surface O3 mixing ratios increased by up to 300 per cent8–10 over that time period. However, the accuracy and diagnostic power of these measurements remains controversial2. Here we use a record of the clumped-isotope composition of molecular oxygen (18O18O in O2) trapped in polar firn and ice from 1590 to 2016 ad, as well as atmospheric chemistry model simulations, to constrain changes in tropospheric O3 concentrations. We find that during the second half of the twentieth century, the proportion of 18O18O in O2 decreased by 0.03 ± 0.02 parts per thousand (95 per cent confidence interval) below its 1590–1958 ad mean, which implies that tropospheric O3 increased by less than 40 per cent during that time. These results corroborate model predictions of global-scale increases in surface pollution and vegetative stress caused by increasing anthropogenic emissions of O3 precursors4,5,11. We also estimate that the radiative forcing of tropospheric O3 since 1850 ad is probably less than +0.4 watts per square metre, consistent with results from recent climate modelling studies12. Isotope data from polar firn and ice are used to constrain the increase in tropospheric ozone between 1850 and 2005 ad.
59 citations
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Université catholique de Louvain1, Australian National University2, Cooperative Research Centre3, Australian Antarctic Division4, University of Grenoble5, Centre national de la recherche scientifique6, Oeschger Centre for Climate Change Research7, Lund University8, Lamont–Doherty Earth Observatory9, Ca' Foscari University of Venice10, Alfred Wegener Institute for Polar and Marine Research11
TL;DR: In this paper, Stenni et al. used pseudoproxy experiments and data assimilation experiments to assess the potential for reconstructing the Antarctic temperature over the last 2 millennia based on a database of stable oxygen isotopes in ice cores compiled in the framework of Antarctica2k.
Abstract: . The Antarctic temperature changes over the past millennia remain more
uncertain than in many other continental regions. This has several origins:
(1) the number of high-resolution ice cores is small, in particular on the
East Antarctic plateau and in some coastal areas in East Antarctica; (2) the
short and spatially sparse instrumental records limit the calibration period
for reconstructions and the assessment of the methodologies; (3) the link
between isotope records from ice cores and local climate is usually complex
and dependent on the spatial scales and timescales investigated. Here, we use
climate model results, pseudoproxy experiments and data assimilation
experiments to assess the potential for
reconstructing the Antarctic temperature over the last 2 millennia based on a
new database of stable oxygen isotopes in ice cores compiled in the framework
of Antarctica2k ( Stenni et al. , 2017 ) . The well-known covariance between
δ18O and temperature is reproduced in the two isotope-enabled
models used (ECHAM5/MPI-OM and ECHAM5-wiso), but is generally weak over the
different Antarctic regions, limiting the skill of the reconstructions.
Furthermore, the strength of the link displays large variations over the past
millennium, further affecting the potential skill of temperature
reconstructions based on statistical methods which rely on the assumption
that the last decades are a good estimate for longer temperature
reconstructions. Using a data assimilation technique allows, in theory, for
changes in the δ18O –temperature link through time and space
to be taken into account. Pseudoproxy experiments confirm the benefits of
using data assimilation methods instead of statistical methods that provide
reconstructions with unrealistic variances in some Antarctic subregions. They
also confirm that the relatively weak link between both variables leads to a
limited potential for reconstructing temperature based on
δ18O . However, the reconstruction skill is higher and more
uniform among reconstruction methods when the reconstruction target is the
Antarctic as a whole rather than smaller Antarctic subregions. This
consistency between the methods at the large scale is also observed when
reconstructing temperature based on the real δ18O regional
composites of Stenni et al. ( 2017 ) . In this case, temperature reconstructions
based on data assimilation confirm the long-term cooling over Antarctica
during the last millennium, and the later onset of anthropogenic warming
compared with the simulations without data assimilation, which is especially
visible in West Antarctica. Data assimilation also allows for models and
direct observations to be reconciled by reproducing the east–west contrast
in the recent temperature trends. This recent warming pattern is likely
mostly driven by internal variability given the large spread of individual
Paleoclimate Modelling Intercomparison Project (PMIP)/Coupled Model
Intercomparison Project (CMIP) model realizations in simulating it. As in the
pseudoproxy framework, the reconstruction methods perform differently at the
subregional scale, especially in terms of the variance of the time series
produced. While the potential benefits of using a data assimilation method
instead of a statistical method have been highlighted in a pseudoproxy
framework, the instrumental series are too short to confirm this in a
realistic setup.
21 citations
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TL;DR: In this article, the authors present the first continuous measurements of δ 18 O and d-excess in water vapor over Adelie Land during a period from 26/12/2016 to 03/02/2017.
15 citations
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TL;DR: In this paper, high-resolution δ15N and deuterium excess (d-excess) data from the EPICA Dome C (EDC) Antarctic ice core was used to provide a detailed temperature change estimate during the last 9 deglaciations of the Quaternary.
8 citations
01 Apr 2019
3 citations