Showing papers by "Camille Risi published in 2022"
TL;DR: In this paper , the authors demonstrate that Barents-Kara Sea (BKS) winter sea ice variability is primarily driven by atmospheric, rather than oceanic, processes, and that increased transport of atmospheric heat and moisture into the BKS region increases downward longwave radiation, contributing to warming and sea ice decline.
Abstract: Significance The recent decline and variability in Arctic winter sea ice have been viewed as a combined response to oceanic and atmospheric processes. Disentangling the relative importance of these processes is challenging due to strong ocean-atmosphere coupling. Here, we demonstrate that Barents-Kara Sea (BKS) winter sea ice variability is primarily driven by atmospheric, rather than oceanic, processes. Increased transport of atmospheric heat and moisture into the BKS region increases downward longwave radiation, contributing to warming and sea ice decline. Our results reinforce the importance of atmospheric processes for Arctic winter sea ice variability and changes and have potential implications for climate and environment in the Arctic and beyond.
14 citations
DOI•
19 Nov 2022
TL;DR: In this paper , the authors evaluate the simulation of the seasonal cycle of water isotopic composition over Tibetan Plateau regions (TP) from six isotope-enabled general circulation models (GCMs) participating in the second Phase of Stable Water Isotope Intercomparison Group.
Abstract: This study evaluates the simulation of the seasonal cycle of water isotopic composition over Tibetan Plateau regions (TP) from six isotope‐enabled general circulation models (GCMs) participating in the second Phase of Stable Water Isotope Intercomparison Group. For both meteorological factors (precipitation rate and wind field) and isotopic composition, GCMs generally agree with reanalysis data and in‐situ observations, but there is a significant spread across models and the isotopic seasonality is systematically underestimated. In the southern TP, the precipitation isotopic composition is more depleted in summer than in winter, and the amplitude of the simulated isotopic seasonal variations is primarily driven by the amplitude of the simulated upstream precipitation. In contrast, in the northern TP, the precipitation isotopic composition is more depleted in winter than in summer, and the amplitude of the simulated seasonal variability of isotopes is mainly driven by the simulated strength of the zonal wind. We conclude that the skill of a GCM to simulate the seasonal cycle in the isotopic composition depends mainly on the skill of the GCM to simulate the Indian summer monsoon precipitation and the westerlies. The same causes contributing to the underestimated seasonality at present‐day may also contribute to the underestimated δ18O change at the mid‐Holocene.
1 citations
DOI•
TL;DR: In this article , a high-resolution (∼0.75°) isotope-enabled general circulation model with time-specific boundary conditions was used to investigate changes in temperature, precipitation, and δ18O in precipitation (δ18Op).
Abstract: The Middle Miocene (15.99–11.65 Ma) of Europe witnessed major climatic, environmental, and vegetational change, yet we are lacking detailed reconstructions of Middle Miocene temperature and precipitation patterns over Europe. Here, we use a high‐resolution (∼0.75°) isotope‐enabled general circulation model (ECHAM5‐wiso) with time‐specific boundary conditions to investigate changes in temperature, precipitation, and δ18O in precipitation (δ18Op). Experiments were designed with variable elevation configurations of the European Alps and different atmospheric CO2 levels to examine the influence of Alpine elevation and global climate forcing on regional climate and δ18Op patterns. Modeling results are in agreement with available paleobotanical temperature data and with low‐resolution Middle Miocene experiments of the Miocene Model Intercomparison Project (MioMIP1). However, simulated precipitation rates are 300–500 mm/yr lower in the Middle Miocene than for pre‐industrial times for central Europe. This result is consistent with precipitation estimates from herpetological fossil assemblages, but contradicts precipitation estimates from paleobotanical data. We attribute the Middle Miocene precipitation change in Europe to shifts in large‐scale pressure patterns in the North Atlantic and over Europe and associated changes in wind direction and humidity. We suggest that global climate forcing contributed to a maximum δ18Op change of ∼2‰ over high elevation (Alps) and ∼1‰ over low elevation regions. In contrast, we observe a maximum modeled δ18Op decrease of 8‰ across the Alpine orogen due to Alpine topography. However, the elevation‐δ18Op lapse rate shallows in the Middle Miocene, leading to a possible underestimation of paleotopography when using present‐day δ18Op—elevation relationships data for stable isotope paleoaltimetry studies.
1 citations
TL;DR: Sodemann et al. as mentioned in this paper proposed a new method for climate modeling based on the data from the Bjerknes Centre for Climate Research, Bergen, Norway and the Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland.
Abstract: Harald Sodemann1,2*, Franziska Aemisegger3, and Camille Risi4 1 Geophysical Institute, University of Bergen, Norway 2 Bjerknes Centre for Climate Research, Bergen, Norway 3 Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland 4 Laboratoire de Météorologie Dynamique, IPSL, CNRS, Sorbonne Université, Paris, France *Author contact: harald.sodemann@uib.no Manuscript (non-LaTeX)
TL;DR: Wang et al. as mentioned in this paper built a high-resolution 15 precipitation oxygen isoscape in China for a period of 148 years by integrating observed and iGCMs-simulated precipitation oxygen isotope composition ( δ 18 O p ) using data fusion and bias correction methods.
Abstract: . The precipitation oxygen isotopic composition is a useful environmental tracer for climatic and hydrological studies. However, the observed precipitation oxygen is limited at both temporal and spatial scales. Isotope-equipped general circulation models (iGCMs) can compensate for the temporal and spatial discontinuity of observation networks, but they suffer from coarse spatial resolutions and systematic biases. The objective of this study is to build a high-resolution 15 precipitation oxygen isoscape in China for a period of 148 years by integrating observed and iGCMs-simulated precipitation oxygen isotope composition ( δ 18 O p ) using data fusion and bias correction methods. The temporal and spatial resolutions are month and 50-60 km for the isoscape, respectively. Prior to building the oxygen isoscape, the performance of two bias correction methods (BCMs) and three data fusion methods (DFMs) is compared after post-processing of eight iGCM simulations. Results show that the outputs of the Convolutional Neural Networks (CNN) fusion method exhibit the strongest 20 correlation with observations with correlation coefficient mostly larger than 0.8, and the smallest bias with root mean square error mostly smaller than 2‰. The other two DFMs also perform slightly better than the two BCMs, which show similar performance. Thus, precipitation oxygen isoscape is generated by using the CNN fusion method for the 1969-2007 period in which all iGCMs have output and by using the bias correction methods for the remaining years. Based on the precipitation oxygen isoscape, the spatiotemporal patterns of δ 18 O p across China are investigated. The generated isoscape shows similar 25 spatial and temporal distribution characteristics to observations. In general, the distribution pattern of δ 18 O p is consistent with the temperature effect in northern China, and with the precipitation amount effect in southern China, and be more specific in the Qinghai-Tibet Plateau of China. The δ 18 O p time series mirrors a fluctuating upward trend of the temperature or precipitation in most regions of China. The temporal and spatial distribution characteristics of the generated isoscape are consistent with the characteristics of atmospheric circulation and climate change, indicating successful assimilation and 30 extension of the observed precipitation oxygen isotopes in time and space. Overall, the built isoscape is reliable and useful for providing strong support for tracking atmospheric and hydrological processes. The dataset is available in Zenodo at