Abstract
Abstract. In mid and high latitudes, the stable isotope ratio in precipitation is driven by changes in temperature, which control atmospheric distillation. This relationship forms the basis for many continental paleoclimatic reconstructions using direct (e.g. ice cores) or indirect (e.g. tree ring cellulose, speleothem calcite) archives of past precipitation. However, the archiving process is inherently biased by intermittency of precipitation. Here, we use two sets of atmospheric reanalyses (NCEP (National Centers for Environmental Prediction) and ERA-interim) to quantify this precipitation intermittency bias, by comparing seasonal (winter and summer) temperatures estimated with and without precipitation weighting. We show that this bias reaches up to 10 °C and has large interannual variability. We then assess the impact of precipitation intermittency on the strength and stability of temporal correlations between seasonal temperatures and the North Atlantic Oscillation (NAO). Precipitation weighting reduces the correlation between winter NAO and temperature in some areas (e.g. Québec, South-East USA, East Greenland, East Siberia, Mediterranean sector) but does not alter the main patterns of correlation. The correlations between NAO, δ18O in precipitation, temperature and precipitation weighted temperature are investigated using outputs of an atmospheric general circulation model enabled with stable isotopes and nudged using reanalyses (LMDZiso (Laboratoire de Météorologie Dynamique Zoom)). In winter, LMDZiso shows similar correlation values between the NAO and both the precipitation weighted temperature and δ18O in precipitation, thus suggesting limited impacts of moisture origin. Correlations of comparable magnitude are obtained for the available observational evidence (GNIP (Global Network of Isotopes in Precipitation) and Greenland ice core data). Our findings support the use of archives of past δ18O for NAO reconstructions.
Highlights
Solid EarthThe North Atlantic Oscillation (NAO) is known to have large impacts on mid to high latitudes climate, affecting daily to seasonal patterns of precipitation or temperature (Wanner et al, 2001; Hurrell et al, 2003)
In order to assess the impact of precipitation intermittency bias on temperature–NAO relationships, we need to have access to daily, coherent and global precipitation and surface air temperature datasets
Small differences may be caused by the resolution of atmospheric models and the choice of individual atmospheric model grid points. This coherency justifies the use of the reanalyses and LMDZiso for investigating NAO–climate relationships in a realistic framework
Summary
The North Atlantic Oscillation (NAO) is known to have large impacts on mid to high latitudes climate, affecting daily to seasonal patterns of precipitation or temperature (Wanner et al, 2001; Hurrell et al, 2003). Because temperature and precipitation can co-vary at daily, seasonal or interannual timescales, this precipitation intermittency bias may distort the original NAO-temperature signal in climate archives This source of uncertainty was recently investigated for Greenland, using atmospheric reanalyses (Persson et al, 2011). In order to assess the impact of precipitation intermittency bias on temperature–NAO relationships, we need to have access to daily, coherent and global precipitation and surface air temperature datasets For this purpose, we used different sources of information: (i) two atmospheric reanalysis datasets and (ii) a simulation conducted with an atmospheric model equipped with water stable isotopes.
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