Abstract
The North Atlantic Oscillation (NAO) is the most recognized and leading mode of atmospheric variability observed over the Atlantic sector of the Northern Hemisphere, and its impacts on weather and climate over the North Atlantic and Eurasia via large-scale teleconnections have been extensively studied. Here we use a multidata synthesis approach to analyze surface and tropospheric variables from multiple long-term observational and reanalysis datasets to identify the NAO’s footprint on interannual temperature variability over the vast but least-studied Sahara Desert during December–January–February–March for the satellite era (1979–2022) and century-long periods. Our results present evidence for a solid teleconnection pattern in surface and tropospheric temperatures associated with the NAO over the Sahara and document some major spatial–temporal and vertical characteristics of this pattern. It is found that the Saharan temperature anomalies are negatively correlated with the NAO index and this correlation is very strong, consistent, and statistically significant between different periods and across different datasets. The teleconnection is closely linked to large-scale circulation anomalies throughout the troposphere over the North Atlantic–Sahara sector, where the anomalous horizontal wind components and geopotential height exhibit opposite changes in sign with altitude from the lower to upper troposphere. During the negative NAO− (positive NAO+) phase, above-normal (below-normal) temperatures over the Sahara could be mainly explained by three major processes: (1) advection of climatological warm and moist (cold and dry) air over the North Atlantic (northern higher latitudes) by the anomalous southwesterly (northeasterly) flow in the lower troposphere; (2) advection of anomalous North Atlantic warm (cold) air by the climatological strong westerlies in the middle and upper troposphere; and (3) strengthened (weakened) vertical mixing in the atmospheric boundary layer. These results suggest that the NAO plays an important role in modulating the interannual temperature variability over the Sahara, and that this NAO footprint is mostly realized through horizontal temperature advection and vertical heat transfer by turbulent mixing.
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Data availability
The NCAR NAOI dataset was downloaded from https://climatedataguide.ucar.edu/climate-data/ and the NOAA NAOI dataset was downloaded from https://www.ncdc.noaa.gov/teleconnections/nao/. The NASA’s GISTEMP dataset was downloaded from https://data.giss.nasa.gov/gistemp/. The BEST dataset was downloaded from https://berkeleyearth.org/data/. The ERA5 reanalysis was downloaded from https://cds.climate.copernicus.eu/#!/search?text=ERA5&type=dataset. The second Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) was downloaded from https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/data_access/. The GHCNMv4 was downloaded from https://www.ncei.noaa.gov/pub/data/ghcn/v4/. The 20CRv3 was downloaded from http://apdrc.soest.hawaii.edu/datadoc/20century_reanalysisV3.php). The CERA-20C was downloaded from https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/cera-20c.
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Acknowledgements
We would like to thank Daniel Keyser at UAlbany for frequent discussions and extensive comments on this work. L.Z. was supported by the National Science Foundation (NSF AGS-1952745 and AGS-1854486). W.H. was supported by the National Natural Science Foundation of China (42075022). Support for the Twentieth Century Reanalysis Project version 3 dataset is provided by the U.S. Department of Energy, Office of Science Biological and Environmental Research (BER), by the National Oceanic and Atmospheric Administration Climate Program Office, and by the NOAA Earth System Research Laboratory Physical Sciences Laboratory.
Funding
This work is supported by the National Science Foundation (NSF AGS-1952745 and AGS-1854486). W.H. was supported by the National Natural Science Foundation of China (42075022).
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All authors contributed to the study conception and design. Data collection and analysis were performed by LZ and WH. The initial manuscript was written by LZ. All authors contributed to the interpretation of results and commented on the previous versions of the manuscript. All authors read and approved the final manuscript.
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Zhou, L., Hua, W., Nicholson, S.E. et al. Interannual teleconnections in the Sahara temperatures associated with the North Atlantic Oscillation (NAO) during boreal winter. Clim Dyn 62, 1123–1143 (2024). https://doi.org/10.1007/s00382-023-06962-w
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DOI: https://doi.org/10.1007/s00382-023-06962-w