A new study finds significant uncertainties in how well different reanalysis datasets capture the strength of atmospheric circulation changes associated with El Nino events. Researchers from the Institute of Atmospheric Physics at the Chinese Academy of Sciences examine the performance of eight prominent reanalysis datasets in capturing regional Hadley Circulation (HC) responses to El Nino–Southern Oscillation (ENSO) events and found that while they accurately represent the spatial pattern of circulation anomalies during El Nino events, the magnitudes of these changes can vary by up to a factor of 2.7 between different reanalyses.
ENSO, as a dominant mode of global interannual variability, influences the intensity and meridional extension of the Hadley Circulation, which plays a crucial role in shaping weather patterns worldwide. While previous studies have focused on assessing the global HC using zonal-mean mass stream function (MSF), this study takes a regional perspective by adopting a newly developed technique to construct the three-dimensional structure of HC.
The results demonstrate that all eight reanalysis datasets successfully reproduce the spatial structure of HC responses to ENSO events. Notably, an intensified HC is observed in the central-eastern Pacific, accompanied by weakened circulations in the Indo-Pacific warm pool and tropical Atlantic. The high spatial correlation coefficient (>0.93) among each pair of these eight datasets validates the consistency in capturing the spatial patterns of HC anomalies.
However, the study reveals significant uncertainties in the amplitude of HC responses across the datasets. In particular, the variability of equatorially asymmetric HC anomalies associated with ENSO events exhibits substantial differences, with the Climate Forecast System Reanalysis (
CFSR) showing approximately 2.7 times greater amplitude compared to the Twentieth Century Reanalysis (
20CR). CFSR
is a third generation global, high resolution, coupled atmosphere-ocean-land surface-sea ice system
designed to provide the best estimate of the state of these coupled domains over 1979-2009, while 20CR is a comprehensive global atmospheric circulation data set spanning 1850-2014.
These findings caution researchers and climate scientists about the limitations and potential biases when using reanalysis data to evaluate the intensity of ENSO-related HC anomalies. The study underscores the importance of considering uncertainties in interpreting the role of HC in ENSO dynamics and its implications for regional climate variations.
"This research sheds light on the challenges we face in accurately quantifying the intensity of HC anomalies associated with ENSO events," commented corresponding author LI Xichen, the corresponding author. "Understanding these uncertainties will guide future investigations and improve our ability to evaluate the impacts of ENSO on regional climates."
Citation: Li, Y. D., X. C. Li, J. Feng, Y. Zhou, W. Z. Wang, and Y. R. Hou, 2023: Uncertainties of the ENSO-related regional Hadley Circulation anomalies within eight reanalysis datasets. Adv. Atmos. Sci., https://doi.org/10.1007/s00376-023-3047-0.
