Inter-reanalysis differences of the temperature trends in the MERRA-2.0 and ERA-lnterim: comparison of the middle and lower atmosphere

摘要

Studying the long-term temperature variations and trends helps to understand the role of human activities in climate change. We present the temperature trends (calculated by the linear regression method) in the Northern hemisphere in all seasons for the period of 1980-2016 for the ERA-Interim and MERRA-2.0 reanalyses. The temperature trends are analyzed for the six standard post-processed pressure levels (850, 500, and 250hPa for the troposphere and 70, 10, and 2hPa for the stratosphere). In addition, we calculate the non-parametric Mann-Kendall test to detect the statistically significant temperature trends in different pressure levels and seasons. It is found that both reanalyses have a negative temperature trend (cooling) in the stratosphere, and the magnitude of the cooling rates increases with increasing height. While the largest cooling trend (by considering all pressure levels and seasons) occurs in the autumn for the MERRA-2.0 (-0.167K/year), the largest cooling trend is in winter for the ERA-Interim (-0.118K/year). Furthermore, the results of the MANN-Kendall test reveal considerable differences in terms of statistically significant temperature changes between two reanalyses at 10hPa where the cooling trends are statistically significant at 99% level in all seasons in MERRA-2.0 reanalysis while the temperature changes are only significant at 99% level in autumn in ERA-Interim. In general, the magnitude of the cooling trends in the middle and upper stratosphere is higher for the MERRA-2.0 than ERA-Interim. Positive temperature trends (warming) are found for the bulk of troposphere, though the magnitude of the temperature changes over the study period is higher in the lower troposphere (at 850hPa at 99% confidence level) for both reanalyses. The largest warming rates are found during autumn season where the magnitude of the temperature changes are +0.031 (K/year) and +0.033 (K/year) for the MERRA-2.0 and ERA-Interim, respectively. Our results suggest a high level of uncertainty in the temperature trends in the middle and upper stratosphere and a reasonable agreement between ERA-Interim and MERRA-2.0 warming trend in the troposphere. We also briefly discuss the role of different sources of uncertainty of the temperature trends in the middle and upper stratosphere.