The stratospheric Brewer-Dobson circulation inferred from age of air in the ERA5 reanalysis
The stratospheric Brewer-Dobson circulation inferred from age of air in the ERA5 reanalysis
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DOI：
10.5194/acp-21-8393-2021
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发表时间：
2021-01
影响因子：
6.3
通讯作者：
F. Ploeger;Mohamadou A. Diallo;E. Charlesworth;P. Konopka;B. Legras;J. Laube;J. Grooß;G. Günther-G.-Günthe
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文献类型：
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作者：
F. Ploeger;Mohamadou A. Diallo;E. Charlesworth;P. Konopka;B. Legras;J. Laube;J. Grooß;G. Günther-G.-Günthe
本文研究了欧洲中期天气预报中心（ECMWF） ERA5气象再分析中全球平流层Brewer-Dobson环流（BDC）。该分析基于对平流层空气平均年龄的模拟，包括完整的年龄谱，使用拉格朗日输运模式CLaMS，由风和再分析的总非绝热加热率驱动。将基于era5的结果与之前的ERA-Interim再分析结果进行比较。我们的研究结果表明，ERA5的BDC明显慢于ERA-Interim，表现为较弱的绝热升温速率和较大的空气年龄。在热带平流层下层，ERA5的升温速率弱30-40%，可能纠正了ERA-Interim的已知偏差。上图中，与示踪剂观测相比，空气的ERA5年龄显得稍微偏大，BDC略慢。正如气候模式预测的那样，1989-2018年期间ERA5在整个平流层的年龄趋势为负。然而，年龄的下降在一个时期内不是线性的，而是呈阶梯变化，这可能是由多年变率或同化系统的变化引起的。在2002—2012年期间，ERA5年龄表现出与ERA-Interim相似的半球偶极子趋势，年龄在北半球增大，在南半球减小。年龄谱峰和剩余环流过境时间的变化表明，年龄的再分析差异可能是由剩余环流的差异引起的。特别是，在两次重新分析中，浅BDC分支加速相似，而深分支在ERA5中加速，在ERA-Interim中减速。
This paper investigates the global stratospheric Brewer-Dobson circulation (BDC) in the ERA5 meteorological reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF). The analysis is based on simulations of stratospheric mean age of air, including the full age spectrum, with the Lagrangian transport model CLaMS, driven by winds and total diabatic heating rates from the reanalysis. ERA5-based results are compared to those of the preceding ERA-Interim reanalysis. Our results show a significantly slower BDC for ERA5 than for ERA-Interim, manifesting in weaker diabatic heating rates and larger age of air. In the tropical lower stratosphere, heating rates are 30-40% weaker in ERA5, likely correcting a known bias in ERA-Interim. Above, ERA5 age of air appears slightly high-biased and the BDC slightly slow compared to tracer observations. The age trend in ERA5 over 1989-2018 is negative throughout the stratosphere, as climate models predict in response to global warming. However, the age decrease is not linear over the period but exhibits steplike changes which could be caused by muti-annual variability or changes in the assimilation system. Over the 2002-2012 period, ERA5 age shows a similar hemispheric dipole trend pattern as ERA-Interim, with age increasing in the NH and decreasing in the SH. Shifts in the age spectrum peak and residual circulation transit times indicate that reanalysis differences in age are likely caused by differences in the residual circulation. In particular, the shallow BDC branch accelerates similarly in both reanalyses while the deep branch accelerates in ERA5 and decelerates in ERA-Interim.