Abstract
Abstract. The circulation of the stratosphere, also known as the Brewer–Dobson circulation, transports water vapor and ozone, with implications for radiative forcing and climate. This circulation is typically quantified from model output by calculating the tropical upwelling vertical velocity in the residual circulation framework, and it is estimated from observations by using time series of tropical water vapor to infer a vertical velocity. Recent theory has introduced a method to calculate the strength of the global mean diabatic circulation through isentropes from satellite measurements of long-lived tracers. In this paper, we explore this global diabatic circulation as it relates to the residual circulation vertical velocity, stratospheric water vapor, and ozone at interannual timescales. We use a comprehensive climate model, three reanalysis data products, and satellite ozone data. The different metrics for the circulation have different properties, especially with regards to the vertical autocorrelation. In the model, the different residual circulation metrics agree closely and are well correlated with the global diabatic circulation, except in the lowermost stratosphere. In the reanalysis products, however, there are more differences throughout, indicating the dynamical inconsistencies of these products. The vertical velocity derived from the time series of water vapor in the tropics is significantly correlated with the global diabatic circulation, but this relationship is not as strong as that between the global diabatic circulation and the residual circulation vertical velocity. We find that the global diabatic circulation in the lower to middle stratosphere (up to 500 K) is correlated with the total column ozone in the high latitudes and in the tropics. The upper-level circulation is also correlated with the total column ozone, primarily in the subtropics, and we show that this is due to the correlation of both the circulation and the ozone with upper-level temperatures.
Highlights
The Brewer–Dobson circulation (BDC) is important for the distribution of trace gases in the stratosphere (Butchart, 2014) including water vapor, the radiative effects of which have been shown to impact surface climate (Dessler et al, 2013), and ozone, which impacts tropospheric circulation (e.g., Polvani et al, 2011) and human health (e.g., Abarca and Casiccia, 2002)
We find that the choice of averaging latitudes – whether fixed tropics (30◦ S–30◦ N) or turnaround latitudes – has an effect on the deseasonalized variability that depends on the method
These methods result in different vertical structures; the calculation based on the principle of downward control has a much broader vertical autocorrelation than the calculation from diabatic heating rates
Summary
The Brewer–Dobson circulation (BDC) is important for the distribution of trace gases in the stratosphere (Butchart, 2014) including water vapor, the radiative effects of which have been shown to impact surface climate (Dessler et al, 2013), and ozone, which impacts tropospheric circulation (e.g., Polvani et al, 2011) and human health (e.g., Abarca and Casiccia, 2002). In the Northern Hemisphere, the variability in hemispherically averaged upward Eliassen–Palm (EP) flux at 100 hPa from the early NCEP reanalysis data product has been shown to explain about 50 % of the interannual variability of total column ozone in wintertime (Fusco and Salby, 1999), with the influence of the wave driving dependent on the latitude (Reinsel et al, 2005) These strong relationships are a motivating factor in using the TEM residual mean vertical velocity, which is directly related to the EP flux, as a metric for the BDC strength. We compare the global diabatic circulation to the more traditionally used TEM vertical velocity calculated in these three different ways (Abalos et al, 2015) for three different reanalysis products and for the Whole Atmosphere Community Climate Model (WACCM).
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