Methane as a diagnostic tracer of changes in the Brewer–Dobson circulation of the stratosphere

Abstract

Abstract. This study makes use of time series of methane (CH 4 ) data from the Halogen Occultation Experiment (HALOE) to detect whether there were any statistically significant changes of the Brewer-Dobson circulation (BDC) within the stratosphere during 1992-2005. The HALOE CH 4 profiles are in terms of mixing ratio versus pressure altitude and are binned into latitude zones within the Southern Hemisphere and the Northern Hemisphere. Their separate time series are then analyzed using multiple linear regression (MLR) techniques. The CH 4 trend terms for the Northern Hemisphere are significant and positive at 10 • N from 50 to 7 hPa and larger than the tropospheric CH 4 trends of about 3 % decade −1 from 20 to 7 hPa. At 60 • N the trends are clearly negative from 20 to 7 hPa. Their combined trends indicate an acceleration of the BDC in the middle stratosphere of the Northern Hemisphere during those years, most likely due to changes from the effects of wave activity. No similar significant BDC acceleration is found for the Southern Hemisphere. Trends from HALOE H 2 O are analyzed for consistency. Their mutual trends with CH 4 are anti-correlated qualitatively in the middle and upper stratosphere, where CH 4 is chemically oxidized to H 2 O. Conversely, their mutual trends in the lower stratosphere are dominated by their trends upon entry to the tropical stratosphere. Time series residuals for CH 4 in the lower mesosphere also exhibit structures that are anti-correlated in some instances with those of the tracer-like species HCl. Their occasional aperiodic structures indicate the effects of transport following episodic, wintertime wave activity. It is concluded that observed multi-year, zonally averaged distributions of CH 4 can be used to diagnose major instances of wave-induced transport in the middle atmosphere and to detect changes in the stratospheric BDC.

Observed Responses of Mesospheric Water Vapor to Solar Cycle and Dynamical Forcings

“…MLR analyses of CH 4 , a companion tracer of H 2 O, yield significant positive responses to ENSO at 0.7 hPa across all latitudes (Table —top rows). Inclusion of the ENSO and Lya terms improve the MLR model fit to the time series of HALOE CH 4 data shown earlier by Remsberg (). The anticorrelated responses of CH 4 and H 2 O to ENSO are because the mixing ratio gradients for CH 4 near the stratopause are opposite to those of H 2 O.…”

Stratospheric age of air variations between 1600 and 2100

“…While the simulated results for the last decades of the twentieth century draw a very consistent picture of AoA and BDC changes, no agreement is found in observation‐based studies. The results of these studies range from a slight increase [e.g., Engel et al , ] (based on SF 6 and CO 2 measurements from high‐altitude balloon flights for the period 1975–2005) to a clear reduction of AoA [e.g., Remsberg , ] (using CH 4 records for the period 1995–2005). These AoA observations, however, are based on spatially and temporally sparse observations and are therefore associated with large uncertainties [ Waugh , ; Garcia et al , ].…”

Hemispheric asymmetry in stratospheric NO<sub>2</sub> trends

“…Such models have been extensively used in recent years to infer trends in long-term atmospheric time series of groundbased instruments; in particular, they have been used to study the evolution of stratospheric ozone (Bodeker et al, 1998;Wohltmann et al, 2007;Fioletov, 2008;Mäder et al, 2010), NO 2 ( Van der A et al, 2006Van der A et al, , 2008Gruzdev, 2009;Hendrick et al, 2012) and other species (i.e. Remsberg, 2015).…”