Abstract
Using the Microwave Limb Sounding measurements and the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis product, we have investigated the response of carbon monoxide (CO) mixing ratio within the Asian Summer Monsoon Anticyclone (ASMA) region to the Quasi-Biennial Oscillation (QBO) and the potential dynamical mechanisms behind it. The results showed that the mixing ratio of CO within the ASMA is significantly higher at both 100 hPa and 147 hPa in the east phase of QBO (EQBO) years than in the west phase of QBO (WQBO) years, especially in the eastern part of the ASMA. The CO difference between EQBO and WQBO years is consistent with the interannual variation of the location and strength of the ASMA. Specifically, during the EQBO years, the area of the ASMA reduces to the southeast in the upper troposphere, while the westerly jet on the north side of the anticyclone and the southerly winds on the west side of the anticyclone both strengthen. These variations are associated with tropospheric circulation anomalies. The ascending motions over the Tibetan Plateau (TP) are enhanced during the EQBO years, which are correlated with the relatively high CO at 100 hPa. Consistently, an anomalous cyclonic circulation is found at 500 hPa over the TP when the QBO is on its east phase, which promotes the convergence of air mass and carries CO from the surface to the Upper Troposphere and Lower Stratosphere (UTLS).
Highlights
The Asian Summer Monsoon Anticyclone (ASMA) is the dominant circulation system in the northern hemisphere, which extends from Asia to the Middle East in boreal summer (June–September) (Mason and Anderson, 1963; Hokins and Rodwell, 1995; Randel et al, 2001; Randel and Park, 2006)
It is found that there exist positive carbon monoxide (CO) anomalies (∼2 ppbv) at 68.1 hPa (Figure 2A) over the area of 15°–35° N, 30°–150° E, which indicates that relatively high CO can be found within the ASMA when the Quasi-Biennial Oscillation (QBO) is on the east phase
The Tibetan Plateau (TP) is an important channel for tropospheric chemicals to enter the Upper Troposphere and Lower Stratosphere (UTLS) (e.g., Luo et al, 2018), and the anomalous upward movements shown in Figure 8 are conducive to the transportation of CO from the surface to the UTLS within the ASMA when the QBO is on its east phase
Summary
The Asian Summer Monsoon Anticyclone (ASMA) is the dominant circulation system in the northern hemisphere, which extends from Asia to the Middle East in boreal summer (June–September) (Mason and Anderson, 1963; Hokins and Rodwell, 1995; Randel et al, 2001; Randel and Park, 2006). QBO and CO in UTLS (UTLS) region, the ASMA behaves as a strong horizontal transport barrier, which consists of a westerly jet in the north and an easterly jet in the south (Dunkerton, 1995; Highwood and Hoskins, 1998; Randel and Park, 2006). Relatively high concentrations of water vapor (Ronsenlof et al, 1997), methane, nitrogen oxides (Park et al, 2004), and carbon monoxide (CO) (Li et al, 2005) and relatively low concentrations of ozone (Randel et al, 2001) are trapped within the ASMA
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