Abstract. In this study, we analyze the Aura Microwave Limb Sounder water vapor data in the tropical upper troposphere and the lower and middle stratosphere (UTLMS) (from 215 to 6 hPa) for the period from August 2004 to September 2017 using time-lag regression analysis and composite analysis to explore the interannual variations of tropical UTLMS water vapor and their connections to El Niño–Southern Oscillation (ENSO) and quasi-biennial oscillation (QBO). Our analysis shows that the interannual tropical UTLMS water vapor anomalies are strongly related to ENSO and QBO which together can explain more than half (∼ 50 %–60 %) but not all variance of the interannual tropical water vapor anomalies. We find that ENSO's impact is strong in the upper troposphere (∼ 215–∼ 120 hPa) and near the tropopause (∼ 110–∼ 90 hPa), with a ∼ 3-month lag but weak in the lower and middle stratosphere (∼ 80 to ∼ 6 hPa). In contrast, QBO's role is large in the lower and middle stratosphere, with an upward-propagating signal starting at the tropopause (100 hPa) with a ∼ 2-month lag, peaking in the middle stratosphere near 15 hPa with a ∼ 21-month lag. The phase lag is based on the 50 hPa QBO index used by many previous studies. This observational evidence supports that the QBO's impact on the tropical stratospheric water vapor is from its modulation on the tropical tropopause temperature and then transported upward with the tape recorder as suggested by many previous studies. In the upper troposphere, ENSO is more important than QBO for the interannual tropical water vapor anomalies that are positive during the warm ENSO phases but negative during the cold ENSO phases. Near the tropopause, both ENSO and QBO are important for the interannual tropical water vapor anomalies. Warm ENSO phase and westerly QBO phase tend to cause positive water vapor anomalies, while cold ENSO phase and easterly QBO phase tend to cause negative water vapor anomalies. As a result, the interannual tropical water vapor anomalies near the tropopause are different depending on different ENSO and QBO phase combinations. In the lower and middle stratosphere, QBO is more important than ENSO for the interannual tropical water vapor anomalies. For the westerly QBO phases, interannual tropical water vapor anomalies are positive near the tropopause and in the lower stratosphere but negative in the middle stratosphere and positive again above. Vice versa for the easterly QBO phases.

<p><strong>Abstract.</strong> In this study, we analyze the Aura Microwave Limb Sounder water vapor data in the tropical upper troposphere and the lower and middle stratosphere (UTLMS) (from 215 hPa to 6 hPa) for the period from August 2004 to September 2017 using time-lag regression analysis and composite analysis to explore the interannual variations of tropical UTLMS water vapor and their connections to El Nino Southern Oscillation (ENSO) and quasi-biennial oscillation (QBO). Our analysis shows that ENSO’s impact on the interannual tropical water vapor anomalies is strong in the upper troposphere (~215 to ~120 hPa) and near the tropopause (~110 to ~90 hPa) with a ~3-month lag but weak in the lower and middle stratosphere (~80 to ~6 hPa). In contrast, QBO has a large impact on the interannual tropical water vapor anomalies in the lower and middle stratosphere with an upward propagating signal starting at the tropopause (100 hPa), peaking first in the lower stratosphere near 68 hPa with a ~7-month lag and then in the middle stratosphere near 15 hPa with a ~24-month lag. The phase lag is based on the 30-hPa QBO index and should be different from that found by previous studies based on the 50-hPa QBO index. In the upper troposphere, interannual tropical water vapor anomalies are positive during the warm ENSO phases but negative during the cold ENSO phases no matter what QBO phases are. Near the tropopause, interannual tropical water vapor anomalies are different depending on different ENSO and QBO phase combinations. In the lower and middle stratosphere, interannual tropical water vapor anomalies are mainly determined by QBO instead of ENSO. For the easterly QBO phases, interannual tropical water vapor anomalies are positive in the lower stratosphere but negative in the middle stratosphere. Vice versa for the westerly QBO phases.</p>

We study the properties of oscillatory double-diffusive convection (ODDC) in the presence of a uniform vertical background magnetic field. ODDC takes place in stellar regions that are unstable according to the Schwarzschild criterion and stable according to the Ledoux criterion (sometimes called semiconvective regions), which are often predicted to reside just outside the core of intermediate-mass main-sequence stars. Previous hydrodynamic studies of ODDC have shown that the basic instability saturates into a state of weak wave-like convection, but that a secondary instability can sometimes transform it into a state of layered convection, where layers then rapidly merge and grow until the entire region is fully convective. We find that magnetized ODDC has very similar properties overall, with some important quantitative differences. A linear stability analysis reveals that the fastest-growing modes are unaffected by the field, but that other modes are. Numerically, the magnetic field is seen to influence the saturation of the basic instability, overall reducing the turbulent fluxes of temperature and composition. This in turn affects layer formation, usually delaying it, and occasionally suppressing it entirely for sufficiently strong fields. Further work will be needed, however, to determine the field strength above which layer formation is actually suppressed in stars. Potential observational implications are briefly discussed.