The plot is made by: 1) reading all daily sondes for the full month (generally twice per day at 0Z and 12Z), 2) vertically interpolating the zonal wind to missing levels (no extrapolation to levels above balloon burst altitudes), and 3) time interpolating for missing levels above the top of the balloon profile. The thick dotted line shows the tropopause calculated from the thermal lapse rate. Units are meters per second.

The plot is generated from the monthly mean MERRA-2 zonal mean winds. The thick dotted line shows the tropopause calculated from the thermal lapse rate. The noted easterly (E) and westerly (W) phases are derived from the Singapore sonde above. Units are meters per second.

The plot shows the daily zonal mean winds from the twice per day (0Z and 12Z) Singapore radiosondes. Each sonde is interpolated to a 0.5 km vertical grid. Above the burst altitude, either MERRA-2 or GEOS-FP data are used to fill this vertical grid. The black line shows the tropopause as computed from the lapse rate. Units are meters per second.

The latitudinal structure of the zonal mean wind QBO from MERRA-2 at 70 hPa. These data have had the annual cycle removed to reveal the QBO. Units are meters per second.

The latitudinal structure of the zonal mean wind QBO from MERRA-2 at 40 hPa. These data have had the annual cycle removed to reveal the QBO. Units are meters per second.

The latitudinal structure of the zonal mean wind QBO from MERRA-2 at 10 hPa. These data have had the annual cycle removed to reveal the QBO. Units are meters per second.

Left panel: Wind anomlies (\(\Delta \overline u \) = \(\overline u\) - <\(\overline u \)>, where overbars are zonal means, and brackets are multi-year averages. Positive anomalies are red and negative anomalies are blue (units = m/s). The white lines show the wind climatology and the thick blue line is the climatological tropopause (computed from the Brunt-Vaisalla frequency). The left y-axis is pressure (hPa), and the right y-axis is pressure altitude (km). Right panel: Normalized wind anomalies (\(\Delta \overline u/\sigma \)). \(\sigma \) (the multi-year time series' standard deviation) is calculated from the same 15-day periods over the 43 years 1980–2022 MERRA-2 climatology. As an example, values of of \(\Delta \overline u/\sigma = 2 \) are two standard deviations above the norm. The (solid and dashed) thick white lines on this RHS indicate record (positive and negative) anomaly values. The actual anomaly values are plotted as the thin white lines.

Phase diagram of the first two leading modes of the calculated EOFs from the Singapore winds shown above. On the rim of the figure are the simple reconstructions of the zonal wind profile for the various phases. The last 3 calendar years are colored. Circles indicate the month number for the corresponding year.

The plot is generated by: 1) reading in monthly mean temperatures, 2) detrending the temperature time series, 3) subtracting off the annual cycle at all levels, and 4) smoothing the data with a 1-2-1 Gaussian filter (effectively removing variability with periods of 5 months or less. The thick dotted line shows the tropopause calculated from the thermal lapse rate. Units are Kelvin.

This temperature plot is generated by: 1) reading in the monthly mean MERRA-2 zonal mean temperature, 2) subtracting the long-term averaged monthly mean, and 3) performing a linear detrending of the residual temperature. The thick dotted line shows the tropopause calculated from the thermal lapse rate. Note that the QBO wind peaks tend to fall along the "zero" temperature lines. Units are Kelvin.

Daily zonal mean temperatures from the twice per day (0Z and 12Z) Singapore radiosondes. Each sonde is interpolated to a 0.5 km vertical grid. Above the burst altitude, either MERRA-2 or GEOS-FP data are used to fill this vertical grid. The 3-year time average profile is subtracted from the data (annual cycle is still embedded in the plot). The tropopause is shown as the black line (computed from the lapse rate). Units are Kelvin.

As with the zonal winds, this temperature plot is generated by taking the monthly mean MERRA-2 zonal mean temperatures, subtracting the long-term monthly mean, and then linearly detrending the residual temperature. The easterly (E) and westerly (W) points are from the Singapore zonal winds, and are defined by the EOF-1 and EOF-2 phase diagram above. Units are Kelvin.

As with the zonal winds, this T plot is generated by taking the monthly mean MERRA-2 zonal mean temperatures, and then subtracting the long-term monthly mean, and then linearly detrending the residual temperature. The easterly (E) and westerly (W) points are from the Singapore zonal winds, and are defined by the EOF-1 and EOF-2 phase diagram above. Units are Kelvin.

As with the zonal winds, this T plot is generated by taking the monthly mean MERRA-2 zonal mean temperatures, and then subtracting the long-term monthly mean, and then linearly detrending the residual temperature. The easterly (E) and westerly (W) points are from the Singapore zonal winds, and are defined by the EOF-1 and EOF-2 phase diagram above. Units are Kelvin.

Left panel: Temperature anomlies (\(\Delta \overline T \) = \(\overline T\) - <\(\overline T \)>, where overbars are zonal means, and brackets are multi-year averages. Positive anomalies are red and negative anomalies are blue (units = K). The white lines show the \(\overline u\) wind climatology and the thick blue line is the climatological tropopause (computed from the Brunt-Vaisalla frequency). The left y-axis is pressure (hPa), and the right y-axis is pressure altitude (km). Right panel: Normalized temperature anomalies (\(\Delta \overline T/\sigma \)). The temperature standard deviation (\(\sigma \)) is calculated from the same 15-day periods over the 43 years 1980–2022 MERRA-2 climatology. As an example, values of of \(\Delta \overline T/\sigma = 2 \) are two standard deviations above the norm. The (solid and dashed) thick white lines on this RHS indicate record (positive and negative) anomaly values. The actual temperature values are plotted as the thin white lines.

This \(\overline {w}^*\) plot is generated from MERRA-2 zonal mean values. The annual cycle and the linear trend of the 1980–present time series are both removed, and the values are band pass filtered with a Gaussian filter (8.5–48.0 months). The thick dotted line shows the tropopause calculated from the thermal lapse rate. The QBO is well correlated in the post-1999 period, but relatively poor prior to that date. This is probably related to the increased assimilation of satellite data in the post-1999 period.

As with the zonal winds, this \(\overline {w}^*\) plot is generated from the monthly mean MERRA-2 zonal mean omega, heat flux, and temperature values. The long-term monthly means are subtacted, and then linearly detrended. The easterly (E) and westerly (W) points are from the Singapore zonal winds, and are defined by the EOF-1 and EOF-2 phase diagram above. Units are millimeters per second.

As with the zonal winds, this \(\overline {w}^*\) plot is generated from the monthly mean MERRA-2 zonal mean omega, heat flux, and temperature values. The long-term monthly means are subtacted, and then linearly detrended. The easterly (E) and westerly (W) points are from the Singapore zonal winds, and are defined by the EOF-1 and EOF-2 phase diagram above. Units are millimeters per second.

As with the zonal winds, this \(\overline {w}^*\) plot is generated from the monthly mean MERRA-2 zonal mean omega, heat flux, and temperature values. The long-term monthly means are subtacted, and then linearly detrended. The easterly (E) and westerly (W) points are from the Singapore zonal winds, and are defined by the EOF-1 and EOF-2 phase diagram above. Units are millimeters per second.

Total ozone monthly means versus latitude. The plot is generated by: 1) reading in monthly mean total ozone, 2) subtracting off the annual cycle at all levels, 3) detrending the total ozone time series with a linear term over the entire time series, and 4) smoothing the data with a 1-2-1 Gaussian filter (effectively removing variability with periods of 4 months or less. The easterly (E) and westerly (W) points are as shown in the Singapore zonal winds, and are derived (see text with EOF figure) from the EOF-1 and EOF-2 phase diagram above. Units are Dobson Units (DU).

Total ozone versus latitude for daily values. The plot is generated by: 1) reading in 3-years of daily zonal mean total ozone, 2) reading in the 1979–2017 daily zonal mean data and creating a 365-day climatology, 3) subtracting this annual cycle climatology from the 3-years of daily data, 4) applying a Gaussian smoothing filter with a 6.7 day half-amplitude (i.e., high frequency features are smoothed out). Units are Dobson Units (DU).

Ozone versus pressure at the equator from the NASA JPL Microwave Limb Sounder (MLS) on the NASA Aura satellite. Each day's MLS ozone is read, and all profiles within 2.5 degrees of the equator are averaged together to produce the daily ozone profiles. The annual cycle is subtracted from the profiles, and missed profiles are added by temporal linear interpolation. A Gaussian smoothing is applied (half-amplitude = 20 days) to remove higher frequency structure. The easterly (E) and westerly (W) points are as shown in the Singapore zonal winds, and are derived (see text with EOF figure) from the EOF-1 and EOF-2 phase diagram above. Units are parts per million (ppm).

MLS ozone latitudinal profile versus time. The data are binned into 5 degree boxes from 45°S–45°N. The easterly (E) and westerly (W) points are as shown in the Singapore zonal winds, and are derived (see text with EOF figure) from the EOF-1 and EOF-2 phase diagram above. Units are parts per million (ppmv).

Water versus pressure at the equator from the NASA JPL Microwave Limb Sounder (MLS) on the NASA Aura satellite. Each day's MLS water is read, and all profiles within 2.5 degrees of the equator are averaged together to produce the daily water profiles. The annual cycle is subtracted from the profiles, and missed profiles are added by temporal linear interpolation. A Gaussian smoothing is applied (half-amplitude = 20 days) to remove higher frequency structure. The easterly (E) and westerly (W) points are as shown in the Singapore zonal winds, and are derived (see text with EOF figure) from the EOF-1 and EOF-2 phase diagram above. Units are parts per million (ppm).

MLS water latitudinal profile versus time. The data are binned into 5 degree boxes from 45°S–45°N. A Gaussian smoothing is applied (half-amplitude = 20 days) to remove higher frequency structure. The easterly (E) and westerly (W) points are as shown in the Singapore zonal winds, and are derived (see text with EOF figure) from the EOF-1 and EOF-2 phase diagram above. Units are parts per million (ppmv). Units are parts per million (ppm).