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The Stratospheric Quasi-biennial Oscillation (QBO)


  Table of Contents

  Introduction

The Quasi-biennial Oscillation or QBO is a tropical lower stratospheric, downward propagating zonal wind variation, with an average period of ~28 months, but its period is variable by more than a year between the shortest and longest QBO periods. Ebdon [1960] and Reed et al. [1961] independently first detected the QBO. Tropical radiosonde wind observations that document the QBO have been made continuously since 1953 [e.g., Naujokat, 1986]. The importance of the QBO is that it dominates the variability of the tropical lower stratospheric meteorology [Wallace , 1973]. A comprehesive summary of the QBO can be found in Baldwin et al. [2001].

Herein we use radiosondes from the Meteorological Service Singapore Upper Air Observatory (station code 48698). The station is located at 1.34041N, 103.888E at an altitude of 21m.

The Modern-Era Retrospective analysis for Research and Applications, Version -2 (MERRA-2) provides data beginning in 1980 and runs a few weeks behind real time [Gelaro et al., 2017]. The structure, dynamics, and ozone for the QBO in MERRA-2 is documented in Coy and Wargan [2016].

These plots also reveal the QBO disruption that occured from late 2015 through about February 2017 [Newman et al., 2016; Osprey et al., 2017]. A more complete dynamical explanation of the disruption can be found in Coy et al. [2017]. The impact on ozone, water, etc., can be found in Tweedy et al. [2017].


  Zonal winds


Singapore sonde 1980-present QBO from monthly mean zonal wind

The plot is generated by: 1) reading all of the daily sondes for the full month, 2) vertically interpolating the zonal wind to the 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.

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Data file


MERRA-2 1980-present QBO monthly mean zonal wind at the Equator

The plot is generated by taking the monthly mean MERRA-2 zonal mean winds, and then subtracting the long-term monthly mean, and then linearly detrending the residual winds. The thick dotted line shows the tropopause calculated from the thermal lapse rate. The easterly and westerly phases are derived from the Singapore sonde above. Units are meters per second. The plot differs from the Singapore plot above because this MERRA-2 plot has been detrended and has the monthly mean removed.

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The last 3 years of the QBO from the Singapore sonde daily zonal wind

The plot shows the daily zonal mean winds from the twice per day (0Z and 12Z) Singapore radiosondes. Each sonde is interpolated to a 0.5km 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.

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MERRA-2 1980-present QBO monthly mean zonal wind versus latitude

The latitudinal structure of the zonal mean wind from MERRA-2 at 40hPa. These data INCLUDE the annual cycle in order to show how the QBO phase connects to mid-latitude, mid-winter westerlies. Units are meters per second.

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The EOFs of the 1980-present QBO from the Singapore sonde monthly mean winds

The plot shows the phase diagram of the two leading modes of the calculated empirical orthogonal functions (EOF). The EOFs represent the major components of the QBO variability, and have been calculated following [Wallace et al., 1993]. The EOFs were derived from the 1979-present deaseasonalized monthly mean Singapore radiosonde zonal winds (shown above). The first two EOFs show the circular polarization that is characteristic of the QBO in the counter-clockwise rotation. On the rim of the figure are the simple reconstructuions of the zonal wind profile for the various phases. The last 3 calendar years are colored. This plot was recently shown in Tweedy et al. [2017]. Units are meters per second.

Most of the plots on this page have superimposed easterly (E) and westerly (W) points. These E and W points are derived from this EOF-1 and EOF-2 phase diagram above. The W (E) points are calculated when the phase angle is 45 (225) degrees, corresponding to a dominant westerly (easterly) in the 70-10 hPa part of the stratosphere.

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EOF coefficient data file

EOF function values vs. pressure data file


  Temperatures


Singapore sonde temperature QBO from monthly mean data

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 2 months or less. The thick dotted line shows the tropopause calculated from the thermal lapse rate. Units are Kelvin.

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MERRA-2 temperature QBO from monthly mean data at the Equator

As with the zonal winds, the T plot is generated by taking the monthly mean MERRA-2 zonal mean temperature, and then subtracting the long-term monthly mean, and then 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.

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The last 3 years of the temperature QBO from the Singapore sonde daily

The plot shows the daily zonal mean temperatures from the twice per day (0Z and 12Z) Singapore radiosondes. Each sonde is interpolated to a 0.5km 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.

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MERRA-2 temperature QBO from monthly mean data versus latitude

As with the zonal winds, the 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 points are as shown in the Singapore zonal winds, and are defined by the EOF-1 and EOF-2 phase diagram above. Units are Kelvin.

High-res PDF version


  Ozone


Total ozone from TOMS/OMI versus latitude (deseasonalized)

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 2 months or less. The white "stipes" are data voids (e.g., in 1995 nd 1996), while the white spots (e.g., 30N in early 1985) show where the anomalies exceed the color scale maximum or minimum. The easterly (E) and westerly 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).

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Daily total ozone (last 3 years) from TOMS/OMI versus latitude (deseasonalized)

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 1/2 amplitude (i.e., high frequency features are smoothed out). Units are Dobson Units (DU).

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Ozone versus pressure from MLS

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 (1/2 amplitude = 10.1 days) to remove higher frequency structure. The easterly (E) and westerly 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).

High-res PDF version


  Water (H2O)


Water (H2O) versus pressure from MLS

Water (H2O) 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 (H2O) profiles. The annual cycle is subtracted from the profiles, and missed profiles are added by temporal linear interpolation. A Gaussian smoothing is applied (1/2 amplitude = 30 days) to remove higher frequency structure. The easterly (E) and westerly 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).

The QBO in water is different than most QBO structures because of the impact of the QBO forced temperature anomalies at the tropical tropopause. There is still downward progression of the QBO above 10 hPa. This behavior is explained by Kawatani et al. [2014] using these same MLS data.

High-res PDF version

The non-deseasonalized tropical water profile showing the tape recorder is also herein as a png plot and a high-res pdf plot.


  QBO movie

  Data Links

  Some Related External links

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