Ozone and Temperature QBO

Using six years of nighttime differential absorption lidar (DIAL) ozone, and Rayleigh/Raman lidar temperature measurements obtained by the Jet Propulsion Laboratory at Mauna Loa Observatory, Hawaii, the stratospheric Quasi-Biennial Oscillation (QBO) signatures (15-55 km) in ozone and temperature were revealed. Several clear QBO signatures have been observed in both temperature and ozone.

The QBO signature in temperature maximizes at 35 km (5 K amplitude) and is seasonally synchronized (winter) and out-of-phase with the expected signature at the equator (Figure 2). Also, for the periods 1994-1996 and 1998-2000, the QBO is observable above 45 km, and near 24 km, with opposite phase to that observed at 35 km. The clearest QBO signature in stratospheric ozone maximizes near 31 km and is also seasonally synchronized in late winter-early spring and out-of-phase with the expected equatorial ozone QBO anomaly (Figure 3). Other signatures are observed in winter-spring near 47 km, in summer near 26 km, and in winter-spring near 22 km, respectively in-phase, in-phase, and out-of-phase with the expected equatorial ozone QBO. The observed temperature and ozone QBO signature were both strongly obscured below 25-27 km by the strong 1997/1998 El Nino the Southern Oscillation (ENSO) warm event.

These QBO anomalies identified in ozone and temperature are highly consistent with the previously observed and modeled QBO anomalies assuming that Hawaii is located in the subtropical branch of the asymmetrical QBO-induced meridional circulation. The strength and possibly the seasonal synchronization of the extra-tropical ozone QBO is thought to be a consequence of the vertical position (i.e., timing) of the equatorial QBO wind regime relative to the altitude of the ozone peak, the altitude separating the photochemical and dynamical driving of stratospheric ozone, and the altitude of latitudinal gradient reversal. The vertical structure of the temperature QBO is more straightforward: The thermal wind balance causes the QBO signature in the subtropics to be out-of-phase with that at the equator. The warm (respectively cold) phase in Hawaii coincides with the maximum Easterly (respectively Westerly) shear at the equator (Figure 1). Both the ozone and temperature QBO signatures suggest that Hawaii is located in the extra-tropical branch of the QBO-induced circulation (Figure 4).

The magnitude of the QBO-related variability in the stratosphere demonstrates that mid-term, and longer-term variability studies are essential in order to understand and quantify their contributions to issues such as global change or ozone depletion, especially if performed in the framework of a network like NDACC.

Figure 1Figure 2
Figure 1: Left: Monthly mean zonal winds at the equator and MLO. Right: 2D time-altitude contour of the MLO wind deviaiton form long-term mean.

Figure 2: Ozone QBO observed by the MLO lidar (below left):

  • “W” and “E” circles refer to Westerly and Easterly phases of the QBO
  • Max QBO ozone signature at 31 km
  • Seasonally synchronized (winter-spring), positive anomaly during Easterly phase, negative during Westerly.
  • Weak but observable signature around 45 km out-of-phase with that at 31 km.
  • Weak but observable signature at 23 km in-ohase with that at 31 km.
  • QBO signature strongly disturbed by El Nino below 27 km (ozone-poor air)
Figure 3 Figure 4
Figure 2, 3

Figure 3: Temperature QBO observed by the MLO lidar (above right):

  • “W” and “E” circles refer to Westerly and Easterly phases of the QBO
  • Max QBO temperature signature around 35-36 km
  • Seasonally synchronized (winter), positive anomaly during period of equatorial Easterly shear, negative during periods of equatorial Westerly shear.
  • Weak but observable signature around 45 km out-of-phase with that at 31 km.
  • Weak but observable signature near 25 km out-of-hase with that at 31 km (slight sign of downward propagation).
  • QBO signature strongly disturbed by El Nino below 27 km (cold lower stratosphere)
fig 4
Figure 4: Schematic of the QBO-induced perturbations associated with its residual circulation.

References

Leblanc, T., and I. S. McDermid, Quasi-biennial oscillation signatures in ozone and temperature observed by lidar at Mauna Loa, Hawaii (19.5ºN, 155.6ºW), J. Geophys. Res., 106, 14,869-14,874, 2001.

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