Signatures of the Madden-Julian Oscillation in Stratospheric Temperature from Aura MLS

The Madden-Julian oscillation (MJO) is a major source of intraseasonal variability in the tropical troposphere. It refers to a recurring pattern of strong convection, which travels from the Indian ocean over the Maritime Continent to the Pacific ocean with time scales of 30 to 90 days.

Although some studies have recently indicated that the occurrence of tropospheric MJO events could also affect stratospheric parameters, the MJO is not very much recognized as a source of stratospheric variability. This bears the risk of mixing it up with other sources of variability on this time scale, e.g., with signatures of the solar 27-day variations. Many of the studies that have found MJO signatures in the stratosphere are, however, based on either modelled or reanalyzed data. Particularly, we are not aware of any purely observational studies related to the temperature response in the middle atmosphere.

To fill this gap, we analyze the signature of the MJO in stratospheric temperatures measured by the Microwave Limb Sounder (MLS) satellite instrument aboard the Aura satellite. Analyzing the period from about 2004 to 2018, we indeed identify corresponding temperature variations in various altitudes and locations with many of them being significant according to Monte Carlo tests. The amplitudes of these signatures are on the order of 0.5 K. Moreover, basic characteristics of signatures, which have been identified in the preceding publications, are confirmed in this study based on purely observational data.

Hence, our study supports the coupling of parts of the stratospheric variability on the intraseasonal time scale to anomalous tropospheric convection represented by the MJO.