The Influence of Solar Activity Level on Sudden Stratospheric Warming Events During Solar Cycle 23 (1998-2008)

Abstract

The Sudden Stratospheric Warming (SSW) events which occurred during solar cycle 23 (1998-2008) were investigated using daily stratospheric data (temperature, planetary wave, and zonal mean wind). A total of 10 events that occurred in the period were investigated, and they were all major events. The Wavelet Power Spectrum approach was also used to analyze the stratospheric parameters. It provides more details about the transient variabilities in stratospheric parameters. The analysis of the effect of the solar activity level on sudden stratospheric warming and the direction or phase of the Quasi-Biennial Oscillation (QBO) were also considered. The planetary wave (PW) amplification was observed to precede the rise in temperature and the reduction in speed of the zonal mean wind. It was noted that planetary wave amplification drives SSW. When the QBO was westerly, the stratospheric temperature shows a positive correlation with solar activity level, PW-1 showed a weak positive correlation (0.21), while PW-2 showed a negative correlation (-0.55). In the easterly phase, temperature and solar activity level show an inverse relationship, while both PW-1 and 2 showed a positive correlation with solar activity level. The result suggested that in the westerly phase, the solar activity level drives stratospheric temperature via adiabatic energy transfer but has no influence on the strength of the PW. In the easterly phase, the solar activity level does not influence stratospheric temperature, but it influences the generation of stronger PWs which drive intense SSW events. These results clearly show the influence of solar activity level on SSW and the coupling mechanism between the equatorial troposphere and the polar stratosphere.