Chemical composition changes over equator during SSW events are investigated using MLS and MIPAS data sets. It is found that the O3 VMR increases whereas H2O VMR decreases. In the upper stratosphere, the source of water vapor is oxidation of CH4 by OH or O. But, OH does not vary during SSW. The temperature decrease over equator during SSW increases the reaction rate of ozone production to shift the O/O3 ratio towards O3, resulting in decrease of CH4 oxidation and consequent decrease in H2O.

Eastward propagating 18-day waves of zonal wavenumbers (k=1-5) are observed in mid-latitude meridional winds at 200 hPa during December 2012-February 2013. Among these, the 18-day wave of k=5 propagates equatorward. Presence of wave of similar periodicity (18-day) and zonal structure (k=5) in tropical OLR as that of extratropical wave disturbance is first reported. We suggest that the selective response of the tropical wave forcing is due to the lateral forcing of the extra-tropical wave.

A rare occurrence of stratospheric cirrus at 18.6km persisting for about 5 days is observed over India from 3 to 7 March 2014. Due to potential vorticity intrusion, large-scale updrafts and increase in humidity are observed at 18.6km. Relative humidity with respect to ice is ~ 150%, indicating that the cirrus cloud may be formed though homogeneous nucleation of sulfuric acid. The persistence of the cirrus cloud is due to the cold anomaly associated with the presence of a 4-day wave.