Roles of ozone depleting substances and solar activity in observed long-term trends in total ozone column over Indian region

An additive time-series decomposition analysis was performed on the Multi Sensor Reanalysis-2 (MSR-2) monthly mean total ozone column (TOC) time-series dataset spanning over 34 years (January 1979-December 2012) for Indian region (0.0-40.0 degrees N; 67.5-97.5 degrees E). Statistically significant (p-value <0.05) long-term trends in TOC were estimated in the deseasonalized TOC time series. The role of multiple natural and anthropogenic factors: quasi biennial oscillations (QBO), El-Nino Southern Oscillations (ENSO), cyclic variation in solar activity (SA), and ozone depleting substances (ODS) was investigated to explain the long-term trends in TOC over Indian region. Over sub-tropical Indian region (25.0 degrees N- 40.0 degrees N), declining long-term linear trends were estimated, which varied from -0.30% to -1.10% per decade. Interestingly a positive long-term linear-trend (0.10-0.30% per decade) was observed over equatorial-tropical part of Indian region. No statistically significant longterm trend was observed for 30mb Equatorial Zonal Winds and Nino 3.4 index - indicators for QBO and ENSO; however, a positive long-term linear trend of magnitude 17.00 +/- 1.18% per decade was observed in effective equivalent stratospheric chlorine - a proxy for ODS, and a negative long-term linear trend of magnitude 12.72 +/- 2.86% per decade was observed in 10.7 cm Solar Radio Flux - a representative for SF. It is inferred that over the Indian region above tropic of cancer, about 85.00% of the estimated negative long-term linear trend in TOC can be explained by the increase in the stratospheric concentration of ODS; whereas, decrease in the solar activity accounted for 15.00% of the estimated negative long-term linear trend in TOC over sub-tropical Indian region.