The stratospheric response to external factors based on MERRA data using linear multivariate linear regression analysis

Abstract. The stratosphere is influenced by many external forcings (natural or anthropogenic). There are many studies which are focused on this problem and that is why we can compare our results with them. This study is focused on the variability and trends of temperature and circulation characteristics (zonal and meridional wind component) in connection with different phenomena variation in the stratosphere and lower mesosphere. We consider the interactions between the troposphere–stratosphere-lower mesosphere system and external and internal phenomena, e.g. solar cycle, QBO, NAO or ENSO using multiple linear techniques. The analysis was applied to the period 1979–2012 based on the current reanalysis data, mainly the MERRA reanalysis dataset (Modern Era Retrospective-analysis for Research and Applications) for pressure levels: 1000–0.1 hPa. We do not find a strong temperature signal for solar flux over the tropics about 30 hPa (ERA-40 results) but the strong positive signal has been observed near stratopause almost in the whole analyzed area. This could indicate that solar forcing is not represented well in the higher pressure levels in MERRA. The analysis of ENSO and ENSO Modoki shows that we should take into account more than one ENSO index for similar analysis. Previous studies show that the volcanic activity is important parameter. The signal of volcanic activity in MERRA is very weak and insignificant.