Some important recent findings in climate studies are the warming trend in the troposphere and the cooling trend in the stratosphere. However, the evidence for the cooling trend in the stratosphere may need to be revisited. This study presents evidence that the stratosphere is slightly warming since 1996. Using long-term Stratosphere Sounding Unit (SSU) measurements at channels 1 and 2 before 1996, we did obtain a cooling trend in the middle and upper parts of stratosphere similar to the findings for the lower stratosphere in literature (Ramaswamy et al. 2001; Fu et al. 2004). But, we also found that the temperature trend in the middle and upper stratosphere has alternated to warming since 1996. We also analyzed a time series of the Microwave Sounding Unit (MSU) channel 4 brightness temperatures between 1978 and 2006 and found the same reversing trend in the lower stratosphere. The reversing trend may relate to a possible recovery of stratospheric ozone concentration.
2009 by the Meteorological Society of Japan