Hemispheric Differences in Tropical Lower Stratospheric Constituent Seasonal Cycles

Abstract:

The measured seasonal cycle of ozone in the lower stratosphere shows significant differences between the northern and southern tropics. The amplitude of the seasonal cycle is larger in the northern tropics than in the southern tropics with a 2-3 month phase difference between the hemispheres. MLS data shows a distinct double peak in the magnitude of the northern-tropical seasonal cycle of ozone (in percent) with maxima at 100 hPa and 68 hPa and a relative at 82 hPa. SAGE and HALOE data show a single maximum located near 80 hPa. Analysis of two years of OMPS-limb data from the Suomi-NPP mission confirms the double peak structure measured by MLS. We will show comparisons of data from MLS and OMPS-limb and will examine the interannual variability of the double-peak structure from 10 years of MLS data. It appears that vertical advection is the dominant cause of tracer annual cycles in the southern tropics, while horizontal mixing dominates in the northern tropics. We argue that separating data into separate tropical regions for each hemisphere and examining the seasonal cycle and its interannual variability will lead to increased understanding of the processes that govern transport of ozone and other tracers in the tropical and sub-tropical lower stratosphere.