Investigation of double tropopause spatial and temporal variability utilizing HIRDLS temperature observations

The Upper Troposphere Lower Stratosphere (UTLS) region in the Earth's atmosphere plays a critical role in the climate system. Here the tropopause separates these two layers, each with fundamentally different characteristics. The thermal definition of the tropopause shows a break during the winter at mid-latitudes resulting in a double tropopause. Multiple tropopauses have been known to exist since the 1950's and current research has expanded upon that earlier research. These recent studies have examined the spatial distribution, height seasonality and potential vorticity relationship of the double tropopause either through the analysis of radiosonde data or as a case study. This study utilizes V5 temperature observations from the High Resolution Dynamic Limb Sounder (HIRDLS) instrument on the NASA Aura satellite to analyze global and along track variability of the double tropopause. HIRDLS provides global coverage day and night, along with a vertical resolution of ~1 km in the UTLS. Daily activity is examined on an orbit track by orbit track basis to verify that double tropopauses are captured in the HIRDLS observations. The poleward intrusion of low static stability air is clearly seen, along with the corresponding lower layer of high static stability air. Annual variability is examined and highlights an increase in activity and shift in the annual pattern in 2006, the year of a sudden stratospheric warming in the northern hemisphere. A recent study shows a similar increase in ozone lamine. Double tropopause frequency of occurrence is analyzed globally and for the four different seasons. Results show a frequency maximum during the winter of each hemisphere along with preferred longitude regions. This study presents new results on double tropopause areal extent and associated seasonality. Additional analysis, such as height, pressure, temperature and potential temperature tendencies, along with duration calculations, will be presented and discussed.