Investigation of double tropopause spatial and temporal global variability utilizing High Resolution Dynamics Limb Sounder temperature observations

This study examines the seasonal variation of the double tropopause (DT) using data from the High Resolution Dynamics Limb Sounder. The combination of high data density and high vertical resolution available with this satellite instrument allows for the detailed analysis of fine-scale structures such as the DT. The spatial distribution of DT frequency is examined for all seasons from 2005 to 2007. Global analysis of this distribution reveals that DTs have a strong tendency to follow the zonal wind pattern and are present all year over the Andes. Moreover, during Northern Hemisphere winter/spring, there is a 15% decrease in the DT frequency over the eastern Pacific and western Atlantic, two regions of wave breaking produced from a weakening of the zonal flow. Significant DT thickness values are also present over these regions, but are found to extend further poleward than the corresponding frequency pattern. A time series of DT frequencies is analyzed and shows an increase in daily frequencies during 2006 that highlights the interannual variability of this thermal structure. For the first time, DT duration is investigated in the extratropics utilizing a Hovmöller diagram of DT frequency. This representation highlights two preferred regions of formation, the Pacific and Atlantic. The slope of the feature gives it a speed of 18 m/s in the Northern Hemisphere and a slightly faster speed for the Southern Hemisphere. These speeds and the corresponding structures highlight a potential connection between upper tropospheric waves and DTs.