Variability of the "tropical pipe" boundaries in the stratosphere

We extend our previous study of the variability of the boundaries of the "tropical pipe" region of the stratosphere. In our previous work, we used tracer measurements from the Cryogenic Limb Array Etalon Spectrometer (CLAES) instrument on the Upper Atmosphere Research Satellite (UARS). We used the probability distribution function (PDF) of the tracer and defined the "tropical pipe" boundaries as the most probable latitude of the subtropical minimum in the PDF, which corresponds to "transition air" that has neither tropical nor midlatitude tracer characteristics. We determined the position of the boundaries as a function of altitude and examined the motion of the boundaries over a nine month period for which the CLAES data was available.

Here, we also look at other characteristics of these boundaries, such as the amount of atmospheric mass contained in the transition region and the corresponding latitude range occupied by the transition air. In addition, we examine the position of the boundaries as determined by tracer measurements from the Halogen Occultation Experiment (HALOE) instrument on the UARS satellite. The HALOE instrument has sparser data coverage but a longer data record than the CLAES instrument. We examine the statistical robustness of the HALOE data, compare the position of the boundaries determined from the HALOE measurements to those determined from the CLAES measurements for the period in which the data records overlap, and attempt to use the HALOE data to extend our picture of the variability of the boundaries to show a full annual cycle as well as interannual varibility.