Observations of Layered Structures in the Lower Tropical Stratosphere Over Costa Rica During Ticosonde-Aura/TCSP 2005

Radiosondes were launched four times daily (00, 06, 12 and 18 UT) over a period of 10 weeks during the Ticosonde-Aura/TCSP 2005 radiosonde campaign at Alajuela, Costa Rica [10.0°N, 84.2° W]. Of the 277 soundings beginning 16 June at 00 UT, 254 ascended high enough to permit determination of a coded tropopause. Of these 51, or nearly one fifth, also contained layered structures within which a second tropopause was coded. While the sonde record shows some temporal scattering of these ``double tropopause'' soundings throughout the Ticosonde campaign ending August 24, there was a strong tendency for them to cluster in time. For example, beginning 12 UT on July 19 there are four consecutive soundings with a second coded tropopause. As it happens, the CFH water vapor and ozonesonde launched at 18 UT that day provides strong evidence of dehydration at the cold point tropopause just above 16 km. The structure in the next 3 km of the sounding is complex, consisting of 2 well-mixed, near-adiabatic layers in water vapor and ozone separated by strong inversions and easterly shear above 18 km. These structures do not appear to be an isolated phenomenon: we find similar structures in GPS radio occultation (RO) profiles of temperature in the region from the CHAMP satellite. We consider the hypothesis that this layering is related to dynamical processes operating on synoptic scales. First, we provide an overview of the characteristics of these layered structures in the Ticosonde record, including the water vapor and ozone structures in the four ``double tropopause'' soundings that also included measurements of water vapor and ozone with the CFH and ozonesonde payload. We next examine layered structures in the available GPS RO profiles from the region to diagnose coherent dynamical phenomema such as equatorial and tropical waves, particularly those near the inertial frequency. Finally we consider the possibility that the processes producing these layered structures may be related to dehydration events.