The Ticosonde/NAME 2004 Experiment: A Program of High-Frequency Rawinsonde Observations over Costa Rica During Summer

Ticosonde/NAME 2004 is a collaboration between NASA, the North American Monsoon Experiment (NAME), the Instituto Meteorológico Nacional and four other academic and scientific institutions in Costa Rica to characterize the vertical structure and temporal variability of the atmosphere over Central America during summer. The Ticosonde/NAME observations were made four times per day (00, 06, 12 and 18 UT) from Juan Santamaria International Airport (WMO station 78762) between June 16 and September 6, 2004. 318 successful ascents were made over the course of the 83-day campaign with Vaisala GPS rawinsondes, of which 220 were made with the RS-90 sonde equipped with a dual-humicap system for measuring relative humidity; the remaining ascents used the RS80-15G sonde. Despite the frequent presence of deep convective clouds locally, most of the sondes ascended well into the stratosphere, with an average burst altitude of over 23 km or ~30 hPa. Data every two seconds were archived from the sondes, permitting the application of corrections to remove the known time-lag errors in the RS-90 humicap system. Since ascents were routinely made within 90 minutes of both the ascending and descending nodes of the Aqua satellite, the corrected data will provide an opportunity to validate the AIRS water vapor measurements, particularly in the tropical tropopause layer, where accurate humidity measurements are not obtained on a routine basis. The temperature data through the first half of the experiment show a relatively weak cycle in the characteristics of the tropopause, with the time-mean tropopause potential temperature through the end of July ranging from a minimum of 360.6 K at 6 PM (00 UT) to a maximum of 364 K at local noon (18 UT). The tropopause through this same period had a mean pressure, temperature and potential temperature of 115.3 hPa, -78.1 °C and 362.4 K, respectively. Fluctuations about these means were substantial, with the tropopause as high as 88.9 hPa and as low as 141.8 hPa, a variation of nearly 3 kilometers and temperatures varying from -72.8°C to -83.5°C. The preliminary findings suggest that the local convection may have some effect on the tropopause, but that the rawinsonde measurements at Juan Santamaria made during Ticosonde-NAME 2004 as well as those proposed for the upcoming Tropical Cloud Systems Processes experiment in the summer of 2005 are useful for characterizing the temporal variability on a regional scale within the intertropical convergence zone lying over Costa Rica during this period.