Radiosondes and land-based instruments in the OTREC project

Radiosondes and land-based instruments in the OTREC project

As you may already know, OTREC is a field campaign that uses NSF/NCAR Gulfstream-V aircraft to deploy patterns of dropsondes and measure profiles of radar reflectivity and Doppler velocity in order to study atmospheric convection in the tropical east Pacific.  Fascinating, right? However, another important goal of this project is to understand the tropical disturbances over land. Therefore, OTREC has installed portable radiosonde stations in Santa Cruz and Limon in Costa Rica, and Nuqui and Medellin in Colombia (Fig. 1). Here I will talk about these radiosondes and land-based instruments that complement the NSF/NCAR G-V aircraft dataset. 

Fig. 1. Radiosonde stations in OTREC project

Let’s start with Santa Cruz and Limon.  Although the radiosonde launches started a few days late, these places have datasets with at least 2 radiosondes every day throughout the OTREC project. High frequency - every 2 or 3 hours - radiosonde launches were also performed for a week in order to capture the daytime evolution of wind profiles and atmospheric thermodynamics over land. 

           

Fig. 2. Radiosonde launch in Santa Cruz

The radiosonde launches are held at the Santa Cruz UCR campus and Limon airport. These installations are equipped with meteorological stations and GPS precipitable water instruments that measure the atmospheric moisture content from the analysis of temporal delay with the GPS signal. Additionally, rainwater samples are collected to analyze the oxygen isotope ratio and determine the stratiform and convective precipitation fraction and the shape of the vertical structure of convection – bottom heavy and top heavy. The idea is the top (bottom) heavy convection draws in moist air from a deep (shallow) atmospheric layer. Some NCAR surface meteorological stations were also installed around Costa Rica, together with GPS instruments described above, to measure surface temperature, humidity, precipitation, radiation, etc.    

Fig. 3. Radiosonde launch and land-based meteorological station in Limon

Nuqui and Medellin have the most consistent and complete OTREC radiosonde dataset, with at least 2 sounding launches every day and 4 sounding launches during the operational NCAR G-V aircraft flights. The radiosondes are launched entirely by the early warning system of Medellin and Aburra Valley (SIATA in Spanish). The SIATA-OTREC team is supported by students and professors from one of the main Colombian universities.

These radiosondes and land-based instruments will help to increase our understanding of the propagation of tropical easterly waves and their interaction with land surface and topography. The daytime evolution of heat fluxes and wind profiles over land will be also studied by the OTREC project. I have been involved with the aircraft and land-based dataset; I flew on the NCAR G-V aircraft from Liberia airport and launched radiosondes in Santa Cruz and Limon. To conclude, I would like to emphasize that the OTREC project addresses different objectives and the land-based instruments are as important as the aircraft instruments – dropsondes and W-band - they will complement each other in finding the answer to the main OTREC questions about atmospheric convection in the far East Pacific and Central America.