Inner-tropical ozone measurements at the Mérida Atmospheric Research Station (MARS) using ground-based microwave radiometry

Abstract

Since March 2004 the ground-based 268–280 GHz radiometer MIRA 2 has been in quasi-continuous operation at the inner-tropical Mérida Atmospheric Research Station (MARS) on Pico Espejo (8.58°N, 71.15°W, 4765 m above sea level) in the Venezuelan Andes. Using the optimal estimation method concentration profiles of ozone have been retrieved in the stratosphere and mesosphere. In the middle stratosphere variations of ozone on a time scale of several months were revealed in the resulting time series that probably result from the turnaround of the Brewer–Dobson circulation. In the mesosphere photochemistry plays the most important role for the ozone concentration. Therefore a diurnal cycle is observed in the upper part of the retrieved ozone profiles. The measurements are used to verify model results of ozone in the mesosphere obtained by a photochemistry model, which reproduces the diurnal variation of ozone very well. Also an inter-annual variation of mesospheric ozone during the month of November in 2004–2007 was observed, primarily during the night. As the time series is still too short to clearly distinguish solar or QBO signals, the cause of this inter-annual variation cannot yet be related to one or the other. In November 2006 an unusual decrease of the ozone partial columns above 60 km was measured; the cause of this decrease is also not identified so far.

Acknowledgements

We would like to thank the National Centers for Environmental Prediction (NCEP) for providing temperature and pressure data used for the retrievals via the Goddard Automailer system. This work is or has been partially founded by the Federal Ministry of Education and Research for the ENVISAT-validation, by the Helmholtz Association of German Research Centres in the framework of the virtual institute Pole-Equator-Pole (PEP), and by the Deutsche Forschungsgemeinschaft for the project Climate And Weather of the Sun-Earth System (CAWSES). Important for the continuous operation of the MARS station was the persistent support by Teleferico de Merida, offering free access and transportation, and by INPARQUES, the agency responsible for the national park ‘Sierra Nevada’ in which the research station is located.