UAV measurements of turbulence and latent heat fluxes during the Cloud, Aerosol, Radiative forcing, Dynamics EXperiment (CARDEX)

The CARDEX campaign was conducted from the Maldives Climate Observatory (MCOH) on Hanimaadhoo Island during February and March 2012. The overall aim was to explore the interplay between the microphysical modification of trade cumulus clouds by episodic boundary layer pollution, present 1–3 km, and associated direct atmospheric warming.

Three BAE systems Manta fixed-wing UAVSs were equipped with instruments to measure either: aerosol & solar radiation, cloud microphysics, or turbulence and latent heat fluxes. These lightweight, precision autopiloted UAV with scientific telemetry allow minimal aircraft-induced disturbance when investigating small-scale features such as the entrainment zone and cumulus clouds, as well as facilitating synchronous measurements of multiple aspects of the same cloud system when flown in stacked formation. These aircraft were flown for nearly 100 hours in 53 over-the-horizon scientific missions, to altitudes up to 13,00ft. Data collected by the UAVs were analysed alongside those from satellite observations and a 25m tower at MCOH. The cloud microphysics and aerosol/radiation payloads have been flown before at the Maldivian location [1-4]. The turbulent flux package [5], which allows measurement of turbulence properties and water vapour fluxes, is a recent addition to this payload suite and the focus of this presentation. We show latent heat and turbulent kinetic energy (TKE) results from UAV flights, their relationship with equivalent surface measurements, and variability associated with pollution events. Wind measurements from within clouds and concurrent turbulence/cloud microphysical data from stacked flights are also shown and discussed. References 1. Ramanathan, V., et al., Warming trends in Asia amplified by brown cloud solar absorption. Nature, 2007. 448(7153): p. 575-U5. 2. Corrigan, C.E., et al., Vertical profiles of aerosols using unmanned aerial vehicles. Int. Aerosol Conf., 2006. 3. Roberts, G.C., et al., Aerosol, cloud, and radiometric measurements with small autonomous unmanned aerial vehicles. 2005. 4. Ramana, M.V., et al., Albedo, atmospheric solar absorption and heating rate measurements with stacked UAVs. Quarterly Journal of the Royal Meteorological Society, 2007. 133(629): p. 1913-1931. 5. Thomas, R.M., et al., Measurement of turbulent water vapor fluxes using a lightweight unmanned aerial vehicle system. Atmospheric Measurement Techniques, 2012. 5(1): p. 243-257. Acknowledgements The CARDEX field campaign was sponsored and funded by the National Science foundation. E.Wilcox is the Co-PI and H. Nguyen was the field director who conducted the campaign with full support by the government of Maldives.