High-Resolution Measurements of Wind, Waves, Temperature, and Turbulence Structure in and above the Coastal Boundary Layer in Southern Perú (13°56'S, 76°15'W)

We report results of preliminary high-resolution in situ atmospheric measurements through the boundary layer and lower atmosphere over the south coast of Perú. These measurements were obtained using an in-house-constructed, GPS-controlled, micro-autonomous-vehicle (MAV) aircraft (the DataHawk). Measured quantities include meter-scale profiles of temperature, wind, and turbulence structure from the surface to 1300 m. One intriguing result shows the presence of vertically-structured, quasi-sinusoidal, temperature fluctuations centered near the height of a strong (~10°C) temperature inversion topping the boundary layer. The vertical wavelength and maximum amplitude of these fluctuations are ~14.5 m, and ± 0.5 °C, respectively. A second interesting result shows a number of semi-coherent regions of enhanced temperature fluctuations detected when the MAV was flying a large-diameter circle at a constant-altitude below the inversion. These regions have horizontal dimensions of 50-200 meters and exhibit enhanced temperature and temperature fluctuations on the order of 1 °C or more above the ambient background.

This region of the Peruvian coast is of particular interest because it lies near the northern coastal edge of the sub-tropical southeastern Pacific (SEP) region, that includes the largest area in the world having a persistent stratus deck at the top of the marine boundary layer (MBL). Typically, the MBL in this region in winter is topped by a quasi-permanent, well-defined, strong, and very steep temperature gradient. The data presented herein examine fine-scale details of the coastal atmosphere at a point where the edge of the MBL extends over the adjacent coastline as a result of persistent onshore flow.