Boundary-layer measurements of the ITCZ with meteorological quadcopters off a trans-Atlantic ship expedition

STRINQS stands for Soundings and TuRbulent eddy measurements in the ITCZ with a Network of QuadcopterS and is one of the sub-campaigns under the umbrella of ORCESTRA, an international collaboration of measurement campaigns with the larger goal of understanding mesoscale organization of convection in the tropical Atlantic. STRINQS made measurements of the ITCZ boundary layer by employing four meteorological quadcopters, designed and developed by Menapia. Co-ordinated flights were conducted with the German research vessel Meteor as base, a part of the BOWTIE subcampaign in ORCESTRA. The quadcopters, designed to sustain performance in heavy rain and strong wind, provide high-resolution atmospheric soundings of temperature, humidity, pressure, and winds while allowing for high flight ceilings. There are two sets of meteorological sensors in each quadcopter, with a sampling frequency of 10 Hz. Additionally, a sonic anemometer configured on a 1 m arm above the quadcopter body helps provide wind measurements without disturbances due to the wake of the propellers during non-descending trajectories. The team had to initially overcome multiple logistical and technical challenges, unfortunately including mishaps. However eventually, between the period of 30th August and 9th September, the team successfully conducted around 45 vertical profiles reaching altitudes of up to 1500 m (the permitted flight ceiling for STRINQS) in addition to flying horizontal hexagonal patterns that traversed distances between 2 and 4 km horizontally. Some flights recorded intriguing case-studies such as profiling the boundary-layer thrice in a span of 40 minutes as an organized squall-line rain event passed over the ship, thus providing contrasting conditions before, during and after the storm. The meteorological sensors' data show promising results in the drone's capability to sample the boundary layer, but some corrections still need to be made to the retrieval of wind measurements, particularly vertical wind, which is known to be a challenging measurement from UAV (uncrewed aerial vehicle) platforms. Post data-processing and preliminary analyses, the data will be made publicly available in state of the art data formats. Although STRINQS only partially achieved its scientific goal of statistical sampling, the learnings on the measurement capabilities of such methods have been significant. With this demonstration of using a ship as a launchpad for coordinated flights of heavyduty quadcopters even in heavy rain events, STRINQS signals the possibilities of such strategies in future campaigns to provide a rich spatial characterization of the boundary layer.