Aeroclipper Cyclone Intensity Observation – MICA

Tropical cyclones are a major threat for many countries. They generate strong winds and deadly floods that damage buildings and infrastructure and severely disrupt civil and military organization. A precise forecast of the trajectory and intensity of tropical cyclones makes it possible to take the necessary measures to protect people and property while avoiding false alarms. The quality of the forecasts, however, depends largely on the quality of the observations. For the moment, only airborne measurements provide accurate in situ observations for the initialization of tropical cyclone prediction models. For this reason, the United States Air Force (USAF) and the National Oceanic and Atmospheric Administration (NOAA) have been deploying considerable resources for the observation of cyclones in the North Atlantic and East Pacific for several decades. These airborne measurements, carried out quite systematically by the USA and sporadically by Taiwan, are however exceptions worldwide. No airborne measurements are made in the South Indian Ocean, where the island of La Reunion is however regularly exposed to cyclones. Most of the real-time information collected by the Regional Specialized Meteorological Centers (RSMCs) therefore comes from satellite observations. These observations are irreplaceable, but they are sometimes inaccurate and are also too sporadic (a measurement every 12 hours for polar satellite instruments). In particular, the central pressure is a fundamental parameter for estimating the intensity of a cyclone, but satellite remote sensing approaches to assess the central pressure of cyclones are highly indirect and lack precision.

Aeroclippers are balloons connected by a guide rope to the surface of the ocean. They evolve in the atmospheric surface layer, typically at a height of 30 to 50 meters. These balloons are carried away horizontally toward the eye of cyclones and then remain captured. The Aeroclipper is currently the only vector capable of giving an in situ measurement of the surface wind as it passes through the eyewall, then to provide continuous and real time measurements of the surface pressure in the eye until the cyclone dissipates. This balloon thus provides a unique possibility: (i) to follow the position and intensity of the cyclones; (ii) to improve the forecast of cyclones by assimilating the evolution of the central pressure; (iii) to evaluate and improve satellite approaches; and (iv) to correct possible biases in historical databases and thus to better detect a possible trend of the cyclonic characteristics during the last decades. The unique measurements given by Aeroclippers should also help improve our knowledge of cyclones. This is necessary to better predict the evolution of their characteristics in a warmer climate, in particular their poleward migration and their interaction with mid-latitude storms.

Two Aeroclippers were already captured in Cyclone Dora in the Indian Ocean in 2007. After an interruption, developments resumed in 2015 with technical and financial support from the French center for space studies (CNES, Centre National d’Études Spatiales). Due to lack of human and funding resources, CNES must now suspend this development for an indefinite period of time (several years). The Aeroclipper system is however perfectly mature and it is not justified to postpone the first campaigns. The aim of this proposal is to validate the entire Aéroclipper system by conducting a test campaigns in 2020 and in 2021 with a new mechanical system and a new gondola currently under development at the Laboratoire de Météorologie Dynamique (LMD).