Cloud distribution evaluated by the WRF model during the EUSO-SPB1 flight

Abstract

EUSO-SPB1 was a balloon-borne mission of the JEM-EUSO (Joint Experiment Missions for Extreme Universe Space Observatory) Program aiming at the ultra-high energy cosmic ray (UHECR) observations from space. We operated the EUSO-SPB1 telescope consisting of 1 m2 Fresnel refractive optics and multi-anode photomultiplier tubes. With a total of 2304 channels, each performed the photon counting every 2.5 µs, allowing for spatiotemporal imaging of the air shower events in an ~ 11°× 11° field of view. EUSO-SPB1 was the first balloon-borne fluorescence detector with a potential to detect air shower events initiated by the EeV energy cosmic rays. On 24 April 2017 UTC, EUSO-SPB1 was launched on the NASA’s Super Pressure Balloon that flew at ~16 – 33 km flight height for ~12 days. Before the flight was terminated, ~27 hours of data acquired in the air shower detection mode were transmitted to the ground. In the present work, we aim at evaluating the role of the clouds during the operation of EUSO-SPB1. We employ the WRF (Weather Research and Forecasting) model to numerically simulate the cloud distribution below EUSO-SPB1. We discuss the key results of the WRF model and the impact of the clouds on the air shower measurement and the efficiency of the cosmic ray observation. The present work is a part of the collaborative effort to estimate the exposure for air shower detections.