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

K Shinozaki,Me Bertaina,M Vrabel,S Ferrarese,A Bruno,S Monte,A Anzalone,M Manfrin,J Eser,A Michel,F Fenu,F Bisconti,A Diaz,L Wiencke

doi:10.1051/epjconf/201921005006

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.

Highlights

Efficient observations of ultra-high energy cosmic rays (UHECRs) are a fundamental requirement for studying their origin
We ran the Weather Research and Forecasting (WRF) model to simulate the cloud fraction in each grid-box within the domain area chosen ∼300 km × 300 km to fit a distance travelled by EUSO-SPB1 in 24 hours
We focus on the application of the WRF model to describe the cloud properties, cloudtop height (CTH), during the EUSO-SPB1 flight

Summary

Introduction

Efficient observations of ultra-high energy cosmic rays (UHECRs) are a fundamental requirement for studying their origin. The leading ground-based experiments, i.e., the Pierre Auger Observatory [1] and the Telescope Array (TA) [2] reported anisotropy of the UHECR arrival direction distribution above 8 × 1018 eV and ∼6 × 1019 eV, respectively The latter energy, the cosmic ray fluxes are as small as 1 per km in a century with a steepening spectral index [3]. In the JEM-EUSO framework, two full-scale missions, i.e., K-EUSO (KLYPVE-EUSO) [7] and POEMMA (Probe Of Extreme Multi-Messenger Astrophysics) [8], are promoted The former will be based on the International Space Station (ISS). The instantaneous apertures of the UHECR observation decrease in terms of the area, while the trigger algorithm can be designed to be operational for the rest of the FOV Another obstacle is the presence of clouds. The presented work is one step towards the goal to estimate the exposure for EUSO-SPB1 and has applications in space-based UHECR observation

EUSO-SPB1 flight

Weather Research and Forecast model

Result

Summary and discussion