Assimilation of shipborne precipitable water vapour by Global Navigation Satellite Systems for extreme precipitation events

• DOI: 10.1002/qj.4192
• Publication Date: 2021-10-16T15:10:50Z
• Authors: Yasutaka Ikuta; Hiromu Seko; Yoshinori Shoji
• Keywords: Precipitable water

Abstract Water vapour advection from the sea causes extremely heavy rainfall in Japan. Therefore, accurately describing water distribution over a forecast model's initial conditions should improve prediction accuracy of events. Thus, we assimilated shipborne precipitable (PWV) observed by Global Navigation Satellite Systems (GNSS) onboard ships to show its impact on event July 2020. We obtained GNSS observations during continuous observation campaign conducted at sea, one few world. In this study, applied PWV, upwind side rainfall, four‐dimensional variational data assimilation method and assimilation–forecast cycles. Although PWV is point observation, it can be as covering space time because conducting sailed around addition, cycle, effect spread widely area. ship motion affects observations, found that negligible for practical use. For temporal thinning slot an interval 30 min more effective than 1 hr. As result assimilating disastrous 2020, especially amount, was improved. also statistical improvements could profiles wind velocity field lower atmosphere. demonstrate