Global Positioning System precipitable water vapour (GPS-PWV) jumps before intense rain events: A potential application to nowcasting

Abstract

A rapid increase in atmospheric water vapour is a fundamental ingredient for many intense rainfall events. High-frequency precipitable water vapour (PWV) estimates (1 min) from a Global Positioning System (GPS) meteorological site are evaluated in this paper for intense rainfall events during the CHUVA Vale field campaign in Brazil (November and December 2011) in which precipitation events of differing intensities and spatial dimensions, as observed by an X-band radar, were explored. A sharp increase in the GPS-PWV before the more intense events was found and termed GPS-PWV “jumps.” These jumps are probably associated with water vapour convergence and the continued formation of cloud condensate and precipitation particles. A wavelet correlation analysis between the high temporal-resolution GPS-PWV time series and rainfall events evaluated in this study shows that there are oscillations in the PWV time series correlated with the more intense rainfall events. These oscillations are on scales related to periods from about 32 to 64 min (associated with GPS-PWV jumps) and from 16 to 34 min (associated with positive pulses of the PWV). The GPS-PWV time-derivative histogram for the time window before the rainfall event reveals different distributions influenced by positive pulses of the GPS-PWV (derivative > 9.5 mm/hr) for higher intensity and extension events. These features are indicative of the occurrence of intense precipitation and, consequently, have the potential for application in nowcasting activities.