Peak precipitation intensity in relation to atmospheric conditions and large‐scale forcing at midlatitudes

Abstract

Research on relations between atmospheric conditions and extreme precipitation is important to understand and model present-day climate extremes and assess how precipitation extremes might evolve in a future climate. Here we present a statistical analysis of the relation between large-scale conditions and hourly precipitation at midlatitudes, by using observations of the Netherlands combined with a regional reanalysis. The aim is to gain a better understanding of the typical large-scale atmospheric conditions and large-scale forcing associated with extreme hourly precipitation and determine the typical differences between cases of extreme precipitation and weaker events. To avoid double counting, we perform an event-based analysis and consider the hourly peak intensity, rather than all hourly data. Atmospheric large-scale profiles consistently show a clear separation between precipitation deciles, characterized by increasing instability and moisture content of the atmosphere for more extreme precipitation. Furthermore, stronger events are characterized by larger atmospheric forcing preceding the event, which primarily relates to vertical motions. Based on these results, four atmospheric parameters, describing atmospheric moisture, stability and large-scale convergence, are analyzed as potential indicators of strong precipitation events. Despite positive relations between these parameters and the peak intensity, their correlations are found to be weak. Key Points:• Climatological analysis of relations between atmospheric conditions and precipitation extremes • Heavy precipitation events occur under warmer, moister conditions, under stronger LS convergence • Four atmospheric parameters were evaluated as precipitation indicators, but correlations were weak Correspondence to:At midlatitudes, strong convection tends to occur ahead of synoptic disturbances, where upward vertical motions lead to moistening and destabilization of the atmosphere [Doswell and Bosart, 2001]. Studies have tried to connect extreme precipitation to cyclones [Pfahl and Wernli, 2012] and fronts [Catto and Pfahl, 2013]. A large amount of 6-hourly precipitation extremes were associated with fronts. Since many precipitation extremes occur under a combination of convective and large-scale precipitation, in this study we will not make an explicit distinction between the different precipitation types.

Sensitivity of extreme precipitation to temperature: the variability of scaling factors from a regional to local perspective

“…However, further research is needed to test this assumption in our study region. Recent contributions to the literature by Loriaux et al (2016a) and Loriaux et al (2016b) demonstrate that considering relative humidity alone is not sufficient to explain the intensification of extreme precipitation. Through including atmospheric control factors such as large scale moisture convergence and atmospheric stability, they deliver valuable contributions to process understanding.…”

Impact of Boreal Summer Intraseasonal Oscillation on Rainfall Extremes in Southeastern China and its Predictability in CFSv2

“…Several studies have suggested that the changes in upward motion and moisture are directly related to extreme rainfall changes (Loriaux et al, ; O'Gorman & Schneider, ). To better understand the moisture processes with the occurrence of the extreme rainfall, we have examined the moisture flux divergence ( ), which is considered as an important factor of heavy rainfall during BSISO1 phases and BSISO2 phases.…”

“…In order to further demonstrate the contributions of upward motion and vertical moisture transport to rainfall extremes, Figures and show the mean profiles of vertical pressure velocity ( ω ) and vertical moisture advection ( ), which are supposed to be related to extreme rainfall (Loriaux et al, ). Figure shows the vertical velocity profiles, which are closely related to large‐scale convergence.…”

Impact of Madden–Julian Oscillation upon Winter Extreme Rainfall in Southern China: Observations and Predictability in CFSv2

“…Several studies have suggested that changes in extremes are directly linked to changes in upward motion and moisture, among other factors [28,29,53,54]. To better understand the moisture processes associated with the occurrence of the extreme rainfall, we have examined column-integrated horizontal moisture convergence (− Figure 5a-c, but with the shadings representing column-integrated moisture advection and the vectors representing 850-hPa winds.…”

“…Unlike moisture convergence, the direct contributions from horizontal moisture advection may be insignificant (Figure 5d-f). Figure 6 shows the mean profiles of vertical pressure velocity ( ω , as seen in Figure 6a) and vertical moisture advection ( p ∂ ∂q -ω , as seen in Figure 6b), which are supposed to be related to the extreme rainfall [54]. Figure 6a shows the vertical velocity profile, which is an indirect measure of the large-scale convergence.…”