Convective rain cell properties and the resulting precipitation scaling in a warm‐temperate climate

• Published in: Quarterly journal of the Royal Meteorological Society Vol. 148; no. 745; pp. 1768 - 1781
• Main Authors: Purr, Christopher, Brisson, Erwan, Schlünzen, K. Heinke, Ahrens, Bodo
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.04.2022; Wiley Subscription Services, Inc
• Subjects: Atmospheric precipitations; Clausius–Clapeyron scaling; Climate; Climatic conditions; Convection; Convective available potential energy; Convective precipitation; convective storms; Dew; Dew point; Energy; Future climates; Heavy precipitation; Maximum precipitation; Potential energy; Precipitation; Properties; Radar; Rain; Rain cells; Rain gauges; Rainfall; Rainfall intensity; Scaling; Temperate climates; Temperature; tracking; Vertical wind shear; Wind; Wind shear
• ISSN: 0035-9009; 1477-870X
• DOI: 10.1002/qj.4277

Convective precipitation events have been shown to intensify at rates exceeding the Clausius–Clapeyron rate (CC rate) of ca. 7% K−1 under current climate conditions. In this study, we relate atmospheric variables (low‐level dew point temperature, convective available potential energy, and vertical wind shear), which are regarded as ingredients for severe deep convection, to properties of convective rain cells (cell area, maximum precipitation intensity, lifetime, precipitation sum, and cell speed). The rain cell properties are obtained from a rain gauge‐adjusted radar dataset in a mid‐latitude region, which is characterized by a temperate climate with warm summers (Germany). Different Lagrangian cell properties scale with dew point temperature at varying rates. While the maximum precipitation intensity of cells scales consistently at the CC rate, the area and precipitation sum per cell scale at varying rates above the CC rate. We show that this super‐CC scaling is caused by a covarying increase of convective available potential energy with dew point temperature. Wind shear increases the precipitation sum per cell mainly by increasing the spatial cell extent. From a Eulerian point of view, this increase is partly compensated by a higher cell velocity, which leads to Eulerian precipitation scaling rates close to and slightly above the CC rate. Thus, Eulerian scaling rates of convective precipitation are modulated by convective available potential energy and vertical wind shear, making it unlikely that present scaling rates can be applied to future climate conditions. Furthermore, we show that cells that cause heavy precipitation at fixed locations occur at low vertical wind shear and, thus, move relatively slowly compared to typical cells. We relate properties of convective rain cells obtained from tracking rain gauge‐adjusted radar data to their atmospheric environment characterized by low‐level dew point temperature, convective available potential energy, and vertical wind shear. Maximum precipitation intensity scales with dew point temperature consistently at the CC rate whereas the area and precipitation sum per cell scale at varying rates above the CC rate, which is caused by a covarying increase of convective available potential energy with dew point temperature and increasing wind shear. High wind shear leads to higher cell velocity, which leads to Eulerian precipitation scaling rates close to and slightly above the CC rate. Furthermore, cells that cause heavy precipitation at fixed locations tend to occur at low wind shear and, thus, move relatively slowly compared to typical cells.