Temperature and moist‐stability effects on midlatitude orographic precipitation

Abstract

Idealized, convection-resolving simulations of moist orographic flows are conducted to investigate the influence of temperature and moist stability on the drying ratio (DR), defined as the fraction of the impinging water mass removed as orographic precipitation. In flow past a long ridge, where most of the air rises over the barrier rather than detouring around it, DR decreases as the surface temperature (T s ) increases, even as the orographic cap cloud becomes statically unstable at higher T s and develops embedded convection. This behaviour is explained by a few physical principles: (1) the Clausius-Clapeyron equation dictates that the normalized condensation rate decreases as the flow gets warmer, (2) the replacement of ice-phase precipitation growth with warm-rain processes decreases the efficiency by which condensate is converted to precipitation, thereby lowering precipitation efficiency, and (3) embedded convection acts more to vertically redistribute moisture than to enhance precipitation. Over an isolated mountain, the effects of (1) and (2) are counteracted by moisture deflection around the barrier, which is stronger in the colder, more stable flows.

Sensitivity of historical orographically enhanced extreme precipitation events to idealized temperature perturbations

“…In a warmer climate the DR is reduced to 23.1 ± 5.2%, where two of the cases experienced a small increase in DR. Thus, by increasing the temperature the extreme cases in general experienced a slightly lower precipitation efficiency, consistent with the results found in Kirshbaum and Smith (2008). This slight reduction of only 0.5% suggest that the enhanced moisture effect on precipitation change dominated any change in precipitation efficiency.…”

“…For warm cloud processes, the precipitation growth is dominated by the collision-coalescence process. However, as shown in both Kirshbaum and Smith (2008) and Siler and Roe (2014) the increase in condensation rate is less than the increase in atmospheric water vapor. In other words, the air needs to be lifted further up to reach condensation.…”

“…The advantage of this quantity is that it can take into account the multiple condensation and evaporation cycles over the complex terrain of southwest Norway. With an idealized cloud resolving model, Kirshbaum and Smith (2008) found a decrease in DR with an increase in temperature while RH was kept constant for a mountainous area. They argue that the main reason for this relationship is that the normalized (by incoming vapor flux) condensation rate decreases with increased temperature as dictated by the CC-relation, as well as a reduction in the precipitation efficiency due to a decrease in ice-phased precipitation growth.…”

Climate change, forests, fire, water, and fish: Building resilient landscapes, streams, and managers

“…Between, there is large uncertainty (Solomon 1986). Within the western United States, for example, there is substantial uncertainty with respect to changes in orographic precipitation from mountains (Dettinger and others 2004;Kirshbaum and Smith 2008). One of the clear needs that emerges from evaluating risks is the need to pay attention to what changes actually occur and what the responses are to those changes.…”

Flood-Related Extreme Precipitation in Southwestern Germany: Development of a Two-Dimensional Stochastic Precipitation Model

“…(e.g., Fuhrer and Schär, 2005;Kirshbaum and Smith, 2008). These two components were included because linear theory assumes waves that penetrate through the whole atmosphere, leading to an overestimation of precipitation totals, whereas at the same time, low intensities are underestimated (e.g., Kunz, 2011).…”