The Landfall and Inland Penetration of a Flood-Producing Atmospheric River in Arizona. Part II: Sensitivity of Modeled Precipitation to Terrain Height and Atmospheric River Orientation

Abstract

This manuscript documents numerical modeling experiments based on a January 2010 atmospheric river (AR) event that caused extreme precipitation in Arizona. The control experiment (CNTL), using the Weather Research and Forecasting (WRF) Model with 3-km grid spacing, agrees well with observations. Sensitivity experiments in which 1) model grid spacing decreases sequentially from 81 to 3 km and 2) upstream terrain is elevated are used to assess the sensitivity of interior precipitation amounts and horizontal water vapor fluxes to model grid resolution and height of Baja California terrain. The drying ratio, a measure of airmass drying after passage across terrain, increases with Baja's terrain height and decreases with coarsened grid spacing. Subsequently, precipitation across Arizona decreases as the Baja terrain height increases, although it changes little with coarsened grid spacing. Northern Baja's drying ratio is much larger than that of southern Baja. Thus, ARs with a southerly orientation, with water vapor transports that can pass south of the higher mountains of northern Baja and then cross the Gulf of California, can produce large precipitation amounts in Arizona. Further experiments are performed using a linear model (LM) of orographic precipitation for a central-Arizona-focused subdomain. The actual incidence angle of the AR (2118) is close to the optimum angle for large region-mean precipitation. Changes in region-mean precipitation amounts are small (;6%) owing to AR angle changes; however, much larger changes in basinmean precipitation of up to 33% occur within the range of physically plausible AR angles tested. Larger LM precipitation sensitivity is seen with the Baja-terrain-modification experiments than with AR-angle modification.

Moisture transport associated with large precipitation events in the Upper Colorado River Basin

“…Locations in the southern Intermountain West, including the southern portions of the UCRB and the Lower Colorado River Basin, have observed extensive flooding events attributable to atmospheric rivers advancing from the southwest, over Southern California and Baja California, during synoptic conditions consistent with Pattern 7 produced in this study (Neiman et al, 2013;Werner and Yeager, 2013;Hughes et al, 2014). LPEs in the southern portions of the UCRB occur most frequently during southwesterly flow, pulling tropical Pacific moisture around the high Sierra Nevada.…”

Simulating and Evaluating Atmospheric River‐Induced Precipitation Extremes Along the U.S. Pacific Coast: Case Studies From 1980–2017

“…The WRF V3.8.1 (Skamarock & Klemp, ) is used in the present analysis. WRF has been used extensively in previous studies of general precipitation extremes, as well as specifically within an AR context (Eldardiry et al, ; Hughes et al, ; Leung & Qian, ; Martin et al, ; Pontoppidan et al, ). We use atmospheric reanalysis data (ERA‐Interim) data ( 80 km) to provide 6‐hourly initial and boundary conditions to force the nested WRF simulations, including sea surface temperature.…”

Characterizing the influence of atmospheric river orientation and intensity on precipitation distributions over North Coastal California

“…[] and Hughes et al . [] illustrate the importance of IVT direction along an AR in the production of extreme precipitation in Arizona during an event in 2010. The south‐southwesterly IVT direction along an AR on 21–22 January 2010 allowed for water vapor flux through an area of lower terrain on the Baja Peninsula of Mexico, resulting in enhanced inland upslope water vapor flux over the northwest‐southeast oriented Mogollon Rim in Arizona.…”