Atmospheric Rivers and Rainfall during NASA’s Iowa Flood Studies (IFloodS) Campaign*

Abstract

Atmospheric rivers (ARs) play a major role in causing extreme precipitation and flooding over the central United States (e.g., Midwest floods of 1993 and 2008). The goal of this study is to characterize rainfall associated with ARs over this region during the Iowa Flood Studies (IFloodS) campaign that took place in April–June 2013. Total precipitation during IFloodS was among the five largest accumulations recorded since the mid-twentieth century over most of this region, with three of the heavy rainfall events associated with ARs. As a preliminary step, the authors evaluate how well different remote sensing–based precipitation products captured the rainfall associated with the ARs and find that stage IV is the product that shows the closest agreement to the reference data. Two of the three ARs during IFloodS occurred within extratropical cyclones, with the moist ascent associated with the presence of cold fronts. In the third AR, mesoscale convective systems resulted in intense rainfall at many locations. In all the three cases, the continued supply of warm water vapor from the tropics and subtropics helped sustain the convective systems. Most of the rainfall during these ARs was concentrated within ~100 km of the AR major axis, and this is the region where the rainfall amounts were highly positively correlated with the vapor transport intensity. Rainfall associated with ARs tends to be larger as these events mature over time. Although no major diurnal variation is detected in the AR occurrences, rainfall amounts during nocturnal ARs were higher than for ARs that occurred during the daytime.

Remote sensing-based characterization of rainfall during atmospheric rivers over the central United States

“…To the best of our knowledge, only Nayak et al (2016) provide preliminary insights on the distribution of rainfall during ARs over the central United States, even though the results are limited to a very small sample sizea study period of 66 days in April-June 2013 in which only three ARs occurred. The lack of knowledge regarding the rainfall distribution in ARs is a major gap in the understanding of the science of ARs.…”

“…Lavers and Villarini (2013) showed that more than 60% of the annual maximum floods during 1979-2011 period were associated with ARs over much of the central United States, with seven out of the ten largest floods associated with these storms. Moreover, ARs are the mechanisms responsible for some of the most devastating flooding events over this region in recent decades, including the floods of July 1993 (Dirmeyer and Kinter, 2009), June 2008 floods over eastern Iowa (Budikova et al, 2010;Smith et al, 2013), May 2010 flood in Nashville (Tennessee) and surrounding areas (Moore et al, 2012), and the flood of April 2013 over Chicago and eastern Iowa (Campos and Wang, 2015;Nayak et al, 2016).…”

“…A more recent study by Prat and Nelson (2015) also highlights the poor performance of satellite and remote sensing products in capturing extreme rainfall. Further challenges arise due to the peculiar structure of narrow and long rain bands that have been observed in some ARs studied over the central United States (for example, Moore et al, 2012;Nayak et al, 2016). Hence, from an AR perspective, it is important to evaluate different remote sensing products to select the best product before performing rainfall characterization in ARs.…”

“…If three consecutive time steps (18 hours) are identified as AR steps, we consider the collection of the AR steps as a persistent AR (or simply an AR). This methodology was extensively evaluated inNayak et al (2016).…”

Using the Multisensor Advected Layered Precipitable Water Product in the Operational Forecast Environment

“…More recently, however, attention has been placed on atmospheric rivers [e.g., Newell et al 1992; Cooperative Institute for Research in the Atmosphere (CIRA) 2016)] and how these elongated corridors of strong water vapor transport influence excessive rain and snowfall production across coastal and mountainous areas of the western United States (e.g., Zhu and Newell 1998;Neiman et al 2002;Ralph et al 2004;Dacre et al 2015;Cordeira et al 2017). Despite this recent interest, only limited discussion has occurred on the influence these atmospheric rivers have on heavy precipitation production outside of areas along the West Coast, especially for locations far removed from the original moisture source regions (Moore et al 2012;Lavers and Villarini 2013;Nayak et al 2016). In fact, Mahoney et al (2016) briefly addressed geographical differences by discussing how southeastern United States heavy rain events often differ from traditional West Coast atmospheric river cases-noting how the former events may experience moisture advection from multiple source regions.…”