Detection of atmospheric rivers: Evaluation and application of an algorithm for global studies

Abstract

Atmospheric rivers (ARs) are narrow, elongated, synoptic jets of water vapor that play important roles in the global water cycle and regional weather/hydrology. A technique is developed for objective detection of ARs on the global domain based on characteristics of the integrated water vapor transport (IVT). AR detection involves thresholding 6‐hourly fields of ERA‐Interim IVT based on the 85th percentile specific to each season and grid cell and a fixed lower limit of 100 kg m−1 s−1 and checking for the geometry requirements of length >2000 km, length/width ratio >2, and other considerations indicative of AR conditions. Output of the detection includes the AR shape, axis, landfall location, and basic statistics of each detected AR. The performance of the technique is evaluated by comparison to AR detection in the western North America, Britain, and East Antarctica with three independently conducted studies using different techniques, with over ~90% agreement in AR dates. Among the parameters tested, AR detection shows the largest sensitivity to the length criterion in terms of changes in the resulting statistical distribution of AR intensity and geometry. Global distributions of key AR characteristics are examined, and the results highlight the global footprints of ARs and their potential importance on global and regional scales. Also examined are seasonal dependence of AR frequency and precipitation and their modulation by four prominent modes of large‐scale climate variability. The results are in broad consistency with previous studies that focused on landfalling ARs in the west coasts of North America and Europe.

Skillful empirical subseasonal prediction of landfalling atmospheric river activity using the Madden–Julian oscillation and quasi-biennial oscillation

“…This study illuminates the predictive potential of the relationship between anomalous landfalling AR activity along the west coast of Earlier works have documented an MJO-AR relationship in terms of the modulation of AR occurrences [30][31][32] and their impacts, 29 but here we demonstrate that the time-lagged modulation of AR activity by the extratropical response to the MJO can be leveraged for skillful subseasonal forecasts. We further show that the MJO-AR relationship is influenced by the QBO.…”

“…26,27 Several studies suggest the potential for skillful subseasonal prediction based on observed relationships between the MJO and AR activity. [28][29][30][31][32] Here, we show that knowledge of the state of the MJO and the QBO can provide skillful predictions of anomalous AR activity up to 5 weeks in advance during boreal winter months. Because of the wide-ranging impacts associated with landfalling ARs, myriad sectors of society may benefit from skillful predictions of anomalous AR activity along the west coast of North America.…”

Evaluation of the moisture sources in two extreme landfalling atmospheric river events using an Eulerian WRF tracers tool

“…Guan and Waliser (2015) have estimated that ARs have a median length of about 3600 km, a median length / width ratio of about 7 and a mean integrated vapor transport (IVT) of 370 kg m −1 s −1 . ARs are associated with the pre-cold frontal region and the warm conveyor belt (WCB) of extratropical cyclones .…”

Wet Spells and Associated Moisture Sources Anomalies across Danube River Basin

“…Then, this fast corridor of moisture (but with lower intensity) penetrated the Mediterranean basin during the following day (Figure 10b), and on the 23 September 1996 ( Figure 10d) the anomalous transport of moisture reached the Danube River Basin, associated with the low situated over our area of study. A close look at the global ARs database of Guan and Waliser [46] indicates that this particular pattern of IVT along the Mediterranean and North Africa towards the Danube is also an AR event. …”