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Atmospheric river, a term encompassing different meteorological patterns

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Abstract The study of atmospheric rivers (ARs) and their impacts on extreme precipitation are currently of great research interest in view of their clear socioeconomical implications. However, studies of this type generally contain caveats. The first of these is of a meteorological nature, and is concerned with the diversity of the different meteorological patterns that can be associated in the phenomenological definition, in that there is no guarantee that all so‐called ARs follow the same one. The second concern involves the initial definition of an AR, which implicitly assumes the subtropical origin of the atmospheric moisture that feeds it. To date, it has been observed that in many cases of ARs, most of the moisture originates in regions at higher latitudes. The aim of this article is to open a debate on these two aspects by using well‐known examples of ARs which fit different meteorological patterns, and showing a climatology of the moisture sources that feed ARs. This article is categorized under: Science of Water > Hydrological Processes Science of Water > Water Extremes
Schematics showing the structure and strength of an atmospheric river (AR) based on dropsonde measurements deployed from research aircraft for many ARs and on corresponding reanalyses giving the plan‐view context. The magnitudes of the variables relate to an average midlatitude AR. Average width is based on boundaries of an AR defined by vertically integrated water vapor transport (IVT; from surface to 300 hPa) lateral boundary threshold of 250 kg m−1 s−1. Depth corresponds to the altitude below which 75% of IVT occurs. The total water vapor transport corresponds to the transport along an AR, bounded laterally by the positions of IVT = 250 kg m−1 s−1 and vertically by the surface and 300 hPa. (a) Plan view including parent low pressure system and associated cold, warm, and warm‐occluded surface fronts. IVT is shown by color fill (magnitude; kg m−1 s−1) and direction in the core (white arrow). Vertically integrated water vapor (IWV; cm) is contoured. A representative length scale is shown. The position of the cross‐section shown in (b) is denoted by the dashed line A–A′. (b) Vertical cross‐sectional perspective, including the core of the water vapor transport in the AR (orange contours and color fill) and the pre‐cold‐frontal low‐level jet (LLJ), in the context of the jet‐front system and the tropopause. Water vapor mixing ratio (green dotted lines; g kg−1) and cross‐section‐normal isotachs (blue contours; m s−1) are shown. Figure reproduced from Ralph et al. (2018) © American Meteorological Society. Used with permission. Schematic prepared by F. M. Ralph, J. M. Cordeira, and P. J. Neiman and adapted from Ralph et al. (2004), Cordeira et al. (2013), and Ralph et al. (2018)
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Positions of the centroids (colored dots) of the areas of moisture contribution associated with each of the landfalling atmospheric river (AR) events analyzed in Algarra et al. (2020). Each region of landfalling AR is denoted by R and a number (from 1 to 24) and a color; each AR centroid is dotted with the same color as its R of landfall
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Meteorological configuration for two atmospheric rivers (ARs) that landfall on the SE coast of the United States and flow northwards on May 1, 2010 and July 8, 2010, selected from the database of Guan & Waliser (2015). (a,b) The AR axes before landfall are denoted by the red boxes, the point of landfall is shown filled in. Orange filled boxes in (b) show the axis of the Great Plain low level jet detected as in Algarra et al. (2019). The magenta line (A–B) denotes the positions of the vertical cross sections used in (c‐f). The arrows symbolize the integrated water vapor flux (IVT; kg m−1 s−1) from the surface to 300 hPa. Colored contour in blue is the thermal front parameter (TFP) at 700 hPa, and green lines represent the equivalent thickness at 500/850 hPa (units: dam). (c–f) Vertical cross sections for A–B, the point of landfall is denoted with the red box in the abscissa in each plot. Contours in black represent the isentropes (units: °C). Colored contours denote: (c,d) vorticity advection (units: 10e8 s−2 12 h−1), and (e,f) temperature advection (units: °C 12 h−1)
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Schematic meteorological configuration (a,b) and vertical cross section (c,d), for two atmospheric rivers (ARs) that landfall on the SE coast of the United States and flow northwards through the Great Plains on May 1, 2010 and July 8, 2010, selected from the database of Guan & Waliser (2015). (a,b) Based on Figures 2 and S1. The ARs are denoted by the blue arrow, and the landfall location is marked by the red filled box. The blue field represents high anomalies of integrated vapor water (IWV) associated with the AR. The yellow arrow marks the position of the wind maximum. Contours in black are mean sea level pressure (MSLP), and L and H are the position of a low level pressure and the anticyclone location. Dark blue, red, and magenta lines around the L in (a) represent the typical cold, warm, and occluded fronts, respectively. Dark green contours are the equivalent thickness at 500/850 hPa. Red filled area is the temperature advection at 500/1000 hPa. The straight magenta line from A to B denotes the positions of the vertical cross sections used in panels below. (c,d) Based on Figures 4 and S2. The red box in the abscissa in each plot marks the point of AR landfall. Contours in black represent the isentropes. The remaining colored contours denote: in shaded blue the relative humidity (moist) content up to 80%, in orange the wind maxima, in green the positive vorticity advection maxima (PVA), in magenta the wind convergence (con) and divergence (div), in red the warm temperature advection (WA), in dashed blue the cold temperature advection (CA), and in light blue the vertical velocity (w)
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Meteorological configuration for two atmospheric rivers (ARs) that landfall on the SE coast of the United States and flow northwards on May 1, 2010 (a) and July 8, 2010 (b), selected from the database of Guan & Waliser (2015). The AR axes before landfall are denoted by the empty white boxes, the point of landfall is shown filled in. White filled boxes show the axis of the Great Plain low level jet detected as in Algarra et al. (2019). The white line denotes the positions of the vertical cross sections used in Figure 4 (and Figure S2). The arrows symbolize the integrated water vapor flux (IVT; kg m−1 s−1) from the surface to 300 hPa. The colored field represents the integrated vapor water (IWV; kg m−2). Black contours indicate the mean sea level pressure (MSLP; hPa), the center of the low level system pressure is highlighted with the letter L
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