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1. Atmospheric river contributions to ice sheet hydroclimate at the Last Glacial Maximum

   https://doi.org/10.5281/zenodo.7339985  

   Skinner, Christopher ; Lora, Juan ; Tabor, Clay ; Zhu, Jiang ( January 2022 , Zenodo)

   This dataset contains the atmospheric river catalogues and the associated precipitation and temperature data for the Preindustrial and Last Glacial Maximum CESM2 simulations presented in the GRL manuscript:  Atmospheric river contributions to ice sheet hydro climate at the Last Glacial Maximum. The atmospheric river catalogue files (zipped) are in netcdf format and organized by year. There are 100 years of data for both simulations.  The Preindustrial simulation catalogue begins in model year 41 and ends in model year 140.  The LGM simulation catalogue begins in model year 1 and ends in year 100. Each yearly file has a temporal resolution of 6 hours (1460 time steps each file) and a spatial resolution of 0.9° x 1.25° (the native resolution of the CESM simulation). A variable in the file called "ar_binary_tag" indicates whether an atmospheric river is present at each grid cell and each tilmestep: 1 indicates an atmospheric river is present; 0 indicates an atmospheric river is not present.  The precipitation and temperature files are 100-year annual or 100-year seasonal averages of atmospheric river precipitation/temperature. See the Methods section of the article for more details on the atmospheric river detection algorithm and precipitation/temperature calculations.

   Associated article abstract:

   Atmospheric rivers (ARs) are an important driver of surface mass balance over today’s Greenland and Antarctic ice sheets. Using paleoclimate simulations with the Community Earth System Model, we find ARs also had a key influence on the extensive ice sheets of the Last Glacial Maximum (LGM). ARs provide up to 53% of total precipitation along the margins of the eastern Laurentide ice sheet and up to 22-27% of precipitation along the margins of the Patagonian, western Cordilleran, and western Fennoscandian ice sheets. Despite overall cold conditions at the LGM, surface temperatures during AR events are often above freezing, resulting in more rain than snow along ice sheet margins and conditions that promote surface melt. The results suggest  ARs may have had an important role in ice sheet growth and melt during previous glacial periods and may have accelerated ice sheet retreat following the LGM.

    

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2. Evaluating the Representations of Atmospheric Rivers and Their Associated Precipitation in Reanalyses With Satellite Observations

   https://doi.org/10.1029/2023JD038937  

   Ma, Weiming ; Chen, Gang ; Guan, Bin ; Shields, Christine A. ; Tian, Baijun ; Yanez, Emilio ( November 2023 , Journal of Geophysical Research: Atmospheres)

   Atmospheric rivers (ARs) are filaments of enhanced horizontal moisture transport in the atmosphere. Due to their prominent role in the meridional moisture transport and regional weather extremes, ARs have been studied extensively in recent years. Yet, the representations of ARs and their associated precipitation on a global scale remains largely unknown. In this study, we developed an AR detection algorithm specifically for satellite observations using moisture and the geostrophic winds derived from 3D geopotential height field from the combined retrievals of the Atmospheric Infrared Sounder and the Advanced Microwave Sounding Unit on NASA Aqua satellite. This algorithm enables us to develop the first global AR catalog based solely on satellite observations. The satellite‐based AR catalog is then combined with the satellite‐based precipitation (Integrated Muti‐SatellitE Retrievals for GPM) to evaluate the representations of ARs and AR‐induced precipitation in reanalysis products. Our results show that the spreads in AR frequency and AR length distribution are generally small across data sets, while the spread in AR width is relatively larger. Reanalysis products are found to consistently underestimate both mean and extreme AR‐related precipitation. However, all reanalyses tend to precipitate too often under AR conditions, especially over low latitude regions. This finding is consistent with the “drizzling” bias which has plagued generations of climate models. Overall, the findings of this study can help to improve the representations of ARs and associated precipitation in reanalyses and climate models.

    

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3. Evaluating Uncertainty and Modes of Variability for Antarctic Atmospheric Rivers

   https://doi.org/10.1029/2022GL099577  

   Shields, Christine A. ; Wille, Jonathan D. ; Marquardt Collow, Allison B. ; Maclennan, Michelle ; Gorodetskaya, Irina V. ( August 2022 , Geophysical Research Letters)

   Antarctic atmospheric rivers (ARs) are driven by their synoptic environments and lead to profound and varying impacts along the coastlines and over the continent. The definition and detection of ARs over Antarctica accounts for large uncertainty in AR metrics, and consequently, impacts quantification. We find that Antarctic‐specific detection tools consistently capture the AR footprint inland over ice sheets, whereas most global detection tools do not. Large‐scale synoptic environments and associated ARs, however, are broadly consistent across detection tools. Using data from the Atmospheric River Tracking Method Intercomparison Project and global reanalyses, we quantify the uncertainty in Antarctic AR metrics and evaluate large‐scale environments in the context of decadal and interannual modes of variability. The Antarctic western hemisphere has stronger connections to both decadal and interannual modes of variability compared to East Antarctica, and the Indian Ocean Dipole’s influence on Antarctic ARs is stronger while in phase with El Nino Southern Oscillation.

    

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4. Antarctic Atmospheric River Climatology and Precipitation Impacts

   https://doi.org/10.1029/2020JD033788  

   Wille, Jonathan D. ; Favier, Vincent ; Gorodetskaya, Irina V. ; Agosta, Cécile ; Kittel, Christoph ; Beeman, Jai Chowdhry ; Jourdain, Nicolas C. ; Lenaerts, Jan T. M. ; Codron, Francis ( April 2021 , Journal of Geophysical Research: Atmospheres)

   The Antarctic ice sheet (AIS) is sensitive to short‐term extreme meteorological events that can leave long‐term impacts on the continent's surface mass balance (SMB). We investigate the impacts of atmospheric rivers (ARs) on the AIS precipitation budget using an AR detection algorithm and a regional climate model (Modèle Atmosphérique Régional) from 1980 to 2018. While ARs and their associated extreme vapor transport are relatively rare events over Antarctic coastal regions (∼3 days per year), they have a significant impact on the precipitation climatology. ARs are responsible for at least 10% of total accumulated snowfall across East Antarctica (localized areas reaching 20%) and a majority of extreme precipitation events. Trends in AR annual frequency since 1980 are observed across parts of AIS, most notably an increasing trend in Dronning Maud Land; however, interannual variability in AR frequency is much larger. This AR behavior appears to drive a significant portion of annual snowfall trends across East Antarctica, while controlling the interannual variability of precipitation across most of the AIS. AR landfalls are most likely when the circumpolar jet is highly amplified during blocking conditions in the Southern Ocean. There is a fingerprint of the Southern Annular Mode (SAM) on AR variability in West Antarctica with SAM+ (SAM−) favoring increased AR frequency in the Antarctic Peninsula (Amundsen‐Ross Sea coastline). Given the relatively large influence ARs have on precipitation across the continent, it is advantageous for future studies of moisture transport to Antarctica to consider an AR framework especially when considering future SMB changes.

    

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5. Ocean Surface Salinity Response to Atmospheric River Precipitation in the California Current System

   https://doi.org/10.1175/jpo-d-21-0272.1  

   Hoffman, Lauren ; Mazloff, Matthew R. ; Gille, Sarah T. ; Giglio, Donata ; Varadarajan, Aniruddh ( August 2022 , Journal of Physical Oceanography)

   Abstract Atmospheric rivers (ARs) result in precipitation over land and ocean. Rainfall on the ocean can generate a buoyant layer of freshwater that impacts exchanges between the surface and the mixed layer. These “fresh lenses” are important for weather and climate because they may impact the ocean stratification at all time scales. Here we use in situ ocean data, collocated with AR events, and a one-dimensional configuration of a general circulation model, to investigate the impact of AR precipitation on surface ocean salinity in the California Current System (CCS) on seasonal and event-based time scales. We find that at coastal and onshore locations the CCS freshens through the rainy season due to AR events, and years with higher AR activity are associated with a stronger freshening signal. On shorter time scales, model simulations suggest that events characteristic of CCS ARs can produce salinity changes that are detectable by ocean instruments (≥0.01 psu). Here, the surface salinity change depends linearly on rain rate and inversely on wind speed. Higher wind speeds ( U > 8 m s −1 ) induce mixing, distributing freshwater inputs to depths greater than 20 m. Lower wind speeds ( U ≤ 8 m s −1 ) allow freshwater lenses to remain at the surface. Results suggest that local precipitation is important in setting the freshwater seasonal cycle of the CCS and that the formation of freshwater lenses should be considered for identifying impacts of atmospheric variability on the upper ocean in the CCS on weather event time scales. Significance Statement Atmospheric rivers produce large amounts of rainfall. The purpose of this study is to understand how this rain impacts the surface ocean in the California Current System on seasonal and event time scales. Our results show that a greater precipitation over the rainy season leads to a larger decrease in salinity over time. On shorter time scales, these atmospheric river precipitation events commonly produce a surface salinity response that is detectable by ocean instruments. This salinity response depends on the amount of rainfall and the wind speed. In general, higher wind speeds will cause the freshwater input from rain to mix deeper, while lower wind speeds will have reduced mixing, allowing a layer of freshwater to persist at the surface. 

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