Atmospheric River Signatures in Radiosonde Profiles and Reanalyses at the Dronning Maud Land Coast, East Antarctica

Abstract

Atmospheric rivers (ARs) are an important component of the hydrological cycle linking moisture sources in lower latitudes to the Antarctic surface mass balance. We investigate AR signatures in the atmospheric vertical profiles at the Dronning Maud Land coast, East Antarctica, using regular and extra radiosonde measurements conducted during the Year of Polar Prediction Special Observing Period November 2018 to February 2019. Prominent AR events affecting the locations of Neumayer and Syowa cause a strong increase in specific humidity extending through the mid-troposphere and a strong low-level jet (LLJ). At Neumayer, the peak in the moisture inversion (up to 4 g kg−1) is observed between 800 and 900 hPa, while the LLJ (up to 32 m s−1) is concentrated below 900 hPa. At Syowa the increase in humidity is less pronounced and peaks near the surface, while there is a substantial increase in wind speed (up to 40 m s−1) between 825 and 925 hPa. Moisture transport (MT) within the vertical profile during the ARs attains a maximum of 100 g kg−1 m s−1 at both locations, and is captured by both ERA-Interim and ERA5 reanalysis data at Neumayer, but is strongly underestimated at Syowa. Composites of the enhanced MT events during 2009-19 show that these events represent an extreme state of the lower-tropospheric profile compared to its median values with respect to temperature, humidity, wind speed and, consequently, MT. High temporal- and vertical-resolution radiosonde observations are important for understanding the contribution of these rare events to the total MT towards Antarctica and improving their representation in models.