A 25‐year climatology of low‐tropospheric temperature and humidity inversions for contrasting synoptic regimes at Neumayer Station, Antarctica

Abstract

A 25‐year set of daily radiosonde data was used to investigate temperature and humidity inversions at Neumayer Station, coastal Dronning Maud Land, Antarctica. For the first time, inversions were studied differentiating between different synoptic conditions and different height levels. It was shown that, generally, inversions occurred on the majority (78%) of the days, with simultaneous occurrence of humidity and temperature inversions being observed on approximately two thirds of all days. Multiple inversions are common in all seasons for cyclonic and noncyclonic conditions, however, typically occur more frequently under cyclonic conditions. The seasonality of inversion occurrence and features, that is, inversion strength, depth and vertical gradients, was analysed statistically. Different formation mechanisms depending on inversion levels and prevailing weather situations are related to typical annual courses of certain inversion features. Winter maxima were found for the features that are mostly connected to the temperature close to the surface, which is mainly a result of the negative energy balance, thus influencing surface‐based inversions. At the second level, both temperature and humidity inversions are often caused by advection of comparably warm and moist air masses related to the passage of cyclones and their frontal systems. Hence, maxima in several inversion features are found in spring and fall, when cyclonic activity is strongest. Monthly mean profiles of humidity and temperature inversions reveal that elevated inversions are often obscured in average profiles due to large variations in inversion height and depth.

Forcing for varying boundary layer stability across Antarctica

“…Located near sea level on the Ekström Ice Shelf, Neumayer is characterized by flat and homogeneous terrain. Neumayer is influenced by cyclone activity in the circumpolar trough, which can act to quickly impact boundary layer stability at this site (Silva et al, 2022). Radiosonde and surface radiative flux data from Neumayer Station are from BSRN, recorded from 1 June 2018 to 31 January 2021, with radiosonde launches occurring once per day at 12:00 UTC, and when conditions are favorable during austral summer, a second launch occurs at 05:00 UTC.…”

“…Now, the three coastal sites will be analyzed: McMurdo, Neumayer, and Syowa. In comparison to the continental interior sites, a wider range of boundary layer stability regimes are present at these sites (Dice et al, 2023) and are expected to have more complex forcing mechanisms, such as temperature advection (Dice and Cassano, 2022), katabatic winds (Murakoshi, 1958;Hudson and Brandt, 2005;Lazzara et al, 2012), and cyclonic activity (Silva et al, 2022). Specifically at McMurdo, Dice et 2023) found that the summer was largely dominated by the NN, VSM, and WS regimes (92.1 %), while near-surface stability in the winter was more varied but found that MS or SS conditions occur near the surface or aloft 84.6 % of the winter season.…”

“…Neumayer, Silva et al (2022) noted strong temperature inversions, especially during the winter when solar radiation is low or zero during polar night. Hudson and Brandt (2005) found that inversion strength decreases with increasing radiative flux in the winter at the South Pole and Dome Concordia ("Dome C").…”

“…Dice and Cassano (2022) found the strongest inversions occurring with wind speeds less than 4.3 m s −1 at McMurdo. Silva et al (2022) investigated boundary layer stability at Neumayer and found strong inversions were associated with low wind speeds. Hudson and Brandt (2005) found that, while it is generally expected that increasing wind speeds will reduce near-surface stability by mixing warmer air from aloft to the surface, the strongest stability conditions occur when wind speeds are 3 to 5 m s −1 rather than calm at the South Pole and Dome C, which was also noted by other studies in the coastal regions of Antarctica (Cassano et al, 2016).…”

“…It is also possible that cyclonic activity can alter near-surface boundary layer stability, through changes in wind speed and cloud cover associated with the cyclone. At Neumayer, cyclonic activity reaches a maximum in the fall and spring, during which temperature inversions are rarely observed, whereas during non-cyclonic periods, temperature inversions are observed 3 times as often compared to during the cyclonic periods (Silva et al, 2022). Additionally, katabatic flow from the continental interior has been observed to impact conditions at Syowa and can flow from the plateau located just above the South Pole as well.…”