Interannual Variability of Winds in the Antarctic Mesosphere and Lower Thermosphere Over Rothera (67°S, 68°W) During 2005–2021 in Meteor Radar Observations and WACCM‐X.

The mesosphere and lower thermosphere (MLT) plays a critical role in linking the middle and upper atmosphere. However, many General Circulation Models do not model the MLT and those that do remain poorly constrained. We use long‐term meteor radar observations (2005–2021) from Rothera (67°S, 68°W) on the Antarctic Peninsula to evaluate the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X) and investigate interannual variability. We find some significant differences between WACCM‐X and observations. In particular, at upper heights, observations reveal eastwards wintertime (April–September) winds, whereas the model predicts westwards winds. In summer (October–March), the observed winds are northwards but predictions are southwards. Both the model and observations reveal significant interannual variability. We characterize the trend and the correlation between the winds and key phenomena: (a) the 11‐year solar cycle, (b) El Niño Southern Oscillation, (c) Quasi‐Biennial Oscillation and (d) Southern Annular Mode using a linear regression method. Observations of the zonal wind show significant changes with time. The summertime westwards wind near 80 km is weakening by up to 4–5 ms−1 per decade, whilst the eastward wintertime winds around 85–95 km are strengthening at by around 7 ms−1 per decade. We find that at some times of year there are significant correlations between the phenomena and the observed/modeled winds. The significance of this work lies in quantifying the biases in a leading General Circulation Model and demonstrating notable interannual variability in both modeled and observed winds. Plain Language Summary: The mesosphere and lower thermosphere (MLT), at heights of 80–100 km is an important region for the coupling of the middle and upper atmosphere. We carry out a study of the winds above Rothera (Antarctic Peninsula) for the years 2005–2021. We use observations from a meteor radar which measures winds at heights of 80–100 km and compare with the eXtended version of the Whole Atmosphere Community Climate Model (WACCM‐X), a leading general circulation model. We find that although most of the seasonal cycle in the winds is captured well, WACCM‐X exhibits biases in the winds at upper heights. In wintertime, the zonal winds are westwards whereas in observations they are eastward. In summertime WACCM‐X model meridional winds at 90–100 km are southwards but observations northwards. The observed and modeled winds also display significant interannual variability. We characterize the trends of the winds and the correlation with various drivers (the 11‐year solar cycle, El Niño Southern Oscillation, the Quasi‐Biennial Oscillation and the Southern Annular Mode), using a multi‐linear regression method. The study uses a uniquely long data set of Antarctic MLT winds to test and further develop general circulation models and quantifies the relationship between these winds and drivers such as the solar cycle. Key Points: We characterize the variability of monthly mean winds in the mesosphere and lower thermosphere (MLT) over 17 years at Rothera using meteor radar observations and the eXtended version of the Whole Atmosphere Community Climate Model (WACCM‐X)WACCM‐X displays biases in the wintertime winds in the upper MLT. Observed winds are eastwards whilst WACCM‐X winds are westwardsSignificant variability, trends and intermittent correlations with the solar cycle, Quasi‐Biennial Oscillation and Southern Annular Mode are found in the observed and modeled winds [ABSTRACT FROM AUTHOR]