Speaker
Description
The mesosphere–lower thermosphere (MLT) is a dynamically complex region where gravity wave breaking, atmospheric tides and planetary waves drive the large-scale circulation, and where tidal motions play a fundamental role in modulating wind variability and vertical coupling processes. Understanding the long-term behaviour of mesospheric wind velocity and tidal amplitude is essential for improving knowledge of atmospheric dynamics and their impact on space weather and radio wave propagation. However, assessing how well global circulation models reproduce both wind variability and tidal structure remains a key challenge. This study presents a comparative analysis of long-term variations in mesospheric winds derived from the SANAE IV SuperDARN HF radar and simulated by the Whole Atmosphere Community Climate Model with Thermosphere and Ionosphere Extension (WACCM-X) over the period 1998–2019. SuperDARN meteor echoes provide effective-height wind measurements (~93 ± 3 km), while WACCM-X provides altitude-resolved winds between approximately 80 and 100 km, enabling investigation of the vertical structure of both wind velocity and associated tidal variability. The analysis examines climatological mean structure, annual cycle behaviour, interannual variability and long-term trends, supported by statistical diagnostics including Pearson correlation, bias and root mean square error (RMSE) to quantify agreement as a function of month and altitude. Results show that WACCM-X successfully reproduces the broad seasonal reversal of zonal winds, with strong and statistically significant positive correlations at lower altitudes (~80–85 km), indicating good phase agreement in this region. However, the agreement deteriorates with increasing altitude, with correlations becoming negative at higher levels due to differences in the altitude of the wind reversal and the presence of strong vertical shear. The meridional component exhibits weaker and less consistent agreement, reflecting its smaller amplitudes and stronger sensitivity to tidal forcing, planetary waves and sampling effects. Interannual variability reveals that while the seasonal cycle is persistent in both datasets, variations in amplitude and the vertical position of the reversal layer significantly influence model–observation agreement, particularly in regions where tidal modulation is strong. Month–altitude diagnostics further show that model performance is highly localised, with regions of strong agreement confined to specific seasons and altitude ranges, while regions of negative correlation indicate out-of-phase behaviour associated with differences in tidal phase and vertical structure. Trend analysis based on deseasonalised anomalies indicates weak positive trends in the SuperDARN winds, whereas WACCM-X exhibits altitude-dependent zonal trends and generally weak negative meridional tendencies, highlighting differences in the long-term evolution of both wind velocity and tidal characteristics. Overall, the results demonstrate that WACCM-X captures the large-scale structure of mesospheric winds over SANAE IV, but that detailed agreement in both wind velocity and tidal amplitude depends strongly on altitude, season and the effective sampling height of the radar observations, emphasising the importance of vertical structure when interpreting model–observation comparisons in the MLT.
| Apply for student award at which level: | MSc |
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| Consent on use of personal information: Abstract Submission | Yes, I ACCEPT |