Linking Arctic Variability and Changes in the Stratosphere, Mesosphere, and Lower Thermosphere

The stratospheric polar vortex (SPV) is crucial for predicting cold winters in mid-latitudes and influences variability in the mesosphere, thermosphere, and ionosphere. However, its long-term trends and underlying drivers remain poorly understood. Using Modern-Era Retrospective analysis for Research and Applications-2 (MERRA-2) reanalysis data and Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (SD-WACCM-X) simulations, we analyze SPV trends driven by Arctic variabilities and their impact on the mesosphere and lower thermosphere (MLT). Our results reveal a shift in SPV behavior: a strengthening phase after 2005 contrasts with the weakening observed from 1980 to 2005. This transition is primarily driven by reduced planetary-scale wave activity—especially the wave-1 component—associated with surface temperature changes over the central North Pacific. Corresponding changes are also evident in the zonal mean zonal winds and the migrating solar semidiurnal tide (SW2) in the MLT region. Notably, the SW2 exhibits an ~8% per decade increase before 2005, followed by a ~12% per decade decrease thereafter, signaling substantial changes in MLT dynamics.