The mesopause, the coldest region of Earth’s atmosphere near 85–100 km, is the boundary between mesosphere and thermosphere, yet its variability remains poorly quantified. Using 24 years (2002–2025) of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature measurements, we show that the high-latitude austral summer mesopause height is closely linked to the T80 index—a temperature- based proxy at 80 km for the strength of summer polar upwelling. On interannual timescales, the T80 index is almost perfectly correlated with the December mesopause height across 30° S–80° S, with a correlation coefficient (R) of 0.98 and a sensitivity of 0.36 km K^−1 at 60° S. On daily timescales, this relationship weakens but remains significant (R = 0.48) at latitudes poleward of 55° S. The temperature field exhibits a vertical dipole response to T80 index: stronger upwelling (lower T80) induces adiabatic cooling below ~90 km and chemical/radiative heating above ~90 km through bottom-up coupling among dynamical, microphysical, and chemical processes. This dipole temperature response shifts the temperature profile downward, thereby lowering the mesopause height. The strong month-to-month persistence of both the T80 index and mesopause temperature provides substantial predictive skill, enabling one-month-ahead forecast of December mesopause height with correlation up to 0.90. Our results indicate that internal dynamics dominate the interannual summer mesopause variability, while signals of 11-year solar cycle and long-term CO₂ cooling cannot be reliably isolated from the 24-year observations.