The upper mesosphere and lower thermosphere (UMLT) is the least explored atmospheric region, with the variability of water vapor, ozone, and temperature remaining poorly understood. This study demonstrates that the UMLT climate during non-summer months is governed by bottom-up processes. Specifically, tropical upwelling drives the transport of H2O, which negatively modulates the secondary ozone layer, while radiative heating of O3 influences temperatures above 90 km (T90). This “upwelling—H2O—O3—T90” link is non-localized, propagating upward and poleward at each step, creating a highly structured climate. Temperatures near 80 km (T80), dominated by adiabatic cooling, serve as an indicator of upwelling. Notably, high-latitude T90 is positively correlated with low-latitude T80 in both hemispheres, and the interannual variability of H2O, O3, and T90 exhibits interhemispheric symmetry. This study challenges the conventional view that UMLT climate is primarily driven by solar and CO2 forcing, highlighting the critical role of atmospheric dynamics.