|An existing time-dependent 3-dimensional numerical chemical transport model (CTM) was improved and coupled with two different versions of a dynamical model. All physical processes believed to be important are simulated, including chemical interactions, photochemical dissociation, eddy and molecular diffusion, and advection. The most essential improvements concern the implementation of a new transport scheme marked by almost zero numerical diffusion and the derivation of the solar Lyman-α flux from the sunspot number as proxy and its consideration in the photolysis rate of water vapor. The CTM was coupled with the dynamical models calculating climatologic means (COMMA-IAP) and computing the dynamical state for real dates (LIMA). These coupled models were applied to study some particular phenomena in the mesosphere-lower thermosphere (MLT-region) such as the influence of the variable Lyman-α radiation on the aeronomy, the autocatalytic water vapor production as a source of large mixing ratios within the middle to upper mesosphere in high summery latitudes during, the so-called tertiary ozone maximum formation, the investigation of nonlinear effects of the chemistry, trends of mesospheric minor constituents due to the increase of methane, nitrous oxide and carbon dioxide since the pre-industrial area.