Vertical coupling in the low-latitude atmosphere-ionosphere system driven by the 2-day wave in the tropical MLT region has been investigated. The problem is studied from an observational point of view. Three different types of data were analyzed in order to detect and extract the 2-day wave signals. The 2-day wave event during the period from 1 December 2002 to 28 February 2003 was identified in the neutral winds by radar measurements located at four tropical stations. The 2-day variations in the ionospheric electric currents (registered by perturbations in the geomagnetic field) and in the F-region electron densities were detected in the data from 23 magnetometer and seven ionosonde stations situated at low latitudes. Two features for each kind of wave were investigated in detail: the variation with time of the wave amplitude and the zonal wave number. The results show that the westward propagating global 2-day wave with zonal wave number 2 seen in the ionospheric currents and in F-region plasma is forced by the simultaneous 2-day wave activity in the MLT region. The main forcing agent in this atmosphere-ionosphere coupling seems to be the modulated tides, particularly the semidiurnal tide. This tide has a larger vertical wavelength than the diurnal tide and propagates well into the thermosphere. The parameter that appears to be affected, and thus drives the observed 2-day wave response of the ionosphere, is the dynamo electric field.