The altitude of the ionospheric lower layer ( D-region ) is highly influenced by the solar UV flux affecting in turn , the propagation of Very Low Frequency ( VLF ) signals inside the waveguide formed between this layer and the Earth surface . The day/night modulation observed in these signals is generally used to model the influence of the solar irradiance onto the D-region . Although , these changes are relatively slow and the transitions are “ contaminated ” by mode coalescences . In this way , a rapid change of the solar irradiance , as during a solar eclipse , can help to understand the details of the energy transfer of the solar radiation onto the ionospheric D-layer . Using the ” Latin American VLF Network ” ( LAVNet-Mex ) receiver station in Mexico City , Mexico , we detected the phase and amplitude changes of the VLF signals transmitted by the NDK station at 25.2 kHz in North Dakota , USA during the August 21 , 2017 solar eclipse . As the Sun light was eclipsed , the rate of ionization in the ionosphere ( D-region ) was reduced and the effective reflection height increased , causing a considerable drop of the phase and amplitude of the observed VLF waves . The corresponding waveguide path is 3007.15 km long and crossed almost perpendicularly the total eclipse path . Circumstantially , at the time of the total eclipse a C3 flare took place allowing us to isolate the flare flux from the background flux of a large portion of the disk . In this work we report the observations and present a new model of the ionospheric effects of the eclipse and flare . The model is based on a detailed setup of the degree of Moon shadow that affects the entire Great Circle Path ( GCP ) . This relatively simple model , represents a new approach to obtain a good measure of the reflection height variation during the entire eclipse time interval . During the eclipse , the maximum phase variation was -63.36 ^ { \circ } at 18:05 UT which , according to our model , accounts for a maximum increase of the reflection height of 9.3 km .