Context : The mesosphere of Venus is a critical range of altitudes in which complex temperature variability has been extensively studied by the space mission Venus Express ( VEx ) during its eight-year mission ( 2006-2014 ) .
In particular , the Solar Occultation in the InfraRed ( SOIR ) instrument probed the morning and evening terminator in the 70–170 km altitude region , at latitudes extending from pole to pole , using spectroscopic multiband observations collected during occultations of the Sun at the limb .
Data collected at different epochs and latitudes show evidence of short and medium timescale variability as well as latitudinal differences .
Spatial and temporal variability is also predicted in mesospheric and thermospheric terminator models with lower boundary conditions at 70 km near cloud tops .

Aims : The Venus transit on June 5-6 , 2012 was the first to occur with a spacecraft in orbit around Venus .
It has been shown that sunlight refraction in the mesosphere of Venus is able to provide useful constraints on mesospheric temperatures at the time of the transit .
The European Space Agency’s Venus Express provided space-based observations of Venus during the transit .
Simultaneously , the Venus aureole photometry was observed using ground-based facilities and solar telescopes orbiting Earth ( NASA ’ s Solar Dynamic Observatory , JAXA ’ s HINODE ) .
As the properties of spatial and temporal variability of the mesosphere are still debated , the opportunity of observing it at all latitudes at the same time , offered by the transit , is rather unique .
In this first paper , we establish new methods for analyzing the photometry of the so-called aureole that is produced by refraction of the solar light , and we investigate the choice of physical models that best reproduce the observations .

Methods : We compared the refractivity profile obtained by SOIR at the time of the June 2012 transit to the aureole photometry .
For this goal , we explored isothermal and multilayered refraction models of the terminator atmosphere based on the vertical density profile obtained by VeX/SOIR at a latitude of +49 ^ { \circ } and successfully compared it to the aureole photometry observed from space by the HMI instrument of the Solar Dynamic Observatory ( SDO ) .

Results : We obtain an independent constraint of 4.8 ± 0.5 km for the aerosol scale height in the upper haze region above 80 km .
We show that a full multiple-layer approach is required to adequately reproduce the aureole photometry , which appears to be sensitive to several second-order variations in the vertical refractivity .

Conclusions :