Large scale magnetic fields and response of dayside Venus ionosphere

When solar wind dynamic pressure is close to or more than the subsolar ionospheric thermal pressure (overpressure conditions), the Venus ionosphere is permeated with large scale horizontal magnetic fields. There were speculations that these fields basically represented conditions, which could inhibit: (1)vertical diffusive transport, thereby affecting the vertical ion and electron distribution and (2) vertical thermal conduction, thereby affecting the vertical ion and electron temperatures. We therefore first review the main features of these fields and then present and discuss different results reported by various authors on the effects of these fields on the ionospheric plasma. We point out that an important feature of the ionospheric plasma as well as of the magnetic fields, in this context, is that both of these are limited to altitudes below 200 km during these overpressure conditions and here local equilibrium conditions prevail. Latest observational results indicate that these solar wind induced fields that do not have any detectable effect on the Venus ionosphere. These observational results are also discussed in the light of ionospheric measurements at Mars.