Behavior of the Martian dayside electron density peak during global dust storms

A photochemical equilibrium model of the Martian ionosphere is used to model its behavior during the global dust storm of 1971–1972. In particular, the model is used to explain the observed increase in altitude of the ionospheric peak electron density and for the constancy of the peak electron density. During a dust storm, the lower neutral atmosphere of Mars is heated, and it expands. This leads to both a density increase of the neutral atmosphere and an increase of the altitude of the turbopause. The increase of the turbopause leads to a change of the vertical distribution of the neutral constituents. In response to this, the altitude profiles of electron production rates, as well as the electron density profile, are displaced upwards in altitude. The altitude of the peak electron density can increase by up to about 30 km, depending on the increase of the thermospheric density and on the solar zenith angle. The peak value of electron density at a fixed solar zenith angle shows no significant variation between clear and dusty air cases. It is found that the neutral atmospheric temperature increase in itself contributes much less to the variations in the ionosphere than does the associated neutral density increase. The temperature increase acts mainly as the cause for the density increase in the lower thermosphere, and it is this neutral density increase which plays the dominant role in influencing the ionosphere electron density profile.