Lower atmosphere variations in the martian water vapour and hydrogen abundance during the Mars Year (MY) 34 C storm from L_S=326.1^◦-333.5^◦ and their associated effect on hydrogen escape are investigated using a multi-spacecraft assimilation of atmospheric retrievals into a Martian global circulation model. Elevation of the hygropause and associated increase in middle atmosphere hydrogen at the peak of the MY 34 C storm led to a hydrogen escape rate of around 1.4×10⁹ cm⁻²s⁻¹ , meaning the MY 34 C storm enhanced water loss rates on Mars to levels observed during global-scale dust storms.
The water loss rate during the MY 34 C storm (a loss of 15% of the total annual water loss during only 5% of the year) was three times stronger than the weak MY 30 C storm assimilation, demonstrating that interannual variations in C storm strength must be considered when calculating the integrated loss of water on Mars.