Simultaneous measurements of HDO, H2O, and CH4 with MIPAS-B: Hydrogen budget and indication of dehydration inside the polar vortex

For the first time, vertical profiles of HDO inside the Arctic vortex along with CH4 and H2O were retrieved from nighttime infrared limb emission spec tra measured by the Michelson Interferometer for Passive Atmospheric Soundi ng, Balloonborne instrument (MIPAS-B) from Kiruna (Sweden, 68 degrees N) on February 11, 1995 and March 24, 1997, The deuterium to hydrogen ratio (D/H ) of water vapor shows a strong depletion in comparison to that of standard mean ocean water (SMOW), particularly in the lower stratosphere for the Fe bruary 1995 flight. This extraordinarily strong depletion indicates an addi tional isotopic effect due to dehydration by polar stratospheric cloud part icles. The maximum dehydration occurs at a lower altitude than that of the denitrification measured on the same flight. A dehydration of up to 0.7(+/- 0.4) ppmv is seen in the compact correlation between CH4 and H2O, For the M arch 1997 results the exceptionally low D/H ratios and a deviation from the linear H2O - CH4 correlation could not be found. The H2O results of the Fe bruary 1995 flight show a peak mixing ratio of 7.1 ppmv at 17.1 hPa and a m inimum of 3.6 ppmv at 137.5 hPa, The analysis of the March flight shows a s imilar profile, but the vertical gradient is less pronounced. The total hyd rogen budget of the stratosphere was examined by evaluating the quantity [H ]=[H2O] + 2[CH4], revealing values of around 7.25 ppmv on average for both flights. All profiles reflect the subsidence of polar vortex air.