Measurements of stratospheric hydrogen cyanide at McMurdo Station, Antarctica: Further evidence of winter stratospheric subsidence?

We have made measurements of hydrogen cyanide (HCN) in the springtime Antarctic stratosphere using ground‐based millimeter wave spectroscopy. We find a steeper decrease in volume mixing ratio with altitude than that found at tropical latitudes, from an assumed value of ∼160 pptv in the troposphere to a value of 65±30 pptv at 40 km, which may be further evidence of substantial vertical subsidence of the Antarctic winter stratosphere.