Water vapour and ozone profiles in the midlatitude upper troposphere G. Vaughan1,*, C. Cambridge1, L. Dean1, and A. W. Phillips1,** 1Institute of Mathematical and Physical Sciences, University of Wales, Aberystwyth, UK *now at: SEAES, University of Manchester, UK **now at: Department of Physics, University of Cambridge, UK
Abstract. We present an investigation of upper tropospheric humidity profiles measured
with a standard radiosonde, the Vaisala RS80-A, and a commercial frost-point
hygrometer, the Snow White. Modifications to the Snow White, to enable the
mirror reflectivity and Peltier cooling current to be monitored during
flight, were found to be necessary to determine when the instrument was
functioning correctly; a further modification to prevent hydrometeors
entering the inlet was also implemented. From 23 combined flights of an
ozonesonde, radiosonde and Snow White between September 2001 and July 2002,
clear agreement was found between the two humidity sensors, with a mean
difference of <2% in relative humidity from 2 to 10km, and 2.2%
between 10 and 13km. This agreement required a correction to the radiosonde
humidity, as described by Miloshevich et al. (2001). Using this result, the
dataset of 324 ozonesonde/RS80-A profiles measured from Aberystwyth between
1991 and 2002 was examined to derive statistics for the distribution of
water vapour and ozone. Supersaturation with respect to ice was frequently
seen at the higher levels - 24% of the time in winter between 8 and 10km.
The fairly uniform distribution of relative humidity persisted to
120% in winter, but decreased rapidly above 100% in summer.
Citation: Vaughan, G., Cambridge, C., Dean, L., and Phillips, A. W.: Water vapour and ozone profiles in the midlatitude upper troposphere, Atmos. Chem. Phys., 5, 963-971, doi:10.5194/acp-5-963-2005, 2005.