Comparison of ground-based and satellite measurements of water vapour vertical profiles over Ellesmere Island, Nunavut
Abstract. Improving measurements of water vapour in the upper troposphere and lower stratosphere (UTLS) is a priority for the atmospheric
science community. In this work, UTLS water vapour profiles derived from
Atmospheric Chemistry Experiment (ACE) satellite measurements are assessed
with coincident ground-based measurements taken at a high Arctic observatory
at Eureka, Nunavut, Canada. Additional comparisons to satellite measurements
taken by the Atmospheric Infrared Sounder (AIRS), Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), Microwave Limb
Sounder (MLS), Scanning Imaging Absorption Spectrometer for Atmospheric
CHartography (SCIAMACHY), and Tropospheric Emission Spectrometer (TES) are included to put the
ACE Fourier transform
spectrometer (ACE-FTS) and ACE Measurement of Aerosol Extinction in the
Stratosphere and Troposphere Retrieved by Occultation (ACE-MAESTRO) results in context. Measurements of water vapour profiles at Eureka are made using a Bruker
125HR solar absorption Fourier transform infrared spectrometer at the Polar
Environment Atmospheric Research Laboratory (PEARL) and radiosondes launched
from the Eureka Weather Station. Radiosonde measurements used in this study
were processed with software developed by the Global Climate Observing
System (GCOS) Reference Upper-Air Network (GRUAN) to account for known
biases and calculate uncertainties in a well-documented and consistent
manner. ACE-FTS measurements were within 11 ppmv (parts per million by volume; 13 %) of 125HR measurements
between 6 and 14 km. Between 8 and 14 km ACE-FTS profiles showed a small wet
bias of approximately 8 % relative to the 125HR. ACE-FTS water vapour
profiles had mean differences of 13 ppmv (32 %) or better when compared to
coincident radiosonde profiles at altitudes between 6 and 14 km; mean
differences were within 6 ppmv (12 %) between 7 and 11 km. ACE-MAESTRO
profiles showed a small dry bias relative to the 125HR of approximately
7 % between 6 and 9 km and 10 % between 10 and 14 km. ACE-MAESTRO
profiles agreed within 30 ppmv (36 %) of the radiosondes between 7 and
14 km. ACE-FTS and ACE-MAESTRO comparison results show closer agreement with
the radiosondes and PEARL 125HR overall than other satellite datasets –
except for AIRS. Close agreement was observed between AIRS and the 125HR and
radiosonde measurements, with mean differences within 5 % and correlation
coefficients above 0.83 in the troposphere between 1 and 7 km. Comparisons to MLS at altitudes around 10 km showed a dry bias, e.g. mean
differences between MLS and radiosondes were −25.6  %. SCIAMACHY
comparisons were very limited due to minimal overlap between the vertical
extent of the measurements. TES had no temporal overlap with the radiosonde
dataset used in this study. Comparisons between TES and the 125HR showed a
wet bias of approximately 25 % in the UTLS and mean differences within
14 % below 5 km.