Upper tropospheric water vapour variability at high latitudes – Part 1: Influence of the annular modes
Seasonal and monthly zonal medians of water vapour in the upper troposphere and lower stratosphere (UTLS) are calculated for both Atmospheric Chemistry Experiment (ACE) instruments for the northern and southern high-latitude regions (60–90° N and 60–90° S). Chosen for the purp...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/3265/2016/acp-16-3265-2016.pdf |
| Summary: | Seasonal and monthly zonal medians of water vapour in the upper troposphere
and lower stratosphere (UTLS) are calculated for both Atmospheric Chemistry
Experiment (ACE) instruments for the northern and southern high-latitude
regions (60–90° N and 60–90° S). Chosen for the purpose
of observing high-latitude processes, the ACE orbit provides sampling of both
regions in 8 of 12 months of the year, with coverage in all seasons. The ACE
water vapour sensors, namely MAESTRO (Measurements of Aerosol Extinction in
the Stratosphere and Troposphere Retrieved by Occultation) and the Fourier
Transform Spectrometer (ACE-FTS) are currently the only satellite instruments
that can probe from the lower stratosphere down to the mid-troposphere to
study the vertical profile of the response of UTLS water vapour to the
annular modes.
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The Arctic oscillation (AO), also known as the northern annular mode (NAM),
explains 64 % (<i>r</i> = −0.80) of the monthly variability in water vapour at
northern high latitudes observed by ACE-MAESTRO between 5 and 7 km using
only winter months (January to March, 2004–2013). Using a seasonal time step
and all seasons, 45 % of the variability is explained by the AO at
6.5 ± 0.5 km, similar to the 46 % value obtained for southern high
latitudes at 7.5 ± 0.5 km explained by the Antarctic oscillation or
southern annular mode (SAM). A large negative AO event in March 2013 produced
the largest relative water vapour anomaly at 5.5 km (+70 %) over the
ACE record. A similarly large event in the 2010 boreal winter, which was the
largest negative AO event in the record (1950–2015), led to
> 50 % increases in water vapour observed by MAESTRO and
ACE-FTS at 7.5 km. |
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| ISSN: | 1680-7316 1680-7324 |