Interannual variations of water vapor in the tropical upper troposphere and the lower and middle stratosphere and their connections to ENSO and QBO
<p>In this study, we analyze the Aura Microwave Limb Sounder water vapor data in the tropical upper troposphere and the lower and middle stratosphere (UTLMS) (from 215 to 6 hPa) for the period from August 2004 to September 2017 using time-lag regression analysis and composite analys...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/9913/2019/acp-19-9913-2019.pdf |
| Summary: | <p>In this study, we analyze the Aura Microwave Limb Sounder
water vapor data in the tropical upper troposphere and the lower and middle
stratosphere (UTLMS) (from 215 to 6 hPa) for the period from August 2004
to September 2017 using time-lag regression analysis and composite analysis
to explore the interannual variations of tropical UTLMS water vapor and
their connections to El Niño–Southern Oscillation (ENSO) and quasi-biennial
oscillation (QBO). Our analysis shows that the interannual tropical UTLMS
water vapor anomalies are strongly related to ENSO and QBO which together
can explain more than half (<span class="inline-formula">∼</span> 50 %–60 %) but not all variance
of the interannual tropical water vapor anomalies. We find that ENSO's
impact is strong in the upper troposphere (<span class="inline-formula">∼</span> 215–<span class="inline-formula">∼</span> 120 hPa) and near the tropopause (<span class="inline-formula">∼</span> 110–<span class="inline-formula">∼</span> 90 hPa), with a <span class="inline-formula">∼</span> 3-month lag but weak in the
lower and middle stratosphere (<span class="inline-formula">∼</span> 80 to <span class="inline-formula">∼</span> 6 hPa).
In contrast, QBO's role is large in the lower and middle stratosphere, with
an upward-propagating signal starting at the tropopause (100 hPa) with a
<span class="inline-formula">∼</span> 2-month lag, peaking in the middle stratosphere near 15 hPa
with a <span class="inline-formula">∼</span> 21-month lag. The phase lag is based on the 50 hPa
QBO index used by many previous studies. This observational evidence
supports that the QBO's impact on the tropical stratospheric water vapor is
from its modulation on the tropical tropopause temperature and then
transported upward with the tape recorder as suggested by many previous
studies. In the upper troposphere, ENSO is more important than QBO for the
interannual tropical water vapor anomalies that are positive during the warm
ENSO phases but negative during the cold ENSO phases. Near the tropopause,
both ENSO and QBO are important for the interannual tropical water vapor
anomalies. Warm ENSO phase and westerly QBO phase tend to cause positive
water vapor anomalies, while cold ENSO phase and easterly QBO phase tend to
cause negative water vapor anomalies. As a result, the interannual tropical
water vapor anomalies near the tropopause are different depending on
different ENSO and QBO phase combinations. In the lower and middle
stratosphere, QBO is more important than ENSO for the interannual tropical
water vapor anomalies. For the westerly QBO phases, interannual tropical
water vapor anomalies are positive near the tropopause and in the lower
stratosphere but negative in the middle stratosphere and positive again
above. Vice versa for the easterly QBO phases.</p> |
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| ISSN: | 1680-7316 1680-7324 |