Vertical structure of the lower-stratospheric moist bias in the ERA5 reanalysis and its connection to mixing processes
<p>Numerical weather prediction (NWP) models are known to possess a distinct moist bias in the mid-latitude lower stratosphere, which is expected to affect the ability to accurately predict weather and climate. This paper investigates the vertical structure of the moist bias in the European Ce...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2022-12-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/15559/2022/acp-22-15559-2022.pdf |
| _version_ | 1811179155131203584 |
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| author | K. Krüger A. Schäfler M. Wirth M. Weissmann G. C. Craig |
| author_facet | K. Krüger A. Schäfler M. Wirth M. Weissmann G. C. Craig |
| author_sort | K. Krüger |
| collection | DOAJ |
| description | <p>Numerical weather prediction (NWP) models are known to possess a distinct
moist bias in the mid-latitude lower stratosphere, which is expected to affect
the ability to accurately predict weather and climate. This paper
investigates the vertical structure of the moist bias in the European Centre
for Medium-Range Weather Forecasts (ECMWF) latest global reanalysis ERA5
using a unique multi-campaign data set of highly resolved water vapour
profiles observed with a differential absorption lidar (DIAL) on board the
High Altitude and LOng range research aircraft (HALO). In total, 41 flights
in the mid-latitudes from six field campaigns provide roughly 33 000 profiles
with humidity varying by 4 orders of magnitude. The observations cover
different synoptic situations and seasons and thus are suitable to
characterize the strong vertical gradients of moisture in the upper
troposphere and lower stratosphere (UTLS). The comparison to ERA5 indicates
high positive and negative deviations in the UT, which on average lead to a
slightly positive bias (15 %–20 %). In the LS, the moist bias rapidly
increases up to a maximum of 55 % at 1.3 km altitude above the thermal
tropopause (tTP) and decreases again to 15 %–20 % at 4 km altitude. Such a
vertical structure is frequently observed, although the magnitude varies
from flight to flight. The layer depth of increased moist bias is smaller at
high tropopause altitudes and larger when the tropopause is low. Our results
also suggest a seasonality of the moist bias, with the maximum in summer
exceeding autumn by up to a factor of 3. During one field campaign, collocated
ozone and water vapour profile observations enable a classification of
tropospheric, stratospheric, and mixed air using water vapour–ozone
correlations. It is revealed that the moist bias is high in the mixed air
while being small in tropospheric and stratospheric air, which highlights
that excessive transport of moisture into the LS plays a decisive role for
the formation of the moist bias. Our results suggest that a better
representation of mixing processes in NWP models could lead to a reduced LS
moist bias that, in turn, may lead to more accurate weather and climate
forecasts. The lower-stratospheric moist bias should be borne in mind for
climatological studies using reanalysis data.</p> |
| first_indexed | 2024-04-11T06:30:01Z |
| format | Article |
| id | doaj.art-dec871fd34dd4972aeda7ff36a0cda1f |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-11T06:30:01Z |
| publishDate | 2022-12-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-dec871fd34dd4972aeda7ff36a0cda1f2022-12-22T04:40:10ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242022-12-0122155591557710.5194/acp-22-15559-2022Vertical structure of the lower-stratospheric moist bias in the ERA5 reanalysis and its connection to mixing processesK. Krüger0A. Schäfler1M. Wirth2M. Weissmann3G. C. Craig4Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, GermanyDeutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, GermanyDeutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, GermanyInstitut für Meteorologie und Geophysik, Universität Wien, Vienna, AustriaMeteorologisches Institut München, Ludwig-Maximilians-Universität, Munich, Germany<p>Numerical weather prediction (NWP) models are known to possess a distinct moist bias in the mid-latitude lower stratosphere, which is expected to affect the ability to accurately predict weather and climate. This paper investigates the vertical structure of the moist bias in the European Centre for Medium-Range Weather Forecasts (ECMWF) latest global reanalysis ERA5 using a unique multi-campaign data set of highly resolved water vapour profiles observed with a differential absorption lidar (DIAL) on board the High Altitude and LOng range research aircraft (HALO). In total, 41 flights in the mid-latitudes from six field campaigns provide roughly 33 000 profiles with humidity varying by 4 orders of magnitude. The observations cover different synoptic situations and seasons and thus are suitable to characterize the strong vertical gradients of moisture in the upper troposphere and lower stratosphere (UTLS). The comparison to ERA5 indicates high positive and negative deviations in the UT, which on average lead to a slightly positive bias (15 %–20 %). In the LS, the moist bias rapidly increases up to a maximum of 55 % at 1.3 km altitude above the thermal tropopause (tTP) and decreases again to 15 %–20 % at 4 km altitude. Such a vertical structure is frequently observed, although the magnitude varies from flight to flight. The layer depth of increased moist bias is smaller at high tropopause altitudes and larger when the tropopause is low. Our results also suggest a seasonality of the moist bias, with the maximum in summer exceeding autumn by up to a factor of 3. During one field campaign, collocated ozone and water vapour profile observations enable a classification of tropospheric, stratospheric, and mixed air using water vapour–ozone correlations. It is revealed that the moist bias is high in the mixed air while being small in tropospheric and stratospheric air, which highlights that excessive transport of moisture into the LS plays a decisive role for the formation of the moist bias. Our results suggest that a better representation of mixing processes in NWP models could lead to a reduced LS moist bias that, in turn, may lead to more accurate weather and climate forecasts. The lower-stratospheric moist bias should be borne in mind for climatological studies using reanalysis data.</p>https://acp.copernicus.org/articles/22/15559/2022/acp-22-15559-2022.pdf |
| spellingShingle | K. Krüger A. Schäfler M. Wirth M. Weissmann G. C. Craig Vertical structure of the lower-stratospheric moist bias in the ERA5 reanalysis and its connection to mixing processes Atmospheric Chemistry and Physics |
| title | Vertical structure of the lower-stratospheric moist bias in the ERA5 reanalysis and its connection to mixing processes |
| title_full | Vertical structure of the lower-stratospheric moist bias in the ERA5 reanalysis and its connection to mixing processes |
| title_fullStr | Vertical structure of the lower-stratospheric moist bias in the ERA5 reanalysis and its connection to mixing processes |
| title_full_unstemmed | Vertical structure of the lower-stratospheric moist bias in the ERA5 reanalysis and its connection to mixing processes |
| title_short | Vertical structure of the lower-stratospheric moist bias in the ERA5 reanalysis and its connection to mixing processes |
| title_sort | vertical structure of the lower stratospheric moist bias in the era5 reanalysis and its connection to mixing processes |
| url | https://acp.copernicus.org/articles/22/15559/2022/acp-22-15559-2022.pdf |
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