Metrics of the Hadley circulation strength and associated circulation trends
<p>This study compares trends in the Hadley cell (HC) strength using different metrics applied to the ECMWF ERA5 and ERA-Interim reanalyses for the period 1979–2018. The HC strength is commonly evaluated by metrics derived from the mass-weighted zonal-mean stream function in isobaric coordinat...
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-06-01
|
| Series: | Weather and Climate Dynamics |
| Online Access: | https://wcd.copernicus.org/articles/3/625/2022/wcd-3-625-2022.pdf |
| _version_ | 1818470525068902400 |
|---|---|
| author | M. Pikovnik Ž. Zaplotnik L. Boljka N. Žagar |
| author_facet | M. Pikovnik Ž. Zaplotnik L. Boljka N. Žagar |
| author_sort | M. Pikovnik |
| collection | DOAJ |
| description | <p>This study compares trends in the Hadley cell (HC) strength using different metrics applied to the ECMWF ERA5 and ERA-Interim reanalyses for the period 1979–2018. The HC strength is commonly evaluated by metrics derived from the mass-weighted zonal-mean stream function in isobaric coordinates. Other metrics include the upper tropospheric velocity potential, the vertical velocity in the mid-troposphere, and the water vapour transport in the lower troposphere. Seven known metrics of HC strength are complemented here by a metric of the spatially averaged HC strength, obtained by averaging the stream function in the latitude–pressure (<span class="inline-formula"><i>φ</i></span>–<span class="inline-formula"><i>p</i></span>) plane, and by the total energy of zonal-mean unbalanced circulation in the normal-mode function decomposition. It is shown that metrics, which rely on single-point values in the <span class="inline-formula"><i>φ</i></span>–<span class="inline-formula"><i>p</i></span> plane, produce unreliable 40-year trends in both the northern and southern HCs, especially in ERA-Interim; magnitudes and even the signs of the trends depend on the choice of the HC strength metric. The two new metrics alleviate the vertical and meridional inhomogeneities of the trends in HC strength. The unbalanced energy metric suggests a positive HC trend in both reanalyses, whereas the metric based on averaging the stream function finds a significant positive trend only in ERA5.</p> |
| first_indexed | 2024-04-13T21:38:09Z |
| format | Article |
| id | doaj.art-9a189067f83c478fb1711b9817ec4a66 |
| institution | Directory Open Access Journal |
| issn | 2698-4016 |
| language | English |
| last_indexed | 2024-04-13T21:38:09Z |
| publishDate | 2022-06-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Weather and Climate Dynamics |
| spelling | doaj.art-9a189067f83c478fb1711b9817ec4a662022-12-22T02:28:51ZengCopernicus PublicationsWeather and Climate Dynamics2698-40162022-06-01362564410.5194/wcd-3-625-2022Metrics of the Hadley circulation strength and associated circulation trendsM. Pikovnik0Ž. Zaplotnik1L. Boljka2N. Žagar3Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, 1000, SloveniaFaculty of Mathematics and Physics, University of Ljubljana, Ljubljana, 1000, SloveniaGeophysical Institute, University of Bergen and Bjerknes Centre for Climate Research, Bergen, 5020, NorwayMeteorological Institute, Center for Earth System Research and Sustainability, Universität Hamburg, 20146 Hamburg, Germany<p>This study compares trends in the Hadley cell (HC) strength using different metrics applied to the ECMWF ERA5 and ERA-Interim reanalyses for the period 1979–2018. The HC strength is commonly evaluated by metrics derived from the mass-weighted zonal-mean stream function in isobaric coordinates. Other metrics include the upper tropospheric velocity potential, the vertical velocity in the mid-troposphere, and the water vapour transport in the lower troposphere. Seven known metrics of HC strength are complemented here by a metric of the spatially averaged HC strength, obtained by averaging the stream function in the latitude–pressure (<span class="inline-formula"><i>φ</i></span>–<span class="inline-formula"><i>p</i></span>) plane, and by the total energy of zonal-mean unbalanced circulation in the normal-mode function decomposition. It is shown that metrics, which rely on single-point values in the <span class="inline-formula"><i>φ</i></span>–<span class="inline-formula"><i>p</i></span> plane, produce unreliable 40-year trends in both the northern and southern HCs, especially in ERA-Interim; magnitudes and even the signs of the trends depend on the choice of the HC strength metric. The two new metrics alleviate the vertical and meridional inhomogeneities of the trends in HC strength. The unbalanced energy metric suggests a positive HC trend in both reanalyses, whereas the metric based on averaging the stream function finds a significant positive trend only in ERA5.</p>https://wcd.copernicus.org/articles/3/625/2022/wcd-3-625-2022.pdf |
| spellingShingle | M. Pikovnik Ž. Zaplotnik L. Boljka N. Žagar Metrics of the Hadley circulation strength and associated circulation trends Weather and Climate Dynamics |
| title | Metrics of the Hadley circulation strength and associated circulation trends |
| title_full | Metrics of the Hadley circulation strength and associated circulation trends |
| title_fullStr | Metrics of the Hadley circulation strength and associated circulation trends |
| title_full_unstemmed | Metrics of the Hadley circulation strength and associated circulation trends |
| title_short | Metrics of the Hadley circulation strength and associated circulation trends |
| title_sort | metrics of the hadley circulation strength and associated circulation trends |
| url | https://wcd.copernicus.org/articles/3/625/2022/wcd-3-625-2022.pdf |
| work_keys_str_mv | AT mpikovnik metricsofthehadleycirculationstrengthandassociatedcirculationtrends AT zzaplotnik metricsofthehadleycirculationstrengthandassociatedcirculationtrends AT lboljka metricsofthehadleycirculationstrengthandassociatedcirculationtrends AT nzagar metricsofthehadleycirculationstrengthandassociatedcirculationtrends |