Warm Conveyor Belts in the ERA-Interim Dataset (1979–2010): Part I: Climatology and Potential Vorticity Evolution

Madonna, Erica; Wernli, Heini; Joos, Hanna; Martius, Olivia (2014). Warm Conveyor Belts in the ERA-Interim Dataset (1979–2010): Part I: Climatology and Potential Vorticity Evolution. Journal of Climate, 27(1), pp. 3-26. American Meteorological Society 10.1175/JCLI-D-12-00720.1

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A global climatology of warm conveyor belts (WCBs) is presented for the years 1979–2010, based on trajectories calculated with Interim ECMWF Re-Analysis (ERA-Interim) data. WCB trajectories are identified as strongly ascending air parcels (600 hPa in 2 days) near extratropical cyclones. Corroborating earlier studies, WCBs are more frequent during winter than summer and they ascend preferentially in the western ocean basins between 25° and 50° latitude. Before ascending, WCB trajectories typically approach from the subtropics in summer and from more midlatitude regions in winter. Considering humidity, cloud water, and potential temperature along WCBs confirms that they experience strong condensation and integrated latent heating during the ascent (typically >20 K). Liquid and ice water contents along WCBs peak at about 700 and 550 hPa, respectively. The mean potential vorticity (PV) evolution shows typical tropospheric values near 900 hPa, followed by an increase to almost 1 potential vorticity unit (PVU) at 700 hPa, and a decrease to less than 0.5 PVU at 300 hPa. These low PV values in the upper troposphere constitute significant negative anomalies with amplitudes of 1–3 PVU, which can strongly influence the downstream flow. Considering the low-level diabatic PV production, (i) WCBs starting at low latitudes (<40°) are unlikely to attain high PV (due to weak planetary vorticity) although they exhibit the strongest latent heating, and (ii) for those ascending at higher latitudes, a strong vertical heating gradient and high absolute vorticity are both important. This study therefore provides climatological insight into the cloud diabatic formation of significant positive and negative PV anomalies in the extratropical lower and upper troposphere, respectively.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geography > Physical Geography > Unit Impact
10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR)
08 Faculty of Science > Institute of Geography

UniBE Contributor:

Romppainen-Martius, Olivia

Subjects:

500 Science > 550 Earth sciences & geology
900 History > 910 Geography & travel

ISSN:

0894-8755

Publisher:

American Meteorological Society

Language:

English

Submitter:

Monika Wälti-Stampfli

Date Deposited:

10 Sep 2014 16:58

Last Modified:

02 Apr 2019 16:15

Publisher DOI:

10.1175/JCLI-D-12-00720.1

BORIS DOI:

10.7892/boris.52377

URI:

https://boris.unibe.ch/id/eprint/52377

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