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Diabatic generation of negative potential vorticity and its impact on the North Atlantic jet stream

Harvey, Ben and Methven, John and Sanchez, Claudio and Schäfler, Andreas (2020) Diabatic generation of negative potential vorticity and its impact on the North Atlantic jet stream. Quarterly Journal of the Royal Meteorological Society, pp. 1477-1497. Wiley. doi: 10.1002/qj.3747. ISSN 0035-9009.

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Official URL: https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/qj.3747


Localised regions of negative potential vorticity (PV) are frequently seen on the equatorward flank of the upper‐tropospheric jet streams in analysis and forecast products. Their positioning, on the anticyclonic side of the jet and often close to the jet core, suggest they are associated with an enhancement of jet stream maximum winds. Given that PV is generally positive in the northern hemisphere and is materially conserved under adiabatic conditions, the presence of negative PV is indicative of recent diabatic activity. However, little is understood on the mechanisms for its generation and subsequent impacts. In this paper, aircraft measurements from a recent field campaign are used to provide direct observational evidence for the presence of negative PV on the anticyclonic side of an upper‐tropospheric jet. Theory is then developed to understand the process by which PV can turn negative. The key ingredient is diabatic heating in the presence of vertical wind shear, and the resulting PV anomalies are shown to always result from a flux of PV directed “down the isentropic slope”. This explains why, for the typical situation of heating in a warm conveyor belt, negative PV values appear on the equatorward side of the upper‐tropospheric jet stream close to the jet core. These ideas are illustrated with a semi‐geostrophic model and the processes responsible for the observed negative PV are explored using an operational forecast model with online PV tracer diagnostics. The diabatic influence on jet stream winds and shear is of interest because it is pertinent to the predictability of extreme jet stream events and associated flight‐level turbulence, and is crucial to the propagation of Rossby waves at tropopause level, development of midlatitude weather systems and their subsequent impacts at the surface.

Item URL in elib:https://elib.dlr.de/134895/
Document Type:Article
Title:Diabatic generation of negative potential vorticity and its impact on the North Atlantic jet stream
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Harvey, BenUniv. of Reading, UKUNSPECIFIED
Methven, JohnUniv. of Reading, UKUNSPECIFIED
Sanchez, ClaudioMet Office, UKUNSPECIFIED
Schäfler, AndreasDLR, IPAhttps://orcid.org/0000-0002-6165-6623
Date:21 February 2020
Journal or Publication Title:Quarterly Journal of the Royal Meteorological Society
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In ISI Web of Science:Yes
DOI :10.1002/qj.3747
Page Range:pp. 1477-1497
Keywords:NAWDEX, observations, warm conveyor belt, Rossby waves
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Earth Observation
DLR - Research theme (Project):R - LIDAR research and development
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics
Institute of Atmospheric Physics > Lidar
Deposited By: Schäfler, Andreas
Deposited On:13 May 2020 12:23
Last Modified:13 May 2020 12:23

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