Jemmett-Smith, BC, Ross, AN orcid.org/0000-0002-8631-3512, Sheridan, PF et al. (2 more authors) (2019) A case‐study of cold‐air pool evolution in hilly terrain using field measurements from COLPEX. Quarterly Journal of the Royal Meteorological Society, 145 (720). pp. 1290-1306. ISSN 0035-9009
Abstract
A case‐study investigation of cold‐air pool (CAP) evolution in hilly terrain is conducted using field measurements made during IOP 16 of the COLd‐air Pool EXperiment (COLPEX). COLPEX was designed to study cold‐air pooling in small‐scale valleys typical of the UK (∼100–200 m deep, ∼1 km wide). The synoptic conditions during IOP 16 are typical of those required for CAPs to form during the night, with high pressure, clear skies and low ambient winds. Initially a CAP forms around sunset and grows uninterrupted for several hours. However, starting 4 hr after sunset, a number of interruptions to this steady cooling rate occur. Three episodes are highlighted from the observations and the cause of disruption attributed to (a) wave activity, in the form of gravity waves and/or Kelvin–Helmholtz (KH) instability, (b) increases in the above‐valley winds resulting from the development of a nocturnal low‐level jet (NLLJ), (c) shear‐induced mixing resulting from instability of the NLLJ. A weakly stable residual layer provides the conditions for wave activity during Episode 1. This residual layer is eroded by a developing NLLJ from the top down during Episode 2. The sustained increase in winds at hill‐top levels – attributed to the NLLJ – continue to disrupt the CAP through Episode 3. Although cooling is interrupted, the CAP is never completely eroded during the night. Complete CAP break‐up occurs some 3.5 hr after local sunrise. This case‐study highlights a number of meteorological phenomena that can disrupt CAP evolution even in ideal CAP conditions. These processes are unlikely to be sufficiently represented by current operational weather forecast models and can be challenging even for high‐resolution research models.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2019 Crown copyright. Quarterly Journal of the Royal Meteorological Society © 2019 Royal Meteorological Society. This is the peer reviewed version of the following article: Jemmett‐Smith, BC, Ross, AN, Sheridan, PF, Hughes, JK, Vosper, SB. A case‐study of cold‐air pool evolution in hilly terrain using field measurements from COLPEX. Q J R Meteorol Soc. 2019; 145: 1290– 1306, which has been published in final form at https://doi.org/10.1002/qj.3499. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | complex terrain; cold-air pools; COLPEX; gravity waves; Kelvin–Helmholtz instability; nocturnal low-level jet; stable boundary layer |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst for Climate & Atmos Science (ICAS) (Leeds) |
Funding Information: | Funder Grant number NERC NE/I007679/1 |
Depositing User: | Symplectic Publications |
Date Deposited: | 08 Feb 2019 09:37 |
Last Modified: | 08 Feb 2020 01:38 |
Status: | Published |
Publisher: | Wiley |
Identification Number: | 10.1002/qj.3499 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:142347 |