Isolating the effects of moisture entrainment on convectively coupled equatorial waves in an aquaplanet GCM

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Peatman, S. C., Methven, J. ORCID: https://orcid.org/0000-0002-7636-6872 and Woolnough, S. J. ORCID: https://orcid.org/0000-0003-0500-8514 (2018) Isolating the effects of moisture entrainment on convectively coupled equatorial waves in an aquaplanet GCM. Journal of the Atmospheric Sciences, 75 (9). pp. 3139-3157. ISSN 1520-0469 doi: 10.1175/JAS-D-18-0098.1

Abstract/Summary

The rate of humidity entrainment in the convective parametrization scheme in a general circulation model affects the simulation of convectively-coupled waves. However, it is unclear whether this is caused directly by the effects of entrainment on waves or indirectly through associated impacts such as on the basic state. Therefore, using an aquaplanet model, we employ a novel framework in which we entrain a weighted average of the resolved humidity field and a prescribed zonally symmetric field, with the weighting controlled by a decoupling parameter. Hence, we can vary the entrainment rate of basic state humidity independently of the entrainment of humidity perturbations, simultaneously minimizing changes in basic state. Thus we isolate the effect of moisture entrainment on the waves. Enhancing entrainment rate increases spectral power over all zonal wavenumbers and frequencies, with an increase in the ratio of eastward-to-westward power. The Kelvin wave speed decreases as entrainment increases, which can be partially accounted for by an associated change in basic state humidity. Increasing the decoupling parameter reduces spectral power in Kelvin waves relative to the background, with only long waves still prominent when entrainment is almost fully decoupled from the resolved moisture field, suggesting the wave structure in humidity is required for convection to organize into short wave structures. For long waves the increase in the ratio of eastward-to-westward power as entrainment rate increases cannot be explained by the changes in the coupling with the wave structure in humidity, but is consistent with the changes in the basic state.

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Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/77851
Item Type	Article
Refereed	Yes
Divisions	Science > School of Mathematical, Physical and Computational Sciences > NCAS Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Publisher	American Meteorological Society
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Funders:	Natural Environment Research Council Natural Environment Research Council	The sponsoring bodies who contributed funding for the creation of this item. Example: NERC Example: The Royal Society of Chemistry A pick list of funders may appear as you type in the funder's name in full or as an acronym. Select a correct match to complete the field or type in a new entry in full. For new entries, the full name is preferred.
Projects:	Fundamental influences of large-scale wave dynamics on tropical weather systems Funded by: Natural Environment Research Council (NE/I012419/1 - £344,278) Project Lead: John Methven 1 December 2011 - 30 June 2016 NCAS Climate 2014/15 Funded by: Natural Environment Research Council (R8/H12/83/001 - £1,047,658) Local Lead (PI): Rowan Sutton 1 April 2014 - 31 March 2015	Click Add to select your project (received at Reading) from an autocomplete list.

Deposit Details

Date Deposited:	28 Jun 2018 11:58	Date item deposited into CentAUR
Last Modified:	09 Jun 2024 05:03	Date item last modified

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