Phadtare, JA, Fletcher, JK, Ross, AN orcid.org/0000-0002-8631-3512 et al. (2 more authors) (2022) Froude-number-based rainfall regimes over the Western Ghats mountains of India. Quarterly Journal of the Royal Meteorological Society, 148 (748). pp. 3388-3405. ISSN 0035-9009
Abstract
The variations in the character of monsoonal rainfall over the Western Ghats region on the west coast of India are studied using radiosondes, satellite observations and reanalysis products. Summer monsoon rainfall over this region occurs in alternate offshore and onshore phases. It is shown that these phases are primarily controlled by the strength of the low-level westerly jet. Thus, a classification based on the Froude number, F = U/NH, of the onshore flow is proposed, where, H is the mountain height, U is the mean wind speed and N is the mean Brunt-Väisäla frequency over depth H. At low F (< 0.5), onshore winds are weak and the diurnal thermal fluctuation over the orography is strong; the land-sea and mountain-valley circulations are enhanced leading to a stronger diurnal control over the rainfall. A nocturnal offshore propagation of rainfall from the west coast is seen during this phase. Rainfall over the rainshadow region to the east of the Western Ghats also increases due to a weaker lee effect while it decreases over the Western Ghats due to a greater blocking effect. At high F (> 1), the orographic blocking of the low-level winds is weak. Thus, rainfall is enhanced over the Western Ghats and reduced over the rainshadow region due to a stronger lee effect. In this phase, the diurnal thermal fluctuation over the orography is weak. The bulk Richardson number is less than 1 suggesting a dominance of vertical wind shear over the buoyancy forces. The level of free convection and convective inhibition over the west coast are also very low. Hence, at high F, rainfall over the west coast mainly results from the mechanical uplifting of the westerly winds by the Western Ghats with no preference to a particular time of the day. These findings will help in improving the representation of orographic effects and the diurnal cycle of rainfall in numerical models.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | This article is protected by copyright. All rights reserved. This is the peer reviewed version of the following article: Phadtare, J.A., Fletcher, J.K., Ross, A.N., Turner, A.G. and Schiemann, R.K.H. (2022), Froude number-based Rainfall Regimes over the Western Ghats Mountains of India. Q J R Meteorol Soc., 148(748), 3388-3405, which has been published in final form at https://doi.org/10.1002/qj.4367. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited. |
Keywords: | Flow over orography, Land-sea/Mountain-valley circulation, Indian monsoon, Coastal meteorology. |
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 Met Office IND3 |
Depositing User: | Symplectic Publications |
Date Deposited: | 02 Sep 2022 10:28 |
Last Modified: | 26 Aug 2023 00:13 |
Status: | Published |
Publisher: | Wiley |
Identification Number: | 10.1002/qj.4367 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:190460 |