On the structure and dynamics of Indian monsoon depressions

Hunt, K. M. R. ORCID: https://orcid.org/0000-0003-1480-3755, Turner, A. G. ORCID: https://orcid.org/0000-0002-0642-6876, Inness, P. M. ORCID: https://orcid.org/0009-0005-5795-6841, Parker, D. E. and Levine, R. C. (2016) On the structure and dynamics of Indian monsoon depressions. Monthly Weather Review, 144 (9). pp. 3391-3416. ISSN 0027-0644 doi: 10.1175/MWR-D-15-0138.1

Abstract/Summary

ERA-Interim reanalysis data from the past 35 years have been used with a newly-developed feature tracking algorithm to identify Indian monsoon depressions originating in or near the Bay of Bengal. These were then rotated, centralised and combined to give a fully three-dimensional 106-depression composite structure – a considerably larger sample than any previous detailed study on monsoon depressions and their structure. Many known features of depression structure are confirmed, particularly the existence of a maximum to the southwest of the centre in rainfall and other fields, and a westward axial tilt in others. Additionally, the depressions are found to have significant asymmetry due to the presence of the Himalayas; a bimodal mid-tropospheric potential vorticity core; a separation into thermally cold- (~–1.5K) and neutral- (~0K) cores near the surface with distinct properties; and that the centre has very large CAPE and very small CIN. Variability as a function of background state has also been explored, with land/coast/sea, diurnal, ENSO, active/break and Indian Ocean Dipole contrasts considered. Depressions are found to be markedly stronger during the active phase of the monsoon, as well as during La Niña. Depressions on land are shown to be more intense and more tightly constrained to the central axis. A detailed schematic diagram of a vertical cross-section through a composite depression is also presented, showing its inherent asymmetric structure.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/38263
Identification Number/DOI	10.1175/MWR-D-15-0138.1
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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