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Small scale characteristics during the Indian summer monsoon

Kleinskalige Charakteristiken des indischen Sommermonsuns

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Summary

The daily upper-air wind data, obtained from the MONEX-79 ship observing platforms, are subjected to a 2-D filter, whose wavenumber response is such as to filter out waves having wavelengths less than 760 km. The filtered wind components are referred to as “eddies”. The kinetic energies of these eddies during the three phases of the monsoon, viz. (a) pre-onset (May), (b) onset (June), (c) established (July) are studied. It is found that the contribution to the kinetic energies of the total wind, by the eddies, vary from a minimum of about 15.5% during the pre-onset phase to a maximum of 40% during the established phase.

The energy exchanges between the eddy and large-scale wind components, indicate that during the established phase the lower troposphere, upto 700 mb, appears to have a baroclinically unstable basic flow, while during the other phases, the basic flow is, in general, barotropically unstable.

Zusammenfassung

Die täglichen Höhenwindbeobachtungsdaten, die von Schiffsbeobachtungen im MONEX-79 erhalten wurden, sind einer 2-D Filterung unterworfen worden, deren Reaktion hinsichtlich der Wellenzahl so ist, daß Wellen mit Wellenlängen kleiner als 760 km ausgefiltert wurden. Diese gefilterten Windkomponenten wurden „Wirbeln” zugeordnet. Die kinetische Energie dieser „Wirbel” in 3 Phasen des Monsuns, nämlich vor dem Beginn des Monsuns (Mai), zum Monsuneinsatz (Juni) und im vollentwickelten Monsun (Juli), wird untersucht. Es wurde festgestellt, dass der Beitrag dieser „Wirbel” zur kinetischen Energie des Gesamtwindes von einem Minimum von 15,5% in der Vormonsunzeit bis 40% in der Phase des voll entwickelten Monsuns variiert. Der Energieaustausch zwischen den „Wirbeln” und den grosskaligen Windkomponenten zeigt an, daß während der Phase des entwickelten Monsuns die untere Troposphäre bis 700 mb eine baroklin instabile Grundströmung zu haben scheint, während in den anderen Phasen die Grundströmung im allgemeinen barotrop instabil ist.

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Sinha, S., Sinha, S.K. Small scale characteristics during the Indian summer monsoon. Arch. Met. Geoph. Biocl. A. 32, 281–288 (1983). https://doi.org/10.1007/BF02291898

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  • DOI: https://doi.org/10.1007/BF02291898

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